import zlib
import bps.operations as ops

def make_bps(source, target):
    # This function was adapted from
    # https://github.com/Alcaro/Flips/blob/master/libbps.cpp
    # originally written by Alcaro, used under the GPLv3.0 license
    sourcelen = len(source)
    targetlen = len(target)
    sourcepos = 0
    targetpos = 0
    lastknownchange = 0

    yield ops.Header(sourcelen, targetlen, "")
    while targetpos < targetlen:
        numunchanged = 0
        while (sourcepos+numunchanged < sourcelen and
                targetpos+numunchanged < targetlen and
                source[sourcepos+numunchanged] == target[targetpos+numunchanged]):
            numunchanged += 1
        if numunchanged > 1 or numunchanged == targetlen - targetpos:
            yield ops.SourceRead(numunchanged)
            sourcepos += numunchanged
            targetpos += numunchanged

        numchanged = 0
        if lastknownchange > targetpos:
            numchanged = lastknownchange - targetpos
        while targetpos + numchanged < targetlen and not (
                sourcepos + numchanged < sourcelen and
                source[sourcepos+numchanged] == target[targetpos+numchanged] and
                source[sourcepos+numchanged+1] == target[targetpos+numchanged+1] and
                source[sourcepos+numchanged+2] == target[targetpos+numchanged+2]):
            numchanged += 1
            if sourcepos+numchanged >= sourcelen:
                numchanged = targetlen - targetpos
        lastknownchange = targetpos + numchanged
        if numchanged:
            rle1start = max(targetpos, 1)
            while rle1start+3 < targetpos+numchanged:
                if (target[rle1start-1] == target[rle1start+0] and
                    target[rle1start+0] == target[rle1start+1] and
                    target[rle1start+1] == target[rle1start+2] and
                    target[rle1start+2] == target[rle1start+3]):
                    numchanged = rle1start - targetpos
                    break

                if rle1start >= 2 and rle1start+4 < targetpos+numchanged:
                    if (target[rle1start-2] == target[rle1start+0] and
                        target[rle1start-1] == target[rle1start+1] and
                        target[rle1start+0] == target[rle1start+2] and
                        target[rle1start+1] == target[rle1start+3] and
                        target[rle1start+2] == target[rle1start+4]):
                        numchanged = rle1start - targetpos
                        break
                rle1start += 1
            assert numchanged >= 0, numchanged
            if numchanged:
                yield ops.TargetRead(target[targetpos:targetpos+numchanged])
                sourcepos += numchanged
                targetpos += numchanged
            if (targetpos >= 2 and targetpos+2 < targetlen and
                target[targetpos-2] == target[targetpos+0] and
                target[targetpos-1] == target[targetpos+1] and
                target[targetpos-0] == target[targetpos+2]):
                # Two-byte RLE
                rlelen = 0
                while (targetpos + rlelen < targetlen and
                       target[targetpos+0] == target[targetpos+rlelen+0] and
                       target[targetpos+1] == target[targetpos+rlelen+1]):
                    rlelen += 2
                yield ops.TargetCopy(rlelen, targetpos - 2)
                sourcepos += rlelen
                targetpos += rlelen
            elif (targetpos >= 1 and targetpos+1 < targetlen and
                  target[targetpos-1] == target[targetpos+0] and
                  target[targetpos-0] == target[targetpos+1]):
                # One-byte RLE
                rlelen = 0
                while (targetpos + rlelen < targetlen and
                       target[targetpos] == target[targetpos+rlelen]):
                    rlelen += 1
                yield ops.TargetCopy(rlelen, targetpos - 1)
                sourcepos += rlelen
                targetpos += rlelen

    yield ops.SourceCRC32(zlib.crc32(source) & 0xFFFFFFFF)
    yield ops.TargetCRC32(zlib.crc32(target) & 0xFFFFFFFF)

def main():
    import bps.io
    import bps.apply
    import bps.validate
    import sys
    with open(sys.argv[1], "rb") as f:
        source = f.read()
    with open(sys.argv[2], "rb") as f:
        target = f.read()

    l = list(
        bps.validate.check_stream(
            make_bps(source, target)))

    target2 = bytearray(len(target))
    bps.apply.apply_to_bytearrays(l, source, target2)
    assert target == bytes(target2), "invalid patch created"

    bps.io.write_bps(l, sys.stdout.buffer)

main()