using System.Collections;

namespace PkmnLib.Plugin.Gen7.SourceGen;

/// <summary>
/// An immutable array wrapper with sequence-based equality, so that incremental generator pipeline
/// values containing collections cache correctly.
/// </summary>
public readonly struct EquatableArray<T> : IEquatable<EquatableArray<T>>, IReadOnlyList<T> where T : IEquatable<T>
{
    private readonly T[]? _array;

    public EquatableArray(T[] array)
    {
        _array = array;
    }

    public int Count => _array?.Length ?? 0;

    public T this[int index] => _array![index];

    public bool Equals(EquatableArray<T> other)
    {
        if (Count != other.Count)
            return false;
        for (var i = 0; i < Count; i++)
        {
            if (!this[i].Equals(other[i]))
                return false;
        }
        return true;
    }

    public override bool Equals(object? obj) => obj is EquatableArray<T> other && Equals(other);

    public override int GetHashCode()
    {
        unchecked
        {
            var hash = 17;
            for (var i = 0; i < Count; i++)
            {
                hash = hash * 31 + this[i].GetHashCode();
            }
            return hash;
        }
    }

    public IEnumerator<T> GetEnumerator() => ((IEnumerable<T>)(_array ?? [])).GetEnumerator();

    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
}