"""Regression tests for LIT-4185 — /v1/responses streaming must stamp
completion_start_time on the first chunk so downstream TTFT consumers
(Prometheus, OTEL, SpendLogs completionStartTime) do not fall back to
completion_start_time = end_time."""

import json
from datetime import datetime
from typing import Optional
from unittest.mock import Mock

import httpx
import pytest

from litellm.litellm_core_utils.litellm_logging import Logging as LiteLLMLoggingObj
from litellm.llms.base_llm.responses.transformation import BaseResponsesAPIConfig
from litellm.responses.streaming_iterator import (
    ResponsesAPIStreamingIterator,
    SyncResponsesAPIStreamingIterator,
)
from litellm.types.llms.openai import (
    ResponseCompletedEvent,
    ResponsesAPIResponse,
    ResponsesAPIStreamEvents,
)


def _sse_event(payload: dict) -> bytes:
    return f"data: {json.dumps(payload)}\n\n".encode("utf-8")


def _mock_config() -> Mock:
    mock_config = Mock(spec=BaseResponsesAPIConfig)
    mock_responses_api_response = Mock(spec=ResponsesAPIResponse)
    mock_responses_api_response.id = "resp_ttft"

    def _transform(model, parsed_chunk, logging_obj):
        evt_type = parsed_chunk.get("type")
        if evt_type == "response.completed":
            completed = Mock(spec=ResponseCompletedEvent)
            completed.type = ResponsesAPIStreamEvents.RESPONSE_COMPLETED
            completed.response = mock_responses_api_response
            return completed
        stub = Mock()
        stub.type = evt_type
        return stub

    mock_config.transform_streaming_response.side_effect = _transform
    return mock_config


def _make_iterator(
    *,
    sse_events: list[bytes],
    logging_obj: LiteLLMLoggingObj,
    trailing_error: Optional[Exception] = None,
) -> ResponsesAPIStreamingIterator:
    async def aiter_bytes():
        for evt in sse_events:
            yield evt
        if trailing_error is not None:
            raise trailing_error

    mock_response = Mock()
    mock_response.headers = {}
    mock_response.aiter_bytes = aiter_bytes

    return ResponsesAPIStreamingIterator(
        response=mock_response,
        model="gpt-4o-mini",
        responses_api_provider_config=_mock_config(),
        logging_obj=logging_obj,
        litellm_metadata={},
        custom_llm_provider="openai",
    )


def _make_sync_iterator(
    *,
    sse_events: list[bytes],
    logging_obj: LiteLLMLoggingObj,
    trailing_error: Optional[Exception] = None,
) -> SyncResponsesAPIStreamingIterator:
    def iter_bytes():
        for evt in sse_events:
            yield evt
        if trailing_error is not None:
            raise trailing_error

    mock_response = Mock()
    mock_response.headers = {}
    mock_response.iter_bytes = iter_bytes

    return SyncResponsesAPIStreamingIterator(
        response=mock_response,
        model="gpt-4o-mini",
        responses_api_provider_config=_mock_config(),
        logging_obj=logging_obj,
        litellm_metadata={},
        custom_llm_provider="openai",
    )


def _logging_obj_stub() -> Mock:
    logging_obj = Mock(spec=LiteLLMLoggingObj)
    logging_obj.completion_start_time = None
    logging_obj.model_call_details = {"litellm_params": {}}
    return logging_obj


@pytest.mark.asyncio
async def test_responses_streaming_stamps_completion_start_time_on_first_chunk():
    """Without the fix, `logging_obj.completion_start_time` stays None across the
    entire stream and _success_handler_helper_fn falls back to end_time — collapsing
    the reported TTFT to full generation time."""
    logging_obj = Mock(spec=LiteLLMLoggingObj)
    logging_obj.completion_start_time = None
    logging_obj.model_call_details = {"litellm_params": {}}
    stamped: list[datetime] = []

    def _update(*, completion_start_time):
        stamped.append(completion_start_time)
        logging_obj.completion_start_time = completion_start_time
        logging_obj.model_call_details["completion_start_time"] = completion_start_time

