import pytest

from gns_snapshot_envelope import (
    HEADER_SIZE,
    MAGIC,
    SnapshotEnvelopeError,
    decode_snapshot,
    encode_snapshot,
)
from packet_codec import MAX_MESSAGE_BYTES


def test_transform_and_npc_snapshots_round_trip_with_sequence():
    transform = encode_snapshot("transform", b'{"type":"transform","x":1}', 7)
    decoded_transform = decode_snapshot(transform)
    assert decoded_transform is not None
    assert decoded_transform.packet_type == "transform"
    assert decoded_transform.sequence == 7
    assert decoded_transform.payload == b'{"type":"transform","x":1}'

    npc = encode_snapshot("npcState", b'{"type":"npcState","npcs":[]}', 9)
    decoded_npc = decode_snapshot(npc)
    assert decoded_npc is not None
    assert decoded_npc.packet_type == "npcState"
    assert decoded_npc.sequence == 9


def test_reliable_json_is_not_misidentified_as_snapshot_envelope():
    assert decode_snapshot(b'{"type":"playerState"}') is None


def test_snapshot_envelope_rejects_invalid_family_sequence_and_size():
    with pytest.raises(SnapshotEnvelopeError):
        encode_snapshot("playerState", b"{}", 1)
    with pytest.raises(SnapshotEnvelopeError):
        encode_snapshot("transform", b"{}", 0)
    with pytest.raises(SnapshotEnvelopeError):
        encode_snapshot("transform", b"x" * MAX_MESSAGE_BYTES, 1)


def test_snapshot_decoder_rejects_truncated_or_corrupt_headers():
    with pytest.raises(SnapshotEnvelopeError):
        decode_snapshot(MAGIC)

    valid = bytearray(encode_snapshot("transform", b"{}", 1))
    valid[4] = 99
    with pytest.raises(SnapshotEnvelopeError):
        decode_snapshot(valid)

    valid = bytearray(encode_snapshot("transform", b"{}", 1))
    valid[5] = 99
    with pytest.raises(SnapshotEnvelopeError):
        decode_snapshot(valid)

    valid = bytearray(encode_snapshot("transform", b"{}", 1))
    valid[6:8] = b"\x00\x01"
    with pytest.raises(SnapshotEnvelopeError):
        decode_snapshot(valid)


def test_snapshot_header_leaves_payload_under_native_64k_cap():
    payload = b"x" * (MAX_MESSAGE_BYTES - HEADER_SIZE)
    message = encode_snapshot("transform", payload, 0xFFFFFFFF)
    assert len(message) == MAX_MESSAGE_BYTES