flag.go

// Copyright 2014-2021 Ulrich Kunitz. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

/*
Package gflag implements GNU-style command line flag parsing. It
supports the transformation of programs using the Go standard library
flag package. However it doesn't target full compatibility with the Go
standard library flag package. The Flag structure doesn't support all
fields of the flag package and the Var method and function does have a
different signature.

The typical use case looks like this:

  b := Bool("flag-b", "b", false, "boolean flag")
  h := Bool("help", "h", false, "prints this message")

  Parse()

  if *h {
	  gflag.Usage()
  }
*/
package gflag

import (
	"bytes"
	"fmt"
	"io"
	"os"
	"sort"
	"strconv"
	"strings"
)

// CommandLine is the default set of command-line flags parsed from
// os.Args. The top-level functions such as BoolVar, Arg, etc. are
// wrappers for the methods of command line.
var CommandLine = NewFlagSet(os.Args[0], ExitOnError)

// ErrorHandling defines how flag parsing errors are handled.
type ErrorHandling int

// The constants define how errors should be handled.
const (
	ContinueOnError ErrorHandling = iota
	ExitOnError
	PanicOnError
)

// HasArg defines whether a flag argument is required, optional or not
// supported.
type HasArg int

// The constants define whether a flag argument is required, not
// supported or optional.
const (
	RequiredArg HasArg = iota
	NoArg
	OptionalArg
)

// Value is the interface to the value of a specific flag.
type Value interface {
	Set(string) error
	Update()
	Get() interface{}
	String() string
}

// Flag represents a single flag.
type Flag struct {
	Name       string
	Shorthands string
	HasArg     HasArg
	Value      Value
}

// line provides a single line of usage information.
type line struct {
	flags string
	usage string
}

// lineFlags computes the flags string for a usage line.
func lineFlags(name, shorthands, defaultValue string) string {
	buf := new(bytes.Buffer)
	if shorthands != "" {
		for i, r := range shorthands {
			if i > 0 {
				fmt.Fprint(buf, ", ")
			}
			fmt.Fprintf(buf, "-%c", r)
		}
	}
	if name != "" {
		if buf.Len() > 0 {
			fmt.Fprintf(buf, ", ")
		}
		fmt.Fprint(buf, "--", name)
		if defaultValue != "" {
			fmt.Fprintf(buf, "=%s", defaultValue)
		}
	}
	return buf.String()
}

// lines provides a set of usage lines.
type lines []line

// writeLines writes usage line to the writer.
func writeLines(w io.Writer, ls lines) (n int, err error) {
	l := make(lines, len(ls))
	copy(l, ls)
	sort.Sort(l)
	maxLenFlags := 0
	for _, line := range l {
		k := len(line.flags)
		if k > maxLenFlags {
			maxLenFlags = k
		}
	}
	for _, line := range l {
		format := fmt.Sprintf("  %%-%ds  %%s\n", maxLenFlags)
		var k int
		k, err = fmt.Fprintf(w, format, line.flags, line.usage)
		n += k
		if err != nil {
			return
		}
	}
	return
}

func (l lines) Len() int           { return len(l) }
func (l lines) Swap(i, j int)      { l[i], l[j] = l[j], l[i] }
func (l lines) Less(i, j int) bool { return l[i].flags < l[j].flags }

// FlagSet represents a set of option flags.
type FlagSet struct {
	// Provides a custom usage function if set.
	Usage func()

	name          string
	parsed        bool
	actual        map[string]*Flag
	formal        map[string]*Flag
	lines         lines
	args          []string
	output        io.Writer
	errorHandling ErrorHandling
	preset        bool
}

// Init initializes a flag set variable.
func (f *FlagSet) Init(name string, errorHandling ErrorHandling) {
	f.name = name
	f.errorHandling = errorHandling
}

// NewFlagSet creates a new flag set.
func NewFlagSet(name string, errorHandling ErrorHandling) *FlagSet {
	f := new(FlagSet)
	f.Init(name, errorHandling)
	return f
}

