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

namespace ln.objects.collections
{
    public class LazyList<T> : IList<T> where T:class
    {
        ObjectStore objectStore;
        List<ListItem> listItems = new List<ListItem>();

        public LazyList(ObjectStore objectStore)
            :this(objectStore, new Guid[0]) { }

        public LazyList(ObjectStore objectStore,Guid[] initialItems)
        {
            this.objectStore = objectStore;
        }

        public T this[int index]
        {
            get
            {
                ListItem listItem = listItems[index];
                if (Object.ReferenceEquals(null, listItem.Value))
                {
                    if (Guid.Empty.Equals(listItem.UID))
                        return null;

                    listItem.Value = objectStore.LoadObject<T>(listItem.UID);
                }
                return listItem.Value;
            }
            set
            {
                ListItem listItem = listItems[index];
                listItem.Value = value;
                listItem.UID = Guid.Empty;
            }
        }

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

        public void Add(T item)=> listItems.Add(new ListItem() { Value = item });
        public void Clear() => listItems.Clear();
        public bool Contains(T item)
        {
            Guid uid = objectStore.GetObjectUID(item);
            foreach (ListItem listItem in listItems)
                if (listItem.UID.Equals(uid) || Object.ReferenceEquals(item, listItem.Value))
                    return true;
            return false;
        }

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

        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
        public IEnumerator<T> GetEnumerator()
        {
            for (int i = 0; i < Count; i++)
                yield return this[i];
        }
        public int IndexOf(T item)
        {
            Guid uid = objectStore.GetObjectUID(item);
            for (int i = 0; i < Count; i++)
            {
                ListItem listItem = listItems[i];
                if (listItem.UID.Equals(uid) || Object.ReferenceEquals(item, listItem.Value))
                    return i;
            }
            return -1;
        }

        public void Insert(int index, T item) => listItems.Insert(index, new ListItem() { Value = item });
        public bool Remove(T item)
        {
            Guid uid = objectStore.GetObjectUID(item);
            for (int i = 0; i < Count; i++)
            {
                ListItem listItem = listItems[i];
                if (listItem.UID.Equals(uid) || Object.ReferenceEquals(item, listItem.Value))
                {
                    listItems.RemoveAt(i);
                    return true;
                }
            }
            return false;
        }

        public void RemoveAt(int index) => listItems.RemoveAt(index);

        class ListItem
        {
            public Guid UID;    // Identifier of reference in objectStore
            public T Value;     // Loaded Reference
        }

    }
}