core.d

/**
Implements logging facilities.

Message logging is a common approach to expose runtime information of a
program. Logging should be easy, but also flexible and powerful, therefore
$(D D) provides a standard interface for logging.

The easiest way to create a log message is to write
$(D import std.logger; log("I am here");) this will print a message to the
$(D stderr) device.  The message will contain the filename, the linenumber, the
name of the surrounding function, the time and the message.

Copyright: Copyright Robert "burner" Schadek 2013 --
License: <a href="http://www.boost.org/LICENSE_1_0.txt">Boost License 1.0</a>.
Authors: $(WEB http://www.svs.informatik.uni-oldenburg.de/60865.html, Robert burner Schadek)

-------------
log("Logging to the stdlog with its default LogLevel");
logf(LogLevel.info, 5 < 6, "%s to the stdlog with its LogLevel.info", "Logging");
info("Logging to the stdlog with its info LogLevel");
warning(5 < 6, "Logging to the stdlog with its LogLevel.warning if 5 is less than 6");
error("Logging to the stdlog with its error LogLevel");
errorf("Logging %s the stdlog %s its error LogLevel", "to", "with");
critical("Logging to the"," stdlog with its error LogLevel");
fatal("Logging to the stdlog with its fatal LogLevel");

auto fLogger = new FileLogger("NameOfTheLogFile");
fLogger.log("Logging to the fileLogger with its default LogLevel");
fLogger.info("Logging to the fileLogger with its default LogLevel");
fLogger.warning(5 < 6, "Logging to the fileLogger with its LogLevel.warning if 5 is less than 6");
fLogger.warningf(5 < 6, "Logging to the fileLogger with its LogLevel.warning if %s is %s than 6", 5, "less");
fLogger.critical("Logging to the fileLogger with its info LogLevel");
fLogger.log(LogLevel.trace, 5 < 6, "Logging to the fileLogger"," with its default LogLevel if 5 is less than 6");
fLogger.fatal("Logging to the fileLogger with its warning LogLevel");
-------------

Top-level calls to logging-related functions go to the default $(D Logger)
object called $(D stdlog).
$(LI $(D log))
$(LI $(D trace))
$(LI $(D info))
$(LI $(D warning))
$(LI $(D critical))
$(LI $(D fatal))
The default $(D Logger) will by default log to $(D stderr) and has a default
$(D LogLevel) of $(D LogLevel.all). The default Logger can be accessed by
using the property called $(D stdlog). This property a reference to the
current default $(D Logger). This reference can be used to assign a new
default $(D Logger).
-------------
stdlog = new FileLogger("New_Default_Log_File.log");
-------------

Additional $(D Logger) can be created by creating a new instance of the
required $(D Logger).

The $(D LogLevel) of an log call can be defined in two ways. The first is by
calling $(D log) and passing the $(D LogLevel) explicit as the first argument.
The second way of setting the $(D LogLevel) of a
log call, is by calling either $(D trace), $(D info), $(D warning),
$(D critical), or $(D fatal). The log call will than have the respective
$(D LogLevel). If no $(D LogLevel) is defined the log call will use the
current $(D LogLevel) of the used $(D Logger). If data is logged with
$(D LogLevel) $(D fatal) by default an $(D Error) will be thrown.
This behaviour can be modified by using the member $(D fatalHandler) to
assign a custom delegate to handle log call with $(D LogLevel) $(D fatal).

Conditional logging can be achieved be appending passing a $(D bool) as first
argument to a log function.  If conditional logging is used the condition must
be $(D true) in order to have the log message logged.

In order to combine an explicit $(D LogLevel) passing with conditional
logging, the $(D LogLevel) has to be passed as first argument followed by the
$(D bool).

Messages are logged if the $(D LogLevel) of the log message is greater than or
equal to than the $(D LogLevel) of the used $(D Logger) and additionally if the
$(D LogLevel) of the log message is greater equal to the global $(D LogLevel).
If a condition is passed into the log call, this condition must be true.

The global $(D LogLevel) is accessible by using $(D globalLogLevel).
To assign the $(D LogLevel) of a $(D Logger) use the $(D logLevel) property of
the logger.

If $(D printf)-style logging is needed add a $(B f) to the logging call, such as
$(D myLogger.infof("Hello %s", "world");) or $(fatalf("errno %d", 1337))
The additional $(B f) enables $(D printf)-style logging for call combinations of
explicit $(D LogLevel) and conditional logging functions and methods.

To customize the $(D Logger) behavior, create a new $(D class) that inherits from
the abstract $(D Logger) $(D class), and implements the $(D writeLogMsg)
method.
-------------
class MyCustomLogger : Logger
{
    this(string newName, LogLevel lv) @safe
    {
        super(newName, lv);
    }

    override void writeLogMsg(ref LogEntry payload)
    {
        // log message in my custom way
    }
}

auto logger = new MyCustomLogger();
logger.log("Awesome log message");
-------------

To gain more precise control over the logging process, additionally to
overwriting the $(D writeLogMsg) method the methods $(D beginLogMsg),
$(D logMsgPart) and $(D finishLogMsg) can be overwritten.

In order to disable logging at compile time, pass $(D StdLoggerDisableLogging) as a
version argument to the $(D D) compiler when compiling your program code.
This will disable all logging functionality.
Specific $(D LogLevel) can be disabled at compile time as well.
In order to disable logging with the $(D trace) $(D LogLevel) pass
$(D StdLoggerDisableTrace) as a version.
The following table shows which version statement disables which
$(D LogLevel).
$(TABLE
    $(TR $(TD $(D LogLevel.trace) ) $(TD StdLoggerDisableTrace))
    $(TR $(TD $(D LogLevel.info) ) $(TD StdLoggerDisableInfo))
    $(TR $(TD $(D LogLevel.warning) ) $(TD StdLoggerDisableWarning))
    $(TR $(TD $(D LogLevel.error) ) $(TD StdLoggerDisableError))
    $(TR $(TD $(D LogLevel.critical) ) $(TD StdLoggerDisableCritical))
    $(TR $(TD $(D LogLevel.fatal) ) $(TD StdLoggerDisableFatal))
)
Such a version statement will only disable logging in the associated compile
unit.

By default four $(D Logger) implementations are given. The $(D FileLogger)
logs data to files. It can also be used to log to $(D stdout) and $(D stderr)
as these devices are files as well. A $(D Logger) that logs to $(D stdout) can
therefore be created by $(D new FileLogger(stdout)).
The $(D MultiLogger) is basically an associative array of $(D string)s to
$(D Logger). It propagates log calls to its stored $(D Logger). The
$(D ArrayLogger) contains an array of $(D Logger) and also propagates log
calls to its stored $(D Logger). The $(D NullLogger) does not do anything. It
will never log a message and will never throw on a log call with $(D LogLevel)
$(D error).
*/
module std.experimental.logger.core;

import std.array;
import std.stdio;
import std.conv;
import std.datetime;
import std.string;
import std.range;
import std.traits;
import std.exception;
import std.concurrency;
import std.format;
import core.sync.mutex : Mutex;

import std.experimental.logger.filelogger;

shared static this() {
    __stdloggermutex = new Mutex;
}

/** This template evaluates if the passed $(D LogLevel) is active.
The previously described version statements are used to decide if the
$(D LogLevel) is active. The version statements only influence the compile
unit they are used with, therefore this function can only disable logging this
specific compile unit.
*/
pure bool isLoggingActiveAt(LogLevel ll)() @safe nothrow @nogc
{
    static assert(__ctfe);
    version (StdLoggerDisableLogging)
    {
        return false;
    }
    else
    {
        static if (ll == LogLevel.trace)
        {
            version (StdLoggerDisableTrace) return false;
        }
        else static if (ll == LogLevel.info)
        {
            version (StdLoggerDisableInfo) return false;
        }
        else static if (ll == LogLevel.warning)
        {
            version (StdLoggerDisableWarning) return false;
        }
        else static if (ll == LogLevel.error)
        {
            version (StdLoggerDisableError) return false;
        }
        else static if (ll == LogLevel.critical)
        {
            version (StdLoggerDisableCritical) return false;
        }
        else static if (ll == LogLevel.fatal)
        {
            version (StdLoggerDisableFatal) return false;
        }
    }

    return true;
}

/// Ditto
@property pure bool isLoggingActive()() @safe nothrow @nogc
{
    return isLoggingActiveAt!(LogLevel.all)();
}

/** This functions is used at runtime to determine if a $(D LogLevel) is
active. The same previously defined version statements are used to disable
certain levels. Again the version statements are associated with a compile
unit and can therefore not disable logging in other compile units.
pure bool isLoggingEnabled()(LogLevel ll) @safe nothrow @nogc
*/
bool isLoggingEnabled()(LogLevel ll, LogLevel loggerLL,
    LogLevel globalLL, lazy bool condition = true) @trusted
{
    switch (ll)
    {
        case LogLevel.trace:
            version (StdLoggerDisableTrace) return false;
            else break;
        case LogLevel.info:
            version (StdLoggerDisableInfo) return false;
            else break;
        case LogLevel.warning:
            version (StdLoggerDisableWarning) return false;
            else break;
        case LogLevel.critical:
            version (StdLoggerDisableCritical) return false;
            else break;
        case LogLevel.fatal:
            version (StdLoggerDisableFatal) return false;
            else break;
        default: break;
    }

    return ll >= globalLL
        && ll >= loggerLL
        && globalLL != LogLevel.off
        && loggerLL != LogLevel.off
        && condition;
}

/* This function formates a $(D SysTime) into an $(D OutputRange).

The $(D SysTime) is formatted similar to
$(LREF std.datatime.DateTime.toISOExtString) expect the fractional second part.
The sub second part is the upper three digest of the microsecond.
*/
void systimeToISOString(OutputRange)(OutputRange o, const ref SysTime time)
    if(isOutputRange!(OutputRange,string))
{
    auto fsec = time.fracSec.usecs / 1000;

    formattedWrite(o, "%04d-%02d-%02dT%02d:%02d:%02d.%03d",
        time.year, time.month, time.day, time.hour, time.minute, time.second,
        fsec);
}

/** This function logs data.

In order for the data to be processed the $(D LogLevel) of the log call must
be greater or equal to the $(D LogLevel) of the $(D stdlog) and the
$(D defaultLogLevel) additionally the condition passed must be $(D true).

