#!/usr/bin/env python3
"""Dump Minecraft NBT files (level.dat, data/*.dat, players/*.dat) and Anvil
region chunks (region/, entities/, poi/) as readable SNBT-like text.

  anvil_dump.py FILE.dat [PATH...]
  anvil_dump.py r.0.0.mca [CX CZ] [PATH...]

PATH selects nested keys (for example `sections 3 block_states`). Long
arrays are summarised unless --full is given; --typed suffixes numbers
with their NBT type (b, s, l, f, d; plain ints are TAG_Int). Used to compare Horizon saves
with worlds written by the vanilla server.
"""
import gzip
import io
import json
import struct
import sys
import zlib


def read_tag(f, tag_id):
    if tag_id == 1:
        return ('b', struct.unpack('>b', f.read(1))[0])
    if tag_id == 2:
        return ('s', struct.unpack('>h', f.read(2))[0])
    if tag_id == 3:
        return struct.unpack('>i', f.read(4))[0]
    if tag_id == 4:
        return ('l', struct.unpack('>q', f.read(8))[0])
    if tag_id == 5:
        return ('f', struct.unpack('>f', f.read(4))[0])
    if tag_id == 6:
        return ('d', struct.unpack('>d', f.read(8))[0])
    if tag_id == 7:
        n = struct.unpack('>i', f.read(4))[0]
        return ('B', list(struct.unpack(f'>{n}b', f.read(n))))
    if tag_id == 8:
        n = struct.unpack('>H', f.read(2))[0]
        return f.read(n).decode('utf-8', 'replace')
    if tag_id == 9:
        inner, n = struct.unpack('>bi', f.read(5))
        return [read_tag(f, inner) for _ in range(max(n, 0))]
    if tag_id == 10:
        out = {}
        while True:
            t = f.read(1)[0]
            if t == 0:
                return out
            n = struct.unpack('>H', f.read(2))[0]
            name = f.read(n).decode('utf-8', 'replace')
            out[name] = read_tag(f, t)
    if tag_id == 11:
        n = struct.unpack('>i', f.read(4))[0]
        return ('I', list(struct.unpack(f'>{n}i', f.read(4 * n))))
    if tag_id == 12:
        n = struct.unpack('>i', f.read(4))[0]
        return ('L', list(struct.unpack(f'>{n}q', f.read(8 * n))))
    raise ValueError(f'bad tag id {tag_id}')


def read_named(data):
    f = io.BytesIO(data)
    t = f.read(1)[0]
    n = struct.unpack('>H', f.read(2))[0]
    f.read(n)
    return read_tag(f, t)


def read_dat(path):
    raw = open(path, 'rb').read()
    if raw[:2] == b'\x1f\x8b':
        raw = gzip.decompress(raw)
    return read_named(raw)


def region_chunks(path):
    data = open(path, 'rb').read()
    out = {}
    for i in range(1024):
        off = int.from_bytes(data[i * 4:i * 4 + 3], 'big')
        if off == 0:
            continue
        start = off * 4096
        length = struct.unpack('>i', data[start:start + 4])[0]
        codec = data[start + 4] & 0x7F
        payload = data[start + 5:start + 4 + length]
        if codec == 1:
            payload = gzip.decompress(payload)
        elif codec == 2:
            payload = zlib.decompress(payload)
        out[(i & 31, i >> 5)] = read_named(payload)
    return out


def plain(v, full, typed=False):
    if isinstance(v, tuple):
        kind, val = v
        if kind in 'bsldf':
            return f'{val}{kind}' if typed else val
        if not full and len(val) > 8:
            return f'{kind}[{len(val)}: {val[:4]}...]'
        return val
    if isinstance(v, dict):
        return {k: plain(x, full, typed) for k, x in v.items()}
    if isinstance(v, list):
        return [plain(x, full, typed) for x in v]
    return v


def select(v, path):
    for p in path:
        if isinstance(v, list):
            v = v[int(p)]
        elif isinstance(v, tuple):
            v = v[1][int(p)]
        else:
            v = v[p]
    return v


def main(argv):
    full = '--full' in argv
    typed = '--typed' in argv
    argv = [a for a in argv if a not in ('--full', '--typed')]
    if not argv:
        print(__doc__)
        return 1
    path = argv[0]
    rest = argv[1:]
    if path.endswith('.mca'):
        chunks = region_chunks(path)
        if len(rest) >= 2 and rest[0].lstrip('-').isdigit():
            cx, cz = int(rest[0]) & 31, int(rest[1]) & 31
            value = chunks[(cx, cz)]
            rest = rest[2:]
        else:
            print(json.dumps(sorted(chunks)))
            return 0
    else:
        value = read_dat(path)
    print(json.dumps(plain(select(value, rest), full, typed), indent=1))
    return 0


if __name__ == '__main__':
    sys.exit(main(sys.argv[1:]))