"""Multi-fragment AIS assembler: strict-order and strengthened-key tests.

These tests exercise the assembler logic only up to fragment validation.
Actual decoding with pyais is covered by a separate integration check
if pyais is importable.
"""

from __future__ import annotations

import pytest

from ais_hub.core.stats import Stats
from ais_hub.parser.ais import AisAssembler


SRC_A = "ais_udp:10.0.0.1:5000"
SRC_B = "ais_udp:10.0.0.2:5000"


def _frag(total: int, n: int, seq: str, channel: str = "A", payload: str = "abcd", fill: str = "0") -> str:
    # Compute checksum so parse_sentence accepts the line.
    body = f"AIVDM,{total},{n},{seq},{channel},{payload},{fill}"
    cs = 0
    for ch in body.encode("ascii"):
        cs ^= ch
    return f"!{body}*{cs:02X}"


def test_single_fragment_fast_path_attempts_decode():
    """A single-fragment sentence is passed to pyais; decode may fail, but
    the assembler must not keep any buffers for it."""
    stats = Stats()
    a = AisAssembler(stats=stats)
    line = _frag(1, 1, "")
    a.feed(SRC_A, line)
    # No multi-fragment buffers.
    assert len(a._buffers) == 0


def test_multi_fragment_happy_path_clears_buffer():
    stats = Stats()
    a = AisAssembler(stats=stats)
    a.feed(SRC_A, _frag(2, 1, "3"))
    assert len(a._buffers) == 1
    a.feed(SRC_A, _frag(2, 2, "3"))
    # After the final fragment arrives, the buffer is removed (regardless
    # of whether pyais decodes successfully).
    assert len(a._buffers) == 0


def test_out_of_order_fragment_triggers_error_and_reset():
    stats = Stats()
    a = AisAssembler(stats=stats)
    a.feed(SRC_A, _frag(3, 1, "7"))
    a.feed(SRC_A, _frag(3, 3, "7"))  # skipped fragment 2
    assert stats.counters["ais_fragment_errors"] >= 1


def test_duplicate_fragment_is_error():
    stats = Stats()
    a = AisAssembler(stats=stats)
    a.feed(SRC_A, _frag(2, 1, "9"))
    a.feed(SRC_A, _frag(2, 1, "9"))  # duplicate
    assert stats.counters["ais_fragment_errors"] >= 1


def test_mid_stream_fragment_without_leading_is_error():
    stats = Stats()
    a = AisAssembler(stats=stats)
    a.feed(SRC_A, _frag(2, 2, "4"))
    assert stats.counters["ais_fragment_errors"] >= 1
    assert len(a._buffers) == 0


def test_strengthened_key_isolates_sources():
    """Two sources reusing the same seq_id must not cross-contaminate."""
    stats = Stats()
    a = AisAssembler(stats=stats)
    a.feed(SRC_A, _frag(2, 1, "5"))
    a.feed(SRC_B, _frag(2, 1, "5"))
    assert len(a._buffers) == 2  # two independent buffers
    assert stats.counters.get("ais_fragment_errors", 0) == 0


def test_multi_fragment_without_seq_id_is_error():
    stats = Stats()
    a = AisAssembler(stats=stats)
    a.feed(SRC_A, _frag(2, 1, ""))  # empty seq_id on a multi-fragment
    assert stats.counters["ais_fragment_errors"] >= 1


def test_total_mismatch_on_followup_is_error():
    stats = Stats()
    a = AisAssembler(stats=stats)
    a.feed(SRC_A, _frag(2, 1, "2"))
    # Fragment claims total=3 now; must be treated as a fresh start or error.
    a.feed(SRC_A, _frag(3, 2, "2"))
    assert stats.counters["ais_fragment_errors"] >= 1


def test_ttl_gc_evicts_stale_buffers():
    stats = Stats()
    a = AisAssembler(stats=stats, ttl_sec=1.0)
    a.feed(SRC_A, _frag(2, 1, "8"), ts=1000.0)
    assert len(a._buffers) == 1
    a.gc(now=1002.0)
    assert len(a._buffers) == 0
    assert stats.counters["ais_fragment_timeouts"] >= 1


def test_bad_checksum_ignored_with_counter():
    stats = Stats()
    a = AisAssembler(stats=stats)
    a.feed(SRC_A, "!AIVDM,1,1,,A,x,0*00")  # deliberately wrong checksum
    assert stats.counters["parser_checksum_errors"] >= 1