import * as SQLite from 'expo-sqlite';
import { LockManager } from './LockManager';
import { DB_CONFIG, getDbName } from './DatabaseConfig';
import { runMigrations } from '../schema/MigrationManager';

type SQLiteDatabase = SQLite.SQLiteDatabase;

class DatabaseManager {
  private static instance: DatabaseManager;
  private db: SQLiteDatabase | null = null;
  private currentUserId: string | null = null;
  private initPromise: Promise<void> | null = null;
  private initTargetUserId: string | null = null;
  private isInitialized = false;

  static getInstance(): DatabaseManager {
    if (!DatabaseManager.instance) {
      DatabaseManager.instance = new DatabaseManager();
    }
    return DatabaseManager.instance;
  }

  async initialize(userId?: string | null): Promise<void> {
    const targetUserId = userId || null;
    const callId = Date.now();

    console.log(`[DatabaseManager ${callId}] initialize 开始, userId=${targetUserId}, 当前db=${!!this.db}, 当前userId=${this.currentUserId}`);

    if (this.db && this.currentUserId === targetUserId) {
      console.log(`[DatabaseManager ${callId}] 已是目标数据库，直接返回`);
      this.isInitialized = true;
      return;
    }

    if (this.initPromise && this.initTargetUserId === targetUserId) {
      console.log(`[DatabaseManager ${callId}] 等待进行中的初始化`);
      await this.initPromise;
      console.log(`[DatabaseManager ${callId}] 初始化完成`);
      return;
    }

    if (this.initPromise) {
      console.log(`[DatabaseManager ${callId}] 等待其他初始化完成`);
      await this.initPromise.catch(() => {});
    }

    if (this.db && this.currentUserId === targetUserId) {
      console.log(`[DatabaseManager ${callId}] 其他初始化已完成目标，直接返回`);
      this.isInitialized = true;
      return;
    }

    this.initTargetUserId = targetUserId;
    console.log(`[DatabaseManager ${callId}] 开始实际初始化`);

    this.initPromise = LockManager.withMutex(async () => {
      const mutexId = callId;
      console.log(`[DatabaseManager ${mutexId}] 获得互斥锁`);

      if (this.db && this.currentUserId === targetUserId) {
        console.log(`[DatabaseManager ${mutexId}] 互斥锁内检查：已是目标数据库`);
        this.isInitialized = true;
        return;
      }

      const isWeb = typeof window !== 'undefined';

      if (this.db) {
        console.log(`[DatabaseManager ${mutexId}] 关闭旧数据库连接...`);
        try {
          await this.db.closeAsync();
          console.log(`[DatabaseManager ${mutexId}] 旧连接已关闭`);
        } catch (e) {
          console.warn(`[DatabaseManager ${mutexId}] 关闭旧连接失败:`, e);
        }
        this.db = null;
        this.currentUserId = null;
        this.isInitialized = false;

        if (isWeb) {
          await new Promise(r => setTimeout(r, DB_CONFIG.WEB_CLOSE_DELAY));
        }
      }

      const dbName = getDbName(targetUserId);
      console.log(`[DatabaseManager ${mutexId}] 打开数据库: ${dbName}`);

      const database = await this.openDatabaseWithRetry(dbName);
      console.log(`[DatabaseManager ${mutexId}] 数据库已打开，执行迁移`);

      await runMigrations(database);
      console.log(`[DatabaseManager ${mutexId}] 迁移完成`);

      this.db = database;
      this.currentUserId = targetUserId;
      this.isInitialized = true;
      console.log(`[DatabaseManager ${mutexId}] 初始化完成`);
    }).finally(() => {
      console.log(`[DatabaseManager ${callId}] 清理初始化状态`);
      this.initPromise = null;
      this.initTargetUserId = null;
    });

    await this.initPromise;
    console.log(`[DatabaseManager ${callId}] initialize 返回`);
  }

  private async openDatabaseWithRetry(dbName: string): Promise<SQLiteDatabase> {
    const isWeb = typeof window !== 'undefined';

    return LockManager.withWebLock(`${DB_CONFIG.LOCK_PREFIX}${dbName}`, async () => {
      for (let attempt = 0; attempt <= DB_CONFIG.MAX_RETRIES; attempt++) {
        try {
          const database = await SQLite.openDatabaseAsync(dbName);
          console.log(`[DatabaseManager] 成功打开数据库 (尝试 ${attempt + 1}/${DB_CONFIG.MAX_RETRIES + 1})`);
          return database;
        } catch (error) {
          const msg = String(error);
          console.error(`[DatabaseManager] 打开失败 (尝试 ${attempt + 1}/${DB_CONFIG.MAX_RETRIES + 1}):`, msg);

          if (attempt < DB_CONFIG.MAX_RETRIES) {
            const delay = isWeb ? DB_CONFIG.WEB_RETRY_DELAY_BASE * (attempt + 1) : DB_CONFIG.NATIVE_RETRY_DELAY;
            console.warn(`[DatabaseManager] ${delay}ms 后重试...`);
            await new Promise(r => setTimeout(r, delay));
          } else {
            throw error;
          }
        }
      }
      throw new Error('打开数据库失败');
    });
  }

  async close(): Promise<void> {
    if (this.initPromise) {
      await this.initPromise.catch(() => {});
    }

    const dbName = getDbName(this.currentUserId);

    await LockManager.withWebLock(`${DB_CONFIG.LOCK_PREFIX}${dbName}`, async () => {
      await LockManager.withMutex(async () => {
        if (!this.db) return;

        try {
          await this.db.closeAsync();
          console.log('[DatabaseManager] 数据库已关闭');

          if (typeof window !== 'undefined') {
            await new Promise(r => setTimeout(r, DB_CONFIG.WEB_FINAL_CLOSE_DELAY));
          }
        } catch (e) {
          console.warn('[DatabaseManager] 关闭失败:', e);
        }
        this.db = null;
        this.currentUserId = null;
        this.isInitialized = false;
      });
    });
  }

  async getDb(timeout: number = 10000): Promise<SQLiteDatabase> {
    if (this.isInitialized && this.db) return this.db;

    if (this.initPromise) {
      const timeoutPromise = new Promise<null>((_, reject) =>
        setTimeout(() => reject(new Error('等待数据库初始化超时')), timeout)
      );

      await Promise.race([this.initPromise, timeoutPromise]);

      if (this.db) return this.db;
    }

    throw new Error('数据库未初始化，请先调用 initialize(userId)');
  }

  getDbSync(): SQLiteDatabase | null {
    return this.db;
  }

  getCurrentUserId(): string | null {
    return this.currentUserId;
  }

  isReady(): boolean {
    return this.isInitialized && this.db !== null;
  }

  async withMutex<T>(fn: () => Promise<T>): Promise<T> {
    return LockManager.withMutex(fn);
  }
}

export const databaseManager = DatabaseManager.getInstance();
export { DatabaseManager };