// Arg returns the argument number i after parsing has been successful.
func (f *FlagSet) Arg(i int) string {
	if !(0 <= i && i < len(f.args)) {
		return ""
	}
	return f.args[i]
}

// Arg provides the argument number i after parsing of the command line
// flags.
func Arg(i int) string {
	return CommandLine.Arg(i)
}

// Args returns all arguments after parsing.
func (f *FlagSet) Args() []string { return f.args }

// Args returns all arguments after the command line flags have been
// parsed.
func Args() []string { return CommandLine.args }

// NArg returns the number of remaining arguments after parsing.
func (f *FlagSet) NArg() int { return len(f.args) }

// NArg returns the number of remaining arguments after command line
// parsing.
func NArg() int { return len(CommandLine.args) }

// Parsed returns whether the command line has already been parsed.
func Parsed() bool {
	return CommandLine.parsed
}

// Parsed returns whether the flag set has already been parsed.
func (f *FlagSet) Parsed() bool {
	return f.parsed
}

// Parse parses the command line.
func Parse() {
	// errors are ignored because CommandLine is set on ExitOnError
	CommandLine.Parse(os.Args[1:])
}

// lookupLongOption looks up a long option flag.
func (f *FlagSet) lookupLongOption(name string) (flag *Flag, err error) {
	if len(name) < 2 {
		f.panicf("%s is not a long option", name)
	}
	var ok bool
	if flag, ok = f.formal[name]; !ok {
		return nil, fmt.Errorf("long option %s is unsupported", name)
	}
	if flag.Name != name {
		f.panicf("got %s flag; want %s flag", flag.Name, name)
	}
	return flag, nil
}

// lookupShortOption looks a short option up.
func (f *FlagSet) lookupShortOption(r rune) (flag *Flag, err error) {
	var ok bool
	name := string([]rune{r})
	if flag, ok = f.formal[name]; !ok {
		return nil, fmt.Errorf("short option %s is unsupported", name)
	}
	if !strings.ContainsRune(flag.Shorthands, r) {
		f.panicf("flag supports shorthands %q; but doesn't contain %s",
			flag.Shorthands, name)
	}
	return flag, nil
}

// processExtraFlagArg processes a flag with extra arguments not using
// the form --long-option=arg.
func (f *FlagSet) processExtraFlagArg(flag *Flag, i int) error {
	if flag.HasArg == NoArg {
		// no argument required
		flag.Value.Update()
		return nil
	}
	if i < len(f.args) {
		arg := f.args[i]
		if len(arg) == 0 || arg[0] != '-' {
			err := flag.Value.Set(arg)
			switch flag.HasArg {
			case RequiredArg:
				f.removeArg(i)
				return err
			case OptionalArg:
				if err != nil {
					flag.Value.Update()
					return nil
				}
				f.removeArg(i)
				return nil
			}
		}
	}
	// no argument
	if flag.HasArg == RequiredArg {
		return fmt.Errorf("no argument present")
	}
	// flag.HasArg == OptionalArg
	flag.Value.Update()
	return nil
}

// removeArg removes the arguments at position i from the args field of
// the flag set.
func (f *FlagSet) removeArg(i int) {
	copy(f.args[i:], f.args[i+1:])
	f.args = f.args[:len(f.args)-1]
}

// parseArg parses the argument i.
func (f *FlagSet) parseArg(i int) (next int, err error) {
	arg := f.args[i]
	if len(arg) < 2 || arg[0] != '-' {
		return i + 1, nil
	}
	if arg[1] == '-' {
		// argument starts with --
		f.removeArg(i)
		if len(arg) == 2 {
			// argument is --; remove it and ignore all
			// following arguments
			return len(f.args), nil
		}
		arg = arg[2:]
		flagArg := strings.SplitN(arg, "=", 2)
		flag, err := f.lookupLongOption(flagArg[0])
		if err != nil {
			return i, err
		}
		// case 1: no equal sign
		if len(flagArg) == 1 {
			err = f.processExtraFlagArg(flag, i)
			return i, err
		}
		// case 2: equal sign
		if flag.HasArg == NoArg {
			err = fmt.Errorf("option %s doesn't support argument",
				arg)
		} else {
			err = flag.Value.Set(flagArg[1])
		}
		return i, err
	}
	// short options
	f.removeArg(i)
	arg = arg[1:]
	for _, r := range arg {
		flag, err := f.lookupShortOption(r)
		if err != nil {
			return i, err
		}
		if err = f.processExtraFlagArg(flag, i); err != nil {
			return i, err
		}
	}
	return i, nil
}

