"""
SSE utilities for AI Service.
[AC-AISVC-06, AC-AISVC-07, AC-AISVC-08, AC-AISVC-09] SSE event generation and state machine.
"""

import asyncio
import json
import logging
from enum import Enum
from typing import Any, AsyncGenerator

from sse_starlette.sse import EventSourceResponse, ServerSentEvent

from app.core.config import get_settings
from app.models import SSEErrorEvent, SSEEventType, SSEFinalEvent, SSEMessageEvent

logger = logging.getLogger(__name__)


class SSEState(str, Enum):
    INIT = "INIT"
    STREAMING = "STREAMING"
    FINAL_SENT = "FINAL_SENT"
    ERROR_SENT = "ERROR_SENT"
    CLOSED = "CLOSED"


class SSEStateMachine:
    """
    [AC-AISVC-08, AC-AISVC-09] SSE state machine ensuring proper event sequence.
    State transitions: INIT -> STREAMING -> FINAL_SENT/ERROR_SENT -> CLOSED
    """

    def __init__(self):
        self._state = SSEState.INIT
        self._lock = asyncio.Lock()

    @property
    def state(self) -> SSEState:
        return self._state

    async def transition_to_streaming(self) -> bool:
        async with self._lock:
            if self._state == SSEState.INIT:
                self._state = SSEState.STREAMING
                logger.debug(f"[AC-AISVC-07] SSE state transition: INIT -> STREAMING")
                return True
            return False

    async def transition_to_final(self) -> bool:
        async with self._lock:
            if self._state == SSEState.STREAMING:
                self._state = SSEState.FINAL_SENT
                logger.debug(f"[AC-AISVC-08] SSE state transition: STREAMING -> FINAL_SENT")
                return True
            return False

    async def transition_to_error(self) -> bool:
        async with self._lock:
            if self._state in (SSEState.INIT, SSEState.STREAMING):
                self._state = SSEState.ERROR_SENT
                logger.debug(f"[AC-AISVC-09] SSE state transition: {self._state} -> ERROR_SENT")
                return True
            return False

    async def close(self) -> None:
        async with self._lock:
            self._state = SSEState.CLOSED
            logger.debug("SSE state transition: -> CLOSED")

    def can_send_message(self) -> bool:
        return self._state == SSEState.STREAMING


def format_sse_event(event_type: SSEEventType, data: dict[str, Any]) -> ServerSentEvent:
    """Format data as SSE event."""
    return ServerSentEvent(
        event=event_type.value,
        data=json.dumps(data, ensure_ascii=False),
    )


def create_message_event(delta: str) -> ServerSentEvent:
    """[AC-AISVC-07] Create a message event with incremental content."""
    event_data = SSEMessageEvent(delta=delta)
    return format_sse_event(SSEEventType.MESSAGE, event_data.model_dump())


def create_final_event(
    reply: str,
    confidence: float,
    should_transfer: bool,
    transfer_reason: str | None = None,
    metadata: dict[str, Any] | None = None,
) -> ServerSentEvent:
    """[AC-AISVC-08] Create a final event with complete response."""
    event_data = SSEFinalEvent(
        reply=reply,
        confidence=confidence,
        should_transfer=should_transfer,
        transfer_reason=transfer_reason,
        metadata=metadata,
    )
    return format_sse_event(SSEEventType.FINAL, event_data.model_dump(exclude_none=True))


def create_error_event(
    code: str,
    message: str,
    details: list[dict[str, Any]] | None = None,
) -> ServerSentEvent:
    """[AC-AISVC-09] Create an error event."""
    event_data = SSEErrorEvent(
        code=code,
        message=message,
        details=details,
    )
    return format_sse_event(SSEEventType.ERROR, event_data.model_dump(exclude_none=True))


async def ping_generator(interval_seconds: int) -> AsyncGenerator[str, None]:
    """
    [AC-AISVC-06] Generate ping comments for SSE keep-alive.
    Sends ': ping' as comment lines (not events) to keep connection alive.
    """
    while True:
        await asyncio.sleep(interval_seconds)
        yield ": ping\n\n"


class SSEResponseBuilder:
    """
    Builder for SSE response with proper event sequencing and ping keep-alive.
    """

    def __init__(self):
        self._state_machine = SSEStateMachine()
        self._settings = get_settings()

    async def build_response(
        self,
        content_generator: AsyncGenerator[ServerSentEvent, None],
    ) -> EventSourceResponse:
        """
        Build SSE response with ping keep-alive mechanism.
        [AC-AISVC-06] Implements ping keep-alive to prevent connection timeout.
        """

        async def event_generator() -> AsyncGenerator[ServerSentEvent, None]:
            await self._state_machine.transition_to_streaming()
            try:
                async for event in content_generator:
                    if self._state_machine.can_send_message():
                        yield event
                    else:
                        break
            except Exception as e:
                logger.error(f"[AC-AISVC-09] Error during SSE streaming: {e}")
                if await self._state_machine.transition_to_error():
                    yield create_error_event(
                        code="STREAMING_ERROR",
                        message=str(e),
                    )
            finally:
                await self._state_machine.close()

        return EventSourceResponse(
            event_generator(),
            ping=self._settings.sse_ping_interval_seconds,
        )