using System.Collections;
using System.Collections.Generic;

namespace Engine.Core;

public class FastList<T> : IReadOnlyList<T>, IEnumerable<T> where T : notnull
{
    private readonly List<T> items = [];
    private readonly Dictionary<T, int> indexMap = [];

    public int Count => items.Count;

    public T this[int index] => items[index];

    public void Add(T item)
    {
        indexMap[item] = items.Count;
        items.Add(item);
    }

    public void RemoveAt(int i) => Remove(items[i], i);
    public bool Remove(T item)
    {
        if (!indexMap.TryGetValue(item, out int index))
            return false;

        Remove(item, index);

        return true;
    }

    private void Remove(T item, int index)
    {
        int lastIndex = items.Count - 1;
        T lastItem = items[lastIndex];

        items[index] = lastItem;
        indexMap[lastItem] = index;

        items.RemoveAt(lastIndex);
        indexMap.Remove(item);
    }

    public void Insert(int index, T item)
    {
        items.Insert(index, item);

        for (int i = index; i < items.Count; i++)
            indexMap[items[i]] = i;
    }

    public void Clear()
    {
        items.Clear();
        indexMap.Clear();
    }

    public bool Contains(T item) => indexMap.ContainsKey(item);

    public int BinarySearch(T item, IComparer<T>? comparer = null) => items.BinarySearch(item, comparer);
    public void Sort(IComparer<T> comparer)
    {
        items.Sort(comparer);

        for (int i = 0; i < items.Count; i++)
            indexMap[items[i]] = i;
    }

    public IEnumerator<T> GetEnumerator() => items.GetEnumerator();
    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

    public FastList() { }
    public FastList(int count) { items.Capacity = count; }
}