"""Inspect a torrent or demonstrate unchanged infohash and damaged piece detection."""
import argparse
import json
from pathlib import Path
import sys
from metainfo import decode, encode, inspect, make_metainfo, verify


def describe(raw):
    meta, infohash = inspect(raw)
    info = meta[b"info"]
    print(json.dumps({
        "announce": meta[b"announce"].decode(),
        "name": info[b"name"].decode(),
        "length": info[b"length"],
        "piece length": info[b"piece length"],
        "pieces (SHA-1)": [info[b"pieces"][i:i + 20].hex()
                           for i in range(0, len(info[b"pieces"]), 20)],
        "infohash (raw bencoded info)": infohash,
    }, indent=2))


def demo(directory):
    directory.mkdir(parents=True, exist_ok=True)
    data = bytes(range(256)) * 1024
    original = encode(make_metainfo("lesson.bin", data))
    meta, original_info = decode(original)
    changed = dict(meta)
    changed[b"announce"] = b"http://127.0.0.1:6970/announce"
    changed[b"comment"] = b"A different comment"
    modified = encode(changed)
    assert decode(modified)[1] == original_info
    damaged = bytearray(data)
    damaged[65536 + 17] ^= 1
    for name, content in [("lesson.bin", data), ("lesson.torrent", original),
                          ("changed.torrent", modified), ("damaged.bin", damaged)]:
        (directory / name).write_bytes(content)
    describe(original)
    print("Original infohash:", inspect(original)[1])
    print("Changed  infohash:", inspect(modified)[1])
    assert inspect(original)[1] == inspect(modified)[1]
    good, _ = verify(original, data)
    bad, indices = verify(original, damaged)
    assert good and not bad and indices == [1]
    print("PASS: changing announce/comment preserved infohash")
    print("PASS: original file verified; damaged file rejected, piece index:", indices)
    print("Files:", directory)


def main():
    parser = argparse.ArgumentParser(description=__doc__)
    subs = parser.add_subparsers(dest="command", required=True)
    p = subs.add_parser("demo")
    p.add_argument("--directory", type=Path, default=Path(".local/metadata"))
    p = subs.add_parser("inspect")
    p.add_argument("torrent", type=Path)
    p = subs.add_parser("verify")
    p.add_argument("torrent", type=Path)
    p.add_argument("file", type=Path)
    args = parser.parse_args()
    if args.command == "demo":
        demo(args.directory)
    elif args.command == "inspect":
        describe(args.torrent.read_bytes())
    else:
        ok, bad = verify(args.torrent.read_bytes(), args.file.read_bytes())
        print("OK" if ok else "FAILED", "bad pieces:", bad)
        return 0 if ok else 1
    return 0


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