// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

/**
 * Applies the given transformer to all keys in the given record's entries and
 * returns a new record containing the transformed entries.
 *
 * If the transformed entries contain the same key multiple times, only the last
 * one will appear in the returned record.
 *
 * @example
 * ```ts
 * import { mapKeys } from "@std/collections/map_keys";
 * import { assertEquals } from "@std/assert/assert_equals";
 *
 * const counts = { a: 5, b: 3, c: 8 };
 *
 * assertEquals(
 *   mapKeys(counts, (it) => it.toUpperCase()),
 *   {
 *     A: 5,
 *     B: 3,
 *     C: 8,
 *   },
 * );
 * ```
 */
export function mapKeys<T>(
  record: Readonly<Record<string, T>>,
  transformer: (key: string) => string,
): Record<string, T> {
  const ret: Record<string, T> = {};

  for (const [key, value] of Object.entries(record)) {
    const mappedKey = transformer(key);
    ret[mappedKey] = value;
  }

  return ret;
}