// 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.Collections.Immutable;
using System.Composition;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CodeFixes;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Diagnostics;
using Microsoft.CodeAnalysis.Editing;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Roslyn.Utilities;
 
using static Microsoft.CodeAnalysis.CSharp.SyntaxFactory;
 
namespace Microsoft.CodeAnalysis.CSharp.UseIsNullCheck;
 
[ExportCodeFixProvider(LanguageNames.CSharp, Name = PredefinedCodeFixProviderNames.UseNullCheckOverTypeCheck), Shared]
[method: ImportingConstructor]
[method: Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
internal sealed class CSharpUseNullCheckOverTypeCheckCodeFixProvider() : SyntaxEditorBasedCodeFixProvider
{
    private static readonly ConstantPatternSyntax s_nullConstantPattern = ConstantPattern(LiteralExpression(SyntaxKind.NullLiteralExpression));
 
    public override ImmutableArray<string> FixableDiagnosticIds
        => [IDEDiagnosticIds.UseNullCheckOverTypeCheckDiagnosticId];
 
    public override Task RegisterCodeFixesAsync(CodeFixContext context)
    {
        RegisterCodeFix(context, CSharpAnalyzersResources.Prefer_null_check_over_type_check, nameof(CSharpAnalyzersResources.Prefer_null_check_over_type_check));
        return Task.CompletedTask;
    }
 
    protected override Task FixAllAsync(
        Document document, ImmutableArray<Diagnostic> diagnostics,
        SyntaxEditor editor, CancellationToken cancellationToken)
    {
        foreach (var diagnostic in diagnostics)
        {
            var node = diagnostic.Location.FindNode(getInnermostNodeForTie: true, cancellationToken: cancellationToken);
            SyntaxNode replacement = node switch
            {
                // Replace 'x is object' with 'x is not null'
                BinaryExpressionSyntax binary =>
                    IsPatternExpression(
                        expression: binary.Left,
                        pattern: UnaryPattern(s_nullConstantPattern)),
                UnaryPatternSyntax =>
                    s_nullConstantPattern,
                // The analyzer reports diagnostic only on BinaryExpressionSyntax and UnaryPatternSyntax.
                _ => throw ExceptionUtilities.Unreachable()
            };
 
            editor.ReplaceNode(node, replacement.WithTriviaFrom(node));
        }
 
        return Task.CompletedTask;
    }
}