auth.guard.ts

import {
  CanActivate,
  ExecutionContext,
  Injectable,
  UnauthorizedException,
} from "@nestjs/common";
import { JwtService } from "@nestjs/jwt";
import type { Request } from "express";

/**
 * JWT authentication guard
 * Validates Bearer tokens on protected endpoints
 */
@Injectable()
export class AuthGuard implements CanActivate {
  constructor(private readonly jwtService: JwtService) {}

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

    if (!token) {
      throw new UnauthorizedException("No token provided");
    }

    try {
      const payload = await this.jwtService.verifyAsync(token);
      // Attach decoded payload to request for downstream use
      request["user"] = payload;
    } catch {
      throw new UnauthorizedException("Invalid or expired token");
    }

    return true;
  }

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