export function groupBy<T>(items: T[], keyGetter: (t: T) => string): Map<string, T[]> {
  const map = new Map();

  if (items) {
    items.forEach((item) => {
      const key = keyGetter(item);
      let collection: T[] = map.get(key);

      if (!collection) {
        collection = new Array<T>();
        map.set(key, collection);
      }

      collection.push(item);
    });
  }

  return map;
}

export function filter<T>(
  items: T[],
  searchString: string,
  fieldsGetter: (t: T) => string | string[]
): T[] {
  return searchString
    ? items.filter((item) => {
        const tempFields = fieldsGetter(item);
        const fields = (typeof tempFields === 'string'
          ? [tempFields]
          : tempFields
        )
          .filter((t) => !!t)
          .map((t) => t.toLowerCase());

        return fields.filter((t) => t.indexOf(searchString) !== -1).length > 0;
      })
    : [...items];
}