#!/usr/bin/env python3
"""Run Space Taxi's depacker to produce a FLAT 64K RAM image.

Why this exists: the disk's "SPACE TAXI+" is a crunched single file (it
matches the running game's memory in 0.6% of bytes), so the speech
samples cannot be read out of it statically.  And a VICE memory dump is
no good either -- it captures the banked-IN view, so $A000-$BFFF comes
back as BASIC ROM and 13 of the 15 utterances are missing.  Every
mem0000*.bin in this tree has that problem.

The way out needs no emulator install: stuff/spacetaxi/cpu6502.py is a
plain 6502 core over a flat 64K bytearray with no banking and no I/O,
which is all a depacker needs.  Load the .prg, run from the BASIC SYS
entry, and the depacked image IS the RAM -- $A000-$BFFF included.

Feed the result to extractSpeech.py.

Usage:  depackSpeechRam.py [spaceTaxiPlus.prg] [out.bin]
        Defaults resolve inside stuff/spacetaxi/ (gitignored research
        area, same as genC64Data.py's inputs).
"""

import os
import sys

HERE  = os.path.dirname(os.path.abspath(__file__))
STUFF = os.path.join(HERE, "..", "..", "..", "stuff", "spacetaxi")

# The BASIC stub is `0B08 D307 9E "2059" 00` -- SYS 2059.
ENTRY      = 0x080B
MAX_STEPS  = 60000000
CHECK_MASK = 0xFFFF          # how often to test for completion

# Completion test: the $9B00 index table is populated and the first
# utterance's $FE lead-in is in place.
TABLE_ADDR = 0x9B00
FIRST_UTT  = 0x9B40


def main():
    prgPath = sys.argv[1] if len(sys.argv) > 1 else os.path.join(STUFF, "extract", "SPACE TAXI+.prg")
    outPath = sys.argv[2] if len(sys.argv) > 2 else os.path.join(STUFF, "staxi-ram.bin")

    sys.path.insert(0, STUFF)
    try:
        from cpu6502 import Cpu6502
    except ImportError:
        sys.exit("depackSpeechRam: need cpu6502.py in %s" % STUFF)

    prg  = open(prgPath, "rb").read()
    load = prg[0] | (prg[1] << 8)
    ram  = bytearray(65536)
    ram[load:load + len(prg) - 2] = prg[2:]
    print("loaded %s at $%04X..$%04X" % (os.path.basename(prgPath), load, load + len(prg) - 3))

    cpu = Cpu6502(ram)
    cpu.pc = ENTRY
    steps  = 0
    done   = False
    try:
        while steps < MAX_STEPS:
            cpu.step()
            steps += 1
            if (steps & CHECK_MASK) == 0:
                if ram[TABLE_ADDR] != 0 and ram[FIRST_UTT] == 0xFE:
                    done = True
                    break
    except Exception as exc:
        # A depacker that runs off into I/O or an undocumented opcode
        # still usually gets the data down first, so report and carry on
        # to the write rather than throwing the work away.
        print("6502 stopped after %d steps at PC=$%04X: %s" % (steps, cpu.pc, exc))

    open(outPath, "wb").write(bytes(ram))
    print("%d steps, depack %s -> %s" % (steps, "detected" if done else "NOT detected", outPath))
    if not done:
        print("WARNING: completion check never fired; the image may be partial.")


if __name__ == "__main__":
    main()