// Package embedding 提供文本向量化服务，支持 OpenAI 兼容的 Embedding API
package embedding

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"
	"time"
)

// Config embedding 服务配置
type Config struct {
	APIKey     string // API 密钥
	BaseURL    string // API 基础 URL（OpenAI 兼容格式）
	Model      string // 模型名称
	Dimensions int    // 向量维度
}

// Client embedding 客户端
type Client struct {
	cfg        Config
	httpClient *http.Client
}

// NewClient 创建 embedding 客户端
func NewClient(cfg Config) *Client {
	if cfg.BaseURL == "" {
		cfg.BaseURL = "https://dashscope.aliyuncs.com/compatible-mode/v1"
	}
	if cfg.Model == "" {
		cfg.Model = "text-embedding-v3"
	}
	if cfg.Dimensions == 0 {
		cfg.Dimensions = 1024
	}
	return &Client{
		cfg: cfg,
		httpClient: &http.Client{
			Timeout: 30 * time.Second,
		},
	}
}

// embeddingRequest OpenAI 兼容的 embedding 请求
type embeddingRequest struct {
	Input      interface{} `json:"input"`
	Model      string      `json:"model"`
	Dimensions int         `json:"dimensions,omitempty"`
}

// embeddingResponse OpenAI 兼容的 embedding 响应
type embeddingResponse struct {
	Data []struct {
		Embedding []float32 `json:"embedding"`
		Index     int       `json:"index"`
	} `json:"data"`
	Usage struct {
		TotalTokens int `json:"total_tokens"`
	} `json:"usage"`
}

// GetEmbedding 获取单条文本的向量嵌入
func (c *Client) GetEmbedding(ctx context.Context, text string) ([]float32, error) {
	if c.cfg.APIKey == "" {
		return nil, fmt.Errorf("embedding API key not configured")
	}

	text = strings.TrimSpace(text)
	if text == "" {
		return nil, fmt.Errorf("empty text")
	}
	// 截断过长文本
	if len([]rune(text)) > 8000 {
		text = string([]rune(text)[:8000])
	}

	req := embeddingRequest{
		Input:      text,
		Model:      c.cfg.Model,
		Dimensions: c.cfg.Dimensions,
	}

	body, err := json.Marshal(req)
	if err != nil {
		return nil, err
	}

	url := strings.TrimRight(c.cfg.BaseURL, "/") + "/embeddings"
	httpReq, err := http.NewRequestWithContext(ctx, "POST", url, bytes.NewReader(body))
	if err != nil {
		return nil, err
	}
	httpReq.Header.Set("Authorization", "Bearer "+c.cfg.APIKey)
	httpReq.Header.Set("Content-Type", "application/json")

	resp, err := c.httpClient.Do(httpReq)
	if err != nil {
		return nil, fmt.Errorf("embedding request failed: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		errBody, _ := io.ReadAll(resp.Body)
		return nil, fmt.Errorf("embedding error (status %d): %s", resp.StatusCode, string(errBody))
	}

	var result embeddingResponse
	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
		return nil, err
	}
	if len(result.Data) == 0 {
		return nil, fmt.Errorf("no embedding data returned")
	}
	return result.Data[0].Embedding, nil
}

// GetEmbeddingBatch 批量获取文本向量嵌入
func (c *Client) GetEmbeddingBatch(ctx context.Context, texts []string) ([][]float32, error) {
	results := make([][]float32, len(texts))
	for i, text := range texts {
		emb, err := c.GetEmbedding(ctx, text)
		if err != nil {
			results[i] = nil
			continue
		}
		results[i] = emb
	}
	return results, nil
}

// IsConfigured 检查 embedding 服务是否已配置
func (c *Client) IsConfigured() bool {
	return c.cfg.APIKey != ""
}