// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System.Collections;

namespace System.Windows.Forms
{
    internal partial class ItemArray
    {
        /// <summary>
        ///  EntryEnumerator is an enumerator that will enumerate over
        ///  a given state mask.
        /// </summary>
        private class EntryEnumerator : IEnumerator
        {
            private readonly ItemArray _items;
            private readonly bool _anyBit;
            private readonly int _state;
            private int _current;
            private readonly int _version;

            /// <summary>
            ///  Creates a new enumerator that will enumerate over the given state.
            /// </summary>
            public EntryEnumerator(ItemArray items, int state, bool anyBit)
            {
                _items = items;
                _state = state;
                _anyBit = anyBit;
                _version = items.Version;
                _current = -1;
            }

            /// <summary>
            ///  Moves to the next element, or returns false if at the end.
            /// </summary>
            bool IEnumerator.MoveNext()
            {
                if (_version != _items.Version)
                {
                    throw new InvalidOperationException(SR.ListEnumVersionMismatch);
                }

                while (true)
                {
                    if (_current < _items.Count - 1)
                    {
                        _current++;

                        var entry = _items._entries[_current];

                        if (_anyBit)
                        {
                            if ((entry.State & _state) != 0)
                            {
                                return true;
                            }
                        }
                        else
                        {
                            if ((entry.State & _state) == _state)
                            {
                                return true;
                            }
                        }
                    }
                    else
                    {
                        _current = _items.Count;
                        return false;
                    }
                }
            }

            /// <summary>
            ///  Resets the enumeration back to the beginning.
            /// </summary>
            void IEnumerator.Reset()
            {
                if (_version != _items.Version)
                {
                    throw new InvalidOperationException(SR.ListEnumVersionMismatch);
                }

                _current = -1;
            }

            /// <summary>
            ///  Retrieves the current value in the enumerator.
            /// </summary>
            object IEnumerator.Current
            {
                get
                {
                    if (_current == -1 || _current == _items.Count)
                    {
                        throw new InvalidOperationException(SR.ListEnumCurrentOutOfRange);
                    }

                    return _items._entries[_current].Item;
                }
            }
        }
    }
}
