/******************************************************************************
 * Copyright (C) Ultraleap, Inc. 2011-2021.                                   *
 *                                                                            *
 * Use subject to the terms of the Apache License 2.0 available at            *
 * http://www.apache.org/licenses/LICENSE-2.0, or another agreement           *
 * between Ultraleap and you, your company or other organization.             *
 ******************************************************************************/

using Leap.Unity.Query;

namespace Leap.Unity
{

    /// <summary>
    /// This easy-to-implement interface represents the ability to index into a collection
    /// of elements of type T. IIndexables inherit Query() via an extension method.
    /// 
    /// IIndexable is fire-and-forget if your implementer is a reference type (class). If
    /// the implementing type is a struct, be mindful of boxing, and consider using
    /// IIndexableStruct and pooling instead.
    /// </summary>
    public interface IIndexable<T>
    {

        T this[int idx] { get; }

        int Count { get; }
    }

    public static class IIndexableExtensions
    {
        public static IndexableEnumerator<T> GetEnumerator<T>(this IIndexable<T> indexable)
        {
            return new IndexableEnumerator<T>(indexable);
        }

        public static Query<T> Query<T>(this IIndexable<T> indexable)
        {
            var arr = ArrayPool<T>.Spawn(indexable.Count);
            for (int i = 0; i < indexable.Count; i++)
            {
                arr[i] = indexable[i];
            }
            return new Query<T>(arr, indexable.Count);
        }
    }

    public struct IndexableEnumerator<Element>
    {
        IIndexable<Element> indexable;
        int index;

        public IndexableEnumerator(IIndexable<Element> indexable)
        {
            this.indexable = indexable;
            index = -1;
        }

        public IndexableEnumerator<Element> GetEnumerator()
        {
            return this;
        }

        public bool MoveNext()
        {
            if (indexable == null) return false;
            index++; return index < indexable.Count;
        }

        public void Reset()
        {
            index = -1;
        }

        public Element Current { get { return indexable[index]; } }

    }

}