#!/usr/bin/env python3
# Part of JoeyLib, Copyright (c) 2026 Scott Duensing, under the MIT License.
# See LICENSE.md for license information.
# SPDX-License-Identifier: MIT

"""Expand a file compressed by Microsoft's COMPRESS.EXE (SZDD, the WINGDE.DL_
kind on Windows 3.x setup disks), what EXPAND.EXE or msexpand do, so the
installer needs neither.

The format: the 8-byte magic, a mode byte ('A'), the name's last character
(the one the _ replaced), the expanded length (32-bit little-endian), then
LZSS: a control byte, its bits low first, a 1 meaning a literal byte and a 0
a two-byte match -- offset b0 | (b1 & 0xF0) << 4 into a 4096-byte window
that starts filled with spaces and written from 4096 - 16, length
(b1 & 0x0F) + 3.

Usage:
    tools/szddExpand.py IN OUT
"""

import sys

MAGIC = b"SZDD\x88\xf0\x27\x33"
HEADER_BYTES = 14
WINDOW_BYTES = 4096
WINDOW_MASK = WINDOW_BYTES - 1
WINDOW_START = WINDOW_BYTES - 16
WINDOW_FILL = 0x20
MATCH_MIN = 3


def expand(data):
    if data[:len(MAGIC)] != MAGIC:
        raise ValueError("not an SZDD file")
    length = int.from_bytes(data[10:HEADER_BYTES], "little")
    window = bytearray([WINDOW_FILL]) * WINDOW_BYTES
    pos = WINDOW_START
    out = bytearray()
    i = HEADER_BYTES
    while i < len(data) and len(out) < length:
        control = data[i]
        i += 1
        for bit in range(8):
            if i >= len(data) or len(out) >= length:
                break
            if control & (1 << bit):
                byte = data[i]
                i += 1
                out.append(byte)
                window[pos] = byte
                pos = (pos + 1) & WINDOW_MASK
            else:
                if i + 1 >= len(data):
                    break
                b0 = data[i]
                b1 = data[i + 1]
                i += 2
                offset = b0 | ((b1 & 0xF0) << 4)
                for k in range((b1 & 0x0F) + MATCH_MIN):
                    byte = window[(offset + k) & WINDOW_MASK]
                    out.append(byte)
                    window[pos] = byte
                    pos = (pos + 1) & WINDOW_MASK
    if len(out) != length:
        raise ValueError("expanded %d bytes, the header says %d" % (len(out), length))
    return bytes(out)


def main():
    if len(sys.argv) != 3:
        sys.stderr.write(__doc__)
        return 2
    with open(sys.argv[1], "rb") as f:
        data = f.read()
    with open(sys.argv[2], "wb") as f:
        f.write(expand(data))
    return 0


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