// 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.Immutable;
using System.Composition;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeFixes;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Editing;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.CSharp.RemoveUnusedLocalFunction;
 
[ExportCodeFixProvider(LanguageNames.CSharp, Name = PredefinedCodeFixProviderNames.RemoveUnusedLocalFunction), Shared]
[ExtensionOrder(After = PredefinedCodeFixProviderNames.AddImport)]
[method: ImportingConstructor]
[method: SuppressMessage("RoslynDiagnosticsReliability", "RS0033:Importing constructor should be [Obsolete]", Justification = "Used in test code: https://github.com/dotnet/roslyn/issues/42814")]
internal sealed class CSharpRemoveUnusedLocalFunctionCodeFixProvider() : SyntaxEditorBasedCodeFixProvider
{
    private const string CS8321 = nameof(CS8321); // The local function 'X' is declared but never used
 
    public sealed override ImmutableArray<string> FixableDiagnosticIds
        => [CS8321];
 
    public override Task RegisterCodeFixesAsync(CodeFixContext context)
    {
        context.RegisterCodeFix(
            CodeAction.Create(
                CSharpCodeFixesResources.Remove_unused_function,
                GetDocumentUpdater(context),
                nameof(CSharpCodeFixesResources.Remove_unused_function)),
            context.Diagnostics);
        return Task.CompletedTask;
    }
 
    protected override Task FixAllAsync(Document document, ImmutableArray<Diagnostic> diagnostics, SyntaxEditor editor, CancellationToken cancellationToken)
    {
        var root = editor.OriginalRoot;
 
        // Order diagnostics in reverse (from latest in file to earliest) so that we process
        // all inner local functions before processing outer local functions.  If we don't
        // do this, then SyntaxEditor will fail if it tries to remove an inner local function
        // after already removing the outer one.
        var localFunctions = diagnostics.OrderBy(static (d1, d2) => d2.Location.SourceSpan.Start - d1.Location.SourceSpan.Start)
                                        .Select(d => root.FindToken(d.Location.SourceSpan.Start))
                                        .Select(t => t.GetAncestor<LocalFunctionStatementSyntax>());
 
        foreach (var localFunction in localFunctions)
        {
            if (localFunction != null)
                editor.RemoveNode(localFunction.Parent is GlobalStatementSyntax globalStatement ? globalStatement : localFunction);
        }
 
        return Task.CompletedTask;
    }
}