Params:
ll = The $(D LogLevel) used by this log call.
condition = The condition must be $(D true) for the data to be logged.
args = The data that should be logged.

Examples:
--------------------
log(LogLevel.warning, true, "Hello World", 3.1415);
--------------------
*/
void log(int line = __LINE__, string file = __FILE__,
    string funcName = __FUNCTION__, string prettyFuncName = __PRETTY_FUNCTION__,
    string moduleName = __MODULE__, A...)(const LogLevel ll,
    lazy bool condition, lazy A args) @trusted
    if (args.length > 1)
{
    static if (isLoggingActive) synchronized (__stdloggermutex)
    {
        stdlogImpl.log!(line, file, funcName, prettyFuncName, moduleName)
            (ll, condition, args);
    }
}

/// Ditto
void log(T)(const LogLevel ll, lazy bool condition, lazy T arg,
    int line = __LINE__, string file = __FILE__,
    string funcName = __FUNCTION__, string prettyFuncName = __PRETTY_FUNCTION__,
    string moduleName = __MODULE__)
    @trusted
{
    static if (isLoggingActive) synchronized (__stdloggermutex)
    {
        stdlogImpl.log!T(ll, condition, arg, line, file, funcName,
                         prettyFuncName, moduleName);
    }
}

/** This function logs data.

In order for the data to be processed the $(D LogLevel) of the log call must
be greater or equal to the $(D LogLevel) of the $(D stdlog).

Params:
ll = The $(D LogLevel) used by this log call.
args = The data that should be logged.

Examples:
--------------------
log(LogLevel.warning, "Hello World", 3.1415);
--------------------
*/
void log(int line = __LINE__, string file = __FILE__,
    string funcName = __FUNCTION__, string prettyFuncName = __PRETTY_FUNCTION__,
    string moduleName = __MODULE__, A...)(const LogLevel ll, lazy A args)
    @trusted
    if (args.length > 1 && !is(Unqual!(A[0]) : bool))
{
    static if (isLoggingActive) synchronized (__stdloggermutex)
    {
        stdlogImpl.log!(line, file, funcName, prettyFuncName, moduleName)
            (ll, args);
    }
}

/// Ditto
void log(T)(const LogLevel ll, lazy T arg, int line = __LINE__,
    string file = __FILE__, string funcName = __FUNCTION__,
    string prettyFuncName = __PRETTY_FUNCTION__, string moduleName = __MODULE__)
    @trusted
{
    static if (isLoggingActive) synchronized (__stdloggermutex)
    {
        stdlogImpl.log!T(ll, arg, line, file, funcName, prettyFuncName,
                         moduleName);
    }
}

/** This function logs data.

In order for the data to be processed the $(D LogLevel) of the
$(D stdlog) must be greater or equal to the $(D defaultLogLevel)
add the condition passed must be $(D true).

Params:
condition = The condition must be $(D true) for the data to be logged.
args = The data that should be logged.

Examples:
--------------------
log(true, "Hello World", 3.1415);
--------------------
*/
void log(int line = __LINE__, string file = __FILE__,
    string funcName = __FUNCTION__, string prettyFuncName = __PRETTY_FUNCTION__,
    string moduleName = __MODULE__, A...)(lazy bool condition, lazy A args)
    @trusted
    if (args.length > 1)
{
    static if (isLoggingActive) synchronized (__stdloggermutex)
    {
        stdlogImpl.log!(line, file, funcName, prettyFuncName,
                        moduleName)(condition, args);
    }
}

/// Ditto
void log(T)(lazy bool condition, lazy T arg, int line = __LINE__,
    string file = __FILE__, string funcName = __FUNCTION__,
    string prettyFuncName = __PRETTY_FUNCTION__, string moduleName = __MODULE__)
    @trusted
{
    static if (isLoggingActive) synchronized (__stdloggermutex)
    {
        stdlogImpl.log!T(condition, arg, line, file, funcName, prettyFuncName,
                         moduleName);
    }
}

/** This function logs data.

In order for the data to be processed the $(D LogLevel) of the
$(D stdlog) must be greater or equal to the $(D defaultLogLevel).

Params:
args = The data that should be logged.

Examples:
--------------------
log("Hello World", 3.1415);
--------------------
*/
void log(int line = __LINE__, string file = __FILE__,
    string funcName = __FUNCTION__, string prettyFuncName = __PRETTY_FUNCTION__,
    string moduleName = __MODULE__, A...)(lazy A args)
    @trusted
    if (args.length > 1 && !is(Unqual!(A[0]) : bool)
         && !is(Unqual!(A[0]) == LogLevel))
{
    static if (isLoggingActive) synchronized (__stdloggermutex)
    {
        stdlogImpl.log!(line, file, funcName, prettyFuncName, moduleName)(args);
    }
}

void log(T)(lazy T arg, int line = __LINE__, string file = __FILE__,
    string funcName = __FUNCTION__, string prettyFuncName = __PRETTY_FUNCTION__,
    string moduleName = __MODULE__)
    @trusted
{
    static if (isLoggingActive) synchronized (__stdloggermutex)
    {
        stdlogImpl.log!T(arg, line, file, funcName, prettyFuncName, moduleName);
    }
}

/** This function logs data in a $(D printf)-style manner.

In order for the data to be processed the $(D LogLevel) of the log call must
be greater or equal to the $(D LogLevel) of the $(D stdlog) and the
$(D defaultLogLevel) additionally the condition passed must be $(D true).

Params:
ll = The $(D LogLevel) used by this log call.
condition = The condition must be $(D true) for the data to be logged.
msg = The $(D printf)-style string.
args = The data that should be logged.

Examples:
--------------------
logf(LogLevel.warning, true, "Hello World %f", 3.1415);
--------------------
*/
void logf(int line = __LINE__, string file = __FILE__,
    string funcName = __FUNCTION__,
    string prettyFuncName = __PRETTY_FUNCTION__,
    string moduleName = __MODULE__, A...)(const LogLevel ll,
    lazy bool condition, lazy string msg, lazy A args)
    @trusted
{
    static if (isLoggingActive) synchronized (__stdloggermutex)
    {
        stdlogImpl.logf!(line, file, funcName, prettyFuncName, moduleName)
            (ll, condition, msg, args);
    }
}

/** This function logs data in a $(D printf)-style manner.

In order for the data to be processed the $(D LogLevel) of the log call must
be greater or equal to the $(D LogLevel) of the $(D stdlog) and the
$(D defaultLogLevel).

Params:
ll = The $(D LogLevel) used by this log call.
msg = The $(D printf)-style string.
args = The data that should be logged.

Examples:
--------------------
logf(LogLevel.warning, true, "Hello World %f", 3.1415);
--------------------
*/
void logf(int line = __LINE__, string file = __FILE__,
    string funcName = __FUNCTION__, string prettyFuncName = __PRETTY_FUNCTION__,
    string moduleName = __MODULE__, A...)(const LogLevel ll, lazy string msg,
        lazy A args) @trusted
    if (args.length == 0 || (args.length > 0 && !is(Unqual!(A[0]) : bool)))
{
    static if (isLoggingActive) synchronized (__stdloggermutex)
    {
        stdlogImpl.logf!(line, file, funcName, prettyFuncName, moduleName)
            (ll, msg, args);
    }
}

/** This function logs data in a $(D printf)-style manner.

In order for the data to be processed the $(D LogLevel) of the log call must
be greater or equal to the $(D defaultLogLevel) additionally the condition
passed must be $(D true).

Params:
condition = The condition must be $(D true) for the data to be logged.
msg = The $(D printf)-style string.
args = The data that should be logged.

Examples:
--------------------
logf(true, "Hello World %f", 3.1415);
--------------------
*/
void logf(int line = __LINE__, string file = __FILE__,
    string funcName = __FUNCTION__, string prettyFuncName = __PRETTY_FUNCTION__,
    string moduleName = __MODULE__, A...)(lazy bool condition,
        lazy string msg, lazy A args)
    @trusted
{
    static if (isLoggingActive) synchronized (__stdloggermutex)
    {
        stdlogImpl.logf!(line, file, funcName, prettyFuncName, moduleName)
            (condition, msg, args);
    }
}

/** This function logs data in a $(D printf)-style manner.

In order for the data to be processed the $(D LogLevel) of the log call must
be greater or equal to the $(D defaultLogLevel).

Params:
msg = The $(D printf)-style string.
args = The data that should be logged.

Examples:
--------------------
logf("Hello World %f", 3.1415);
--------------------
*/
void logf(int line = __LINE__, string file = __FILE__,
    string funcName = __FUNCTION__,
    string prettyFuncName = __PRETTY_FUNCTION__,
    string moduleName = __MODULE__, A...)(lazy string msg, lazy A args)
    @trusted
{
    static if (isLoggingActive) synchronized (__stdloggermutex)
    {
        stdlogImpl.logf!(line, file, funcName,prettyFuncName, moduleName)
            (msg, args);
    }
}

/** This template provides the global log functions with the $(D LogLevel)
is encoded in the function name.

For further information see the the two functions defined inside of this
template.

The aliases following this template create the public names of these log
functions.
*/
template defaultLogFunction(LogLevel ll)
{
    /** This function logs data to the $(D stdlog).

    In order for the resulting log message to be logged the $(D LogLevel) must
    be greater or equal than the $(D LogLevel) of the $(D stdlog) and
    must be greater or equal than the global $(D LogLevel).

    Params:
    args = The data that should be logged.

    Examples:
    --------------------
    trace(1337, "is number");
    info(1337, "is number");
    error(1337, "is number");
    critical(1337, "is number");
    fatal(1337, "is number");
    --------------------
    */
    void defaultLogFunction(int line = __LINE__, string file = __FILE__,
        string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__, A...)(lazy A args) @trusted
        if (args.length > 0 && !is(Unqual!(A[0]) : bool))
    {
        static if (isLoggingActiveAt!ll) synchronized (__stdloggermutex)
        {
            stdlogImpl.memLogFunctions!(ll).logImpl!(line, file, funcName,
                       prettyFuncName, moduleName)(args);
        }
    }

    /** This function logs data to the $(D stdlog) depending on a condition.