// defaultUsage provides the default usage information.
func defaultUsage(f *FlagSet) {
	if f.name == "" {
		fmt.Fprintf(f.out(), "Usage:\n")
	} else {
		fmt.Fprintf(f.out(), "Usage of %s:\n", f.name)
	}
	f.PrintDefaults()
}

// Usage prints the default usage message.
var Usage = func() {
	fmt.Fprintf(CommandLine.out(), "Usage of %s:\n", os.Args[0])
	PrintDefaults()
}

// usage provides the usage information for the flag set.
func (f *FlagSet) usage() {
	if f.Usage == nil {
		if f == CommandLine {
			Usage()
		} else {
			defaultUsage(f)
		}
	} else {
		f.Usage()
	}
}

// Parse parses the arguments. If an error happens the error is printed
// as well as the usage information.
func (f *FlagSet) Parse(arguments []string) error {
	f.parsed = true
	f.args = arguments
	for i := 0; i < len(f.args); {
		var err error
		i, err = f.parseArg(i)
		if err == nil {
			continue
		}
		fmt.Fprintf(f.out(), "%s: %s\n", f.name, err)
		f.usage()
		switch f.errorHandling {
		case ContinueOnError:
			return err
		case ExitOnError:
			os.Exit(2)
		case PanicOnError:
			panic(err)
		}
	}
	return nil
}

// PrintDefaults prints information about all flags.
func (f *FlagSet) PrintDefaults() {
	_, err := writeLines(f.out(), f.lines)
	if err != nil {
		f.panicf("writeLines error %s", err)
	}
}

// PrintDefaults prints the information about all command line flags.
func PrintDefaults() {
	CommandLine.PrintDefaults()
}

// out returns a writer. If the field output has not been set os.Stderr
// is returned.
func (f *FlagSet) out() io.Writer {
	if f.output == nil {
		return os.Stderr
	}
	return f.output
}

// SetOutput sets the default output writer for the flag set.
func (f *FlagSet) SetOutput(w io.Writer) {
	f.output = w
}

// panicf prints a formatted error message and panics.
func (f *FlagSet) panicf(format string, values ...interface{}) {
	var msg string
	if f.name == "" {
		msg = fmt.Sprintf(format, values...)
	} else {
		v := make([]interface{}, 1+len(values))
		v[0] = f.name
		copy(v[1:], values)
		msg = fmt.Sprintf("%s "+format, v...)
	}
	fmt.Fprintln(f.out(), msg)
	panic(msg)
}

// setFormal sets the flag with the given name to the flag parameter.
func (f *FlagSet) setFormal(name string, flag *Flag) {
	if name == "" {
		f.panicf("no support for empty name strings")
	}
	if _, alreadythere := f.formal[name]; alreadythere {
		f.panicf("flag redefined: %s", flag.Name)
	}
	if f.formal == nil {
		f.formal = make(map[string]*Flag)
	}
	f.formal[name] = flag
}

// VarP creates a flag with a long and shorthand options.
func (f *FlagSet) VarP(value Value, name, shorthands string, hasArg HasArg) {
	flag := &Flag{
		Name:       name,
		Shorthands: shorthands,
		Value:      value,
		HasArg:     hasArg,
	}

	if flag.Name == "" && flag.Shorthands == "" {
		f.panicf("flag with no name or shorthands")
	}
	if len(flag.Name) == 1 {
		f.panicf("flag has single character name %q; use shorthands",
			flag.Name)
	}
	if flag.Name != "" {
		f.setFormal(flag.Name, flag)
	}
	if flag.Shorthands != "" {
		for _, r := range flag.Shorthands {
			name := string([]rune{r})
			f.setFormal(name, flag)
		}
	}
}

