"""Быстрые проверки пакетного протокола: protocol/packet.py."""

from __future__ import annotations

import struct

import pytest

from protocol.packet import (
    CRC_SIZE,
    HEADER_SIZE,
    MAX_PAYLOAD_SIZE,
    MESSAGE_TYPE_ACK,
    MESSAGE_TYPE_IMAGE_FRAGMENT,
    MESSAGE_TYPE_TELEMETRY,
    MESSAGE_TYPE_TEXT,
    PROTOCOL_VERSION,
    SYNC_WORD,
    CRCError,
    PacketError,
    build_packet,
    parse_packet,
)


MESSAGE_TYPES = (
    MESSAGE_TYPE_TEXT,
    MESSAGE_TYPE_TELEMETRY,
    MESSAGE_TYPE_IMAGE_FRAGMENT,
    MESSAGE_TYPE_ACK,
)


@pytest.mark.parametrize("message_type", MESSAGE_TYPES)
@pytest.mark.parametrize("payload", [b"", b"H", b"HELLO SDR", bytes(range(256)), b"\x00" * 1024])
def test_roundtrip_preserves_payload(payload: bytes, message_type: int) -> None:
    parsed = parse_packet(build_packet(payload, message_type, 7))
    assert parsed.payload == payload
    assert parsed.message_type == message_type
    assert parsed.sequence_number == 7
    assert parsed.version == PROTOCOL_VERSION


def test_packet_starts_with_sync_word() -> None:
    packet = build_packet(b"data", MESSAGE_TYPE_TEXT, 1)
    assert struct.unpack(">H", packet[:2])[0] == SYNC_WORD


def test_length_is_header_plus_payload_plus_crc() -> None:
    payload = b"x" * 300
    packet = build_packet(payload, MESSAGE_TYPE_TEXT, 1)
    assert len(packet) == HEADER_SIZE + len(payload) + CRC_SIZE


def test_sequence_number_survives_full_range() -> None:
    for sequence_number in (0, 1, 65534, 65535):
        assert parse_packet(build_packet(b"a", MESSAGE_TYPE_TEXT, sequence_number)).sequence_number == sequence_number


@pytest.mark.parametrize("bit_index", [0, 7, 8, 23, 64, 100])
def test_single_bit_corruption_is_detected(bit_index: int) -> None:
    """CRC32 обязан ловить одиночное искажение бита в любом месте пакета."""

    packet = bytearray(build_packet(b"HELLO SDR TELEMETRY", MESSAGE_TYPE_TELEMETRY, 3))
    byte_index, offset = divmod(bit_index, 8)
    assert byte_index < len(packet)
    packet[byte_index] ^= 1 << offset

    with pytest.raises((CRCError, PacketError)):
        parse_packet(bytes(packet))


def test_truncated_packet_is_rejected() -> None:
    packet = build_packet(b"HELLO", MESSAGE_TYPE_TEXT, 1)
    for cut in (0, 1, HEADER_SIZE - 1, len(packet) - 1):
        with pytest.raises(PacketError):
            parse_packet(packet[:cut])


def test_oversized_payload_is_rejected() -> None:
    with pytest.raises((PacketError, ValueError)):
        build_packet(b"\x00" * (MAX_PAYLOAD_SIZE + 1), MESSAGE_TYPE_TEXT, 1)


def test_wrong_sync_word_is_rejected() -> None:
    packet = bytearray(build_packet(b"HELLO", MESSAGE_TYPE_TEXT, 1))
    packet[0] ^= 0xFF
    with pytest.raises(PacketError):
        parse_packet(bytes(packet))


def test_payload_is_not_shared_with_caller() -> None:
    """Разбор не должен возвращать ссылку на изменяемый буфер."""

    packet = bytearray(build_packet(b"HELLO", MESSAGE_TYPE_TEXT, 1))
    parsed = parse_packet(bytes(packet))
    assert isinstance(parsed.payload, bytes)