    In order for the resulting log message to be logged the $(D LogLevel) must
    be greater or equal than the $(D LogLevel) of the $(D stdlog) and
    must be greater or equal than the global $(D LogLevel) additionally the
    condition passed must be $(D true).

    Params:
    condition = The condition must be $(D true) for the data to be logged.
    args = The data that should be logged.

    Examples:
    --------------------
    trace(true, 1337, "is number");
    info(false, 1337, "is number");
    error(true, 1337, "is number");
    critical(false, 1337, "is number");
    fatal(true, 1337, "is number");
    --------------------
    */
    void defaultLogFunction(int line = __LINE__, string file = __FILE__,
        string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__, A...)(lazy bool condition, lazy A args)
        @trusted
    {
        static if (isLoggingActiveAt!ll) synchronized (__stdloggermutex)
        {
            stdlogImpl.memLogFunctions!(ll).logImpl!(line, file, funcName,
                       prettyFuncName, moduleName)(condition, args);
        }
    }
}

/// Ditto
alias trace = defaultLogFunction!(LogLevel.trace);
/// Ditto
alias info = defaultLogFunction!(LogLevel.info);
/// Ditto
alias warning = defaultLogFunction!(LogLevel.warning);
/// Ditto
alias error = defaultLogFunction!(LogLevel.error);
/// Ditto
alias critical = defaultLogFunction!(LogLevel.critical);
/// Ditto
alias fatal = defaultLogFunction!(LogLevel.fatal);

/** This template provides the global $(D printf)-style log functions with
the $(D LogLevel) is encoded in the function name.

For further information see the the two functions defined inside of this
template.

The aliases following this template create the public names of the log
functions.
*/
template defaultLogFunctionf(LogLevel ll)
{
    /** This function logs data to the $(D stdlog) in a $(D printf)-style
    manner.

    In order for the resulting log message to be logged the $(D LogLevel) must
    be greater or equal than the $(D LogLevel) of the $(D stdlog) and
    must be greater or equal than the global $(D LogLevel).

    Params:
    msg = The $(D printf)-style string.
    args = The data that should be logged.

    Examples:
    --------------------
    tracef("is number %d", 1);
    infof("is number %d", 2);
    errorf("is number %d", 3);
    criticalf("is number %d", 4);
    fatalf("is number %d", 5);
    --------------------
    */
    void defaultLogFunctionf(int line = __LINE__, string file = __FILE__,
        string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__, A...)(lazy string msg, lazy A args)
        @trusted
    {
        static if (isLoggingActiveAt!ll) synchronized (__stdloggermutex)
        {
            stdlogImpl.memLogFunctions!(ll).logImplf!(line, file, funcName,
                       prettyFuncName, moduleName)(msg, args);
        }
    }

    /** This function logs data to the $(D stdlog) in a $(D printf)-style
    manner.

    In order for the resulting log message to be logged the $(D LogLevel) must
    be greater or equal than the $(D LogLevel) of the $(D stdlog) and
    must be greater or equal than the global $(D LogLevel).

    Params:
     condition = The condition must be $(D true) for the data to be logged.
    msg = The $(D printf)-style string.
    args = The data that should be logged.

    Examples:
    --------------------
    tracef(false, "is number %d", 1);
    infof(false, "is number %d", 2);
    errorf(true, "is number %d", 3);
    criticalf(true, "is number %d", 4);
    fatalf(someFunct(), "is number %d", 5);
    --------------------
    */
    void defaultLogFunctionf(int line = __LINE__, string file = __FILE__,
        string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__, A...)(lazy bool condition,
            lazy string msg, lazy A args) @trusted
    {
        static if (isLoggingActiveAt!ll) synchronized (__stdloggermutex)
        {
            stdlogImpl.memLogFunctions!(ll).logImplf!(line, file, funcName,
                       prettyFuncName, moduleName)(condition, msg, args);
        }
    }
}

/// Ditto
alias tracef = defaultLogFunctionf!(LogLevel.trace);
/// Ditto
alias infof = defaultLogFunctionf!(LogLevel.info);
/// Ditto
alias warningf = defaultLogFunctionf!(LogLevel.warning);
/// Ditto
alias errorf = defaultLogFunctionf!(LogLevel.error);
/// Ditto
alias criticalf = defaultLogFunctionf!(LogLevel.critical);
/// Ditto
alias fatalf = defaultLogFunctionf!(LogLevel.fatal);

private struct MsgRange
{
    private Logger log;

    this(Logger log)
    {
        this.log = log;
    }

    void put(const(char)[] msg)
    {
        log.logMsgPart(msg);
    }
}

private void formatString(A...)(MsgRange oRange, A args)
{
    import std.format : formattedWrite;

    foreach (arg; args)
    {
        std.format.formattedWrite!(MsgRange,char)(oRange, "%s", arg);
    }
}

/**
There are eight usable logging level. These level are $(I all), $(I trace),
$(I info), $(I warning), $(I error), $(I critical), $(I fatal), and $(I off).
If a log function with $(D LogLevel.fatal) is called the shutdown handler of
that logger is called.
*/
enum LogLevel : ubyte
{
    all = 1, /** Lowest possible assignable $(D LogLevel). */
    trace = 32, /** $(D LogLevel) for tracing the execution of the program. */
    info = 64, /** This level is used to display information about the
                program. */
    warning = 96, /** warnings about the program should be displayed with this
                   level. */
    error = 128, /** Information about errors should be logged with this
                   level.*/
    critical = 160, /** Messages that inform about critical errors should be
                    logged with this level. */
    fatal = 192,   /** Log messages that describe fatal errors should use this
                  level. */
    off = ubyte.max /** Highest possible $(D LogLevel). */
}

/** This class is the base of every logger. In order to create a new kind of
logger a deriving class needs to implement the $(D writeLogMsg) method. By
default this is not thread-safe.

It is also possible to $(D override) the three methods $(D beginLogMsg),
$(D logMsgPart) and $(D finishLogMsg) together, this option gives more
flexibility.
*/
abstract class Logger
{
    /** LogEntry is a aggregation combining all information associated
    with a log message. This aggregation will be passed to the method
    writeLogMsg.
    */
    protected struct LogEntry
    {
        /// the filename the log function was called from
        string file;
        /// the line number the log function was called from
        int line;
        /// the name of the function the log function was called from
        string funcName;
        /// the pretty formatted name of the function the log function was
        /// called from
        string prettyFuncName;
        /// the name of the module the log message is coming from
        string moduleName;
        /// the $(D LogLevel) associated with the log message
        LogLevel logLevel;
        /// thread id of the log message
        Tid threadId;
        /// the time the message was logged
        SysTime timestamp;
        /// the message of the log message
        string msg;
        /// A refernce to the $(D Logger) used to create this $(D LogEntry)
        Logger logger;
    }

    /** This constructor takes a name of type $(D string), and a $(D LogLevel).

    Every subclass of $(D Logger) has to call this constructor from there
    constructor. It sets the $(D LogLevel), the name of the $(D Logger), and
    creates a fatal handler. The fatal handler will throw an $(D Error) if a
    log call is made with a $(D LogLevel) $(D LogLevel.fatal).
    */
    this(LogLevel lv)
    {
        this.logLevel_ = lv;
        this.fatalHandler_ = delegate() {
            throw new Error("A fatal log message was logged");
        };
        this.mutex = new Mutex();

        this.msgAppender = appender!string();
    }

    /** A custom logger must implement this method in order to work in a
    $(D MultiLogger) and $(D ArrayLogger).

    Params:
        payload = All information associated with call to log function.
    See_Also: beginLogMsg, logMsgPart, finishLogMsg
    */
    abstract protected void writeLogMsg(ref LogEntry payload);

    /* The default implementation will use an $(D std.array.appender)
    internally to construct the message string. This means dynamic,
    GC memory allocation. A logger can avoid this allocation by
    reimplementing $(D beginLogMsg), $(D logMsgPart) and $(D finishLogMsg).
    $(D beginLogMsg) is always called first, followed by any number of calls
    to $(D logMsgPart) and one call to $(D finishLogMsg).

    As an example for such a custom $(D Logger) compare this:
    ----------------
    class CLogger : Logger {
        override void beginLogMsg(string file, int line, string funcName,
            string prettyFuncName, string moduleName, LogLevel logLevel,
            Tid threadId, SysTime timestamp)
        {
            ... logic here
        }

        override void logMsgPart(const(char)[] msg)
        {
            ... logic here
        }

        override void finishLogMsg()
        {
            ... logic here
        }

        void writeLogMsg(ref LogEntry payload)
        {
            this.beginLogMsg(payload.file, payload.line, payload.funcName,
                payload.prettyFuncName, payload.moduleName, payload.logLevel,
                payload.threadId, payload.timestamp, payload.logger);

            this.logMsgPart(payload.msg);
            this.finishLogMsg();
        }
    }
    ----------------
    */
    protected void beginLogMsg(string file, int line, string funcName,
        string prettyFuncName, string moduleName, LogLevel logLevel,
        Tid threadId, SysTime timestamp, Logger logger)
        @trusted
    {
        static if (isLoggingActive)
        {
            header = LogEntry(file, line, funcName, prettyFuncName,
                moduleName, logLevel, threadId, timestamp, null, logger);
        }
    }

    /** Logs a part of the log message. */
    protected void logMsgPart(const(char)[] msg)
    {
        static if (isLoggingActive)
        {
            msgAppender.put(msg);
        }
    }

    /** Signals that the message has been written and no more calls to
    $(D logMsgPart) follow. */
    protected void finishLogMsg()
    {
        static if (isLoggingActive)
        {
            header.msg = msgAppender.data;
            this.writeLogMsg(header);
            msgAppender = appender!string();
        }
    }

    /** The $(D LogLevel) determines if the log call are processed or dropped
    by the $(D Logger). In order for the log call to be processed the
    $(D LogLevel) of the log call must be greater or equal to the $(D LogLevel)
    of the $(D logger).

    These two methods set and get the $(D LogLevel) of the used $(D Logger).

