create_route_typed.ts

import t from 'io-ts';
import { Request } from 'hapi';
import { PathReporter } from 'io-ts/lib/PathReporter';
import { fold } from 'fp-ts/lib/Either';
import { pipe } from 'fp-ts/lib/pipeable';
import { identity } from 'fp-ts/lib/function';

interface Params {
  path?: t.HasProps;
  query?: t.HasProps;
  body?: t.Any;
}

type Decode<TParams extends Params> = {
  [key in keyof TParams]: TParams[key] extends t.Any
    ? t.TypeOf<TParams[key]>
    : unknown;
};

interface Route<TParams extends Params> {
  path: string;
  method: 'GET' | 'POST' | 'PUT' | 'DELETE';
  params: TParams;
  handler: (request: Request, data: Decode<TParams>) => {};
}

export function createRoute<TParams extends Params>(route: Route<TParams>) {
  const { params, handler, ...rest } = route;

  return {
    ...rest,
    handler: (request: Request) => {
      const requestData = {
        body: request.payload,
        path: request.params,
        query: request.query
      };

      const data = (Object.keys(params) as Array<keyof Params>).reduce(
        (prev, key) => {
          const codec = params[key];
          if (!codec) {
            return prev;
          }

          const result = codec.decode(requestData[key]);

          return {
            ...prev,
            [key]: pipe(
              result,
              fold(() => {
                throw new Error(PathReporter.report(result).join('\n'));
              }, identity)
            )
          };
        },
        {} as Decode<TParams>
      );

      return handler(request, data);
    }
  };
}