import { find, curry, filter, pipe } from 'ramda';
import { propOr, propSatisfies, not, isNil } from 'crocks';

/**
 * Determines whether at least one of the given fields at the given prefix exists.
 *
 * If the second boolean (exclusive) is set, only one of the fields may exist.
 *
 * objectHasOneOf :: String p -> Boolean e -> [String] f -> Object o -> Boolean b
 */
const objectHasOneOf = curry((exclusive, fields, obj) => {
  const fieldsInObj = filter(field => propSatisfies(field, not(isNil), obj), fields);

  if (fieldsInObj.length === 0) {
    return false;
  }

  if (exclusive && fieldsInObj.length > 1) {
    return false;
  }

  return true;
});

/**
 * Creates a middleware which determines whether one of the two fields appears in all create inputs.
 * The boolean given controls whether or not an exclusive or is used, limiting the input to exactly one of the two fields.
 *
 * If all create inputs are valid, this resolves. If not, it throws an error containing the first bad element.
 *
 * createHasOneOf :: Boolean e -> [String] f -> GraphQLMiddleware m
 */
export const createHasOneOf = curry((exclusive, fields) => {
  const hasOneOf = objectHasOneOf('create', exclusive, fields);
  const doesNotHaveOneOf = not(hasOneOf);

  return async (resolve, parent, args, context, info) => {
    const firstBadElement = find(
      pipe(
        propOr(undefined, 'create'),
        doesNotHaveOneOf
      ),
      args.payload
    );

    if (!firstBadElement) {
      return resolve(parent, args, context, info);
    }

    throw new Error(
      `Invalid create input: ${JSON.stringify(firstBadElement)}. It must have${
        exclusive ? ' exactly ' : ' '
      }one of either ${fields.join(', or ')}.`
    );
  };
});