import forIn from "./forIn"

/**
 * Merges the values from 2 or more Objects or Arrays together into a new Object/Array.
 * Null and Undefined values are handled gracefully, and if the second value is a primitive it will be returned as-is, instead of trying to merge it onto the first.
 *
 * @function
 * @name merge
 * @param {Array<object|Array<*>>} ...val Values to merge together (values with higher precedence should be provided last)
 * @returns {object|Array<*>} A new value that contains the combined values from all the values passed in
 */
function merge(...vals) {
  const numOfVals = vals.length
  if (vals[0] === undefined || vals[1] === undefined) {
    return vals[1] !== undefined ? vals[1] : vals[0]
  }
  if (
    numOfVals === 2
    && (vals[1] == null || typeof vals[1] !== "object" || vals[1].constructor.name !== "Object")
  ) {
    return vals[1]
  }
  const newObj = { }
  forIn((key, val) => { newObj[key] = val }, vals[0])
  for (let i = 1; i < numOfVals; i++) {
    forIn((key, val) => {
      newObj[key] = merge(newObj[key], val)
    }, vals[i])
  }
  return newObj
}

export default merge