import * as plugins from '../plugins.js';
import type { TransactionEngine } from './TransactionEngine.js';

/**
 * Session state
 */
export interface ISession {
  /** Session ID (UUID) */
  id: string;
  /** Timestamp when the session was created */
  createdAt: number;
  /** Timestamp of the last activity */
  lastActivityAt: number;
  /** Current transaction ID if any */
  txnId?: string;
  /** Transaction number for ordering */
  txnNumber?: number;
  /** Whether the session is in a transaction */
  inTransaction: boolean;
  /** Session metadata */
  metadata?: Record<string, any>;
}

/**
 * Session engine options
 */
export interface ISessionEngineOptions {
  /** Session timeout in milliseconds (default: 30 minutes) */
  sessionTimeoutMs?: number;
  /** Interval to check for expired sessions in ms (default: 60 seconds) */
  cleanupIntervalMs?: number;
}

/**
 * Session engine for managing client sessions
 * - Tracks session lifecycle (create, touch, end)
 * - Links sessions to transactions
 * - Auto-aborts transactions on session expiry
 */
export class SessionEngine {
  private sessions: Map<string, ISession> = new Map();
  private sessionTimeoutMs: number;
  private cleanupInterval?: ReturnType<typeof setInterval>;
  private transactionEngine?: TransactionEngine;

  constructor(options?: ISessionEngineOptions) {
    this.sessionTimeoutMs = options?.sessionTimeoutMs ?? 30 * 60 * 1000; // 30 minutes default
    const cleanupIntervalMs = options?.cleanupIntervalMs ?? 60 * 1000; // 1 minute default

    // Start cleanup interval
    this.cleanupInterval = setInterval(() => {
      this.cleanupExpiredSessions();
    }, cleanupIntervalMs);
  }

  /**
   * Set the transaction engine to use for auto-abort
   */
  setTransactionEngine(engine: TransactionEngine): void {
    this.transactionEngine = engine;
  }

  /**
   * Start a new session
   */
  startSession(sessionId?: string, metadata?: Record<string, any>): ISession {
    const id = sessionId ?? new plugins.bson.UUID().toHexString();
    const now = Date.now();

    const session: ISession = {
      id,
      createdAt: now,
      lastActivityAt: now,
      inTransaction: false,
      metadata,
    };

    this.sessions.set(id, session);
    return session;
  }

  /**
   * Get a session by ID
   */
  getSession(sessionId: string): ISession | undefined {
    const session = this.sessions.get(sessionId);
    if (session && this.isSessionExpired(session)) {
      // Session expired, clean it up
      this.endSession(sessionId);
      return undefined;
    }
    return session;
  }

  /**
   * Touch a session to update last activity time
   */
  touchSession(sessionId: string): boolean {
    const session = this.sessions.get(sessionId);
    if (!session) return false;

    if (this.isSessionExpired(session)) {
      this.endSession(sessionId);
      return false;
    }

    session.lastActivityAt = Date.now();
    return true;
  }

  /**
   * End a session explicitly
   * This will also abort any active transaction
   */
  async endSession(sessionId: string): Promise<boolean> {
    const session = this.sessions.get(sessionId);
    if (!session) return false;

    // If session has an active transaction, abort it
    if (session.inTransaction && session.txnId && this.transactionEngine) {
      try {
        await this.transactionEngine.abortTransaction(session.txnId);
      } catch (e) {
        // Ignore abort errors during cleanup
      }
    }

    this.sessions.delete(sessionId);
    return true;
  }

  /**
   * Start a transaction in a session
   */
  startTransaction(sessionId: string, txnId: string, txnNumber?: number): boolean {
    const session = this.sessions.get(sessionId);
    if (!session) return false;

    if (this.isSessionExpired(session)) {
      this.endSession(sessionId);
      return false;
    }

    session.txnId = txnId;
    session.txnNumber = txnNumber;
    session.inTransaction = true;
    session.lastActivityAt = Date.now();

    return true;
  }

  /**
   * End a transaction in a session (commit or abort)
   */
  endTransaction(sessionId: string): boolean {
    const session = this.sessions.get(sessionId);
    if (!session) return false;

    session.txnId = undefined;
    session.txnNumber = undefined;
    session.inTransaction = false;
    session.lastActivityAt = Date.now();

    return true;
  }

  /**
   * Get transaction ID for a session
   */
  getTransactionId(sessionId: string): string | undefined {
    const session = this.sessions.get(sessionId);
    return session?.txnId;
  }

  /**
   * Check if session is in a transaction
   */
  isInTransaction(sessionId: string): boolean {
    const session = this.sessions.get(sessionId);
    return session?.inTransaction ?? false;
  }

  /**
   * Check if a session is expired
   */
  isSessionExpired(session: ISession): boolean {
    return Date.now() - session.lastActivityAt > this.sessionTimeoutMs;
  }

  /**
   * Cleanup expired sessions
   * This is called periodically by the cleanup interval
   */
  private async cleanupExpiredSessions(): Promise<void> {
    const expiredSessions: string[] = [];

    for (const [id, session] of this.sessions) {
      if (this.isSessionExpired(session)) {
        expiredSessions.push(id);
      }
    }

    // End all expired sessions (this will also abort their transactions)
    for (const sessionId of expiredSessions) {
      await this.endSession(sessionId);
    }
  }

  /**
   * Get all active sessions
   */
  listSessions(): ISession[] {
    const activeSessions: ISession[] = [];
    for (const session of this.sessions.values()) {
      if (!this.isSessionExpired(session)) {
        activeSessions.push(session);
      }
    }
    return activeSessions;
  }

  /**
   * Get session count
   */
  getSessionCount(): number {
    return this.sessions.size;
  }

  /**
   * Get sessions with active transactions
   */
  getSessionsWithTransactions(): ISession[] {
    return this.listSessions().filter(s => s.inTransaction);
  }

  /**
   * Refresh session timeout
   */
  refreshSession(sessionId: string): boolean {
    return this.touchSession(sessionId);
  }

  /**
   * Close the session engine and cleanup
   */
  close(): void {
    if (this.cleanupInterval) {
      clearInterval(this.cleanupInterval);
      this.cleanupInterval = undefined;
    }

    // Clear all sessions
    this.sessions.clear();
  }

  /**
   * Get or create a session for a given session ID
   * Useful for handling MongoDB driver session requests
   */
  getOrCreateSession(sessionId: string): ISession {
    let session = this.getSession(sessionId);
    if (!session) {
      session = this.startSession(sessionId);
    } else {
      this.touchSession(sessionId);
    }
    return session;
  }

  /**
   * Extract session ID from MongoDB lsid (logical session ID)
   */
  static extractSessionId(lsid: any): string | undefined {
    if (!lsid) return undefined;

    // MongoDB session ID format: { id: UUID }
    if (lsid.id) {
      if (lsid.id instanceof plugins.bson.UUID) {
        return lsid.id.toHexString();
      }
      if (typeof lsid.id === 'string') {
        return lsid.id;
      }
      if (lsid.id.$binary?.base64) {
        // Binary UUID format
        return Buffer.from(lsid.id.$binary.base64, 'base64').toString('hex');
      }
    }

    return undefined;
  }
}