"""Stream UnityFS nodes to a private workspace; do not load media bundles into RAM."""
from pathlib import Path


def unpack(source: Path, target: Path) -> list[Path]:
    from UnityPy.helpers.CompressionHelper import DECOMPRESSION_MAP
    from UnityPy.streams import EndianBinaryReader

    target.mkdir(parents=True, exist_ok=True)
    with source.open("rb") as stream:
        reader = EndianBinaryReader(stream)
        if reader.read_string_to_null() != "UnityFS":
            raise ValueError(f"Неподдерживаемый Unity-контейнер: {source.name}")
        version = reader.read_u_int()
        reader.read_string_to_null()
        reader.read_string_to_null()
        size = reader.read_long()
        packed, raw, flags = reader.read_u_int(), reader.read_u_int(), reader.read_u_int()
        if version not in {6, 7, 8} or flags & ~0x3ff:
            raise ValueError(f"Неподдерживаемый UnityFS: версия {version}, flags={flags}")
        if version >= 7:
            reader.align_stream(16)
        start = reader.Position
        if flags & 0x80:
            reader.Position = size - packed
        info = EndianBinaryReader(DECOMPRESSION_MAP[flags & 63](reader.read_bytes(packed), raw))
        if flags & 0x80:
            reader.Position = start
        info.read_bytes(16)
        count = info.read_int()
        if not 0 <= count <= 1_000_000:
            raise ValueError("Некорректное количество блоков UnityFS")
        blocks = [(info.read_u_int(), info.read_u_int(), info.read_u_short()) for _ in range(count)]
        count = info.read_int()
        if not 0 <= count <= 100_000:
            raise ValueError("Некорректное количество файлов UnityFS")
        nodes = [(info.read_long(), info.read_long(), info.read_u_int(), info.read_string_to_null())
                 for _ in range(count)]
        if flags & 0x200:
            reader.align_stream(16)
        handles, paths = [], []
        total = sum(b[0] for b in blocks)
        try:
            for offset, length, _, name in nodes:
                path = (target / name).resolve()
                if (not path.is_relative_to(target.resolve()) or path in paths or
                        offset < 0 or length < 0 or offset + length > total):
                    raise ValueError(f"Некорректный файл UnityFS: {name}")
                path.parent.mkdir(parents=True, exist_ok=True)
                handles.append((offset, length, path.open("wb")))
                paths.append(path)
            position = 0
            for raw_size, packed_size, block_flags in blocks:
                chunk = DECOMPRESSION_MAP[block_flags & 63](reader.read_bytes(packed_size), raw_size)
                if len(chunk) != raw_size:
                    raise ValueError("Повреждённый блок UnityFS")
                for offset, length, handle in handles:
                    left, right = max(position, offset), min(position + raw_size, offset + length)
                    if left < right:
                        handle.write(chunk[left - position:right - position])
                position += raw_size
        finally:
            for _, _, handle in handles:
                handle.close()
    return paths