#!/usr/bin/env python
# Attempt to show why a patch was rejected.
# Adam Sampson <ats@offog.org>

import re, os

def read(fn):
	f = open(fn)
	ls = f.readlines()
	f.close()
	return ls

def write(fn, ls):
	f = open(fn, "w")
	f.write("".join(ls))
	f.close()

def parse_rej(rls):
	chunks = []
	n = 0
	while n != len(rls):
		if rls[n] != "***************\n":
			print "No stars line at", n
			return 1
		n += 1

		m = re.match(r'^\*\*\* (\d+),(\d+) \*\*\*.$', rls[n])
		if m is None:
			print "No from line at", n
			return 1
		fromstart = int(m.group(1))
		fromend = int(m.group(2))
		n += 1

		count = (fromend - fromstart) + 1
		fromlines = rls[n:n + count]
		n += count

		m = re.match(r'^--- (\d+),(\d+) ---.$', rls[n])
		if m is None:
			print "No to line at", n, rls[n]
			return 1
		tostart = int(m.group(1))
		toend = int(m.group(2))
		n += 1

		count = (toend - tostart) + 1
		tolines = rls[n:n + count]
		n += count

		chunks.append((fromstart, fromlines, tostart, tolines))

	return chunks

def num_matches(aas, bbs):
	if len(aas) != len(bbs):
		raise "num_matches needs two lists of the same length"
	count = 0
	for i in range(len(aas)):
		if aas[i] == bbs[i]:
			count += 1
	return count

def main(argv):
	if len(argv) not in [2, 3]:
		print "Usage: whyrej <file> [<file.rej>]"
		return 1

	fn = argv[1]
	if len(argv) == 3:
		rejn = argv[2]
	else:
		rejn = fn + ".rej"

	try:
		fls = read(fn)
		rls = read(rejn)
	except IOError:
		print "Error reading files", fn, "and", rejn
		return 1

	for (fromstart, fromlines, tostart, tolines) in parse_rej(rls):
		origlines = [l[2:] for l in fromlines]
		n = len(origlines)

		best = 0
		bestv = -1
		for pos in range(len(fls) - n):
			nm = num_matches(origlines, fls[pos:pos + n])
			if nm > bestv:
				(best, bestv) = (pos, nm)

		print "Chunk at", fromstart, "best fit at", best
		write("a.chunk", origlines)
		write("b.chunk", fls[best:best + n])
		os.system("diff -u a.chunk b.chunk")
		os.unlink("a.chunk")
		os.unlink("b.chunk")

if __name__ == "__main__":
	import sys
	sys.exit(main(sys.argv))