// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

/**
 * Transforms the given array into a Record, extracting the key of each element using the given selector.
 * If the selector produces the same key for multiple elements, the latest one will be used (overriding the
 * ones before it).
 *
 * Example:
 *
 * ```ts
 * import { associateBy } from "https://deno.land/std@$STD_VERSION/collections/mod.ts"
 * import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts";
 *
 * const users = [
 *     { id: 'a2e', userName: 'Anna' },
 *     { id: '5f8', userName: 'Arnold' },
 *     { id: 'd2c', userName: 'Kim' },
 * ]
 * const usersById = associateBy(users, it => it.id)
 *
 * assertEquals(usersById, {
 *     'a2e': { id: 'a2e', userName: 'Anna' },
 *     '5f8': { id: '5f8', userName: 'Arnold' },
 *     'd2c': { id: 'd2c', userName: 'Kim' },
 * })
 * ```
 */
export function associateBy<T>(
  array: readonly T[],
  selector: (el: T) => string,
): Record<string, T> {
  const ret: Record<string, T> = {};

  for (const element of array) {
    const selectedValue = selector(element);

    ret[selectedValue] = element;
  }

  return ret;
}
