ReFuel.Gltf/ReFuel.Gltf/GltfIdCollection.cs

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

namespace ReFuel.Gltf
{
    public abstract class GltfIdObject : GltfObject
    {
        public int Id { get; internal set; }

        public GltfIdObject(GltfDocument document) : base(document)
        {
        }
    }

    public class GltfIdList<T> : IReadOnlyList<T>
        where T : GltfIdObject
    {
        private readonly List<T> items = new List<T>();

        public T this[int index]
        {
            get => items[index];
        }

        public int Count => items.Count;

        public int Append(T item)
        {
            int i = items.Count;

            item.Id = i;
            items.Add(item);

            return i;
        }

        public bool IsSet(int i)
        {
            return i >= 0 && i <= Count;
        }

        public void RemoveAt(int index)
        {
            items.RemoveAt(index);

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

        public IEnumerator<T> GetEnumerator()
        {
            return items.GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return items.GetEnumerator();
        }
    }

    public class GltfRefList<T> : ICollection<T>, IReadOnlyList<T> where T : GltfIdObject
    {
        private readonly List<ItemTuple> items = new List<ItemTuple>();
        private readonly GltfIdList<T> list;

        public IEnumerable<int> Ids
        {
            get
            {
                foreach (ItemTuple tuple in items)
                {
                    yield return tuple.Item?.Id ?? tuple.Id;
                }
            }
        }

        public int Count => items.Count;
        public bool IsReadOnly => false;

        public T this[int index]
        {
            get
            {
                ItemTuple item = items[index];

                if (item.Item != null)
                    return item.Item;

                item.Item = list[item.Id];
                items[index] = item;
                return item.Item;
            }
        }

        public GltfRefList(GltfIdList<T> referencedList)
        {
            list = referencedList;
        }

        public void Add(T item)
        {
            items.Add(new ItemTuple(item.Id, item));
        }

        public void Add(int item)
        {
            items.Add(new ItemTuple(item, null));
        }

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

        public bool Contains(T item)
        {
            return items.FindIndex(x => (x.Item?.Id ?? x.Id) == item.Id) != -1;
        }

        public void CopyTo(T[] array, int arrayIndex)
        {
            for (int i = 0; i < Count; i++)
            {
                array[arrayIndex + i] = this[i];
            }
        }

        public IEnumerator<T> GetEnumerator()
        {
            for (int i = 0; i < Count; i++)
            {
                yield return this[i];
            }
        }

        public bool Remove(T item)
        {
            int idx = items.FindIndex(x => (x.Item?.Id ?? x.Id) == item.Id);

            if (idx == -1)
                return false;

            items.RemoveAt(idx);
            return true;
        }

        public bool Remove(int item)
        {
            int idx = items.FindIndex(x => (x.Item?.Id ?? x.Id) == item);

            if (idx == -1)
                return false;

            items.RemoveAt(idx);
            return true;
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }

        private record struct ItemTuple(int Id, T? Item);
    }

    public struct GltfSmartId<T> where T : GltfIdObject
    {
        private readonly GltfIdList<T> list;
        private int id = -1;
        private T? value = null;

        public int Id
        {
            get => value?.Id ?? id;
            set
            {
                Reset();
                id = value;
            }
        }

        public T Value
        {
            get => value ?? (value = list[id]);
            set
            {
                id = value.Id;
                this.value = value;
            }
        }

        public bool IsSet => list.IsSet(id);

        public GltfSmartId(GltfIdList<T> list)
        {
            this.list = list;
        }

        public void Reset()
        {
            id = -1;
            value = null;
        }

        public static implicit operator T(GltfSmartId<T> id) => id.Value;
    }
}