#!/usr/bin/python
#
# Script to generate distorted text images for a captcha system.
#
# Copyright (C) 2005 Neil Harris
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
# http://www.gnu.org/copyleft/gpl.html
#
# Further tweaks by Brion Vibber <brion@pobox.com>:
# 2006-01-26: Add command-line options for the various parameters
# 2007-02-19: Add --dirs param for hash subdirectory splits
# Tweaks by Greg Sabino Mullane <greg@turnstep.com>:
# 2008-01-06: Add regex check to skip words containing other than a-z

import random
import math
import hashlib
from optparse import OptionParser
import os
import sys
import re

try:
	from PIL import Image
	from PIL import ImageFont
	from PIL import ImageDraw
	from PIL import ImageEnhance
	from PIL import ImageOps
except:
	sys.exit("This script requires the Python Imaging Library - http://www.pythonware.com/products/pil/")

nonalpha = re.compile('[^a-z]') # regex to test for suitability of words

# Does X-axis wobbly copy, sandwiched between two rotates
def wobbly_copy(src, wob, col, scale, ang):
	x, y = src.size
	f = random.uniform(4*scale, 5*scale)
	p = random.uniform(0, math.pi*2)
	rr = ang+random.uniform(-30, 30) # vary, but not too much
	int_d = Image.new('RGB', src.size, 0) # a black rectangle
	rot = src.rotate(rr, Image.BILINEAR)
	# Do a cheap bounding-box op here to try to limit work below
	bbx = rot.getbbox()
	if bbx == None:
		return src
	else:
		l, t, r, b= bbx
	# and only do lines with content on
	for i in range(t, b+1):
		# Drop a scan line in
		xoff = int(math.sin(p+(i*f/y))*wob)
		xoff += int(random.uniform(-wob*0.5, wob*0.5))
		int_d.paste(rot.crop((0, i, x, i+1)), (xoff, i))
	# try to stop blurring from building up
	int_d = int_d.rotate(-rr, Image.BILINEAR)
	enh = ImageEnhance.Sharpness(int_d)
	return enh.enhance(2)


def gen_captcha(text, fontname, fontsize, file_name):
	"""Generate a captcha image"""
	# white text on a black background
	bgcolor = 0x0
	fgcolor = 0xffffff
	# create a font object
	font = ImageFont.truetype(fontname,fontsize)
	# determine dimensions of the text
	dim = font.getsize(text)
	# create a new image significantly larger that the text
	edge = max(dim[0], dim[1]) + 2*min(dim[0], dim[1])
	im = Image.new('RGB', (edge, edge), bgcolor)
	d = ImageDraw.Draw(im)
	x, y = im.size
	# add the text to the image
	d.text((x/2-dim[0]/2, y/2-dim[1]/2), text, font=font, fill=fgcolor)
	k = 3
	wob = 0.20*dim[1]/k
	rot = 45
	# Apply lots of small stirring operations, rather than a few large ones
	# in order to get some uniformity of treatment, whilst
	# maintaining randomness
	for i in range(k):
		im = wobbly_copy(im, wob, bgcolor, i*2+3, rot+0)
		im = wobbly_copy(im, wob, bgcolor, i*2+1, rot+45)
		im = wobbly_copy(im, wob, bgcolor, i*2+2, rot+90)
		rot += 30

	# now get the bounding box of the nonzero parts of the image
	bbox = im.getbbox()
	bord = min(dim[0], dim[1])/4 # a bit of a border
	im = im.crop((bbox[0]-bord, bbox[1]-bord, bbox[2]+bord, bbox[3]+bord))
	# and turn into black on white
	im = ImageOps.invert(im)

	# save the image, in format determined from filename
	im.save(file_name)

def gen_subdir(basedir, md5hash, levels):
	"""Generate a subdirectory path out of the first _levels_
	characters of _hash_, and ensure the directories exist
	under _basedir_."""
	subdir = None
	for i in range(0, levels):
		char = md5hash[i]
		if subdir:
			subdir = os.path.join(subdir, char)
		else:
			subdir = char
		fulldir = os.path.join(basedir, subdir)
		if not os.path.exists(fulldir):
			os.mkdir(fulldir)
	return subdir

def try_pick_word(words, blacklist, verbose, nwords, min_length, max_length):
	if words is not None:
		word = words[random.randint(0,len(words)-1)]
		while nwords > 1:
			word2 = words[random.randint(0,len(words)-1)]
			word = word + word2
			nwords = nwords - 1
	else:
		word = ''
		max_length = max_length if max_length > 0 else 10
		for i in range(0, random.randint(min_length, max_length)):
			word = word + chr(97 + random.randint(0,25))

