"""Decompressore Unix compress (.Z, LZW) minimale, come ncompress."""
import sys, os


def unz(data):
    assert data[0] == 0x1f and data[1] == 0x9d, "non e' un flusso .Z"
    flags = data[2]
    maxbits = flags & 0x1f
    block = bool(flags & 0x80)
    out = bytearray()
    n_bits = 9
    maxcode = (1 << n_bits) - 1
    table = {i: bytes([i]) for i in range(256)}
    free = 257 if block else 256
    pos = 3 * 8                       # posizione in bit
    total = len(data) * 8
    start = pos                       # inizio del gruppo corrente di codici (per il riallineamento)
    old = None
    while pos + n_bits <= total:
        byte = pos >> 3
        chunk = int.from_bytes(data[byte:byte + 4], 'little')
        code = (chunk >> (pos & 7)) & ((1 << n_bits) - 1)
        pos += n_bits
        if old is None:
            old = table[code]
            out += old
            continue
        if code == 256 and block:
            table = {i: bytes([i]) for i in range(256)}
            free = 256
            # riallinea a multipli di 8 codici
            grp = n_bits * 8
            pos = start + ((pos - start + grp - 1) // grp) * grp
            n_bits = 9
            maxcode = (1 << n_bits) - 1
            start = pos
            old = None
            free = 257
            continue
        if code in table:
            entry = table[code]
        elif code == free:
            entry = old + old[:1]
        else:
            raise ValueError(f"codice LZW non valido {code} (free={free}) a bit {pos}")
        out += entry
        if free <= (1 << maxbits) - 1:
            table[free] = old + entry[:1]
            free += 1
        old = entry
        if free > maxcode and n_bits < maxbits:
            grp = n_bits * 8
            pos = start + ((pos - start + grp - 1) // grp) * grp
            n_bits += 1
            maxcode = (1 << n_bits) - 1
            start = pos
    return bytes(out)


if __name__ == '__main__':
    sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
    import prt
    d, secs, order = prt.load(sys.argv[1])
    outdir = sys.argv[2]
    for n in order:
        o, l, f = secs[n]
        b = d[o:o + l]
        if b[:2] == b'\x1f\x9d':
            try:
                u = unz(b)
            except Exception as e:
                print(n, 'ERR', e)
                continue
            print(n, 'compressa', l, '->', len(u), 'dichiarata', int(f[0], 16), u[:60])
            open(os.path.join(outdir, n.replace(':', '_') + '.bin'), 'wb').write(u)