key-checking

#include <ApplicationServices/ApplicationServices.h>

#define NEXT_TRACK "osascript -e 'tell application \"iTunes\"' -e 'next track' -e 'end tell'"
#define BACK_TRACK "osascript -e 'tell application \"iTunes\"' -e 'back track' -e 'end tell'"      //  back track - go to beginning of current track, or previous track if at beginning of current.
#define PREVIOUS_TRACK "osascript -e 'tell application \"iTunes\"' -e 'previous track' -e 'end tell'"  //  previous track - start playing previous track
#define PLAYPAUSE "osascript -e 'tell application \"iTunes\"' -e 'playpause' -e 'end tell'"        //  playpause - toggle play/pause of current track, a.k.a. space bar
#define VOLUME_UP "osascript -e 'tell application \"iTunes\"' -e 'set currentVolume to sound volume' -e 'if currentVolume is greater than 90 then' -e 'set currentVolume to 100' -e 'end if' -e 'set sound volume to (currentVolume + 10)' -e 'end tell'"
#define VOLUME_DOWN "osascript -e 'tell application \"iTunes\"' -e 'set currentVolume to sound volume' -e 'if currentVolume is less than 10 then' -e 'set currentVolume to 0' -e 'end if' -e 'set sound volume to (currentVolume - 10)' -e 'end tell'"

CGEventRef myCGEventCallback(CGEventTapProxy proxy, CGEventType type, CGEventRef event, void *refcon)
{
    CGKeyCode keycode = CGEventGetIntegerValueField(event, kCGKeyboardEventKeycode);
	CGEventFlags flags = CGEventGetFlags (event);
	
	if ((flags & kCGEventFlagMaskCommand) &&
		(flags & kCGEventFlagMaskControl) &&
		(flags & kCGEventFlagMaskAlternate))
	{
		if (keycode == 124)
			system(NEXT_TRACK);
		else if (keycode == 123)
			system(PREVIOUS_TRACK);
		else if (keycode == 126)
			system(VOLUME_UP);
		else if (keycode == 125)
			system(VOLUME_DOWN);
		else if (keycode == 49)
			system(PLAYPAUSE);
	}
	
    return event;
}

int main(void)
{
    CFMachPortRef      eventTap;
    CGEventMask        eventMask;
    CFRunLoopSourceRef runLoopSource;
	
	eventMask = (1 << kCGEventKeyUp);
    eventTap = CGEventTapCreate(kCGSessionEventTap, kCGHeadInsertEventTap, kCGEventTapOptionListenOnly, eventMask, myCGEventCallback, NULL);
   
	if (!eventTap) {
        fprintf(stderr, "failed to create event tap\n");
        exit(1);
    }
	
    runLoopSource = CFMachPortCreateRunLoopSource(kCFAllocatorDefault, eventTap, 0);
	
    CFRunLoopAddSource(CFRunLoopGetCurrent(), runLoopSource, kCFRunLoopCommonModes);
	
    CGEventTapEnable(eventTap, true);

	CFRunLoopRun();
	
    exit(0);
}