index.js

import async from 'async';

export function merge () {
  // Merge objects passed as arguments, left to right precidence.

  let result = {};

  for (let i = 0; i < arguments.length; i++) {
    let keys = Object.keys(arguments[i]);
    for (let k = 0; k < keys.length; k++) {
      let key = keys[k];
      if (!result.hasOwnProperty(key)) {
        result[key] = arguments[i][key];
      }
    }
  }

  return result;
}

export function formatError (err) {
  if (err.error) return err;
  if (err instanceof Error) {
    err = err.message || err.toString();
  }
  return { error: err };
}

export function getLastResult (methods, callback, isService) {
  async.reduce(methods, undefined, (lastResult, stored, done) => {
    let {
      service,
      method,
      data = lastResult
    } = stored;

    let call = [
      service,
      method,
      data,
      function (err, result) {
        if (err) {
          let r = {
            error: err,
            method
          };
          if (!isService) {
            r.service = service;
          }
          return done(r);
        }

        if (!isService) {
          var index = methods.indexOf(stored);
          var next = methods[index + 1];

          if (next && next.data && !next.data[0].data) {
            methods[index + 1].data[0].data = result;
          }
        }

        return done(null, result);
      }
    ];

    if (isService) {
      call.shift();
    }

    this.call(...call);
  }, callback);
}