import { isPlainObject } from "./isPlainObject.js";

/**
 * Merge the contents of two or more objects together into the first object.
 * If passing "true" for first argument, the merge becomes recursive (aka. deep copy).
 * @param  {...any} args
 * @returns {Object}
 */
export const extend = (...args) => {
  let deep = false;

  if (typeof args[0] == "boolean") {
    deep = args.shift();
  }

  let result = args[0];

  if (!result || typeof result !== "object") {
    throw new Error("extendee must be an object");
  }

  const extenders = args.slice(1);
  const len = extenders.length;

  for (let i = 0; i < len; i++) {
    const extender = extenders[i];

    for (let key in extender) {
      if (extender.hasOwnProperty(key)) {
        const value = extender[key];

        if (deep && (Array.isArray(value) || isPlainObject(value))) {
          const base = Array.isArray(value) ? [] : {};

          result[key] = extend(true, result.hasOwnProperty(key) ? result[key] : base, value);
        } else {
          result[key] = value;
        }
      }
    }
  }

  return result;
};