// VarP creates a flag for the given value for the command line.
func VarP(value Value, name, shorthands string, hasArg HasArg) {
	CommandLine.VarP(value, name, shorthands, hasArg)
}

// Var creates a flag for the given option name.
func (f *FlagSet) Var(value Value, name string, hasArg HasArg) {
	shorthands := ""
	if len(name) == 1 {
		shorthands = name
		name = ""
	}
	f.VarP(value, name, shorthands, hasArg)
}

// Var creates a flag for the given option name for the command line.
func Var(value Value, name string, hasArg HasArg) {
	CommandLine.Var(value, name, hasArg)
}

// addLine adds a usage line to the flag set.
func (f *FlagSet) addLine(l line) {
	if l.flags == "" {
		f.panicf("no flags for %q", l.usage)
	}
	f.lines = append(f.lines, l)
}

// boolValue represents a bool value in the flag.
type boolValue bool

// newBoolValue creates a new Bool Value.
func newBoolValue(val bool, p *bool) *boolValue {
	*p = val
	return (*boolValue)(p)
}

// Get returns the bool value as boolean.
func (b *boolValue) Get() interface{} {
	return bool(*b)
}

// Set sets the bool value to the value provided by the string.
func (b *boolValue) Set(s string) error {
	v, err := strconv.ParseBool(s)
	*b = boolValue(v)
	return err
}

// Update sets the bool value to true.
func (b *boolValue) Update() {
	*b = true
}

// String returns the boll value as string.
func (b *boolValue) String() string {
	return fmt.Sprintf("%t", *b)
}

// boolLine creates the usage line for a bool flag.
func boolLine(name, shorthands string, value bool, usage string) line {
	defaultValue := ""
	if value {
		defaultValue = "true"
	}
	return line{lineFlags(name, shorthands, defaultValue), usage}
}

// BoolVarP defines a bool flag with specified name, shorthands, default
// value and usage string. The argument p points to a bool variable in
// which to store the value of the flag.
func (f *FlagSet) BoolVarP(p *bool, name, shorthands string, value bool, usage string) {
	f.addLine(boolLine(name, shorthands, value, usage))
	f.VarP(newBoolValue(value, p), name, shorthands, OptionalArg)
}

// BoolP defines a bool flag with specified name, shorthands, default
// value and usage string. The return value is the address of a bool
// variable that stores the value of the flag.
func (f *FlagSet) BoolP(name, shorthands string, value bool, usage string) *bool {
	p := new(bool)
	f.BoolVarP(p, name, shorthands, value, usage)
	return p
}

// BoolP defines a bool flag with specified name, shorthands, default
// value and usage string. The return value is the address of a bool
// variable that stores the value of the flag.
func BoolP(name, shorthands string, value bool, usage string) *bool {
	return CommandLine.BoolP(name, shorthands, value, usage)
}

// BoolVarP defines a bool flag with specified name, shorthands, default
// value and usage string. The argument p points to a bool variable in
// which to store the value of the flag.
func BoolVarP(p *bool, name, shorthands string, value bool, usage string) {
	CommandLine.BoolVarP(p, name, shorthands, value, usage)
}

// BoolVar defines a bool flag with specified name, default value and
// usage string. The argument p points to a bool variable in which to
// store the value of the flag.
func (f *FlagSet) BoolVar(p *bool, name string, value bool, usage string) {
	f.addLine(boolLine(name, "", value, usage))
	f.Var(newBoolValue(value, p), name, OptionalArg)
}

// BoolVar defines a bool flag with specified name, default value and
// usage string. The argument p points to a bool variable in which to
// store the value of the flag.
func BoolVar(p *bool, name string, value bool, usage string) {
	CommandLine.BoolVar(p, name, value, usage)
}

