using System;
using System.Collections.Generic;

namespace Roblox.Common
{
    public static class CollectionsHelper
    {
        public static T GetRandomElement<T>(this IList<T> self)
        {
            if (self.Count == 0) return default(T);

            return self[new Random().Next(self.Count)];
        }
        public static void Swap<T>(T[] array, int i, int j)
        {
            var d = array[i];
            array[i] = array[j];
            array[j] = d;
        }
        public static IEnumerable<T> RandomizeCollection<T>(this ICollection<T> collection, int numberofItemsToReturn)
            => collection.RandomizeCollection(numberofItemsToReturn, _ => true);
        public static IEnumerable<T> RandomizeCollection<T>(this ICollection<T> collection, int numberofItemsToReturn, Func<T, bool> predicate)
        {
            var count = collection.Count;
            var array = new T[count];
            collection.CopyTo(array, 0);
            if (numberofItemsToReturn > count) numberofItemsToReturn = count;
            var newCount = 0;

            while (newCount < numberofItemsToReturn && newCount < count)
            {
                var randIdx = new Random().Next(count);
                if (!predicate(array[randIdx]))
                {
                    count--;
                    Swap(array, randIdx, count);
                    newCount--;
                }
                else Swap(array, newCount, randIdx);
                newCount++;
            }

            if (numberofItemsToReturn > count) numberofItemsToReturn = count;
            for (int i = 0; i < numberofItemsToReturn; i++) yield return array[i];

            yield break;
        }
    }
}