"""Minimal reader for gzipped NBT structure templates (data/*/structure/*.nbt).

Only what the field guide needs: the palette, block-entity strings (loot
tables, jigsaw pools) and entity ids. Returns plain Python values.
"""
import gzip
import io
import struct


def _read(f, tag):
    if tag == 1:
        return struct.unpack(">b", f.read(1))[0]
    if tag == 2:
        return struct.unpack(">h", f.read(2))[0]
    if tag == 3:
        return struct.unpack(">i", f.read(4))[0]
    if tag == 4:
        return struct.unpack(">q", f.read(8))[0]
    if tag == 5:
        return struct.unpack(">f", f.read(4))[0]
    if tag == 6:
        return struct.unpack(">d", f.read(8))[0]
    if tag == 7:
        return f.read(struct.unpack(">i", f.read(4))[0])
    if tag == 8:
        return f.read(struct.unpack(">H", f.read(2))[0]).decode("utf-8", "replace")
    if tag == 9:
        inner, n = struct.unpack(">bi", f.read(5))
        return [_read(f, inner) for _ in range(n)]
    if tag == 10:
        out = {}
        while True:
            t = f.read(1)[0]
            if t == 0:
                return out
            name = f.read(struct.unpack(">H", f.read(2))[0]).decode("utf-8", "replace")
            out[name] = _read(f, t)
    if tag == 11:
        n = struct.unpack(">i", f.read(4))[0]
        return list(struct.unpack(f">{n}i", f.read(4 * n)))
    if tag == 12:
        n = struct.unpack(">i", f.read(4))[0]
        return list(struct.unpack(f">{n}q", f.read(8 * n)))
    raise ValueError(f"bad NBT tag {tag}")


def load(raw):
    data = gzip.decompress(raw) if raw[:2] == b"\x1f\x8b" else raw
    f = io.BytesIO(data)
    tag = f.read(1)[0]
    f.read(struct.unpack(">H", f.read(2))[0])
    return _read(f, tag)


def strings(value):
    """Every string inside a decoded NBT value."""
    if isinstance(value, str):
        yield value
    elif isinstance(value, dict):
        for v in value.values():
            yield from strings(v)
    elif isinstance(value, list):
        for v in value:
            yield from strings(v)