// 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;
using System.ComponentModel.Composition;
using System.Threading;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.Editor.Shared.Extensions;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Text;
using Microsoft.VisualStudio.Commanding;
using Microsoft.VisualStudio.Text;
using Microsoft.VisualStudio.Text.Editor.Commanding.Commands;
using Microsoft.VisualStudio.Utilities;
 
namespace Microsoft.CodeAnalysis.Editor.CSharp.FixInterpolatedVerbatimString;
 
/// <summary>
/// Replaces <c>@$"</c> with <c>$@"</c>, which is the preferred and until C# 8.0 the only supported form
/// of an interpolated verbatim string start token. In C# 8.0 we still auto-correct to this form for consistency.
/// </summary>
[Export(typeof(ICommandHandler))]
[ContentType(ContentTypeNames.CSharpContentType)]
[Name(nameof(FixInterpolatedVerbatimStringCommandHandler))]
internal sealed class FixInterpolatedVerbatimStringCommandHandler : IChainedCommandHandler<TypeCharCommandArgs>
{
    [ImportingConstructor]
    [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
    public FixInterpolatedVerbatimStringCommandHandler()
    {
    }
 
    public string DisplayName => CSharpEditorResources.Fix_interpolated_verbatim_string;
 
    public void ExecuteCommand(TypeCharCommandArgs args, Action nextCommandHandler, CommandExecutionContext executionContext)
    {
        // We need to check for the token *after* the opening quote is typed, so defer to the editor first
        nextCommandHandler();
 
        var cancellationToken = executionContext.OperationContext.UserCancellationToken;
        if (cancellationToken.IsCancellationRequested)
        {
            return;
        }
 
        try
        {
            ExecuteCommandWorker(args, cancellationToken);
        }
        catch (OperationCanceledException)
        {
            // According to Editor command handler API guidelines, it's best if we return early if cancellation
            // is requested instead of throwing. Otherwise, we could end up in an invalid state due to already
            // calling nextCommandHandler().
        }
    }
 
    private static void ExecuteCommandWorker(TypeCharCommandArgs args, CancellationToken cancellationToken)
    {
        if (args.TypedChar == '"')
        {
            var caret = args.TextView.GetCaretPoint(args.SubjectBuffer);
            if (caret != null)
            {
                var position = caret.Value.Position;
                var snapshot = caret.Value.Snapshot;
 
                if (position >= 3 &&
                    snapshot[position - 1] == '"' &&
                    snapshot[position - 2] == '$' &&
                    snapshot[position - 3] == '@')
                {
                    var document = snapshot.GetOpenDocumentInCurrentContextWithChanges();
                    if (document != null)
                    {
                        var root = document.GetRequiredSyntaxRootSynchronously(cancellationToken);
                        var token = root.FindToken(position - 3);
                        if (token.IsKind(SyntaxKind.InterpolatedVerbatimStringStartToken))
                        {
                            args.SubjectBuffer.Replace(new Span(position - 3, 2), "$@");
                        }
                    }
                }
            }
        }
    }
 
    public CommandState GetCommandState(TypeCharCommandArgs args, Func<CommandState> nextCommandHandler)
        => nextCommandHandler();
}