package service

import (
	"bufio"
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"os"
	"strings"
	"sync"
	"time"

	"github.com/google/uuid"
)

// CascadeSession 代表一个 Cascade Agent 会话
type CascadeSession struct {
	ID        string
	ModelName string
	Messages  []map[string]interface{} // {role, content}
	Metadata  map[string]string        // 设备指纹、User-Agent 等
	Token     string                   // OAuth token
	CreatedAt int64
}

// LanguageServerService 业务逻辑层
// 处理 Cascade Agent 流程，转发到上游 API
type LanguageServerService struct {
	// 会话管理
	cascadeSessions map[string]*CascadeSession
	sessionMutex    sync.RWMutex

	// 上游 HTTP 服务（用于发送请求）
	httpUpstream HTTPUpstream

	// 上游配置
	upstreamBaseURL string
	upstreamAPIKey  string

	// 日志
	logger *slog.Logger

	// 改进 1: 速率限制 (令牌桶)
	// 限制并发消息处理数量，保护上游 API
	rateLimiter chan struct{}

	// 改进 3: 会话过期时间 (秒)
	sessionTTLSeconds int64

	// 改进 3: 定期清理后台任务
	cleanupTicker *time.Ticker
	stopCleanup   chan struct{}
}

func NewLanguageServerService(
	logger *slog.Logger,
	httpUpstream HTTPUpstream,
) *LanguageServerService {
	svc := &LanguageServerService{
		cascadeSessions:   make(map[string]*CascadeSession),
		logger:            logger,
		httpUpstream:      httpUpstream,
		upstreamBaseURL:   strings.TrimSuffix(os.Getenv("ANTHROPIC_BASE_URL"), "/"),
		upstreamAPIKey:    os.Getenv("ANTHROPIC_API_KEY"),
		rateLimiter:       make(chan struct{}, 100), // 改进 1: 限制 100 个并发消息
		sessionTTLSeconds: 3600,                      // 改进 3: 会话默认 1 小时过期
		stopCleanup:       make(chan struct{}),
	}

	// 改进 3: 启动后台清理任务
	svc.startSessionCleanup()

	return svc
}

// startSessionCleanup 启动会话定期清理任务
func (svc *LanguageServerService) startSessionCleanup() {
	svc.cleanupTicker = time.NewTicker(1 * time.Minute)

	go func() {
		for {
			select {
			case <-svc.cleanupTicker.C:
				svc.cleanupExpiredSessions()
			case <-svc.stopCleanup:
				svc.cleanupTicker.Stop()
				return
			}
		}
	}()
}

// cleanupExpiredSessions 清理过期的会话
func (svc *LanguageServerService) cleanupExpiredSessions() {
	now := getCurrentTimeMS()
	ttlMs := svc.sessionTTLSeconds * 1000

	svc.sessionMutex.Lock()
	defer svc.sessionMutex.Unlock()

	deletedCount := 0
	for id, session := range svc.cascadeSessions {
		if now-session.CreatedAt > ttlMs {
			delete(svc.cascadeSessions, id)
			deletedCount++
		}
	}

	if deletedCount > 0 {
		svc.logger.Info("expired sessions cleaned up",
			"deleted_count", deletedCount,
			"remaining_sessions", len(svc.cascadeSessions),
		)
	}
}

// Stop 优雅关闭服务
func (svc *LanguageServerService) Stop() {
	select {
	case svc.stopCleanup <- struct{}{}:
	default:
	}
}

// SetSessionTTL sets the session TTL for testing purposes
func (svc *LanguageServerService) SetSessionTTL(ttlSeconds int64) {
	svc.sessionTTLSeconds = ttlSeconds
}

// GetCascadeSessions returns the current cascade sessions map (for testing)
func (svc *LanguageServerService) GetCascadeSessions() map[string]*CascadeSession {
	svc.sessionMutex.RLock()
	defer svc.sessionMutex.RUnlock()
	return svc.cascadeSessions
}

