// 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 Microsoft.CodeAnalysis.Collections;

namespace Microsoft.CodeAnalysis.Formatting
{
    internal partial class TokenStream
    {
        // gain of having hand written iterator seems about 50-100ms over auto generated one.
        // not sure whether it is worth it. but I already wrote it to test, so going to just keep it.
        public readonly struct Iterator(SegmentedList<SyntaxToken> tokensIncludingZeroWidth)
        {
            public Enumerator GetEnumerator()
                => new(tokensIncludingZeroWidth);

            public struct Enumerator
            {
                private readonly SegmentedList<SyntaxToken> _tokensIncludingZeroWidth;
                private readonly int _maxCount;

                private (int index, SyntaxToken currentToken, SyntaxToken nextToken) _current;
                private int _index;

                public Enumerator(SegmentedList<SyntaxToken> tokensIncludingZeroWidth)
                {
                    _tokensIncludingZeroWidth = tokensIncludingZeroWidth;
                    _maxCount = _tokensIncludingZeroWidth.Count - 1;

                    _index = 0;
                    _current = default;
                }

                public bool MoveNext()
                {
                    if (_index < _maxCount)
                    {
                        _current = (_index, _tokensIncludingZeroWidth[_index], _tokensIncludingZeroWidth[_index + 1]);
                        _index++;
                        return true;
                    }

                    return MoveNextRare();
                }

                private bool MoveNextRare()
                {
                    _index = _maxCount + 1;
                    _current = default;
                    return false;
                }

                public readonly (int index, SyntaxToken currentToken, SyntaxToken nextToken) Current => _current;
            }
        }
    }
}
