/**
 * NAC Knowledge Engine - AI智能体对话历史持久化
 *
 * MongoDB集合设计：
 *   agent_conversations: 会话元数据（id, userId, agentType, title, createdAt, updatedAt, messageCount）
 *   agent_messages: 消息记录（id, conversationId, role, content, confidence, sources, createdAt）
 *
 * 无Manus依赖，直接操作MongoDB
 */

import { ObjectId } from "mongodb";
import { getMongoDb, COLLECTIONS } from "./mongodb";
import type { AgentType } from "./aiAgents";

// ─── 类型定义 ─────────────────────────────────────────────────────

export interface AgentConversation {
  _id?: ObjectId;
  conversationId: string;
  userId: number;
  userEmail: string;
  agentType: AgentType;
  title: string;           // 取自第一条用户消息的前50字
  messageCount: number;
  createdAt: Date;
  updatedAt: Date;
}

export interface AgentMessageRecord {
  _id?: ObjectId;
  messageId: string;
  conversationId: string;
  role: "user" | "assistant";
  content: string;
  confidence?: number;     // 仅assistant消息有
  sources?: string[];      // 引用的知识库条目
  suggestions?: string[];  // 后续建议
  createdAt: Date;
}

// ─── 工具函数 ─────────────────────────────────────────────────────

function generateId(): string {
  return new ObjectId().toHexString();
}

function extractTitle(message: string): string {
  return message.slice(0, 50).replace(/\n/g, " ").trim() + (message.length > 50 ? "..." : "");
}

// ─── 会话管理 ─────────────────────────────────────────────────────

/**
 * 创建新会话
 */
export async function createConversation(
  userId: number,
  userEmail: string,
  agentType: AgentType,
  firstMessage: string
): Promise<string> {
  const db = await getMongoDb();
  if (!db) throw new Error("MongoDB不可用");

  const conversationId = generateId();
  const now = new Date();

  const conversation: AgentConversation = {
    conversationId,
    userId,
    userEmail,
    agentType,
    title: extractTitle(firstMessage),
    messageCount: 0,
    createdAt: now,
    updatedAt: now,
  };

  await db.collection(COLLECTIONS.AGENT_CONVERSATIONS).insertOne(conversation);
  return conversationId;
}

/**
 * 获取用户的会话列表（按最近更新排序）
 */
export async function listConversations(
  userId: number,
  agentType?: AgentType,
  limit = 20,
  skip = 0
): Promise<{ conversations: AgentConversation[]; total: number }> {
  const db = await getMongoDb();
  if (!db) return { conversations: [], total: 0 };

  const filter: Record<string, unknown> = { userId };
  if (agentType) filter.agentType = agentType;

  const [conversations, total] = await Promise.all([
    db.collection(COLLECTIONS.AGENT_CONVERSATIONS)
      .find(filter)
      .sort({ updatedAt: -1 })
      .skip(skip)
      .limit(limit)
      .toArray() as Promise<AgentConversation[]>,
    db.collection(COLLECTIONS.AGENT_CONVERSATIONS).countDocuments(filter),
  ]);

  return { conversations, total };
}

/**
 * 获取单个会话信息
 */
export async function getConversation(
  conversationId: string,
  userId: number
): Promise<AgentConversation | null> {
  const db = await getMongoDb();
  if (!db) return null;

  return db.collection(COLLECTIONS.AGENT_CONVERSATIONS)
    .findOne({ conversationId, userId }) as Promise<AgentConversation | null>;
}

/**
 * 删除会话及其所有消息
 */
export async function deleteConversation(
  conversationId: string,
  userId: number
): Promise<boolean> {
  const db = await getMongoDb();
  if (!db) return false;

  const result = await db.collection(COLLECTIONS.AGENT_CONVERSATIONS)
    .deleteOne({ conversationId, userId });

  if (result.deletedCount > 0) {
    await db.collection(COLLECTIONS.AGENT_MESSAGES)
      .deleteMany({ conversationId });
    return true;
  }
  return false;
}

// ─── 消息管理 ─────────────────────────────────────────────────────

/**
 * 保存一对消息（用户消息 + AI回复）到数据库
 */
export async function saveMessagePair(
  conversationId: string,
  userMessage: string,
  assistantMessage: string,
  confidence: number,
  sources?: string[],
  suggestions?: string[]
): Promise<void> {
  const db = await getMongoDb();
  if (!db) return;

  const now = new Date();
  const userRecord: AgentMessageRecord = {
    messageId: generateId(),
    conversationId,
    role: "user",
    content: userMessage,
    createdAt: now,
  };

  const assistantRecord: AgentMessageRecord = {
    messageId: generateId(),
    conversationId,
    role: "assistant",
    content: assistantMessage,
    confidence,
    sources,
    suggestions,
    createdAt: new Date(now.getTime() + 1), // 确保顺序
  };

  await db.collection(COLLECTIONS.AGENT_MESSAGES).insertMany([userRecord, assistantRecord]);

  // 更新会话的消息计数和最后更新时间
  await db.collection(COLLECTIONS.AGENT_CONVERSATIONS).updateOne(
    { conversationId },
    {
      $inc: { messageCount: 2 },
      $set: { updatedAt: new Date() },
    }
  );
}

/**
 * 加载会话的消息历史（用于续接对话）
 */
export async function loadConversationMessages(
  conversationId: string,
  userId: number,
  limit = 20
): Promise<AgentMessageRecord[]> {
  const db = await getMongoDb();
  if (!db) return [];

  // 先验证会话属于该用户
  const conv = await getConversation(conversationId, userId);
  if (!conv) return [];

  return db.collection(COLLECTIONS.AGENT_MESSAGES)
    .find({ conversationId })
    .sort({ createdAt: 1 })
    .limit(limit)
    .toArray() as Promise<AgentMessageRecord[]>;
}

/**
 * 将消息历史转换为Agent可用的格式
 */
export function messagesToAgentHistory(
  messages: AgentMessageRecord[]
): Array<{ role: "user" | "assistant"; content: string }> {
  return messages.map(m => ({
    role: m.role,
    content: m.content,
  }));
}