// Bool defines a bool flag with specified name, default value and
// usage string. The return value is the address of a bool variable that
// stores the value of the flag.
func (f *FlagSet) Bool(name string, value bool, usage string) *bool {
	p := new(bool)
	f.BoolVar(p, name, value, usage)
	return p
}

// Bool defines a bool flag with specified name, default value and
// usage string. The return value is the address of a bool variable that
// stores the value of the flag.
func Bool(name string, value bool, usage string) *bool {
	return CommandLine.Bool(name, value, usage)
}

// intValue stores an integer value.
type intValue int

// newIntValue allocates a new integer value and returns its pointer.
func newIntValue(val int, p *int) *intValue {
	*p = val
	return (*intValue)(p)
}

// Get returns the integer.
func (n *intValue) Get() interface{} {
	return int(*n)
}

// Set sets the integer value.
func (n *intValue) Set(s string) error {
	v, err := strconv.ParseInt(s, 0, 0)
	if err != nil {
		return err
	}
	*n = intValue(v)
	return nil
}

// Update increments the integer value.
func (n *intValue) Update() {
	(*n)++
}

// String represents the integer value as string.
func (n *intValue) String() string {
	return fmt.Sprintf("%d", *n)
}

// counterLine returns the usage line for a counter flag.
func counterLine(name, shorthands, usage string) line {
	return line{lineFlags(name, shorthands, ""), usage}
}

// CounterVarP defines a counter flag with specified name, shorthands, default
// value and usage string. The argument p points to an integer variable in
// which to store the value of the flag.
func (f *FlagSet) CounterVarP(p *int, name, shorthands string, value int, usage string) {
	f.addLine(counterLine(name, shorthands, usage))
	f.VarP(newIntValue(value, p), name, shorthands, OptionalArg)
}

// CounterVarP defines a counter flag with specified name, shorthands, default
// value and usage string. The argument p points to an integer variable in
// which to store the value of the flag.
func CounterVarP(p *int, name, shorthands string, value int, usage string) {
	CommandLine.CounterVarP(p, name, shorthands, value, usage)
}

// CounterP defines a counter flag with specified name, shorthands, default
// value and usage string. The return value is the address of an integer
// variable that stores the value of the flag.
func (f *FlagSet) CounterP(name, shorthands string, value int, usage string) *int {
	p := new(int)
	f.CounterVarP(p, name, shorthands, value, usage)
	return p
}

// CounterP defines a counter flag with specified name, shorthands, default
// value and usage string. The return value is the address of an integer
// variable that stores the value of the flag.
func CounterP(name, shorthands string, value int, usage string) *int {
	return CommandLine.CounterP(name, shorthands, value, usage)
}

// CounterVar defines a counter flag with specified name, default value and
// usage string. The argument p points to an integer variable in which to
// store the value of the flag.
func (f *FlagSet) CounterVar(p *int, name string, value int, usage string) {
	f.addLine(counterLine(name, "", usage))
	f.Var(newIntValue(value, p), name, OptionalArg)
}

// CounterVar defines a counter flag with specified name, default value and
// usage string. The argument p points to an integer variable in which to
// store the value of the flag.
func CounterVar(p *int, name string, value int, usage string) {
	CommandLine.CounterVar(p, name, value, usage)
}

// Counter defines a counter flag with specified name, default value and
// usage string. The return value is the address of an integer variable that
// stores the value of the flag.
func (f *FlagSet) Counter(name string, value int, usage string) *int {
	p := new(int)
	f.CounterVar(p, name, value, usage)
	return p
}

// Counter defines a counter flag with specified name, default value and
// usage string. The return value is the address of an integer variable that
// stores the value of the flag.
func Counter(name string, value int, usage string) *int {
	return CommandLine.Counter(name, value, usage)
}

// intLine returns the usage line for an integer flag.
func intLine(name, shorthands string, value int, usage string) line {
	defaultValue := ""
	if value != 0 {
		defaultValue = fmt.Sprintf("%d", value)
	}
	return line{lineFlags(name, shorthands, defaultValue), usage}
}

