"""FastAPI app factory for Beaver."""

from __future__ import annotations

from collections.abc import AsyncIterator, Callable
from contextlib import asynccontextmanager
from pathlib import Path
from types import SimpleNamespace
from typing import Any

from beaver.services.agent_service import AgentService

from .deps import get_agent_service
from .schemas import WebChatRequest, WebChatResponse, WebErrorResponse, WebStatusResponse

try:
    from fastapi import FastAPI, HTTPException, Request
except ModuleNotFoundError:  # pragma: no cover - fallback for skeleton-only environments
    class HTTPException(Exception):
        """Minimal fallback exception matching FastAPI's constructor shape."""

        def __init__(self, status_code: int, detail: str) -> None:
            super().__init__(detail)
            self.status_code = status_code
            self.detail = detail

    class Request:  # type: ignore[override]
        """Fallback request shim used only for import-time compatibility."""

        def __init__(self, app: Any) -> None:
            self.app = app

    class FastAPI:  # type: ignore[override]
        """Small fallback shim so the package can import before dependencies are installed."""

        def __init__(self, *, title: str, lifespan: Callable[..., Any] | None = None) -> None:
            self.title = title
            self.lifespan = lifespan
            self.state = SimpleNamespace()

        def get(self, _path: str, **_kwargs: Any) -> Callable[[Callable[..., Any]], Callable[..., Any]]:
            def decorator(func: Callable[..., Any]) -> Callable[..., Any]:
                return func

            return decorator

        def post(self, _path: str, **_kwargs: Any) -> Callable[[Callable[..., Any]], Callable[..., Any]]:
            def decorator(func: Callable[..., Any]) -> Callable[..., Any]:
                return func

            return decorator


@asynccontextmanager
async def _app_lifespan(
    app: FastAPI,
    *,
    workspace: str | Path | None,
    service: AgentService | None,
    manage_service_lifecycle: bool | None,
    shutdown_timeout_seconds: float | None,
    shutdown_force: bool,
) -> AsyncIterator[None]:
    """把 Web app 接到 AgentService lifecycle 上。"""

    attached_service = service or AgentService(workspace=workspace)
    owns_service = manage_service_lifecycle if manage_service_lifecycle is not None else service is None
    app.state.agent_service = attached_service
    started = False
    if owns_service:
        try:
            await attached_service.start()
            started = True
        except Exception:
            attached_service.close()
            raise
    try:
        yield
    finally:
        if owns_service and started:
            await attached_service.shutdown(
                timeout_seconds=shutdown_timeout_seconds,
                force=shutdown_force,
            )


def create_app(
    *,
    workspace: str | Path | None = None,
    service: AgentService | None = None,
    manage_service_lifecycle: bool | None = None,
    shutdown_timeout_seconds: float | None = 5.0,
    shutdown_force: bool = True,
) -> FastAPI:
    """Create a Beaver web app hosted by AgentService running mode.

    默认 ownership 语义：
    - 未传 `service`：app 自己创建并接管其 lifecycle
    - 传入外部 `service`：默认只挂载，不自动 start/shutdown

    如果确实需要覆盖默认行为，可以显式传 `manage_service_lifecycle=True/False`。
    """

    app = FastAPI(
        title="Beaver Backend",
        lifespan=lambda fastapi_app: _app_lifespan(
            fastapi_app,
            workspace=workspace,
            service=service,
            manage_service_lifecycle=manage_service_lifecycle,
            shutdown_timeout_seconds=shutdown_timeout_seconds,
            shutdown_force=shutdown_force,
        ),
    )

    @app.get("/api/ping", response_model=WebStatusResponse)
    async def ping(request: Request) -> WebStatusResponse:
        agent_service = get_agent_service(request)
        running = agent_service.is_running
        return WebStatusResponse(
            status="ok",
            running=running,
            mode="running" if running else ("direct" if agent_service.has_loop else "idle"),
        )

    @app.post(
        "/api/chat",
        response_model=WebChatResponse,
        responses={
            400: {"model": WebErrorResponse},
            409: {"model": WebErrorResponse},
            503: {"model": WebErrorResponse},
        },
    )
    async def chat(request: Request, payload: WebChatRequest) -> WebChatResponse:
        agent_service = get_agent_service(request)
        message = payload.message.strip()
        if not message:
            raise HTTPException(status_code=400, detail="'message' is required")

        fallback_target = _model_dump(payload.fallback_target)
        auxiliary_target = _model_dump(payload.auxiliary_target)
        embedding_target = _model_dump(payload.embedding_target)

        try:
            result = await agent_service.submit_direct(
                message,
                session_id=payload.session_id,
                source="web",
                user_id=payload.user_id,
                title=payload.title,
                execution_context=payload.execution_context,
                model=payload.model,
                provider_name=payload.provider_name,
                embedding_model=payload.embedding_model,
                temperature=payload.temperature,
                max_tokens=payload.max_tokens,
                max_tool_iterations=payload.max_tool_iterations,
                fallback_target=fallback_target,
                auxiliary_target=auxiliary_target,
                embedding_target=embedding_target,
            )
        except ValueError as exc:
            raise HTTPException(status_code=400, detail=str(exc)) from exc
        except RuntimeError as exc:
            detail = str(exc)
            if "requires an active run() loop" in detail or "not ready" in detail:
                status_code = 503
            elif "submit_direct" in detail or "running" in detail:
                status_code = 409
            else:
                status_code = 503
            raise HTTPException(status_code=status_code, detail=detail) from exc

        return WebChatResponse(
            session_id=result.session_id,
            run_id=result.run_id,
            output_text=result.output_text,
            finish_reason=result.finish_reason,
            tool_iterations=result.tool_iterations,
            provider_name=result.provider_name,
            model=result.model,
            usage=result.usage,
        )

    return app


def _model_dump(value: Any) -> dict[str, Any] | None:
    """兼容 Pydantic v1/v2 的最小导出辅助。"""

    if value is None:
        return None
    if hasattr(value, "model_dump"):
        return value.model_dump(exclude_none=True)
    if hasattr(value, "dict"):
        return value.dict(exclude_none=True)
    return dict(value)