// ============================================================================
// Cascade 业务逻辑
// ============================================================================

// StartCascade 启动新的 Cascade Agent 会话
func (svc *LanguageServerService) StartCascade(
	ctx context.Context,
	model string,
	systemPrompt string,
	metadata map[string]string,
	token string,
) (string, error) {
	// 1. 验证输入
	if model == "" {
		return "", fmt.Errorf("model is required")
	}

	if token == "" {
		return "", fmt.Errorf("oauth token is required")
	}

	// 2. 生成会话 ID
	sessionID := uuid.New().String()

	// 3. 创建会话
	session := &CascadeSession{
		ID:        sessionID,
		ModelName: model,
		Messages:  make([]map[string]interface{}, 0),
		Metadata:  metadata,
		Token:     token,
		CreatedAt: getCurrentTimeMS(),
	}

	// 如果提供了系统提示，添加为初始消息
	if systemPrompt != "" {
		session.Messages = append(session.Messages, map[string]interface{}{
			"role":    "user",
			"content": systemPrompt,
		})
	}

	// 4. 保存会话
	svc.sessionMutex.Lock()
	svc.cascadeSessions[sessionID] = session
	svc.sessionMutex.Unlock()

	svc.logger.Info("cascade session started",
		"session_id", sessionID,
		"model", model,
		"has_system_prompt", systemPrompt != "")

	return sessionID, nil
}

// SendUserMessage 发送用户消息到 Cascade
// 返回流式更新通道
func (svc *LanguageServerService) SendUserMessage(
	ctx context.Context,
	cascadeID string,
	userMessage string,
	token string,
) (<-chan interface{}, error) {
	// 改进 1: 获取速率限制令牌
	select {
	case svc.rateLimiter <- struct{}{}:
		// 获得令牌，继续
	case <-ctx.Done():
		return nil, fmt.Errorf("context cancelled")
	default:
		// 没有令牌，需要等待
		select {
		case svc.rateLimiter <- struct{}{}:
			// 获得令牌
		case <-ctx.Done():
			return nil, fmt.Errorf("context cancelled while waiting for rate limit")
		case <-time.After(30 * time.Second):
			return nil, fmt.Errorf("rate limit timeout: too many concurrent messages")
		}
	}

	// 1. 获取会话
	svc.sessionMutex.RLock()
	session, exists := svc.cascadeSessions[cascadeID]
	svc.sessionMutex.RUnlock()

	if !exists {
		// 释放令牌
		<-svc.rateLimiter
		return nil, fmt.Errorf("cascade session not found: %s", cascadeID)
	}

	// 2. 验证 token
	if token != session.Token {
		// 释放令牌
		<-svc.rateLimiter
		return nil, fmt.Errorf("invalid token for session")
	}

	// 改进 2: 并发安全的消息追加（深拷贝消息列表）
	svc.sessionMutex.Lock()
	newMessages := make([]map[string]interface{}, len(session.Messages)+1)
	copy(newMessages, session.Messages)
	newMessages[len(newMessages)-1] = map[string]interface{}{
		"role":    "user",
		"content": userMessage,
	}
	session.Messages = newMessages
	svc.sessionMutex.Unlock()

	// 4. 创建响应通道
	updateChan := make(chan interface{}, 100)

	// 5. 启动后台 goroutine 处理 API 调用
	go func() {
		defer func() {
			// 关闭通道
			close(updateChan)
			// 改进 1: 释放速率限制令牌
			<-svc.rateLimiter
		}()

