"""
Chat endpoint for AI Service.
[AC-AISVC-01, AC-AISVC-02, AC-AISVC-06, AC-AISVC-08, AC-AISVC-09] Main chat endpoint with streaming/non-streaming modes.
"""

import logging
from typing import Annotated, Any

from fastapi import APIRouter, Depends, Header, Request
from fastapi.responses import JSONResponse
from sse_starlette.sse import EventSourceResponse

from app.core.middleware import get_response_mode, is_sse_request
from app.core.sse import SSEStateMachine, create_error_event
from app.core.tenant import get_tenant_id
from app.models import ChatRequest, ChatResponse, ErrorResponse
from app.services.orchestrator import OrchestratorService, get_orchestrator_service

logger = logging.getLogger(__name__)

router = APIRouter(tags=["AI Chat"])


@router.post(
    "/ai/chat",
    operation_id="generateReply",
    summary="Generate AI reply",
    description="""
    [AC-AISVC-01, AC-AISVC-02, AC-AISVC-06] Generate AI reply based on user message.
    
    Response mode is determined by Accept header:
    - Accept: text/event-stream -> SSE streaming response
    - Other -> JSON response
    """,
    responses={
        200: {
            "description": "Success - JSON or SSE stream",
            "content": {
                "application/json": {"schema": {"$ref": "#/components/schemas/ChatResponse"}},
                "text/event-stream": {"schema": {"type": "string"}},
            },
        },
        400: {"description": "Invalid request", "model": ErrorResponse},
        500: {"description": "Internal error", "model": ErrorResponse},
        503: {"description": "Service unavailable", "model": ErrorResponse},
    },
)
async def generate_reply(
    request: Request,
    chat_request: ChatRequest,
    accept: Annotated[str | None, Header()] = None,
    orchestrator: OrchestratorService = Depends(get_orchestrator_service),
) -> Any:
    """
    [AC-AISVC-06] Generate AI reply with automatic response mode switching.
    
    Based on Accept header:
    - text/event-stream: Returns SSE stream with message/final/error events
    - Other: Returns JSON ChatResponse
    """
    tenant_id = get_tenant_id()
    if not tenant_id:
        from app.core.exceptions import MissingTenantIdException
        raise MissingTenantIdException()

    logger.info(
        f"[AC-AISVC-06] Processing chat request: tenant={tenant_id}, "
        f"session={chat_request.session_id}, mode={get_response_mode(request)}"
    )

    if is_sse_request(request):
        return await _handle_streaming_request(tenant_id, chat_request, orchestrator)
    else:
        return await _handle_json_request(tenant_id, chat_request, orchestrator)


async def _handle_json_request(
    tenant_id: str,
    chat_request: ChatRequest,
    orchestrator: OrchestratorService,
) -> JSONResponse:
    """
    [AC-AISVC-02] Handle non-streaming JSON request.
    Returns ChatResponse with reply, confidence, shouldTransfer.
    """
    logger.info(f"[AC-AISVC-02] Processing JSON request for tenant={tenant_id}")

    try:
        response = await orchestrator.generate(tenant_id, chat_request)
        return JSONResponse(
            content=response.model_dump(exclude_none=True, by_alias=True),
        )
    except Exception as e:
        logger.error(f"[AC-AISVC-04] Error generating response: {e}")
        from app.core.exceptions import AIServiceException, ErrorCode
        if isinstance(e, AIServiceException):
            raise e
        from app.core.exceptions import AIServiceException
        raise AIServiceException(
            code=ErrorCode.INTERNAL_ERROR,
            message=str(e),
        )


async def _handle_streaming_request(
    tenant_id: str,
    chat_request: ChatRequest,
    orchestrator: OrchestratorService,
) -> EventSourceResponse:
    """
    [AC-AISVC-06, AC-AISVC-07, AC-AISVC-08, AC-AISVC-09] Handle SSE streaming request.
    
    SSE Event Sequence (per design.md Section 6.2):
    - message* (0 or more) -> final (exactly 1) -> close
    - OR message* (0 or more) -> error (exactly 1) -> close
    
    State machine ensures:
    - No events after final/error
    - Only one final OR one error event
    - Proper connection close
    """
    logger.info(f"[AC-AISVC-06] Processing SSE request for tenant={tenant_id}")

    state_machine = SSEStateMachine()

    async def event_generator():
        """
        [AC-AISVC-08, AC-AISVC-09] Event generator with state machine enforcement.
        Ensures proper event sequence and error handling.
        """
        await state_machine.transition_to_streaming()

        try:
            async for event in orchestrator.generate_stream(tenant_id, chat_request):
                if not state_machine.can_send_message():
                    logger.warning("[AC-AISVC-08] Received event after state machine closed, ignoring")
                    break

                if event.event == "final":
                    if await state_machine.transition_to_final():
                        logger.info("[AC-AISVC-08] Sending final event and closing stream")
                        yield event
                    break

                elif event.event == "error":
                    if await state_machine.transition_to_error():
                        logger.info("[AC-AISVC-09] Sending error event and closing stream")
                        yield event
                    break

                elif event.event == "message":
                    yield event

        except Exception as e:
            logger.error(f"[AC-AISVC-09] Streaming error: {e}")
            if await state_machine.transition_to_error():
                yield create_error_event(
                    code="STREAMING_ERROR",
                    message=str(e),
                )

        finally:
            await state_machine.close()
            logger.debug("[AC-AISVC-08] SSE connection closed")

    return EventSourceResponse(event_generator(), ping=15)