from optparse import OptionParser
import os
import sys, string, time
import random

def changeWallpaper(filename):
        cmd = string.join(["gconftool -s /desktop/gnome/background/picture_filename -t string \"",filename,"\""],'')
        os.system(cmd) # execute system command

# Parse commandline arguments
parser = OptionParser()
parser.add_option("-f", "--folder", dest="folder", help="use wallpapers from FOLDER", metavar="FOLDER")
parser.add_option("-i", "--interval", type="float", dest="interval", default=300, help="time interval in seconds", metavar="INTERVAL")
(options, args) = parser.parse_args()

# Validate for presence of valid folder
if options.folder is None:
        raise ValueError, "No valid folder specified"
if not(os.path.isdir(options.folder)):
        raise ValueError, "The folder specified is not valid"

# Make list of images
imagefilelist = [filename for filename in os.listdir(options.folder)
                if (filename.lower().endswith("jpg")
                or filename.lower().endswith("png")
                or filename.lower().endswith("gif"))]
imagefilelist = [string.join([os.path.normpath(options.folder),imgFile],"/") for imgFile in imagefilelist]

# Validate for presence of images
if (len(imagefilelist) == 0):
        raise ValueError, "Folder does not contain any image files"

count=0 #init index
random.shuffle(imagefilelist) #randomize wallpaper order
try:
        while (True):
                if (count < len(imagefilelist) -1):
                        count = count + 1
                else:
                        count = 0
                time.sleep(options.interval)
                changeWallpaper(imagefilelist[count])
except KeyboardInterrupt:
        pass