import {
  CanActivate,
  ExecutionContext,
  Injectable,
  UnauthorizedException,
} from '@nestjs/common';
import { JwtService } from '@nestjs/jwt';
import { ConfigService } from '@nestjs/config';
import { Request } from 'express';

interface JwtPayload {
  sub: string;
  email: string;
}

/**
 * JwtAuthGuard — validates Bearer tokens without Passport.
 * Reads the Authorization header, verifies the JWT, and attaches
 * { userId, email } to request.user for downstream use.
 */
@Injectable()
export class JwtAuthGuard implements CanActivate {
  constructor(
    private readonly jwtService: JwtService,
    private readonly config: ConfigService,
  ) {}

  async canActivate(context: ExecutionContext): Promise<boolean> {
    const request = context.switchToHttp().getRequest<Request>();
    const token = this.extractToken(request);

    if (!token) {
      throw new UnauthorizedException('Missing authentication token');
    }

    try {
      const payload = await this.jwtService.verifyAsync<JwtPayload>(token, {
        secret: this.config.get<string>('JWT_SECRET'),
      });
      // Attach to request for @CurrentUser() decorator
      (request as Request & { user: { userId: string; email: string } }).user = {
        userId: payload.sub,
        email: payload.email,
      };
    } catch {
      throw new UnauthorizedException('Invalid or expired token');
    }

    return true;
  }

  private extractToken(request: Request): string | null {
    const [type, token] = request.headers.authorization?.split(' ') ?? [];
    return type === 'Bearer' ? token : null;
  }
}