// IntVarP defines an integer flag with specified name, shorthands, default
// value and usage string. The argument p points to an integer variable in
// which to store the value of the flag.
func (f *FlagSet) IntVarP(p *int, name, shorthands string, value int, usage string) {
	f.addLine(intLine(name, shorthands, value, usage))
	f.VarP(newIntValue(value, p), name, shorthands, RequiredArg)
}

// IntVarP defines an integer flag with specified name, shorthands, default
// value and usage string. The argument p points to an integer variable in
// which to store the value of the flag.
func IntVarP(p *int, name, shorthands string, value int, usage string) {
	CommandLine.IntVarP(p, name, shorthands, value, usage)
}

// IntP defines an integer flag with specified name, shorthands, default
// value and usage string. The return value is the address of an integer
// variable that stores the value of the flag.
func (f *FlagSet) IntP(name, shorthands string, value int, usage string) *int {
	p := new(int)
	f.IntVarP(p, name, shorthands, value, usage)
	return p
}

// IntP defines an integer flag with specified name, shorthands, default
// value and usage string. The return value is the address of an integer
// variable that stores the value of the flag.
func IntP(name, shorthands string, value int, usage string) *int {
	return CommandLine.IntP(name, shorthands, value, usage)
}

// IntVar defines an integer flag with specified name, default value and
// usage string. The argument p points to an integer variable in which to
// store the value of the flag.
func (f *FlagSet) IntVar(p *int, name string, value int, usage string) {
	f.addLine(intLine(name, "", value, usage))
	f.Var(newIntValue(value, p), name, RequiredArg)
}

// IntVar defines an integer flag with specified name, default value and
// usage string. The argument p points to an integer variable in which to
// store the value of the flag.
func IntVar(p *int, name string, value int, usage string) {
	CommandLine.IntVar(p, name, value, usage)
}

// Int defines an integer flag with specified name, default value and
// usage string. The return value is the address of an integer variable that
// stores the value of the flag.
func (f *FlagSet) Int(name string, value int, usage string) *int {
	p := new(int)
	f.IntVar(p, name, value, usage)
	return p
}

// Int defines an integer flag with specified name, default value and
// usage string. The return value is the address of an integer variable that
// stores the value of the flag.
func Int(name string, value int, usage string) *int {
	return CommandLine.Int(name, value, usage)
}

// The stringValue will store a string option.
type stringValue struct {
	p     *string
	value string
}

// newStringValue will create a new stringValue.
func newStringValue(val string, p *string) *stringValue {
	*p = val
	return &stringValue{p, val}
}

// Get returns the string stored in the stringValue.
func (s *stringValue) Get() interface{} {
	return *s.p
}

// Set sets the string value.
func (s *stringValue) Set(str string) error {
	*s.p = str
	return nil
}

// Update resets the string value to its default.
func (s *stringValue) Update() {
	*s.p = s.value
}

// String returns simply the string stored in the value.
func (s *stringValue) String() string {
	return *s.p
}

// stringLine creates a usage line.
func stringLine(name, shorthands, value, usage string) line {
	return line{lineFlags(name, shorthands, value), usage}
}

// StringVarP defines an string flag with specified name, shorthands, default
// value and usage string. The argument p points to a string variable in
// which to store the value of the flag.
func (f *FlagSet) StringVarP(p *string, name, shorthands, value, usage string) {
	f.addLine(stringLine(name, shorthands, value, usage))
	f.VarP(newStringValue(value, p), name, shorthands, RequiredArg)
}

// StringVarP defines an string flag with specified name, shorthands, default
// value and usage string. The argument p points to a string variable in
// which to store the value of the flag.
func StringVarP(p *string, name, shorthands, value, usage string) {
	CommandLine.StringVarP(p, name, shorthands, value, usage)
}

// StringP defines a string flag with specified name, shorthands, default
// value and usage string. The return value is the address of a string
// variable that stores the value of the flag.
func (f *FlagSet) StringP(name, shorthands, value, usage string) *string {
	p := new(string)
	f.StringVarP(p, name, shorthands, value, usage)
	return p
}