    Example:
    -----------
    auto f = new FileLogger(stdout);
    f.logLevel = LogLevel.info;
    assert(f.logLevel == LogLevel.info);
    -----------
    */
    @property final LogLevel logLevel() const pure @safe @nogc
    {
        synchronized (mutex) return this.logLevel_;
    }

    /// Ditto
    @property final void logLevel(const LogLevel lv) pure @safe @nogc
    {
        synchronized (mutex) this.logLevel_ = lv;
    }

    /** This $(D delegate) is called in case a log message with
    $(D LogLevel.fatal) gets logged.

    By default an $(D Error) will be thrown.
    */
    @property final void delegate() fatalHandler() const pure @safe @nogc
    {
        synchronized (mutex) return this.fatalHandler_;
    }

    /// Ditto
    @property final void fatalHandler(void delegate() fh) pure @safe @nogc
    {
        synchronized (mutex) this.fatalHandler_ = fh;
    }

    /** This method allows forwarding log entries from one logger to another.

    $(D forwardMsg) will ensure proper synchronization and then call
    $(D writeLogMsg). This is an API for implementing your own loggers and
    should not be called by normal user code. A notable difference from other
    logging functions is that the $(D globalLogLevel) wont be evaluated again
    since it is assumed that the caller already checked that.
    */
    final void forwardMsg(ref LogEntry payload)
    {
        static if (isLoggingActive) synchronized (mutex)
        {
            if (isLoggingEnabled(payload.logLevel, this.logLevel_,
                                 LogLevel.all))
            {
                this.writeLogMsg(payload);

                if (payload.logLevel == LogLevel.fatal)
                    this.fatalHandler_();
            }
        }
    }

    /** This template provides the log functions for the $(D Logger) $(D class)
    with the $(D LogLevel) encoded in the function name.

    For further information see the the two functions defined inside of this
    template.

    The aliases following this template create the public names of these log
    functions.
    */
    template memLogFunctions(LogLevel ll)
    {
        /** This function logs data to the used $(D Logger).

        In order for the resulting log message to be logged the $(D LogLevel)
        must be greater or equal than the $(D LogLevel) of the used $(D Logger)
        and must be greater or equal than the global $(D LogLevel).

        Params:
        args = The data that should be logged.

        Examples:
        --------------------
        auto s = new FileLogger(stdout);
        s.trace(1337, "is number");
        s.info(1337, "is number");
        s.error(1337, "is number");
        s.critical(1337, "is number");
        s.fatal(1337, "is number");
        --------------------
        */
        void logImpl(int line = __LINE__, string file = __FILE__,
            string funcName = __FUNCTION__,
            string prettyFuncName = __PRETTY_FUNCTION__,
            string moduleName = __MODULE__, A...)(lazy A args) @trusted
            if (args.length == 0 || (args.length > 0 && !is(A[0] : bool)))
        {
            static if (isLoggingActiveAt!ll) synchronized (mutex)
            {
                if (isLoggingEnabled(ll, this.logLevel_, globalLogLevel))
                {
                    this.beginLogMsg(file, line, funcName, prettyFuncName,
                        moduleName, ll, thisTid, Clock.currTime, this);

                    auto writer = MsgRange(this);
                    formatString(writer, args);

                    this.finishLogMsg();

                    static if (ll == LogLevel.fatal)
                        this.fatalHandler_();
                }
            }
        }

        /** This function logs data to the used $(D Logger) depending on a
        condition.

        In order for the resulting log message to be logged the $(D LogLevel) must
        be greater or equal than the $(D LogLevel) of the used $(D Logger) and
        must be greater or equal than the global $(D LogLevel) additionally the
        condition passed must be $(D true).

        Params:
        condition = The condition must be $(D true) for the data to be logged.
        args = The data that should be logged.

        Examples:
        --------------------
        auto s = new FileLogger(stdout);
        s.trace(true, 1337, "is number");
        s.info(false, 1337, "is number");
        s.error(true, 1337, "is number");
        s.critical(false, 1337, "is number");
        s.fatal(true, 1337, "is number");
        --------------------
        */
        void logImpl(int line = __LINE__, string file = __FILE__,
            string funcName = __FUNCTION__,
            string prettyFuncName = __PRETTY_FUNCTION__,
            string moduleName = __MODULE__, A...)(lazy bool condition,
                lazy A args) @trusted
        {
            static if (isLoggingActiveAt!ll) synchronized (mutex)
            {
                if (isLoggingEnabled(ll, this.logLevel_, globalLogLevel,
                                     condition))
                {
                    this.beginLogMsg(file, line, funcName, prettyFuncName,
                        moduleName, ll, thisTid, Clock.currTime, this);

                    auto writer = MsgRange(this);
                    formatString(writer, args);

                    this.finishLogMsg();

                    static if (ll == LogLevel.fatal)
                        this.fatalHandler_();
                }
            }
        }

        /** This function logs data to the used $(D Logger) in a
        $(D printf)-style manner.

        In order for the resulting log message to be logged the $(D LogLevel)
        must be greater or equal than the $(D LogLevel) of the used $(D Logger)
        and must be greater or equal than the global $(D LogLevel) additionally
           the passed condition must be $(D true).

        Params:
         condition = The condition must be $(D true) for the data to be logged.
        msg = The $(D printf)-style string.
        args = The data that should be logged.

        Examples:
        --------------------
        auto s = new FileLogger(stderr);
        s.tracef(true, "is number %d", 1);
        s.infof(true, "is number %d", 2);
        s.errorf(false, "is number %d", 3);
        s.criticalf(someFunc(), "is number %d", 4);
        s.fatalf(true, "is number %d", 5);
        --------------------
        */
        void logImplf(int line = __LINE__, string file = __FILE__,
            string funcName = __FUNCTION__,
            string prettyFuncName = __PRETTY_FUNCTION__,
            string moduleName = __MODULE__, A...)(lazy bool condition,
                lazy string msg, lazy A args) @trusted
        {
            static if (isLoggingActiveAt!ll) synchronized (mutex)
            {
                if (isLoggingEnabled(ll, this.logLevel_, globalLogLevel,
                                     condition))
                {
                    this.beginLogMsg(file, line, funcName, prettyFuncName,
                        moduleName, ll, thisTid, Clock.currTime, this);

                    auto writer = MsgRange(this);
                    formattedWrite(writer, msg, args);

                    this.finishLogMsg();

                    static if (ll == LogLevel.fatal)
                        this.fatalHandler_();
                }
            }
        }

        /** This function logs data to the used $(D Logger) in a
        $(D printf)-style manner.

        In order for the resulting log message to be logged the $(D LogLevel) must
        be greater or equal than the $(D LogLevel) of the used $(D Logger) and
        must be greater or equal than the global $(D LogLevel).

        Params:
        msg = The $(D printf)-style string.
        args = The data that should be logged.

        Examples:
        --------------------
        auto s = new FileLogger(stderr);
        s.tracef("is number %d", 1);
        s.infof("is number %d", 2);
        s.errorf("is number %d", 3);
        s.criticalf("is number %d", 4);
        s.fatalf("is number %d", 5);
        --------------------
        */
        void logImplf(int line = __LINE__, string file = __FILE__,
            string funcName = __FUNCTION__,
            string prettyFuncName = __PRETTY_FUNCTION__,
            string moduleName = __MODULE__, A...)(lazy string msg, lazy A args)
            @trusted
        {
            static if (isLoggingActiveAt!ll) synchronized (mutex)
            {
                if (isLoggingEnabled(ll, this.logLevel_, globalLogLevel))
                {
                    this.beginLogMsg(file, line, funcName, prettyFuncName,
                        moduleName, ll, thisTid, Clock.currTime, this);

                    auto writer = MsgRange(this);
                    formattedWrite(writer, msg, args);

                    this.finishLogMsg();

                    static if (ll == LogLevel.fatal)
                        this.fatalHandler_();
                }
            }
        }
    }

    /// Ditto
    alias trace = memLogFunctions!(LogLevel.trace).logImpl;
    /// Ditto
    alias tracef = memLogFunctions!(LogLevel.trace).logImplf;
    /// Ditto
    alias info = memLogFunctions!(LogLevel.info).logImpl;
    /// Ditto
    alias infof = memLogFunctions!(LogLevel.info).logImplf;
    /// Ditto
    alias warning = memLogFunctions!(LogLevel.warning).logImpl;
    /// Ditto
    alias warningf = memLogFunctions!(LogLevel.warning).logImplf;
    /// Ditto
    alias error = memLogFunctions!(LogLevel.error).logImpl;
    /// Ditto
    alias errorf = memLogFunctions!(LogLevel.error).logImplf;
    /// Ditto
    alias critical = memLogFunctions!(LogLevel.critical).logImpl;
    /// Ditto
    alias criticalf = memLogFunctions!(LogLevel.critical).logImplf;
    /// Ditto
    alias fatal = memLogFunctions!(LogLevel.fatal).logImpl;
    /// Ditto
    alias fatalf = memLogFunctions!(LogLevel.fatal).logImplf;

    /** This method logs data with the $(D LogLevel) of the used $(D Logger).

    This method takes a $(D bool) as first argument. In order for the
    data to be processed the $(D bool) must be $(D true) and the $(D LogLevel)
    of the Logger must be greater or equal to the global $(D LogLevel).

    Params:
    args = The data that should be logged.
    condition = The condition must be $(D true) for the data to be logged.
    args = The data that is to be logged.

    Returns: The logger used by the logging function as reference.

    Examples:
    --------------------
    auto l = new StdioLogger();
    l.log(1337);
    --------------------
    */
    final void log(int line = __LINE__, string file = __FILE__,
        string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__, A...)(const LogLevel ll,
        lazy bool condition, lazy A args) @trusted
        if (args.length > 1)
    {
        static if (isLoggingActive) synchronized (mutex)
        {
            if (isLoggingEnabled(ll, this.logLevel_, globalLogLevel, condition))
            {
                this.beginLogMsg(file, line, funcName, prettyFuncName,
                    moduleName, ll, thisTid, Clock.currTime, this);

                auto writer = MsgRange(this);
                formatString(writer, args);

                this.finishLogMsg();

                if (ll == LogLevel.fatal)
                    this.fatalHandler_();
            }
        }
    }

    /// Ditto
    final void log(T)(const LogLevel ll, lazy bool condition, lazy T args,
        int line = __LINE__, string file = __FILE__,
        string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__) @trusted
    {
        static if (isLoggingActive) synchronized (mutex)
        {
            if (isLoggingEnabled(ll, this.logLevel_, globalLogLevel,
                condition))
            {
                this.beginLogMsg(file, line, funcName, prettyFuncName,
                    moduleName, ll, thisTid, Clock.currTime, this);
                auto writer = MsgRange(this);
                formatString(writer, args);

                this.finishLogMsg();

                if (ll == LogLevel.fatal)
                    this.fatalHandler_();
            }
        }
    }

    /** This function logs data to the used $(D Logger) with a specific
    $(D LogLevel).

