Adding a base implementation of a database logger. A concrete impleme…

…ntation can easily be built atop this base implementation for whatever database is desired.

Lumberjack/DDAbstractDatabaseLogger.h

@@ -0,0 +1,102 @@
+#import <Foundation/Foundation.h>
+
+#import "DDLog.h"
+
+/**
+ * Welcome to Cocoa Lumberjack!
+ * 
+ * The Google Code page has a wealth of documentation if you have any questions.
+ * http://code.google.com/p/cocoalumberjack/
+ * 
+ * If you're new to the project you may wish to read the "Getting Started" page.
+ * http://code.google.com/p/cocoalumberjack/wiki/GettingStarted
+ * 
+ * 
+ * This class provides an abstract implementation of a database logger.
+ * 
+ * That is, it provides the base implementation for a database logger to build atop of.
+ * All that is needed for a concrete database logger is to extend this class
+ * and override the methods in the implementation file that are prefixed with "db_".
+**/
+
+@interface DDAbstractDatabaseLogger : DDAbstractLogger {
+@protected
+	NSUInteger saveThreshold;
+	NSTimeInterval saveInterval;
+	NSTimeInterval maxAge;
+	NSTimeInterval deleteInterval;
+	BOOL deleteOnEverySave;
+
+	BOOL saveTimerSuspended;
+	NSUInteger unsavedCount;
+	dispatch_time_t unsavedTime;
+	dispatch_source_t saveTimer;
+	dispatch_time_t lastDeleteTime;
+	dispatch_source_t deleteTimer;
+}
+
+/**
+ * Specifies how often to save the data to disk.
+ * Since saving is an expensive operation (disk io) it is not done after every log statement.
+ * These properties allow you to configure how/when the logger saves to disk.
+ * 
+ * A save is done when either (whichever happens first):
+ * 
+ * - The number of unsaved log entries reaches saveThreshold
+ * - The amount of time since the oldest unsaved log entry was created reaches saveInterval
+ * 
+ * You can optionally disable the saveThreshold by setting it to zero.
+ * If you disable the saveThreshold you are entirely dependent on the saveInterval.
+ * 
+ * You can optionally disable the saveInterval by setting it to zero (or a negative value).
+ * If you disable the saveInterval you are entirely dependent on the saveThreshold.
+ * 
+ * It's not wise to disable both saveThreshold and saveInterval.
+ * 
+ * The default saveThreshold is 500.
+ * The default saveInterval is 60 seconds.
+**/
+@property (assign, readwrite) NSUInteger saveThreshold;
+@property (assign, readwrite) NSTimeInterval saveInterval;
+
+/**
+ * It is likely you don't want the log entries to persist forever.
+ * Doing so would allow the database to grow infinitely large over time.
+ * 
+ * The maxAge property provides a way to specify how old a log statement can get
+ * before it should get deleted from the database.
+ * 
+ * The deleteInterval specifies how often to sweep for old log entries.
+ * Since deleting is an expensive operation (disk io) is is done on a fixed interval.
+ * 
+ * An alternative to the deleteInterval is the deleteOnEverySave option.
+ * This specifies that old log entries should be deleted during every save operation.
+ * 
+ * You can optionally disable the maxAge by setting it to zero (or a negative value).
+ * If you disable the maxAge then old log statements are not deleted.
+ * 
+ * You can optionally disable the deleteInterval by setting it to zero (or a negative value).
+ * 
+ * If you disable both deleteInterval and deleteOnEverySave then old log statements are not deleted.
+ * 
+ * It's not wise to enable both deleteInterval and deleteOnEverySave.
+ * 
+ * The default maxAge is 7 days.
+ * The default deleteInterval is 5 minutes.
+ * The default deleteOnEverySave is NO.
+**/
+@property (assign, readwrite) NSTimeInterval maxAge;
+@property (assign, readwrite) NSTimeInterval deleteInterval;
+@property (assign, readwrite) BOOL deleteOnEverySave;
+
+/**
+ * Forces a save of any pending log entries (flushes log entries to disk).
+**/
+- (void)savePendingLogEntries;
+
+/**
+ * Removes any log entries that are older than maxAge.
+**/
+- (void)deleteOldLogEntries;
+
+@end