/**
 * Sorts an array of items into groups. The return value is a map where the keys are
 * the group ids the given getGroupId function produced and the value is an array of
 * each item in that group.
 */
export const groupBy = <T, Key extends string | number | symbol>(
  array: readonly T[],
  getGroupId: (item: T) => Key
): Record<Key, T[]> =>
  array.reduce((acc, item) => {
    const groupId = getGroupId(item);
    if (!acc[groupId]) acc[groupId] = [];
    acc[groupId].push(item);
    return acc;
  }, {} as Record<Key, T[]>);

/**
 * Given a list of items returns a new list with only
 * unique items. Accepts an optional identity function
 * to convert each item in the list to a comparable identity
 * value
 */
export const unique = <T, K extends string | number | symbol>(
  array: readonly T[],
  toKey?: (item: T) => K
): T[] => {
  const valueMap = array.reduce((acc, item) => {
    const key = toKey ? toKey(item) : (item as unknown as string | number | symbol);
    if (acc[key]) return acc;
    acc[key] = item;
    return acc;
  }, {} as Record<string | number | symbol, T>);
  return Object.values(valueMap);
};