// -----------------------------------------------------------------------------
// file="ListSegment"
// Project: StgSharp
// Copyright (c) Nitload.
// SPDX-License-Identifier: MIT
// -----------------------------------------------------------------------------

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using System.Xml.Serialization;

namespace Nitload.Common.Collections
{
    /// <summary>
    ///   Part of a collection. This contains a direct reference to _origin collection, so all
    ///   change to _origin collection will be reflected in this object.
    /// </summary>
    /// <typeparam name="T">
    ///
    /// </typeparam>
    public struct ListSegment<T> : ICollection<T>
    {

        private int _begin;
        private int _length;
        private List<T> _collection;

        public ListSegment(
               List<T> collection,
               int begin,
               int length
        )
        {
            ArgumentNullException.ThrowIfNull(collection);
            ArgumentOutOfRangeException.ThrowIfLessThan(begin, 0);
            ArgumentOutOfRangeException.ThrowIfLessThan(length, 0);
            ArgumentOutOfRangeException.ThrowIfLessThan(begin + length, collection.Count);
            _collection = collection;
            _begin = begin;
            _length = length;
        }

        public T this[
                 int indexValue
        ]
        {
            get
            {
                ArgumentOutOfRangeException.ThrowIfLessThan(indexValue, 0);
                ArgumentOutOfRangeException.ThrowIfGreaterThanOrEqual(indexValue, _length);
                return _collection[indexValue + _begin];
            }
        }

        public T this[
                 Index i
        ]
        {
            get
            {
                int offset = i.IsFromEnd ? (_length - i.Value) : i.Value;
                ArgumentOutOfRangeException.ThrowIfLessThan(offset, 0);
                ArgumentOutOfRangeException.ThrowIfGreaterThanOrEqual(offset, _length);
                return _collection[offset + _begin];
            }
        }

        public bool IsReadOnly => true;

        public int Count => _length;

        public bool Contains(
                    T item
        )
        {
            int index = _collection.IndexOf(item);
            return (index >= _begin) && (index < _length + index);
        }

        public void CopyTo(
                    T[] array,
                    int arrayIndex
        )
        {
            ArgumentNullException.ThrowIfNull(array);
            Span<T> span = CollectionsMarshal.AsSpan<T>(_collection).Slice(_begin, _length);
            Span<T> target = new(array, arrayIndex, _length);
            span.CopyTo(target);
        }

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

        void ICollection<T>.Add(
                            T item
        )
        {
            throw new NotSupportedException();
        }

        void ICollection<T>.Clear()
        {
            throw new NotSupportedException();
        }

        bool ICollection<T>.Remove(
                            T item
        )
        {
            throw new NotSupportedException();
        }

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

    }
}