// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
using System.Linq;
using Microsoft.CodeAnalysis.PooledObjects;
 
namespace System.Collections.Immutable
{
    internal static class ImmutableHashSetExtensions
    {
        public static ImmutableHashSet<T> AddRange<T>(this ImmutableHashSet<T> set1, ImmutableHashSet<T> set2)
        {
            using var _1 = PooledHashSet<T>.GetInstance(out var builder);
 
            foreach (var item in set1)
            {
                builder.Add(item);
            }
 
            foreach (var item in set2)
            {
                builder.Add(item);
            }
 
            if (builder.Count == set1.Count)
            {
                return set1;
            }
 
            if (builder.Count == set2.Count)
            {
                return set2;
            }
 
            return builder.ToImmutable();
        }
 
        public static ImmutableHashSet<T> IntersectSet<T>(this ImmutableHashSet<T> set1, ImmutableHashSet<T> set2)
        {
            if (set1.IsEmpty || set2.IsEmpty)
            {
                return ImmutableHashSet<T>.Empty;
            }
            else if (set1.Count == 1)
            {
                return set2.Contains(set1.First()) ? set1 : ImmutableHashSet<T>.Empty;
            }
            else if (set2.Count == 1)
            {
                return set1.Contains(set2.First()) ? set2 : ImmutableHashSet<T>.Empty;
            }
 
            using var _ = PooledHashSet<T>.GetInstance(out var builder);
            foreach (var item in set1)
            {
                if (set2.Contains(item))
                {
                    builder.Add(item);
                }
            }
 
            if (builder.Count == set1.Count)
            {
                return set1;
            }
            else if (builder.Count == set2.Count)
            {
                return set2;
            }
 
            return builder.ToImmutable();
        }
 
        public static bool IsSubsetOfSet<T>(this ImmutableHashSet<T> set1, ImmutableHashSet<T> set2)
        {
            if (set1.Count > set2.Count)
            {
                return false;
            }
 
            foreach (var item in set1)
            {
                if (!set2.Contains(item))
                {
                    return false;
                }
            }
 
            return true;
        }
    }
}