utils.js

import { curry, equals, groupBy, head, mapObj,
  mapObjIndexed, prop, reject, tap } from 'ramda'

/**
 * takes a function and two objects
 * merges them by applying fn to
 * the same k/v in each.
 *
 * @func
 * @sig (a,a -> a) -> {k: v} -> {k: v} -> {k: v}
 * @param {Function} fn A function used to merge items
 * @param {Object} obj1 The first object
 * @param {Object} obj2 The first object
 * @return {Object} The result of applying fn to each val in obj1 & obj2
 * @example
 *
 *      const fn = R.add
 *      const obj1 = { foo: 1, bar: 10, baz: 5 }
 *      const obj2 = { foo: 8, bar: 20, baz: 7 }
 *      mergeWith(fn, obj1, obj2)
 *      //=> { foo: 9, bar: 30, baz: 12 }
 */
export const mergeWith = curry((fn, a, b) => {
  return mapObjIndexed((va, k) => {
    const vb = prop(k, b)
    return fn(va, vb)
  }, a)
})

// List

// (a -> String) -> [a] -> { String: [a] }
export const indexBy = curry((_prop, list) => {
  return mapObj(head, groupBy(prop(_prop), list))
})

// String -> [String] -> [String]
export const without = curry((a, b) => reject(equals(a), b))

export const log = tap(console.log)