// StringP defines a string flag with specified name, shorthands, default
// value and usage string. The return value is the address of a string
// variable that stores the value of the flag.
func StringP(name, shorthands, value, usage string) *string {
	return CommandLine.StringP(name, shorthands, value, usage)
}

// StringVar defines a string flag with specified name, default value and
// usage string. The argument p points to a string variable in which to
// store the value of the flag.
func (f *FlagSet) StringVar(p *string, name, value, usage string) {
	f.addLine(stringLine(name, "", value, usage))
	f.Var(newStringValue(value, p), name, RequiredArg)
}

// StringVar defines a string flag with specified name, default value and
// usage string. The argument p points to a string variable in which to
// store the value of the flag.
func StringVar(p *string, name, value, usage string) {
	CommandLine.StringVar(p, name, value, usage)
}

// String defines a string flag with specified name, default value and
// usage string. The return value is the address of a string variable that
// stores the value of the flag.
func (f *FlagSet) String(name, value, usage string) *string {
	p := new(string)
	f.StringVar(p, name, value, usage)
	return p
}

// String defines a string flag with specified name, default value and
// usage string. The return value is the address of a string variable that
// stores the value of the flag.
func String(name, value, usage string) *string {
	return CommandLine.String(name, value, usage)
}

// presetValue represents an integer value that can be set with multiple
// flags as -1 ... -9.
type presetValue struct {
	p      *int
	preset int
}

// newPresetValue allocates a new preset value and returns its pointer.
func newPresetValue(p *int, preset int) *presetValue {
	return &presetValue{p, preset}
}

// Get returns the actual preset value as integer.
func (p *presetValue) Get() interface{} {
	return *p.p
}

// Set sets the preset value from an integer string.
func (p *presetValue) Set(s string) error {
	val, err := strconv.ParseInt(s, 0, 0)
	*p.p = int(val)
	return err
}

// Update sets the preset value to the default.
func (p *presetValue) Update() {
	*p.p = p.preset
}

// String returns the integer representation of the preset value.
func (p *presetValue) String() string {
	return fmt.Sprintf("%d", *p.p)
}

// presetLine creates the usage line for a preset value.
func presetLine(start, end int, usage string) line {
	return line{fmt.Sprintf("-%d ... -%d", start, end), usage}
}

// PresetVar defines a range of preset flags starting at start and
// ending at end. The argument p points to a preset variable in which to
// store the value of the flag.
//
// If start is 1 and end is 9 the flags -1 to -9 will be supported.
func (f *FlagSet) PresetVar(p *int, start, end, value int, usage string) {
	if f.preset {
		f.panicf("flagset %s has already a preset", f.name)
	}
	f.addLine(presetLine(start, end, usage))
	*p = value
	for i := start; i <= end; i++ {
		f.Var(newPresetValue(p, i), fmt.Sprintf("%d", i), NoArg)
	}
}

// PresetVar defines a range of preset flags starting at start and
// ending at end. The argument p points to a preset variable in which to
// store the value of the flag.
//
// If start is 1 and end is 9 the flags -1 to -9 will be supported.
func PresetVar(p *int, start, end, value int, usage string) {
	CommandLine.PresetVar(p, start, end, value, usage)
}

// Preset defines a range of preset flags starting at start and
// ending at end. The return value is the address of a preset variable
// in which to store the value of the flag.
//
// If start is 1 and end is 9 the flags -1 to -9 will be supported.
func (f *FlagSet) Preset(start, end, value int, usage string) *int {
	p := new(int)
	f.PresetVar(p, start, end, value, usage)
	return p
}

// Preset defines a range of preset flags starting at start and
// ending at end. The return value is the address of a preset variable
// in which to store the value of the flag.
//
// If start is 1 and end is 9 the flags -1 to -9 will be supported.
func Preset(start, end, value int, usage string) *int {
	return CommandLine.Preset(start, end, value, usage)
}