/**
 * A simple wrapper around native Array.prototype.reduce(), for use in a compose/pipe chain of functions.
 * Can also reduce the key/value pairs of an object, if one is supplied in place of an array.
 *
 * @function
 * @name reduce
 * @param {function} fn A function to control the reduction of each item in the array|object into the single output value
 * @param {*} defaultVal A starting value for the reduction accumulator
 * @param {Array<*>|object} arr An array of values of any type OR an object containing key/value pairs
 * @returns {*} The original Array|Object somehow reduced to one value, according to the supplied function
 */
function reduce(fn, defaultVal, arr) {
  return typeof arr.reduce === "function"
    ? arr.reduce(fn, defaultVal)
    : Object.keys(arr).reduce((acc, key) => fn(acc, arr[key], key), defaultVal)
}

export default reduce