"""重排序服务 — Reranker 适配器外观。

用法::

    from app.ai_provider.reranker import RerankerService

    service = RerankerService(manager)
    result = await service.rerank("查询", ["文档1", "文档2"])
"""

from __future__ import annotations

from app.ai_provider.reranker.base import (
    RerankerProtocol,
    RerankerServiceError,
    RerankRequest,
    RerankResponse,
    RerankResult,
)
from app.ai_provider.types.errors import AIProviderError


class RerankerService:
    """外观类，负责解析 Reranker 模型并委托给 ProviderManager。

    接受 ProviderManager 或实现了以下接口的适配器：
    - ``.model_registry`` → 具有 ``list_by_capability(capability)`` 方法
    - ``.create_reranker(name)`` → 返回 RerankerProtocol 实例
    """

    def __init__(self, manager) -> None:
        self._manager = manager
        self._adapter: RerankerProtocol | None = None

    # ── Registry 兼容适配 ─────────────────────────────────────────

    @property
    def _registry(self):
        mgr = self._manager
        if hasattr(mgr, "model_registry"):
            return mgr.model_registry
        return mgr

    @property
    def _factory(self):
        mgr = self._manager
        if hasattr(mgr, "create_reranker"):
            return mgr
        return None

    # ── Reranker ───────────────────────────────────────────────────

    @property
    def adapter(self) -> RerankerProtocol:
        """解析并缓存 Reranker 适配器。"""
        if self._adapter is None:
            self._adapter = self._resolve()
        return self._adapter

    async def rerank(
        self,
        query: str,
        documents: list[str],
        model_hint: str | None = None,
        top_n: int | None = None,
    ) -> RerankResponse:
        """快捷方法：构造请求并调用 Reranker 适配器。"""
        model = self._resolve_model_name(model_hint)
        request = RerankRequest(
            query=query,
            documents=documents,
            model=model,
            top_n=top_n,
        )
        return await self.adapter.rerank(request)

    # ── 解析 ───────────────────────────────────────────────────────

    def _resolve(self) -> RerankerProtocol:
        """查找第一个活跃的 Reranker 模型并通过工厂创建。"""
        models = self._list_capability_models("reranker")
        if not models:
            raise AIProviderError(
                status_code=503,
                code="reranker_no_model",
                message="No reranker model configured in the model registry.",
            )
        factory = self._factory
        if factory is None:
            raise AIProviderError(
                status_code=501,
                code="reranker_no_factory",
                message="Reranker adapter factory not available (provider manager missing create_reranker).",
            )
        return factory.create_reranker(models[0].name)

    def _resolve_model_name(self, model_hint: str | None) -> str:
        models = self._list_capability_models("reranker")
        if model_hint:
            return model_hint
        if models:
            return models[0].name
        return ""

    def _list_capability_models(self, tag: str):
        reg = self._registry
        if hasattr(reg, "list_capability_models"):
            return reg.list_capability_models(tag)
        if hasattr(reg, "list_by_capability"):
            return reg.list_by_capability(tag)
        return []

    # ── 生命周期 ────────────────────────────────────────────────────

    async def close(self) -> None:
        if self._adapter is not None:
            close = getattr(self._adapter, "close", None)
            if close is not None:
                await close()

    async def __aenter__(self) -> RerankerService:
        return self

    async def __aexit__(self, *exc_info: object) -> None:
        await self.close()


__all__ = [
    "RerankerProtocol",
    "RerankRequest",
    "RerankResponse",
    "RerankResult",
    "RerankerService",
    "RerankerServiceError",
]