const formatErrorResponse = (incoming, source) => {
  switch (source) {
    case 'mongoose':

      if (incoming && incoming.errors) {
        return {
          errors: Object.keys(incoming.errors).reduce((acc, key) => {
            acc.push({
              message: incoming.errors[key].message,
            });
            return acc;
          }, []),
        };
      }

      // If the Mongoose error does not get returned with incoming && incoming.errors,
      // it's of a type that we really don't know how to handle. Sometimes this means a TypeError,
      // which we might be able to manipulate to get the error message itself and send that back.

      return {
        errors: [
          {
            message: 'An unknown error occurred.',
          },
        ],
      };

    case 'APIError':
      return {
        errors: [
          {
            message: incoming.name,
          },
        ],
      };

    default:
      return incoming;
  }
};

module.exports = formatErrorResponse;