    In order for the resulting log message to be logged the $(D LogLevel)
    must be greater or equal than the $(D LogLevel) of the used $(D Logger)
    and must be greater or equal than the global $(D LogLevel).

    Params:
    ll = The specific $(D LogLevel) used for logging the log message.
    args = The data that should be logged.

    Examples:
    --------------------
    auto s = new FileLogger(stdout);
    s.log(LogLevel.trace, 1337, "is number");
    s.log(LogLevel.info, 1337, "is number");
    s.log(LogLevel.warning, 1337, "is number");
    s.log(LogLevel.error, 1337, "is number");
    s.log(LogLevel.fatal, 1337, "is number");
    --------------------
    */
    final void log(int line = __LINE__, string file = __FILE__,
        string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__, A...)(const LogLevel ll, lazy A args)
        @trusted
        if (args.length > 1 && !is(Unqual!(A[0]) : bool))
    {
        static if (isLoggingActive) synchronized (mutex)
        {
            if (isLoggingEnabled(ll, this.logLevel_, globalLogLevel))
            {
                this.beginLogMsg(file, line, funcName, prettyFuncName,
                    moduleName, ll, thisTid, Clock.currTime, this);

                auto writer = MsgRange(this);
                formatString(writer, args);

                this.finishLogMsg();

                if (ll == LogLevel.fatal)
                    this.fatalHandler_();
            }
        }
    }

    /// Ditto
    final void log(T)(const LogLevel ll, lazy T args, int line = __LINE__,
        string file = __FILE__, string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__) @trusted
    {
        static if (isLoggingActive) synchronized (mutex)
        {
            if (isLoggingEnabled(ll, this.logLevel_, globalLogLevel))
            {
                this.beginLogMsg(file, line, funcName, prettyFuncName,
                    moduleName, ll, thisTid, Clock.currTime, this);
                auto writer = MsgRange(this);
                formatString(writer, args);

                this.finishLogMsg();

                if (ll == LogLevel.fatal)
                    this.fatalHandler_();
            }
        }
    }

    /** This function logs data to the used $(D Logger) depending on a
    explicitly passed condition with the $(D LogLevel) of the used
    $(D Logger).

    In order for the resulting log message to be logged the $(D LogLevel)
    of the used $(D Logger) must be greater or equal than the global
    $(D LogLevel) and the condition must be $(D true).

    Params:
    condition = The condition must be $(D true) for the data to be logged.
    args = The data that should be logged.

    Examples:
    --------------------
    auto s = new FileLogger(stdout);
    s.log(true, 1337, "is number");
    s.log(true, 1337, "is number");
    s.log(true, 1337, "is number");
    s.log(false, 1337, "is number");
    s.log(false, 1337, "is number");
    --------------------
    */
    final void log(int line = __LINE__, string file = __FILE__,
        string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__, A...)(lazy bool condition, lazy A args)
        @trusted
        if (args.length > 1)
    {
        static if (isLoggingActive) synchronized (mutex)
        {
            if (isLoggingEnabled(this.logLevel_, this.logLevel_,
                globalLogLevel, condition))
            {
                this.beginLogMsg(file, line, funcName, prettyFuncName,
                    moduleName, this.logLevel_, thisTid, Clock.currTime, this);

                auto writer = MsgRange(this);
                formatString(writer, args);

                this.finishLogMsg();

                if (this.logLevel_ == LogLevel.fatal)
                    this.fatalHandler_();
            }
        }
    }

    /// Ditto
    final void log(T)(lazy bool condition, lazy T args, int line = __LINE__,
        string file = __FILE__, string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__) @trusted
    {
        static if (isLoggingActive) synchronized (mutex)
        {
            if (isLoggingEnabled(this.logLevel_, this.logLevel_, globalLogLevel,
                condition))
            {
                this.beginLogMsg(file, line, funcName, prettyFuncName,
                    moduleName, this.logLevel_, thisTid, Clock.currTime, this);
                auto writer = MsgRange(this);
                formatString(writer, args);

                this.finishLogMsg();

                if (this.logLevel_ == LogLevel.fatal)
                    this.fatalHandler_();
            }
        }
    }

    /** This function logs data to the used $(D Logger) with the $(D LogLevel)
    of the used $(D Logger).

    In order for the resulting log message to be logged the $(D LogLevel)
    of the used $(D Logger) must be greater or equal than the global
    $(D LogLevel).

    Params:
    args = The data that should be logged.

    Examples:
    --------------------
    auto s = new FileLogger(stdout);
    s.log(1337, "is number");
    s.log(info, 1337, "is number");
    s.log(1337, "is number");
    s.log(1337, "is number");
    s.log(1337, "is number");
    --------------------
    */
    final void log(int line = __LINE__, string file = __FILE__,
        string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__, A...)(lazy A args)
        @trusted
        if (args.length > 1
                && !is(Unqual!(A[0]) : bool)
                && !is(Unqual!(A[0]) == LogLevel))
    {
        static if (isLoggingActive) synchronized (mutex)
        {
            if (isLoggingEnabled(this.logLevel_, this.logLevel_,
                globalLogLevel))
            {
                this.beginLogMsg(file, line, funcName, prettyFuncName,
                    moduleName, this.logLevel_, thisTid, Clock.currTime, this);
                auto writer = MsgRange(this);
                formatString(writer, args);

                this.finishLogMsg();

                if (this.logLevel_ == LogLevel.fatal)
                    this.fatalHandler_();
            }
        }
    }

    /// Ditto
    final void log(T)(lazy T arg, int line = __LINE__, string file = __FILE__,
        string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__) @trusted
    {
        static if (isLoggingActive) synchronized (mutex)
        {
            if (isLoggingEnabled(this.logLevel_, this.logLevel_, globalLogLevel))
            {
                this.beginLogMsg(file, line, funcName, prettyFuncName,
                    moduleName, this.logLevel_, thisTid, Clock.currTime, this);
                auto writer = MsgRange(this);
                formatString(writer, arg);

                this.finishLogMsg();

                if (this.logLevel_ == LogLevel.fatal)
                    this.fatalHandler_();
            }
        }
    }

    /** This function logs data to the used $(D Logger) with a specific
    $(D LogLevel) and depending on a condition in a $(D printf)-style manner.

    In order for the resulting log message to be logged the $(D LogLevel)
    must be greater or equal than the $(D LogLevel) of the used $(D Logger)
    and must be greater or equal than the global $(D LogLevel) and the
    condition must be $(D true).

    Params:
    ll = The specific $(D LogLevel) used for logging the log message.
    condition = The condition must be $(D true) for the data to be logged.
    msg = The format string used for this log call.
    args = The data that should be logged.

    Examples:
    --------------------
    auto s = new FileLogger(stdout);
    s.logf(LogLevel.trace, true ,"%d %s", 1337, "is number");
    s.logf(LogLevel.info, true ,"%d %s", 1337, "is number");
    s.logf(LogLevel.warning, true ,"%d %s", 1337, "is number");
    s.logf(LogLevel.error, false ,"%d %s", 1337, "is number");
    s.logf(LogLevel.fatal, true ,"%d %s", 1337, "is number");
    --------------------
    */
    final void logf(int line = __LINE__, string file = __FILE__,
        string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__, A...)(const LogLevel ll,
        lazy bool condition, lazy string msg, lazy A args) @trusted
    {
        static if (isLoggingActive) synchronized (mutex)
        {
            if (isLoggingEnabled(ll, this.logLevel_, globalLogLevel, condition))
            {
                this.beginLogMsg(file, line, funcName, prettyFuncName,
                    moduleName, ll, thisTid, Clock.currTime, this);

                auto writer = MsgRange(this);
                formattedWrite(writer, msg, args);

                this.finishLogMsg();

                if (ll == LogLevel.fatal)
                    this.fatalHandler_();
            }
        }
    }

    /** This function logs data to the used $(D Logger) with a specific
    $(D LogLevel) in a $(D printf)-style manner.

    In order for the resulting log message to be logged the $(D LogLevel)
    must be greater or equal than the $(D LogLevel) of the used $(D Logger)
    and must be greater or equal than the global $(D LogLevel).

    Params:
    ll = The specific $(D LogLevel) used for logging the log message.
    msg = The format string used for this log call.
    args = The data that should be logged.

    Examples:
    --------------------
    auto s = new FileLogger(stdout);
    s.logf(LogLevel.trace, "%d %s", 1337, "is number");
    s.logf(LogLevel.info, "%d %s", 1337, "is number");
    s.logf(LogLevel.warning, "%d %s", 1337, "is number");
    s.logf(LogLevel.error, "%d %s", 1337, "is number");
    s.logf(LogLevel.fatal, "%d %s", 1337, "is number");
    --------------------
    */
    final void logf(int line = __LINE__, string file = __FILE__,
        string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__, A...)(const LogLevel ll,
            lazy string msg, lazy A args) @trusted
        if (args.length == 0 || (args.length > 0 && !is(Unqual!(A[0]) : bool)))
    {
        static if (isLoggingActive) synchronized (mutex)
        {
            if (isLoggingEnabled(ll, this.logLevel_, globalLogLevel))
            {
                this.beginLogMsg(file, line, funcName, prettyFuncName,
                    moduleName, ll, thisTid, Clock.currTime, this);

                auto writer = MsgRange(this);
                formattedWrite(writer, msg, args);

                this.finishLogMsg();

                if (ll == LogLevel.fatal)
                    this.fatalHandler_();
            }
        }
    }

    /** This function logs data to the used $(D Logger) depending on a
    condition with the $(D LogLevel) of the used $(D Logger) in a
    $(D printf)-style manner.

    In order for the resulting log message to be logged the $(D LogLevel)
    of the used $(D Logger) must be greater or equal than the global
    $(D LogLevel) and the condition must be $(D true).

