package service

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

	"github.com/topfans/backend/pkg/logger"
	"go.uber.org/zap"
)

// DifyConfig Dify 客户端配置
// MVP 阶段：直接从环境变量读
// Stage 2+：移到 ai_chat_configs 数据库
type DifyConfig struct {
	APIBase    string
	APIKey     string
	TimeoutSec int
}

// DifyClient Dify HTTP 客户端（MVP 唯一 AI 源）
// ★ 简化：只调 Workflow /v1/workflows/run 流式接口
//   不做：重试循环（V1 Network 错误重试 1 次，MVP 失败直接报错）
//   不做：滑动窗口审计（V1 AuditService 逐 token 拦截已足够）
type DifyClient struct {
	apiBase    string
	apiKey     string
	httpClient *http.Client
}

// NewDifyClient 创建 Dify 客户端
func NewDifyClient(cfg DifyConfig) *DifyClient {
	return &DifyClient{
		apiBase:    cfg.APIBase,
		apiKey:     cfg.APIKey,
		httpClient: &http.Client{Timeout: time.Duration(cfg.TimeoutSec) * time.Second},
	}
}

// StreamRequest 流式调用入参
type StreamRequest struct {
	Query           string
	ConversationID  string
}

// StreamChat 流式调用 Dify Workflow
// 输入：用户消息 + Dify conversation_id（首次为空）
// 输出：返回 (DifyStreamReader, error)
func (c *DifyClient) StreamChat(ctx context.Context, req StreamRequest) (*DifyStreamReader, error) {
	body := map[string]interface{}{
		"inputs":          map[string]string{"query": req.Query},
		"response_mode":   "streaming",
		"conversation_id": req.ConversationID,
		"user":            "aichat-mvp",
	}
	jsonData, err := json.Marshal(body)
	if err != nil {
		return nil, fmt.Errorf("dify request marshal: %w", err)
	}

	url := c.apiBase + "/workflows/run"
	httpReq, err := http.NewRequestWithContext(ctx, "POST", url, bytes.NewReader(jsonData))
	if err != nil {
		return nil, fmt.Errorf("dify request new: %w", err)
	}
	httpReq.Header.Set("Authorization", "Bearer "+c.apiKey)
	httpReq.Header.Set("Content-Type", "application/json")

	resp, err := c.httpClient.Do(httpReq)
	if err != nil {
		return nil, fmt.Errorf("dify request: %w", err)
	}
	if resp.StatusCode != http.StatusOK {
		respBody, _ := io.ReadAll(resp.Body)
		resp.Body.Close()
		return nil, fmt.Errorf("dify returned HTTP %d: %s", resp.StatusCode, string(respBody))
	}
	logger.Logger.Info("Dify stream started", zap.String("url", url))
	return newDifyStreamReader(resp.Body), nil
}

// ============================================================
// DifyStreamReader：解析 SSE 流
// ============================================================

// newDifyStreamReader 创建流式读取器
func newDifyStreamReader(body io.ReadCloser) *DifyStreamReader {
	scanner := bufio.NewScanner(body)
	// 增大 buffer 防止 Dify 流式 chunk 过大被截断
	scanner.Buffer(make([]byte, 64*1024), 1024*1024)
	return &DifyStreamReader{
		body:          body,
		conversationID: "",
		closed:        false,
		scanner:       scanner,
	}
}

// DifyStreamReader Dify SSE 流式读取器
// 简化版本：用 bufio.Scanner 按行读 data: 字段
type DifyStreamReader struct {
	body          io.ReadCloser
	conversationID string
	closed        bool
	scanner       *bufio.Scanner
}

// Next 读下一条数据
// 返回 (content, done, convID)：
//   - content: 当前 token（流式）
//   - done: 流是否结束
//   - convID: 流结束后从 convID 读 Dify conversation_id
func (r *DifyStreamReader) Next() (content string, done bool, convID string) {
	if r.closed {
		return "", true, r.conversationID
	}

	for r.scanner.Scan() {
		line := strings.TrimSpace(r.scanner.Text())
		if line == "" {
			continue
		}
		if !strings.HasPrefix(line, "data: ") {
			continue
		}
		payload := strings.TrimPrefix(line, "data: ")
		if payload == "[DONE]" {
			r.closed = true
			return "", true, r.conversationID
		}

		// ★ MVP 修复：Dify Workflow 端点 (/v1/workflows/run) 的事件格式
		//   - text_chunk: 流式分块，text 字段是内容
		//   - workflow_finished: 结束事件，data.outputs.text 是完整内容
		//   - 没有 conversation_id（Workflow 端点不维护 conversation_id）
		// ★ 与 Chatflow 端点 (/v1/chat-messages) 不同：
		//   - Chatflow 用 event=message, answer 字段
		//   - Workflow 用 event=text_chunk, text 字段
		var event struct {
			Event          string `json:"event"`
			Text           string `json:"text"`           // Chatflow: 顶层 text
			ConversationID string `json:"conversation_id"`
			Message        string `json:"message"`
			Data          struct {
				Text string `json:"text"`               // Workflow: data.text
			} `json:"data"`
		}
		if err := json.Unmarshal([]byte(payload), &event); err != nil {
			continue
		}

		// 记录 conversation_id（仅 Chatflow 有；Workflow 端点通常无）
		if event.ConversationID != "" && r.conversationID == "" {
			r.conversationID = event.ConversationID
		}

		text := event.Data.Text
		if text == "" {
			text = event.Text
		}

		switch event.Event {
		case "text_chunk":
			if text != "" {
				return text, false, ""
			}
		case "message":
			if text != "" {
				return text, false, ""
			}
		case "workflow_finished":
			// ★ MVP 关键：Dify Workflow 结束事件
			r.closed = true
			return "", true, r.conversationID
		case "message_end":
			// Chatflow 端点兼容
			r.closed = true
			return "", true, r.conversationID
		case "error":
			logger.Logger.Error("Dify stream error event", zap.String("message", event.Message))
			r.closed = true
			return "", true, r.conversationID
		}
	}

	// scanner 结束（流关闭或出错）
	r.closed = true
	if err := r.scanner.Err(); err != nil {
		logger.Logger.Warn("Dify stream scan error", zap.Error(err))
	}
	return "", true, r.conversationID
}

// Close 关闭流
func (r *DifyStreamReader) Close() error {
	if r.closed {
		return nil
	}
	r.closed = true
	return r.body.Close()
}

// GetConversationID 获取 Dify 返回的 conversation_id
// 仅在 Next() 返回 done=true 后调用
func (r *DifyStreamReader) GetConversationID() string {
	return r.conversationID
}