    logging_obj._update_completion_start_time.side_effect = _update

    iterator = _make_iterator(
        sse_events=[
            _sse_event({"type": "response.created"}),
            _sse_event({"type": "response.output_text.delta", "delta": "hi"}),
            _sse_event({"type": "response.completed"}),
        ],
        logging_obj=logging_obj,
    )

    async for _ in iterator:
        pass

    assert len(stamped) == 1, (
        f"Expected exactly one first-chunk stamp; got {len(stamped)}. "
        "Later chunks must not re-stamp completion_start_time."
    )
    assert isinstance(stamped[0], datetime)


@pytest.mark.asyncio
async def test_responses_streaming_does_not_reset_prior_completion_start_time():
    """If `completion_start_time` is already set (e.g. by an outer wrapper), the
    iterator must not overwrite it — otherwise TTFT would collapse to
    time-to-last-chunk under contention."""
    prior = datetime(2020, 1, 1, 0, 0, 0)
    logging_obj = Mock(spec=LiteLLMLoggingObj)
    logging_obj.completion_start_time = prior
    logging_obj.model_call_details = {"litellm_params": {}}

    iterator = _make_iterator(
        sse_events=[
            _sse_event({"type": "response.created"}),
            _sse_event({"type": "response.completed"}),
        ],
        logging_obj=logging_obj,
    )

    async for _ in iterator:
        pass

    logging_obj._update_completion_start_time.assert_not_called()
    assert logging_obj.completion_start_time == prior


_COMPLETE_STREAM_EVENTS = [
    _sse_event({"type": "response.created"}),
    _sse_event({"type": "response.output_text.delta", "delta": "hi"}),
    _sse_event({"type": "response.completed"}),
]

_TRAILING_ERRORS = [
    httpx.ReadError("Response payload is not completed"),
    httpx.RemoteProtocolError("peer closed connection without sending complete message body"),
]


@pytest.mark.asyncio
@pytest.mark.parametrize("trailing_error", _TRAILING_ERRORS, ids=type)
async def test_transport_error_after_completed_event_ends_stream_cleanly(trailing_error):
    """A sloppy connection close after `response.completed` must not turn a
    complete stream into an error (regression guard for the transport no longer
    swallowing ClientPayloadError/TransferEncodingError)."""
    iterator = _make_iterator(
        sse_events=_COMPLETE_STREAM_EVENTS,
        logging_obj=_logging_obj_stub(),
        trailing_error=trailing_error,
    )

    seen = [event.type async for event in iterator]

    assert ResponsesAPIStreamEvents.RESPONSE_COMPLETED in seen


@pytest.mark.asyncio
async def test_transport_error_before_completed_event_raises():
    """A connection lost before any terminal event is a real failure and must
    surface, not end the stream as if it completed."""
    iterator = _make_iterator(
        sse_events=_COMPLETE_STREAM_EVENTS[:-1],
        logging_obj=_logging_obj_stub(),
        trailing_error=httpx.ReadError("Response payload is not completed"),
    )

    with pytest.raises(httpx.ReadError):
        async for _ in iterator:
            pass


@pytest.mark.parametrize("trailing_error", _TRAILING_ERRORS, ids=type)
def test_sync_transport_error_after_completed_event_ends_stream_cleanly(trailing_error):
    iterator = _make_sync_iterator(
        sse_events=_COMPLETE_STREAM_EVENTS,
        logging_obj=_logging_obj_stub(),
        trailing_error=trailing_error,
    )

    seen = [event.type for event in iterator]

    assert ResponsesAPIStreamEvents.RESPONSE_COMPLETED in seen


def test_sync_transport_error_before_completed_event_raises():
    iterator = _make_sync_iterator(
        sse_events=_COMPLETE_STREAM_EVENTS[:-1],
        logging_obj=_logging_obj_stub(),
        trailing_error=httpx.ReadError("Response payload is not completed"),
    )

    with pytest.raises(httpx.ReadError):
        for _ in iterator:
            pass