"""Encrypt/decrypt Coruna secondary type-0x01 .min.js packs."""

from __future__ import annotations

import lzma
import struct

from Crypto.Cipher import ChaCha20

WRAP_MAGIC = b"\x0d\xf0\xed\x0b"  # 0x0BEDF00D LE
F00D_MAGIC = 0xF00DBEEF


def build_f00dbeef_type01(dylib: bytes) -> bytes:
    """Single-entry F00DBEEF used by this campaign's secondary packs."""
    header = struct.pack(
        "<6I",
        F00D_MAGIC,
        1,  # version / entry-count field as in sample
        0x00010000,  # type 0x01
        3,
        0x18,  # payload offset
        len(dylib),
    )
    return header + dylib


def wrap_xz(plaintext: bytes) -> bytes:
    compressed = lzma.compress(plaintext, format=lzma.FORMAT_XZ)
    return WRAP_MAGIC + struct.pack("<I", len(plaintext)) + compressed


def unwrap_xz(blob: bytes) -> bytes:
    if blob[:4] != WRAP_MAGIC:
        raise ValueError(f"bad wrap magic: {blob[:4]!r}")
    expected = struct.unpack_from("<I", blob, 4)[0]
    plain = lzma.decompress(blob[8:])
    if len(plain) != expected:
        raise ValueError(f"xz size mismatch: {len(plain)} != {expected}")
    return plain


def chacha_crypt(data: bytes, key: bytes) -> bytes:
    if len(key) != 32:
        raise ValueError("ChaCha20 key must be 32 bytes")
    return ChaCha20.new(key=key, nonce=b"\x00" * 8).encrypt(data)


def encrypt_secondary_minjs(dylib: bytes, key: bytes) -> bytes:
    return chacha_crypt(wrap_xz(build_f00dbeef_type01(dylib)), key)


def decrypt_secondary_minjs(blob: bytes, key: bytes) -> bytes:
    plain = unwrap_xz(chacha_crypt(blob, key))
    if struct.unpack_from("<I", plain, 0)[0] != F00D_MAGIC:
        raise ValueError("not F00DBEEF after decrypt")
    offset = struct.unpack_from("<I", plain, 16)[0]
    size = struct.unpack_from("<I", plain, 20)[0]
    dylib = plain[offset : offset + size]
    if len(dylib) != size:
        raise ValueError("truncated dylib in F00DBEEF")
    return dylib