Nest.js pipe to call a service's method

service-pipe.ts

// Helper type to get all method names from a class
type ExtractMethodNames<T> = {
  [K in keyof T]: T[K] extends (...args: any[]) => any ? K : never;
}[keyof T];

// Pipe to pass a value through a call to a method in an injectable service
function ServicePipe<T extends new (...args: any[]) => any>(
  service: T,
  method: ExtractMethodNames<InstanceType<T>>,
): Type<PipeTransform> {
  class MixinServicePipe implements PipeTransform {
    constructor(
      @Inject(forwardRef(() => service))
      private serviceInstance: InstanceType<T>,
    ) {}

    transform(value: unknown) {
      return this.serviceInstance[method](value);
    }
  }

  return mixin(MixinServicePipe);
}

// Utility type to extract the return type of an async method
type ServicePipeResult<T, N extends ExtractMethodNames<T>> = T[N] extends (
  ...args: any[]
) => any
  ? Awaited<ReturnType<T[N]>>
  : never;

// Usage example
@Controller('products')
export class ProductController {
  @Get(':id')
  findOne(
    @Param('id', ServicePipe(ProductService, 'findOneById'))
    product: ServicePipeResult<ProductService, 'findOneById'>,
  ) {
    return product;
  }
}