import {
  Injectable,
  CanActivate,
  ExecutionContext,
  ServiceUnavailableException,
} from '@nestjs/common';
import { Reflector } from '@nestjs/core';
import { PrismaService } from '../../prisma/prisma.service';
import { JwtService } from '@nestjs/jwt';

@Injectable()
export class MaintenanceGuard implements CanActivate {
  constructor(
    private reflector: Reflector,
    private prisma: PrismaService,
    private jwtService: JwtService,
  ) {}

  async canActivate(context: ExecutionContext): Promise<boolean> {
    // Check if route is exempt from maintenance mode (auth, health, admin routes)
    const isExempt = this.reflector.get<boolean>('skipMaintenance', context.getHandler());
    const isControllerExempt = this.reflector.get<boolean>('skipMaintenance', context.getClass());
    
    if (isExempt || isControllerExempt) {
      return true;
    }

    // Get maintenance mode status from config
    const maintenanceConfig = await this.prisma.appConfig.findUnique({
      where: { key: 'maintenance_mode' },
    });

    const isMaintenanceMode = maintenanceConfig?.value === 'true';

    if (!isMaintenanceMode) {
      return true;
    }

    // Try to extract user from JWT token (if exists)
    const request = context.switchToHttp().getRequest();
    const authHeader = request.headers.authorization;
    
    if (authHeader && authHeader.startsWith('Bearer ')) {
      try {
        const token = authHeader.substring(7);
        const payload = this.jwtService.verify(token);
        
        // If user is admin, allow access
        if (payload.role === 'admin') {
          return true;
        }
      } catch (error) {
        // Invalid token, continue to block
      }
    }

    // Get maintenance message
    const messageConfig = await this.prisma.appConfig.findUnique({
      where: { key: 'maintenance_message' },
    });

    const message =
      messageConfig?.value ||
      'System is under maintenance. Please try again later.';

    throw new ServiceUnavailableException({
      statusCode: 503,
      message: message,
      maintenanceMode: true,
    });
  }
}