import os
import os.path
import time
import pygtk
pygtk.require('2.0')
import gtk
import gobject
 
 
#class used to handle one application instance mechanism
class GTKApplicationInstance:
 
	#specify the base for control files
	def __init__( self, base_control_file, raise_cmd = '' ):
		self.pid_file = base_control_file + '.pid'
		self.raise_file = base_control_file + '.raise'
 
		#remove raise_file is already exists
		try:
			os.remove( self.raise_file )
		except:
			pass
 
		self.check( raise_cmd )
		self.startApplication()
 
	#check if the current application is already running
	def check( self, raise_cmd ):
		#check if the pidfile exists
		if not os.path.isfile( self.pid_file ):
			return
 
		#read the pid from the file
		pid = 0
		try:
			file = open( self.pid_file, 'rt' )
			data = file.read()
			file.close()
			pid = int( data )
		except:
			pass
 
		#check if the process with specified by pid exists
		if 0 == pid:
			return
 
		try:
			os.kill( pid, 0 )	#this will raise an exception if the pid is not valid
		except:
			return
 
		#exit the application
		print "The application is already running !"
 
		#notify raise
		try:
			file = open( self.raise_file, 'wt' )
			file.write( raise_cmd )
			file.close()
		except:
			pass
 
		exit(0) #exit raise an exception so don't put it in a try/except block
 
	#called when the single instance starts to save it's pid
	def startApplication( self ):
		file = open( self.pid_file, 'wt' )
		file.write( str( os.getpid() ) )
		file.close()
 
	#called when the single instance exit ( remove pid file )
	def exitApplication( self ):
		try:
			os.remove( self.pid_file )
		except:
			pass
 
	#check if the application must to be raised
	#return None if no raise needed, or a string command to raise
	def raiseCommand( self ):
		retVal = None
 
		try:
			if os.path.isfile( self.raise_file ):
				file = open( self.raise_file, 'rt' )
				retVal = file.read()
				file.close()
				os.remove( self.raise_file )
		except:
			pass
 
		return retVal
 
 
#Hello World simple window
class HelloWorld:
	def __init__( self, appInstance ):
		self.appInstance = appInstance
		# create Hello World window
		self.window = gtk.Window(gtk.WINDOW_TOPLEVEL)
		self.window.connect("destroy", gtk.main_quit)
		self.window.set_border_width(100)
		self.label = gtk.Label("Hello World !")
		self.window.add(self.label)
		self.label.show()
		self.window.show()
 
		#check every second if the application needs to raise
		gobject.timeout_add( 1000, self.checkRaiseApplication )
 
	def checkRaiseApplication( self ):
		raiseCmd = self.appInstance.raiseCommand()
		if raiseCmd is None: #no raise needed
			return True
		#raise the window
		self.window.present_with_time( int(time.time()) )
		self.window.present()
		return True
 
 
if __name__ == '__main__':
	#create application instance
	appInstance = GTKApplicationInstance( '/tmp/mygtkapp' )
 
	#Hello World application
	print "Start MyGTKApp"
	helloWord = HelloWorld( appInstance )
	gtk.main()
	print "End MyGTKApp"
 
	#remove pid file
	appInstance.exitApplication()