"""
Embedding Service - Ollama BGE-M3 替代方案
==========================================

使用 Ollama qwen2.5:7b-instruct 提供文本向量化功能。
雖非專用 embedding 模型，但支援多語言 (繁中/英文)。

Phase 13.2 #84 - RAG Tool 基礎設施

版本: v1.1
建立日期: 2026-03-26 20:30 (台北時區)
更新日期: 2026-03-29 20:50 (台北時區)
建立者: Claude Code
更新者: Claude Code (P1 修復: 維度配置化)
"""

import asyncio
from typing import Protocol

import httpx
import structlog

from src.core.config import settings

logger = structlog.get_logger(__name__)


# =============================================================================
# Interface (DI Protocol)
# =============================================================================


class IEmbeddingService(Protocol):
    """Embedding 服務介面"""

    async def embed_text(self, text: str) -> list[float]:
        """將單一文本轉換為向量"""
        ...

    async def embed_batch(self, texts: list[str]) -> list[list[float]]:
        """批次向量化多個文本"""
        ...

    @property
    def dimension(self) -> int:
        """向量維度"""
        ...


# =============================================================================
# Implementation
# =============================================================================


class OllamaEmbeddingService:
    """
    Ollama Embedding Service

    使用 Ollama API 進行文本向量化。
    預設使用 qwen2.5:7b-instruct (3584 維向量)。

    Usage:
        service = OllamaEmbeddingService()
        vector = await service.embed_text("維運手冊")
    """

    # 已知模型維度 (P1 修復: 避免硬編碼)
    MODEL_DIMENSIONS: dict[str, int] = {
        "qwen2.5:7b-instruct": 3584,
        "qwen2.5:3b-instruct": 2048,
        "llama3.2:3b": 3072,
        "nomic-embed-text": 768,
    }
    DEFAULT_DIMENSION = 3584  # 未知模型的預設值

    def __init__(
        self,
        model: str = "qwen2.5:7b-instruct",
        ollama_url: str | None = None,
        timeout: float = 30.0,
        default_dimension: int | None = None,
    ) -> None:
        """
        初始化 Embedding Service

        Args:
            model: Ollama 模型名稱 (必須支援 embedding)
            ollama_url: Ollama API URL (預設從 config 讀取)
            timeout: 請求超時 (秒)
            default_dimension: 預設向量維度 (可選，未提供則從 MODEL_DIMENSIONS 查詢)

        P1 修復 (2026-03-29): 維度配置化，支援更多模型
        """
        self._model = model
        self._ollama_url = ollama_url or settings.OLLAMA_URL
        self._timeout = timeout
        self._default_dimension = default_dimension or self.MODEL_DIMENSIONS.get(
            model, self.DEFAULT_DIMENSION
        )
        self._dimension: int | None = None
        self._client: httpx.AsyncClient | None = None

    @property
    def dimension(self) -> int:
        """
        向量維度

        首次 embed 呼叫會自動偵測實際維度並快取。
        偵測前返回 MODEL_DIMENSIONS 中的預設值。
        """
        if self._dimension is None:
            return self._default_dimension
        return self._dimension

    async def _get_client(self) -> httpx.AsyncClient:
        """取得 HTTP Client (連線池共用)"""
        if self._client is None:
            self._client = httpx.AsyncClient(
                timeout=httpx.Timeout(self._timeout),
                limits=httpx.Limits(max_connections=10),
            )
        return self._client

    async def embed_text(self, text: str) -> list[float]:
        """
        將單一文本轉換為向量

        Args:
            text: 要向量化的文本

        Returns:
            list[float]: 向量 (3584 維)

        Raises:
            EmbeddingError: 向量化失敗
        """
        client = await self._get_client()

        try:
            response = await client.post(
                f"{self._ollama_url}/api/embeddings",
                json={
                    "model": self._model,
                    "prompt": text,
                },
            )
            response.raise_for_status()

            data = response.json()
            embedding = data.get("embedding", [])

            # 更新維度快取
            if self._dimension is None and embedding:
                self._dimension = len(embedding)
                logger.info(
                    "embedding_dimension_detected",
                    model=self._model,
                    dimension=self._dimension,
                )

            return embedding

        except httpx.TimeoutException as e:
            logger.error("embedding_timeout", model=self._model, text_len=len(text))
            raise EmbeddingError(f"Embedding timeout after {self._timeout}s") from e
        except httpx.HTTPStatusError as e:
            logger.error(
                "embedding_http_error",
                status=e.response.status_code,
                model=self._model,
            )
            raise EmbeddingError(f"Ollama API error: {e.response.status_code}") from e
        except Exception as e:
            logger.error("embedding_error", error=str(e), model=self._model)
            raise EmbeddingError(f"Embedding failed: {e}") from e

    async def embed_batch(
        self,
        texts: list[str],
        concurrency: int = 5,
    ) -> list[list[float]]:
        """
        批次向量化多個文本

        Args:
            texts: 文本列表
            concurrency: 同時並行數 (避免過載 Ollama)

        Returns:
            list[list[float]]: 向量列表 (與輸入順序對應)
        """
        if not texts:
            return []

        results: list[list[float]] = []
        semaphore = asyncio.Semaphore(concurrency)

        async def embed_with_semaphore(text: str) -> list[float]:
            async with semaphore:
                return await self.embed_text(text)

        tasks = [embed_with_semaphore(text) for text in texts]
        results = await asyncio.gather(*tasks, return_exceptions=False)

        logger.info(
            "batch_embedding_complete",
            count=len(texts),
            model=self._model,
        )

        return results

    async def close(self) -> None:
        """關閉連線"""
        if self._client:
            await self._client.aclose()
            self._client = None


# =============================================================================
# Errors
# =============================================================================


class EmbeddingError(Exception):
    """Embedding 操作錯誤"""

    pass


# =============================================================================
# Singleton Factory
# =============================================================================

_embedding_service: OllamaEmbeddingService | None = None


def get_embedding_service() -> OllamaEmbeddingService:
    """
    取得 Embedding Service 單例

    Returns:
        OllamaEmbeddingService: 共用實例
    """
    global _embedding_service
    if _embedding_service is None:
        _embedding_service = OllamaEmbeddingService()
    return _embedding_service