	if verbose:
		print("word is %s" % word)

	if len(word) < min_length:
		if verbose:
			print("skipping word pair '%s' because it has fewer than %d characters" % (word, min_length))
		return None

	if max_length > 0 and len(word) > max_length:
		if verbose:
			print("skipping word pair '%s' because it has more than %d characters" % (word, max_length))
		return None

	if nonalpha.search(word):
		if verbose:
			print("skipping word pair '%s' because it contains non-alphabetic characters" % word)
		return None

	for naughty in blacklist:
		if naughty in word:
			if verbose:
				print("skipping word pair '%s' because it contains blacklisted word '%s'" % (word, naughty))
			return None
	return word

def pick_word(words, blacklist, verbose, nwords, min_length, max_length):
	for x in range(1000): # If we can't find a valid combination in 1000 tries, just give up
		word = try_pick_word(words, blacklist, verbose, nwords, min_length, max_length)
		if word:
			return word
	sys.exit("Unable to find valid word combinations")

def read_wordlist(filename):
	f = open(filename)
	words = [x.strip().lower() for x in f.readlines()]
	f.close()
	return words

if __name__ == '__main__':
	"""This grabs random words from the dictionary 'words' (one
	word per line) and generates a captcha image for each one,
	with a keyed salted hash of the correct answer in the filename.

	To check a reply, hash it in the same way with the same salt and
	secret key, then compare with the hash value given.
	"""
	script_dir = os.path.dirname(os.path.realpath(__file__))
	parser = OptionParser()
	parser.add_option("--wordlist", help="A list of words (required)", metavar="WORDS.txt")
	parser.add_option("--random", help="Use random charcters instead of a wordlist", action="store_true")
	parser.add_option("--key", help="The passphrase set as $wgCaptchaSecret (required)", metavar="KEY")
	parser.add_option("--output", help="The directory to put the images in - $wgCaptchaDirectory (required)", metavar="DIR")
	parser.add_option("--font", help="The font to use (required)", metavar="FONT.ttf")
	parser.add_option("--font-size", help="The font size (default 40)", metavar="N", type='int', default=40)
	parser.add_option("--count", help="The maximum number of images to make (default 20)", metavar="N", type='int', default=20)
	parser.add_option("--blacklist", help="A blacklist of words that should not be used", metavar="FILE", default=os.path.join(script_dir, "blacklist"))
	parser.add_option("--fill", help="Fill the output directory to contain N files, overrides count, cannot be used with --dirs", metavar="N", type='int')
	parser.add_option("--dirs", help="Put the images into subdirectories N levels deep - $wgCaptchaDirectoryLevels", metavar="N", type='int')
	parser.add_option("--verbose", "-v", help="Show debugging information", action='store_true')
	parser.add_option("--number-words", help="Number of words from the wordlist which make a captcha challenge (default 2)", type='int', default=2)
	parser.add_option("--min-length", help="Minimum length for a captcha challenge", type='int', default=1)
	parser.add_option("--max-length", help="Maximum length for a captcha challenge", type='int', default=-1)

	opts, args = parser.parse_args()

	if opts.wordlist:
		wordlist = opts.wordlist
	elif opts.random:
		wordlist = None
	else:
		sys.exit("Need to specify a wordlist")
	if opts.key:
		key = opts.key
	else:
		sys.exit("Need to specify a key")
	if opts.output:
		output = opts.output
	else:
		sys.exit("Need to specify an output directory")
	if opts.font and os.path.exists(opts.font):
		font = opts.font
	else:
		sys.exit("Need to specify the location of a font")

	blacklist = read_wordlist(opts.blacklist)
	count = opts.count
	fill = opts.fill
	dirs = opts.dirs
	verbose = opts.verbose
	fontsize = opts.font_size

	if fill:
		count = max(0, fill - len(os.listdir(output)))

	words = None
	if wordlist:
		words = read_wordlist(wordlist)
		words = [x for x in words
			if len(x) in (4,5) and x[0] != "f"
			and x[0] != x[1] and x[-1] != x[-2]]

	for i in range(count):
		word = pick_word(words, blacklist, verbose, opts.number_words, opts.min_length, opts.max_length)
		salt = "%08x" % random.randrange(2**32)
		# 64 bits of hash is plenty for this purpose
		md5hash = hashlib.md5((key+salt+word+key+salt).encode('utf-8')).hexdigest()[:16]
		filename = "image_%s_%s.png" % (salt, md5hash)
		if dirs:
			subdir = gen_subdir(output, md5hash, dirs)
			filename = os.path.join(subdir, filename)
		if verbose:
			print(filename)
		gen_captcha(word, font, fontsize, os.path.join(output, filename))