    Params:
    condition = The condition must be $(D true) for the data to be logged.
    msg = The format string used for this log call.
    args = The data that should be logged.

    Examples:
    --------------------
    auto s = new FileLogger(stdout);
    s.logf(true ,"%d %s", 1337, "is number");
    s.logf(true ,"%d %s", 1337, "is number");
    s.logf(true ,"%d %s", 1337, "is number");
    s.logf(false ,"%d %s", 1337, "is number");
    s.logf(true ,"%d %s", 1337, "is number");
    --------------------
    */
    final void logf(int line = __LINE__, string file = __FILE__,
        string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__, A...)(lazy bool condition,
            lazy string msg, lazy A args) @trusted
    {
        static if (isLoggingActive) synchronized (mutex)
        {
            if (isLoggingEnabled(this.logLevel_, this.logLevel_, globalLogLevel,
                condition))
            {
                this.beginLogMsg(file, line, funcName, prettyFuncName,
                    moduleName, this.logLevel_, thisTid, Clock.currTime, this);

                auto writer = MsgRange(this);
                formattedWrite(writer, msg, args);

                this.finishLogMsg();

                if (this.logLevel_ == LogLevel.fatal)
                    this.fatalHandler_();
            }
        }
    }

    /** This method logs data to the used $(D Logger) with the $(D LogLevel)
    of the this $(D Logger) in a $(D printf)-style manner.

    In order for the data to be processed the $(D LogLevel) of the $(D Logger)
    must be greater or equal to the global $(D LogLevel).

    Params:
    msg = The format string used for this log call.
    args = The data that should be logged.

    Examples:
    --------------------
    auto s = new FileLogger(stdout);
    s.logf("%d %s", 1337, "is number");
    s.logf("%d %s", 1337, "is number");
    s.logf("%d %s", 1337, "is number");
    s.logf("%d %s", 1337, "is number");
    s.logf("%d %s", 1337, "is number");
    --------------------
    */
    final void logf(int line = __LINE__, string file = __FILE__,
        string funcName = __FUNCTION__,
        string prettyFuncName = __PRETTY_FUNCTION__,
        string moduleName = __MODULE__, A...)(lazy string msg, lazy A args)
        @trusted
    {
        static if (isLoggingActive) synchronized (mutex)
        {
            if (isLoggingEnabled(this.logLevel_, this.logLevel_,
                globalLogLevel))
            {
                this.beginLogMsg(file, line, funcName, prettyFuncName,
                    moduleName, this.logLevel_, thisTid, Clock.currTime, this);

                auto writer = MsgRange(this);
                formattedWrite(writer, msg, args);

                this.finishLogMsg();

                if (this.logLevel_ == LogLevel.fatal)
                    this.fatalHandler_();
            }
        }
    }

    private void delegate() fatalHandler_;
    private LogLevel logLevel_ = LogLevel.info;
    private Mutex mutex;

    protected Appender!string msgAppender;
    protected LogEntry header;
}

private __gshared Mutex __stdloggermutex;
private __gshared Logger __logger;
private __gshared Logger __defaultLogger;
private shared LogLevel __globalLogLevel = LogLevel.all;


/* This method returns the global default Logger.

Since operations on global state shared between threads must be properly
synchronized, this has package visibility only and is to be used inside
`synchronized (__stdloggermutex)` blocks or in single-threaded unittests.

If public access to the stdlog should be needed we could implement a
`stdlogApply(…)` function that takes a fn/dlg and properly synchronizes
on entry and exit.
*/
package @property Logger stdlogImpl() @trusted
{
    static __gshared ubyte[__traits(classInstanceSize, FileLogger)] buffer;

    if (__defaultLogger is null)
    {
        __defaultLogger = emplace!FileLogger(buffer, stderr, LogLevel.all);
    }
    if (__logger is null)
    {
        __logger = __defaultLogger;
    }
    return __logger;
}

/** This method sets the default $(D Logger).

The default $(D Logger) must be thread-safe.

Example:
-------------
stdlog = new FileLogger(yourFile);
-------------
The example sets a new $(D StdioLogger) as new $(D stdlog).

If at some point you want to use the original default logger again, you can
use $(D stdlog = null;). This will put back the original.
*/
@property void stdlog(Logger logger) @trusted
body
{
    // We don't want to swap out the stdlog while another thread works with it.
    synchronized (__stdloggermutex)
    {
        if (logger is null)
        {
            __logger = __defaultLogger;
        }
        else
        {
            __logger = logger;
        }
    }
}

/** This methods get and set the global $(D LogLevel).

Every log message with a $(D LogLevel) lower as the global $(D LogLevel)
will be discarded before it reaches $(D writeLogMessage) method of any
$(D Logger).
*/
/* Implementation note:
For any public logging call, the global log level shall only be queried once on
entry. Otherwise when another threads changes the level, we wouls work with
different levels at different spots in the code.
*/
@property LogLevel globalLogLevel() @trusted @nogc
{
    import core.atomic;
    return atomicLoad!(MemoryOrder.acq)(__globalLogLevel);
}

/// Ditto
@property void globalLogLevel(LogLevel ll) @trusted
{
    import core.atomic;
    atomicStore!(MemoryOrder.rel)(__globalLogLevel, ll);
}

version (unittest)
{
    import std.array;
    import std.ascii;
    import std.random;

    @trusted package string randomString(size_t upto)
    {
        auto app = Appender!string();
        foreach(_ ; 0 .. upto)
            app.put(letters[uniform(0, letters.length)]);
        return app.data;
    }
}

@safe unittest
{
    LogLevel ll = globalLogLevel;
    globalLogLevel = LogLevel.fatal;
    assert(globalLogLevel == LogLevel.fatal);
    globalLogLevel = ll;
}

version (unittest)
{
    package class TestLogger : Logger
    {
        int line = -1;
        string file = null;
        string func = null;
        string prettyFunc = null;
        string msg = null;
        LogLevel lvl;

        this(const LogLevel lv = LogLevel.info)
        {
            super(lv);
        }

        override protected void writeLogMsg(ref LogEntry payload) @safe
        {
            this.line = payload.line;
            this.file = payload.file;
            this.func = payload.funcName;
            this.prettyFunc = payload.prettyFuncName;
            this.lvl = payload.logLevel;
            this.msg = payload.msg;
        }
    }

    private void testFuncNames(Logger logger) {
        string s = "I'm here";
        logger.log(s);
    }
}


unittest
{
    auto tl1 = new TestLogger();
    testFuncNames(tl1);
    assert(tl1.func == "std.experimental.logger.core.testFuncNames", tl1.func);
    assert(tl1.prettyFunc ==
        "void std.experimental.logger.core.testFuncNames(Logger logger)",
        tl1.prettyFunc);
    assert(tl1.msg == "I'm here", tl1.msg);
}

unittest
{
    import std.experimental.logger.multilogger;

    auto tl1 = new TestLogger;
    auto tl2 = new TestLogger;

    auto ml = new MultiLogger();
    ml.insertLogger("one", tl1);
    ml.insertLogger("two", tl2);
    assertThrown!Exception(ml.insertLogger("one", tl1));

    string msg = "Hello Logger World";
    ml.log(msg);
    int lineNumber = __LINE__ - 1;
    assert(tl1.msg == msg);
    assert(tl1.line == lineNumber);
    assert(tl2.msg == msg);
    assert(tl2.line == lineNumber);

    ml.removeLogger("one");
    ml.removeLogger("two");
    assertThrown!Exception(ml.removeLogger("one"));
}

unittest
{
    bool errorThrown = false;
    auto tl = new TestLogger;
    auto dele = delegate() {
        errorThrown = true;
    };
    tl.fatalHandler = dele;
    tl.fatal();
    assert(errorThrown);
}

unittest
{
    auto l = new TestLogger(LogLevel.info);
    string msg = "Hello Logger World";
    l.log(msg);
    int lineNumber = __LINE__ - 1;
    assert(l.msg == msg);
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    l.log(true, msg);
    lineNumber = __LINE__ - 1;
    assert(l.msg == msg);
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    l.log(false, msg);
    assert(l.msg == msg);
    assert(l.line == lineNumber, to!string(l.line));
    assert(l.logLevel == LogLevel.info);

    msg = "%s Another message";
    l.logf(msg, "Yet");
    lineNumber = __LINE__ - 1;
    assert(l.msg == msg.format("Yet"));
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    l.logf(true, msg, "Yet");
    lineNumber = __LINE__ - 1;
    assert(l.msg == msg.format("Yet"));
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    l.logf(false, msg, "Yet");
    assert(l.msg == msg.format("Yet"));
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    assertThrown!Throwable(l.logf(LogLevel.fatal, msg, "Yet"));
    lineNumber = __LINE__ - 1;
    assert(l.msg == msg.format("Yet"));
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    assertThrown!Throwable(l.logf(LogLevel.fatal, true, msg, "Yet"));
    lineNumber = __LINE__ - 1;
    assert(l.msg == msg.format("Yet"));
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    assertNotThrown(l.logf(LogLevel.fatal, false, msg, "Yet"));
    assert(l.msg == msg.format("Yet"));
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    auto oldunspecificLogger = stdlogImpl;

    assert(oldunspecificLogger.logLevel == LogLevel.all,
         to!string(oldunspecificLogger.logLevel));

    assert(l.logLevel == LogLevel.info);
    stdlog = l;
    assert(globalLogLevel == LogLevel.all,
            to!string(globalLogLevel));

    scope(exit)
    {
        stdlog = oldunspecificLogger;
    }

    assert(stdlogImpl.logLevel == LogLevel.info);
    assert(globalLogLevel == LogLevel.all);

    msg = "Another message";
    log(msg);
    lineNumber = __LINE__ - 1;
    assert(l.logLevel == LogLevel.info);
    assert(l.line == lineNumber, to!string(l.line));
    assert(l.msg == msg, l.msg);

