// 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.
 
#nullable disable
 
using System;
using System.Collections.Generic;
using Microsoft.VisualStudio.TextManager.Interop;
 
namespace Microsoft.VisualStudio.LanguageServices.Implementation.Venus;
 
/// <summary>
/// An implementation of IVsEnumCodeBlocks used in the implementation of
/// IVsContainedCode.EnumOriginalCodeBlocks for each language's Venus interop layer.
/// </summary>
internal class CodeBlockEnumerator : IVsEnumCodeBlocks
{
    private readonly IList<TextSpanAndCookie> _codeBlocks;
    private int _currentElement;
 
    public CodeBlockEnumerator(IList<TextSpanAndCookie> codeBlocks)
    {
        _codeBlocks = codeBlocks;
        _currentElement = 0;
    }
 
    /// <summary>
    /// Clones another instance of a CodeBlockEnumerator.
    /// </summary>
    private CodeBlockEnumerator(CodeBlockEnumerator previousEnumerator)
    {
        _codeBlocks = previousEnumerator._codeBlocks;
        _currentElement = previousEnumerator._currentElement;
    }
 
    public int Clone(out IVsEnumCodeBlocks ppEnum)
    {
        ppEnum = new CodeBlockEnumerator(this);
        return VSConstants.S_OK;
    }
 
    public int Next(uint celt, TextSpanAndCookie[] rgelt, out uint pceltFetched)
    {
        pceltFetched = Math.Min(celt, (uint)(_codeBlocks.Count - _currentElement));
 
        // Copy each element over
        for (var i = 0; i < pceltFetched; i++)
        {
            rgelt[i] = _codeBlocks[_currentElement++];
        }
 
        // If we returned fewer than the requested number of elements, we return S_FALSE
        return celt == pceltFetched
            ? VSConstants.S_OK
            : VSConstants.S_FALSE;
    }
 
    public int Reset()
    {
        _currentElement = 0;
        return VSConstants.S_OK;
    }
 
    public int Skip(uint celt)
    {
        _currentElement += (int)celt;
 
        // If we've advanced past the end, move back. We return S_FALSE only in this case. If we simply move *to*
        // the end, we actually do want to return S_OK.
        if (_currentElement > _codeBlocks.Count)
        {
            _currentElement = _codeBlocks.Count;
            return VSConstants.S_FALSE;
        }
        else
        {
            return VSConstants.S_OK;
        }
    }
}