		// 调用上游 API（关键！这里需要伪装）
		svc.callUpstreamAPI(ctx, session, updateChan)
	}()

	svc.logger.Info("user message sent to cascade",
		"session_id", cascadeID,
		"message_length", len(userMessage),
		"concurrent_requests", 100-len(svc.rateLimiter), // 显示当前并发数
	)

	return updateChan, nil
}

// CancelCascade 取消 Cascade 会话
func (svc *LanguageServerService) CancelCascade(
	ctx context.Context,
	cascadeID string,
) error {
	svc.sessionMutex.Lock()
	_, exists := svc.cascadeSessions[cascadeID]
	svc.sessionMutex.Unlock()

	if !exists {
		return fmt.Errorf("cascade session not found: %s", cascadeID)
	}

	// TODO: 取消正在进行的 API 调用

	svc.logger.Info("cascade cancelled", "session_id", cascadeID)
	return nil
}

// ============================================================================
// 模型配置
// ============================================================================

// ModelConfig 模型配置
type ModelConfig struct {
	Name             string
	DisplayName      string
	MaxTokens        int
	SupportsThinking bool
	ThinkingBudget   int
	SupportsImages   bool
	Provider         string
}

// GetAvailableModels 获取可用模型列表
func (svc *LanguageServerService) GetAvailableModels(ctx context.Context) ([]ModelConfig, error) {
	models := []ModelConfig{
		{
			Name:             "claude-opus-4-6",
			DisplayName:      "Claude Opus 4.6",
			MaxTokens:        200000,
			SupportsThinking: true,
			ThinkingBudget:   32000,
			SupportsImages:   true,
			Provider:         "anthropic",
		},
		{
			Name:             "claude-sonnet-4-6",
			DisplayName:      "Claude Sonnet 4.6",
			MaxTokens:        200000,
			SupportsThinking: false,
			SupportsImages:   true,
			Provider:         "anthropic",
		},
		{
			Name:             "claude-haiku-4-5",
			DisplayName:      "Claude Haiku 4.5",
			MaxTokens:        200000,
			SupportsThinking: false,
			SupportsImages:   true,
			Provider:         "anthropic",
		},
		{
			Name:             "gemini-3-pro",
			DisplayName:      "Gemini 3 Pro",
			MaxTokens:        128000,
			SupportsThinking: false,
			SupportsImages:   true,
			Provider:         "google",
		},
	}

	return models, nil
}

// ============================================================================
// 状态查询
// ============================================================================

// GetStatus 获取服务状态
func (svc *LanguageServerService) GetStatus(ctx context.Context) (string, error) {
	// TODO: 检查上游 API 连接状态
	return "running", nil
}

// ============================================================================
// 内部方法
// ============================================================================

// callUpstreamAPI 调用上游 Anthropic API
// 这是关键方法：需要注入所有伪装信息
//
// 伪装层包括：
// 1. User-Agent（来自 metadata 或动态生成）
// 2. 设备指纹（machine_id, mac_machine_id, dev_device_id, sqm_id）
// 3. TLS 指纹（通过 http.Transport 处理）
// 4. OAuth token 自动刷新
// 5. 请求头完整性
func (svc *LanguageServerService) callUpstreamAPI(
	ctx context.Context,
	session *CascadeSession,
	updateChan chan<- interface{},
) {
	// 检查上游配置
	if svc.upstreamBaseURL == "" || svc.upstreamAPIKey == "" {
		svc.logger.Error("upstream api configuration missing",
			"has_base_url", svc.upstreamBaseURL != "",
			"has_api_key", svc.upstreamAPIKey != "",
		)
		updateChan <- map[string]interface{}{
			"type":  "error",
			"error": "upstream api not configured",
		}
		return
	}

	// 1. 准备请求体
	requestBody := map[string]interface{}{
		"model":    session.ModelName,
		"messages": session.Messages,
		"stream":   true,
	}

	bodyJSON, err := json.Marshal(requestBody)
	if err != nil {
		svc.logger.Error("failed to marshal request",
			"session_id", session.ID,
			"error", err,
		)
		updateChan <- map[string]interface{}{
			"type":  "error",
			"error": "failed to prepare request",
		}
		return
	}

	// 2. 构建上游请求 URL
	upstreamURL := svc.upstreamBaseURL + "/v1/messages"

