policies.guard.ts

import { CanActivate, ExecutionContext, Injectable } from '@nestjs/common';
import { Reflector } from '@nestjs/core';
import { AppAbility } from '../casl/abilities';
import { CaslAbilityFactory } from '../casl/casl-ability.factory';
import { CHECK_POLICIES_KEY, PolicyHandler } from '../casl/policy-handler';

@Injectable()
export class PoliciesGuard implements CanActivate {
  constructor(
    private reflector: Reflector,
    private caslAbilityFactory: CaslAbilityFactory
  ) {}

  async canActivate(context: ExecutionContext): Promise<boolean> {
    const policyHandlers =
      this.reflector.get<PolicyHandler[]>(
        CHECK_POLICIES_KEY,
        context.getHandler()
      ) || [];

    const { jwtPayload, params, user } = context.switchToHttp().getRequest();

    const ability = this.caslAbilityFactory.createForUser(user, jwtPayload, {
      params: {
        userId: params.userId ? Number(params.userId) : params.userId,
      },
    });

    return policyHandlers.every((handler) =>
      this.execPolicyHandler(handler, ability)
    );
  }

  private execPolicyHandler(handler: PolicyHandler, ability: AppAbility) {
    if (typeof handler === 'function') {
      return handler(ability);
    }
    return handler.handle(ability);
  }
}