    log(true, msg);
    lineNumber = __LINE__ - 1;
    assert(l.msg == msg);
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    log(false, msg);
    assert(l.msg == msg);
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    msg = "%s Another message";
    logf(msg, "Yet");
    lineNumber = __LINE__ - 1;
    assert(l.msg == msg.format("Yet"));
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    logf(true, msg, "Yet");
    lineNumber = __LINE__ - 1;
    assert(l.msg == msg.format("Yet"));
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    logf(false, msg, "Yet");
    assert(l.msg == msg.format("Yet"));
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    msg = "%s Another message";
    assertThrown!Throwable(logf(LogLevel.fatal, msg, "Yet"));
    lineNumber = __LINE__ - 1;
    assert(l.msg == msg.format("Yet"));
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    assertThrown!Throwable(logf(LogLevel.fatal, true, msg, "Yet"));
    lineNumber = __LINE__ - 1;
    assert(l.msg == msg.format("Yet"));
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);

    assertNotThrown(logf(LogLevel.fatal, false, msg, "Yet"));
    assert(l.msg == msg.format("Yet"));
    assert(l.line == lineNumber);
    assert(l.logLevel == LogLevel.info);
}

unittest // default logger
{
    import std.file;
    string filename = randomString(32) ~ ".tempLogFile";
    FileLogger l = new FileLogger(filename);
    auto oldunspecificLogger = stdlogImpl;
    stdlog = l;

    scope(exit)
    {
        remove(filename);
        stdlog = oldunspecificLogger;
        globalLogLevel = LogLevel.all;
    }

    string notWritten = "this should not be written to file";
    string written = "this should be written to file";

    globalLogLevel = LogLevel.critical;
    assert(globalLogLevel == LogLevel.critical);

    log(LogLevel.warning, notWritten);
    log(LogLevel.critical, written);

    l.file.flush();
    l.file.close();

    auto file = File(filename, "r");
    assert(!file.eof);

    string readLine = file.readln();
    assert(readLine.indexOf(written) != -1, readLine);
    assert(readLine.indexOf(notWritten) == -1, readLine);
    file.close();
}

unittest
{
    import std.file;
    import core.memory;
    string filename = randomString(32) ~ ".tempLogFile";
    auto oldunspecificLogger = stdlogImpl;

    scope(exit)
    {
        remove(filename);
        stdlog = oldunspecificLogger;
        globalLogLevel = LogLevel.all;
    }

    string notWritten = "this should not be written to file";
    string written = "this should be written to file";

    auto l = new FileLogger(filename);
    stdlog = l;
    stdlogImpl.logLevel = LogLevel.critical;

    log(LogLevel.error, false, notWritten);
    log(LogLevel.critical, true, written);
    destroy(l);

    auto file = File(filename, "r");
    auto readLine = file.readln();
    assert(!readLine.empty, readLine);
    assert(readLine.indexOf(written) != -1);
    assert(readLine.indexOf(notWritten) == -1);
    file.close();
}

unittest
{
    auto tl = new TestLogger(LogLevel.all);
    int l = __LINE__;
    tl.info("a");
    assert(tl.line == l+1);
    assert(tl.msg == "a");
    assert(tl.logLevel == LogLevel.all);
    assert(globalLogLevel == LogLevel.all);
    l = __LINE__;
    tl.trace("b");
    assert(tl.msg == "b", tl.msg);
    assert(tl.line == l+1, to!string(tl.line));
}

// testing possible log conditions
unittest
{
    auto oldunspecificLogger = stdlogImpl;

    auto mem = new TestLogger;
    mem.fatalHandler = delegate() {};
    stdlog = mem;

    scope(exit)
    {
        stdlog = oldunspecificLogger;
        globalLogLevel = LogLevel.all;
    }

    int value = 0;
    foreach(gll; [cast(LogLevel) LogLevel.all, LogLevel.trace,
            LogLevel.info, LogLevel.warning, LogLevel.error,
            LogLevel.critical, LogLevel.fatal, LogLevel.off])
    {

        globalLogLevel = gll;

        foreach(ll; [cast(LogLevel) LogLevel.all, LogLevel.trace,
                LogLevel.info, LogLevel.warning, LogLevel.error,
                LogLevel.critical, LogLevel.fatal, LogLevel.off])
        {

            mem.logLevel = ll;

            foreach(cond; [true, false])
            {
                foreach(condValue; [true, false])
                {
                    foreach(memOrG; [true, false])
                    {
                        foreach(prntf; [true, false])
                        {
                            foreach(ll2; [cast(LogLevel) LogLevel.all, LogLevel.trace,
                                    LogLevel.info, LogLevel.warning,
                                    LogLevel.error, LogLevel.critical,
                                    LogLevel.fatal, LogLevel.off])
                            {
                                foreach(singleMulti; 0 .. 2)
                                {
                                    int lineCall;
                                    mem.msg = "-1";
                                    if (memOrG)
                                    {
                                        if (prntf)
                                        {
                                            if (cond)
                                            {
                                                if (singleMulti == 0)
                                                {
                                                    mem.logf(ll2, condValue, "%s",
                                                        value);
                                                    lineCall = __LINE__;
                                                }
                                                else
                                                {
                                                    mem.logf(ll2, condValue,
                                                        "%d %d", value, value);
                                                    lineCall = __LINE__;
                                                }
                                            }
                                            else
                                            {
                                                if (singleMulti == 0)
                                                {
                                                    mem.logf(ll2, "%s", value);
                                                    lineCall = __LINE__;
                                                }
                                                else
                                                {
                                                    mem.logf(ll2, "%d %d",
                                                        value, value);
                                                    lineCall = __LINE__;
                                                }
                                            }
                                        }
                                        else
                                        {
                                            if (cond)
                                            {
                                                if (singleMulti == 0)
                                                {
                                                    mem.log(ll2, condValue,
                                                        to!string(value));
                                                    lineCall = __LINE__;
                                                }
                                                else
                                                {
                                                    mem.log(ll2, condValue,
                                                        to!string(value), value);
                                                    lineCall = __LINE__;
                                                }
                                            }
                                            else
                                            {
                                                if (singleMulti == 0)
                                                {
                                                    mem.log(ll2, to!string(value));
                                                    lineCall = __LINE__;
                                                }
                                                else
                                                {
                                                    mem.log(ll2,
                                                        to!string(value),
                                                        value);
                                                    lineCall = __LINE__;
                                                }
                                            }
                                        }
                                    }
                                    else
                                    {
                                        if (prntf)
                                        {
                                            if (cond)
                                            {
                                                if (singleMulti == 0)
                                                {
                                                    logf(ll2, condValue, "%s",
                                                        value);
                                                    lineCall = __LINE__;
                                                }
                                                else
                                                {
                                                    logf(ll2, condValue,
                                                        "%s %d", value, value);
                                                    lineCall = __LINE__;
                                                }
                                            }
                                            else
                                            {
                                                if (singleMulti == 0)
                                                {
                                                    logf(ll2, "%s", value);
                                                    lineCall = __LINE__;
                                                }
                                                else
                                                {
                                                    logf(ll2, "%s %s", value,
                                                        value);
                                                    lineCall = __LINE__;
                                                }
                                            }
                                        }
                                        else
                                        {
                                            if (cond)
                                            {
                                                if (singleMulti == 0)
                                                {
                                                    log(ll2, condValue,
                                                        to!string(value));
                                                    lineCall = __LINE__;
                                                }
                                                else
                                                {
                                                    log(ll2, condValue, value,
                                                        to!string(value));
                                                    lineCall = __LINE__;
                                                }
                                            }
                                            else
                                            {
                                                if (singleMulti == 0)
                                                {
                                                    log(ll2, to!string(value));
                                                    lineCall = __LINE__;
                                                }
                                                else
                                                {
                                                    log(ll2, value,
                                                        to!string(value));
                                                    lineCall = __LINE__;
                                                }
                                            }
                                        }
                                    }

                                    string valueStr = to!string(value);
                                    ++value;

                                    bool gllOff = (gll != LogLevel.off);
                                    bool llOff = (ll != LogLevel.off);
                                    bool condFalse = (cond ? condValue : true);
                                    bool ll2VSgll = (ll2 >= gll);
                                    bool ll2VSll = (ll2 >= ll);

                                    bool shouldLog = gllOff && llOff && condFalse
                                        && ll2VSgll && ll2VSll;

                                    /*
                                    writefln(
                                        "go(%b) ll2o(%b) c(%b) lg(%b) ll(%b) s(%b)"
                                        , gll != LogLevel.off, ll2 != LogLevel.off,
                                        cond ? condValue : true,
                                        ll2 >= gll, ll2 >= ll, shouldLog);
                                    */


                                    if (shouldLog)
                                    {
                                        assert(mem.msg.indexOf(valueStr) != -1,
                                            format(
                                            "lineCall(%d) gll(%u) ll(%u) ll2(%u) " ~
                                            "cond(%b) condValue(%b)" ~
                                            " memOrG(%b) shouldLog(%b) %s == %s" ~
                                            " %b %b %b %b %b",
                                            lineCall, gll, ll, ll2, cond,
                                            condValue, memOrG, shouldLog, mem.msg,
                                            valueStr, gllOff, llOff, condFalse,
                                            ll2VSgll, ll2VSll
                                        ));
                                    }
                                    else
                                    {
                                        assert(mem.msg.indexOf(valueStr),
                                            format(
                                            "lineCall(%d) gll(%u) ll(%u) ll2(%u) " ~
                                            " cond(%b)condValue(%b)  memOrG(%b) " ~
                                            "shouldLog(%b) %s != %s", gll,
                                            lineCall, ll, ll2, cond, condValue,
                                            memOrG, shouldLog, mem.msg, valueStr
                                        ));
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

