# Brian Eastwood
# 2/18/2012
# Utility for working with Python Image Library (PIL).

# import PIL and the tk graphics packages
import Tkinter 
import Image, ImageTk

class ImageWindow(object):
	'''
	A class that displays images in a Tkinter window. Note that this class
	is a singleton, so it should only be instantiated once. Access to the
	instance is through the static instance() method.
	'''
	__instance = None
	
	@staticmethod
	def instance():
		if ImageWindow.__instance is None:
			ImageWindow.__instance = ImageWindow()
		return ImageWindow.__instance
	
	def __init__(self):
		'''
		Construct an ImageWindow. This sets up the Tkinter root window, a
		label, and an image object.
		'''
		self.root = Tkinter.Tk()
		self.root.title("Image Window")
		self.tklabel = Tkinter.Label(self.root, image=None)
		self.tkimage = None
		
		# set up tk event bindings
		self.root.bind("<Key>", self.onKey)
	
	def onKey(self, event):
		'''
		Handles destroying the root window if q or esc is pressed.
		
		Parameters:
		event - the tk key event
		'''
		if event.char == 'q' or event.char == '\x1b':
			self.root.destroy()
	
	def setImage(self, image, title=None):
		'''
		Sets the image displayed in the window.
		
		Parameters:
		image - the PIL Image to display
		title - a title for the image window (optional)
		'''
		# ensure image is proper type
		if not isinstance(image, Image.Image):
			print "ERROR: This is not a recognized PIL image: {0}".format(type(image))
			print "Use img = Image.open(\"filename.jpg\") to open an image file."
			return
		
		# update the image
		self.tkimage = ImageTk.PhotoImage(image)
		self.tklabel.config(image=self.tkimage)

		# update the title
		if title is not None:
			self.root.title(title)
		
		# ensure the image displays
		self.tklabel.pack()
		self.root.update()
	

def display(image, title=None):
	'''
	Displays a PIL Image in a window.
	
	Parameters:
	image - the PIL Image to display; must be an Image object
	title - the title for the image window (optional)
	'''
	ImageWindow.instance().setImage(image, title)
	
def wait():
	'''
	Pauses the application until the image window is closed or
	q or esc is pressed.
	'''
	Tkinter.mainloop()
		
def test():
	'''
	Test the functions defined in this file.
	'''
	import time
	filename = "icon.jpg"
	img = Image.open(filename)
	tkimg = display(img, "foo")
	tkimg = display(img, "blah")
	wait()
	
if __name__ == "__main__":
	test()