namespace ShrlAlgoToolkit.Core.Extensions;

/// <summary>
/// 自定义Distinct扩展方法
/// </summary>
public static class DistinctExtensions
{
    public static IEnumerable<T> Distinct<T>(
        this IEnumerable<T> source, Func<T, T, bool> comparer)
        where T : class
        => source.Distinct(new DynamicEqualityComparer<T>(comparer));
    public static IEnumerable<T> Distinct<T, V>(this IEnumerable<T> source, Func<T, V> keySelector)
        => source.Distinct(new CommonEqualityComparer<T, V>(keySelector));
    private sealed class DynamicEqualityComparer<T> : IEqualityComparer<T>
        where T : class
    {
        private readonly Func<T, T, bool> _func;

        public DynamicEqualityComparer(Func<T, T, bool> func)
        {
            _func = func;
        }

        public bool Equals(T x, T y) => _func(x, y);

        public int GetHashCode(T obj) => 0;
    }

    private sealed class CommonEqualityComparer<T, V> : IEqualityComparer<T>
    {
        private readonly Func<T, V> keySelector;

        public CommonEqualityComparer(Func<T, V> keySelector)
        {
            this.keySelector = keySelector;
        }

        public bool Equals(T x, T y)
        {
            return EqualityComparer<V>.Default.Equals(keySelector(x), keySelector(y));
        }

        public int GetHashCode(T obj)
        {
            return EqualityComparer<V>.Default.GetHashCode(keySelector(obj));
        }
    }
}