// more testing
unittest
{
    auto oldunspecificLogger = stdlogImpl;

    auto mem = new TestLogger;
    mem.fatalHandler = delegate() {};
    stdlog = mem;

    scope(exit)
    {
        stdlog = oldunspecificLogger;
        globalLogLevel = LogLevel.all;
    }

    int value = 0;
    foreach(gll; [cast(LogLevel) LogLevel.all, LogLevel.trace,
            LogLevel.info, LogLevel.warning, LogLevel.error,
            LogLevel.critical, LogLevel.fatal, LogLevel.off])
    {

        globalLogLevel = gll;

        foreach(ll; [cast(LogLevel) LogLevel.all, LogLevel.trace,
                LogLevel.info, LogLevel.warning, LogLevel.error,
                LogLevel.critical, LogLevel.fatal, LogLevel.off])
        {

            mem.logLevel = ll;

            foreach(cond; [true, false])
            {
                foreach(condValue; [true, false])
                {
                    foreach(memOrG; [true, false])
                    {
                        foreach(prntf; [true, false])
                        {
                            foreach(singleMulti; 0 .. 2)
                            {
                                int lineCall;
                                mem.msg = "-1";
                                if (memOrG)
                                {
                                    if (prntf)
                                    {
                                        if (cond)
                                        {
                                            if (singleMulti == 0)
                                            {
                                                mem.logf(condValue, "%s",
                                                    value);
                                                lineCall = __LINE__;
                                            }
                                            else
                                            {
                                                mem.logf(condValue,
                                                    "%d %d", value, value);
                                                lineCall = __LINE__;
                                            }
                                        }
                                        else
                                        {
                                            if (singleMulti == 0)
                                            {
                                                mem.logf("%s", value);
                                                lineCall = __LINE__;
                                            }
                                            else
                                            {
                                                mem.logf("%d %d",
                                                    value, value);
                                                lineCall = __LINE__;
                                            }
                                        }
                                    }
                                    else
                                    {
                                        if (cond)
                                        {
                                            if (singleMulti == 0)
                                            {
                                                mem.log(condValue,
                                                    to!string(value));
                                                lineCall = __LINE__;
                                            }
                                            else
                                            {
                                                mem.log(condValue,
                                                    to!string(value), value);
                                                lineCall = __LINE__;
                                            }
                                        }
                                        else
                                        {
                                            if (singleMulti == 0)
                                            {
                                                mem.log(to!string(value));
                                                lineCall = __LINE__;
                                            }
                                            else
                                            {
                                                mem.log(to!string(value),
                                                    value);
                                                lineCall = __LINE__;
                                            }
                                        }
                                    }
                                }
                                else
                                {
                                    if (prntf)
                                    {
                                        if (cond)
                                        {
                                            if (singleMulti == 0)
                                            {
                                                logf(condValue, "%s", value);
                                                lineCall = __LINE__;
                                            }
                                            else
                                            {
                                                logf(condValue, "%s %d", value,
                                                    value);
                                                lineCall = __LINE__;
                                            }
                                        }
                                        else
                                        {
                                            if (singleMulti == 0)
                                            {
                                                logf("%s", value);
                                                lineCall = __LINE__;
                                            }
                                            else
                                            {
                                                logf("%s %s", value, value);
                                                lineCall = __LINE__;
                                            }
                                        }
                                    }
                                    else
                                    {
                                        if (cond)
                                        {
                                            if (singleMulti == 0)
                                            {
                                                log(condValue,
                                                    to!string(value));
                                                lineCall = __LINE__;
                                            }
                                            else
                                            {
                                                log(condValue, value,
                                                    to!string(value));
                                                lineCall = __LINE__;
                                            }
                                        }
                                        else
                                        {
                                            if (singleMulti == 0)
                                            {
                                                log(to!string(value));
                                                lineCall = __LINE__;
                                            }
                                            else
                                            {
                                                log(value, to!string(value));
                                                lineCall = __LINE__;
                                            }
                                        }
                                    }
                                }

                                string valueStr = to!string(value);
                                ++value;

                                bool gllOff = (gll != LogLevel.off);
                                bool llOff = (ll != LogLevel.off);
                                bool llVSgll = (ll >= gll);
                                bool condFalse = (cond ? condValue : true);

                                bool shouldLog = gllOff && llOff && condFalse
                                    && llVSgll;

                                /*
                                writefln(
                                    "go(%b) ll2o(%b) c(%b) lg(%b) ll(%b) s(%b)"
                                    , gll != LogLevel.off, ll2 != LogLevel.off,
                                    cond ? condValue : true,
                                    ll2 >= gll, ll2 >= ll, shouldLog);
                                */


                                if (shouldLog)
                                {
                                    assert(mem.msg.indexOf(valueStr) != -1,
                                        format(
                                        "lineCall(%d) gll(%u) ll(%u) " ~
                                        "cond(%b) condValue(%b)" ~
                                        " memOrG(%b) shouldLog(%b) %s == %s" ~
                                        " %b %b %b",
                                        lineCall, gll, ll,  cond,
                                        condValue, memOrG, shouldLog, mem.msg,
                                        valueStr, gllOff, llOff, condFalse
                                    ));
                                }
                                else
                                {
                                    assert(mem.msg.indexOf(valueStr),
                                        format(
                                        "lineCall(%d) gll(%u) ll(%u) " ~
                                        " cond(%b)condValue(%b)  memOrG(%b) " ~
                                        "shouldLog(%b) %s != %s", gll,
                                        lineCall, ll, cond, condValue,
                                        memOrG, shouldLog, mem.msg, valueStr
                                    ));
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

// testing more possible log conditions
unittest
{
    bool fatalLog;
    auto mem = new TestLogger;
    mem.fatalHandler = delegate() { fatalLog = true; };
    auto oldunspecificLogger = stdlogImpl;

    stdlog = mem;
    scope(exit)
    {
        stdlog = oldunspecificLogger;
        globalLogLevel = LogLevel.all;
    }

    foreach(gll; [cast(LogLevel) LogLevel.all, LogLevel.trace,
            LogLevel.info, LogLevel.warning, LogLevel.error,
            LogLevel.critical, LogLevel.fatal, LogLevel.off])
    {

        globalLogLevel = gll;

        foreach(ll; [cast(LogLevel) LogLevel.all, LogLevel.trace,
                LogLevel.info, LogLevel.warning, LogLevel.error,
                LogLevel.critical, LogLevel.fatal, LogLevel.off])
        {
            mem.logLevel = ll;

            foreach(cond; [true, false])
            {
                assert(globalLogLevel == gll);
                assert(mem.logLevel == ll);

                bool gllVSll = LogLevel.trace >= globalLogLevel;
                bool llVSgll = ll >= globalLogLevel;
                bool lVSll = LogLevel.trace >= ll;
                bool gllOff = globalLogLevel != LogLevel.off;
                bool llOff = mem.logLevel != LogLevel.off;

                bool test = llVSgll && gllVSll && lVSll && gllOff && llOff && cond;

                mem.line = -1;
                /*
                writefln("gll(%3u) ll(%3u) cond(%b) test(%b)",
                    gll, ll, cond, test);
                writefln("%b %b %b %b %b %b test2(%b)", llVSgll, gllVSll, lVSll,
                    gllOff, llOff, cond, test2);
                */

                mem.trace(__LINE__); int line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                trace(__LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                mem.trace(cond, __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                trace(cond, __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                mem.tracef("%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                tracef("%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                mem.tracef(cond, "%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                tracef(cond, "%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                llVSgll = ll >= globalLogLevel;
                lVSll = LogLevel.info >= ll;
                test = llVSgll && gllVSll && lVSll && gllOff && llOff && cond;

                mem.info(__LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                info(__LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                mem.info(cond, __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                info(cond, __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                mem.infof("%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                infof("%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                mem.infof(cond, "%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                infof(cond, "%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                llVSgll = ll >= globalLogLevel;
                lVSll = LogLevel.warning >= ll;
                test = llVSgll && gllVSll && lVSll && gllOff && llOff && cond;

                mem.warning(__LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                warning(__LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                mem.warning(cond, __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                warning(cond, __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                mem.warningf("%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                warningf("%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                mem.warningf(cond, "%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                warningf(cond, "%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                llVSgll = ll >= globalLogLevel;
                lVSll = LogLevel.critical >= ll;
                test = llVSgll && gllVSll && lVSll && gllOff && llOff && cond;

                mem.critical(__LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                critical(__LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                mem.critical(cond, __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                critical(cond, __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                mem.criticalf("%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                criticalf("%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                mem.criticalf(cond, "%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                criticalf(cond, "%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;

                llVSgll = ll >= globalLogLevel;
                lVSll = LogLevel.fatal >= ll;
                test = llVSgll && gllVSll && lVSll && gllOff && llOff && cond;

                mem.fatal(__LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;
                assert(test ? fatalLog : true);
                fatalLog = false;

                fatal(__LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;
                assert(test ? fatalLog : true);
                fatalLog = false;

                mem.fatal(cond, __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;
                assert(test ? fatalLog : true);
                fatalLog = false;

                fatal(cond, __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;
                assert(test ? fatalLog : true);
                fatalLog = false;

                mem.fatalf("%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;
                assert(test ? fatalLog : true);
                fatalLog = false;

                fatalf("%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;
                assert(test ? fatalLog : true);
                fatalLog = false;

                mem.fatalf(cond, "%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;
                assert(test ? fatalLog : true);
                fatalLog = false;

                fatalf(cond, "%d", __LINE__); line = __LINE__;
                assert(test ? mem.line == line : true); line = -1;
                assert(test ? fatalLog : true);
                fatalLog = false;
            }

        }
    }
}

// Issue #5
unittest
{
    auto oldunspecificLogger = stdlogImpl;

    scope(exit)
    {
        stdlog = oldunspecificLogger;
        globalLogLevel = LogLevel.all;
    }

    auto tl = new TestLogger(LogLevel.info);
    stdlog = tl;

    trace("trace");
    assert(tl.msg.indexOf("trace") == -1);
    //info("info");
    //assert(tl.msg.indexOf("info") == 0);
}

// Issue #5
unittest
{
    import std.experimental.logger.multilogger;

    auto oldunspecificLogger = stdlogImpl;

    scope(exit)
    {
        stdlog = oldunspecificLogger;
        globalLogLevel = LogLevel.all;
    }

    auto logger = new MultiLogger(LogLevel.error);

    auto tl = new TestLogger(LogLevel.info);
    logger.insertLogger("required", tl);
    stdlog = logger;

    trace("trace");
    assert(tl.msg.indexOf("trace") == -1);
    info("info");
    assert(tl.msg.indexOf("info") == -1);
    error("error");
    assert(tl.msg.indexOf("error") == 0);
}

unittest
{
    import std.exception : assertThrown;
    auto tl = new TestLogger();
    assertThrown!Throwable(tl.fatal("fatal"));
}

unittest
{
    auto dl = cast(FileLogger)stdlogImpl;
    assert(dl !is null);
    assert(dl.logLevel == LogLevel.all);
    assert(globalLogLevel == LogLevel.all);
}