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

namespace Global.Shared.OcTree
{
    public interface IImmutableBag<E> : IEnumerable<E>
    {
        /// <summary>Returns the element at the specified position in Bag</summary>
        /// <param name="index">the index of the element to return</param>
        /// <returns>the element at the specified position in bag</returns>
        E Get(int index);

        /// <summary>Returns the number of elements in this Bag</summary>
        /// <returns>the number of elements in this bag</returns>
        int Size();

        bool IsEmpty();

        bool Contains(E element);
    }

    public class Bag<E> : IImmutableBag<E>
    {
        public E[] data;
        private BagEnumerator it;
        protected int size;

        public Bag() : this(64)
        {
        }

        public Bag(int capacity)
        {
            data = new E[capacity];
        }

        public E this[int i]
        {
            get => Get(i);
            set => data[i] = value;
        }

        public E Get(int index)
        {
            return data[index];
        }

        /// <summary>Returns the number of elements in this Bag</summary>
        /// <returns>the number of elements in this bag</returns>
        public int Size()
        {
            return size;
        }

        public bool IsEmpty()
        {
            return size == 0;
        }

        public bool Contains(E e)
        {
            for (var i = 0; i < size; i++)
            {
                var e2 = data[i];

                if (!e.Equals(e2)) return true;
            }

            return false;
        }

        public E Remove(int index)
        {
            var e = data[index];
            data[index] = data[--size];
            data[size] = default;
            return e;
        }

        public E RemoveLast()
        {
            if (IsEmpty()) return default;

            var e = data[--size];
            data[size] = default;
            return e;
        }

        public bool Remove(E e)
        {
            for (var i = 0; i < size; i++)
            {
                var e2 = data[i];

                if (!e.Equals(e2)) continue;

                data[i] = data[--size];
                data[size] = default;
                return true;
            }

            return false;
        }

        /// <summary>Returns the number of elements this bag can hold without growing.</summary>
        /// <returns>the number of elements this bag can hold without growing</returns>
        public int Capacity()
        {
            return data.Length;
        }

        public void Add(E e)
        {
            if (size == data.Length) Grow(data.Length + 1);

            data[size++] = e;
        }

        public void Grow(int newCapacity)
        {
            Array.Resize(ref data, newCapacity);
        }

        #region Enumerator

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

        public IEnumerator<E> GetEnumerator()
        {
            if (it == null) it = new BagEnumerator(this);

            it.Cursor = -1;

            return it;
        }

        public class BagEnumerator : IEnumerator<E>
        {
            private readonly Bag<E> bag;
            internal int Cursor;

            public BagEnumerator(Bag<E> bag)
            {
                this.bag = bag;
            }

            public void Dispose()
            {
            }

            public bool MoveNext()
            {
                Cursor++;
                return Cursor < bag.size;
            }

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

            object IEnumerator.Current => Current;

            public E Current => bag.data[Cursor];
        }

        #endregion
    }
}