Extract and inject textures to Falcom's it3 files

it3tex.py

import typing as T
from pathlib import Path
from dataclasses import dataclass

@dataclass
class Chunk:
	type: bytes
	data: bytearray

def read_chunks(f: T.IO[bytes]) -> list[Chunk]:
	chunks = []
	while True:
		fourcc = f.read(4)
		if len(fourcc) != 4: break
		n = int.from_bytes(f.read(4), "little")
		chunks.append(Chunk(fourcc, bytearray(f.read(n))))
	return chunks

def write_chunks(f: T.IO[bytes], chunks: list[Chunk]):
	for chunk in chunks:
		assert len(chunk.type) == 4
		f.write(chunk.type)
		f.write(int.to_bytes(len(chunk.data), 4, "little"))
		f.write(chunk.data)

def dec(x: bytes) -> str:
	return x.split(b"\0")[0].decode("cp932")

def extract(it3file: Path, texdir: Path):
	with it3file.open("rb") as f:
		chunks = read_chunks(f)

	for chunk in chunks:
		match chunk.type:
			case b"TEXI":
				name = dec(chunk.data[:36])
				path = texdir/f"{name}.itp"
				path.write_bytes(chunk.data[36:])
				print(f"TEXI: {name} extracted to {path}")
			case b"TEXF":
				name = dec(chunk.data[:36])
				path = dec(chunk.data[36:])
				print(f"TEXF: {name} is external at {path}")
			case b"TEX2":
				n = int.from_bytes(chunk.data[:4], "little")
				name = dec(chunk.data[4:4+n])
				path = texdir/f"{name}.itp"
				path.write_bytes(chunk.data[4+n:])
				print(f"TEX2: {name} extracted to {path}")
			case a if a.startswith(b"TEX"):
				print("{a.decode('cp932')}: unknown texture type")
			case _: pass

def inject(it3file: Path, texdir: Path):
	with it3file.open("rb") as f:
		chunks = read_chunks(f)

	for chunk in chunks:
		match chunk.type:
			case b"TEXI":
				name = dec(chunk.data[:36])
				path = texdir/f"{name}.itp"
				chunk.data[36:] = path.read_bytes()
				print(f"TEXI: {name} injected from {path}")
			case b"TEXF":
				name = dec(chunk.data[:36])
				path = dec(chunk.data[36:])
				print(f"TEXF: {name} is external at {path}")
			case b"TEX2":
				n = int.from_bytes(chunk.data[:4], "little")
				name = dec(chunk.data[4:4+n])
				path = texdir/f"{name}.itp"
				chunk.data[4+n:] = path.read_bytes()
				print(f"TEX2: {name} injected from {path}")
			case a if a.startswith(b"TEX"):
				print("{a.decode('cp932')}: unknown texture type")
			case _: pass

	with it3file.open("wb") as f:
		write_chunks(f, chunks)

def __main__():
	import argparse
	argp = argparse.ArgumentParser()
	sub = argp.add_subparsers(dest="cmd", required=True)

	ext = sub.add_parser("extract")
	ext.add_argument("-d", "--texdir", type=Path)
	ext.add_argument("it3file", type=Path)

	inj = sub.add_parser("inject")
	inj.add_argument("-d", "--texdir", type=Path)
	inj.add_argument("it3file", type=Path)

	args = argp.parse_args()

	it3file: Path = args.it3file
	texdir: Path|None = args.texdir
	if texdir is None: texdir = it3file.with_suffix("")

	assert it3file.is_file()
	if args.cmd == "extract": texdir.mkdir(parents=True, exist_ok=True)
	assert texdir.is_dir()

	match args.cmd:
		case "extract": extract(it3file, texdir)
		case "inject": inject(it3file, texdir)
		case a: raise Exception(a)

if __name__ == "__main__": __main__()