	// 3. 创建 HTTP 请求
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, upstreamURL, bytes.NewReader(bodyJSON))
	if err != nil {
		svc.logger.Error("failed to create request",
			"session_id", session.ID,
			"error", err,
		)
		updateChan <- map[string]interface{}{
			"type":  "error",
			"error": "failed to create request",
		}
		return
	}

	// 4. 设置基础请求头
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Authorization", "Bearer "+session.Token)
	req.Header.Set("x-api-key", session.Token) // Claude API 兼容

	// 5. 应用伪装信息
	if userAgent := session.Metadata["user-agent"]; userAgent != "" {
		req.Header.Set("User-Agent", userAgent)
	}

	// 提取其他伪装 headers（如果在 metadata 中）
	if customHeaders := session.Metadata["custom-headers"]; customHeaders != "" {
		// 可以在这里解析并应用自定义 headers
	}

	svc.logger.Debug("sending upstream request",
		"session_id", session.ID,
		"url", upstreamURL,
		"model", session.ModelName,
	)

	// 6. 发送请求
	resp, err := svc.httpUpstream.Do(req, "", 0, 10)
	if err != nil {
		svc.logger.Error("upstream request failed",
			"session_id", session.ID,
			"error", err,
		)
		updateChan <- map[string]interface{}{
			"type":  "error",
			"error": fmt.Sprintf("upstream request failed: %v", err),
		}
		return
	}
	defer func() { _ = resp.Body.Close() }()

	// 7. 处理错误响应
	if resp.StatusCode >= 400 {
		respBody, _ := io.ReadAll(io.LimitReader(resp.Body, 2<<20))
		svc.logger.Error("upstream error response",
			"session_id", session.ID,
			"status_code", resp.StatusCode,
			"body", string(respBody),
		)
		updateChan <- map[string]interface{}{
			"type":        "error",
			"status_code": resp.StatusCode,
			"error":       string(respBody),
		}
		return
	}

	// 8. 处理流式响应
	svc.streamUpstreamResponse(ctx, session.ID, resp, updateChan)
}

// streamUpstreamResponse 处理上游 SSE 流式响应
func (svc *LanguageServerService) streamUpstreamResponse(
	ctx context.Context,
	sessionID string,
	resp *http.Response,
	updateChan chan<- interface{},
) {
	scanner := bufio.NewScanner(resp.Body)
	// 设置合理的缓冲区大小
	scanner.Buffer(make([]byte, 64*1024), 512*1024)

	for scanner.Scan() {
		select {
		case <-ctx.Done():
			svc.logger.Info("streaming cancelled", "session_id", sessionID)
			return
		default:
		}

		line := strings.TrimSpace(scanner.Text())

		// 跳过空行
		if line == "" {
			continue
		}

		// 跳过注释行
		if strings.HasPrefix(line, ":") {
			continue
		}

		// 解析 SSE 格式 (data: {...})
		if !strings.HasPrefix(line, "data:") {
			continue
		}

		eventData := strings.TrimPrefix(line, "data:")
		eventData = strings.TrimSpace(eventData)

		// 解析 JSON
		var event map[string]interface{}
		if err := json.Unmarshal([]byte(eventData), &event); err != nil {
			svc.logger.Debug("failed to parse event",
				"session_id", sessionID,
				"error", err,
				"data", eventData,
			)
			continue
		}

		// 发送事件到客户端通道
		select {
		case updateChan <- event:
		case <-ctx.Done():
			return
		case <-time.After(5 * time.Second):
			svc.logger.Warn("channel send timeout",
				"session_id", sessionID,
			)
			return
		}
	}

	if err := scanner.Err(); err != nil {
		svc.logger.Error("scanning upstream response failed",
			"session_id", sessionID,
			"error", err,
		)
	}
}

// getCurrentTimeMS 获取当前时间戳（毫秒）
func getCurrentTimeMS() int64 {
	return time.Now().UnixMilli()
}