// 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.Diagnostics.CodeAnalysis;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeFixes;
using Microsoft.CodeAnalysis.Diagnostics;
using Microsoft.CodeAnalysis.Editing;
using Microsoft.CodeAnalysis.Formatting;
using Microsoft.CodeAnalysis.LanguageService;
using Microsoft.CodeAnalysis.Shared.Extensions;
 
namespace Microsoft.CodeAnalysis.UseCoalesceExpression;
 
[ExportCodeFixProvider(LanguageNames.CSharp, LanguageNames.VisualBasic, Name = PredefinedCodeFixProviderNames.UseCoalesceExpressionForTernaryConditionalCheck), Shared]
[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 UseCoalesceExpressionForTernaryConditionalCheckCodeFixProvider() : SyntaxEditorBasedCodeFixProvider
{
    public override ImmutableArray<string> FixableDiagnosticIds
        => [IDEDiagnosticIds.UseCoalesceExpressionForTernaryConditionalCheckDiagnosticId];
 
    protected override bool IncludeDiagnosticDuringFixAll(Diagnostic diagnostic)
        => !diagnostic.Descriptor.ImmutableCustomTags().Contains(WellKnownDiagnosticTags.Unnecessary);
 
    public override Task RegisterCodeFixesAsync(CodeFixContext context)
    {
        RegisterCodeFix(context, AnalyzersResources.Use_coalesce_expression, nameof(AnalyzersResources.Use_coalesce_expression));
        return Task.CompletedTask;
    }
 
    protected override async Task FixAllAsync(
        Document document, ImmutableArray<Diagnostic> diagnostics,
        SyntaxEditor editor, CancellationToken cancellationToken)
    {
        var semanticModel = await document.GetRequiredSemanticModelAsync(cancellationToken).ConfigureAwait(false);
        var expressionTypeOpt = semanticModel.Compilation.ExpressionOfTType();
        var syntaxFacts = document.GetRequiredLanguageService<ISyntaxFactsService>();
        var semanticFacts = document.GetRequiredLanguageService<ISemanticFactsService>();
 
        foreach (var diagnostic in diagnostics)
        {
            cancellationToken.ThrowIfCancellationRequested();
            ApplyEdit(
                editor, semanticModel, expressionTypeOpt,
                syntaxFacts, semanticFacts,
                diagnostic, cancellationToken);
        }
    }
 
    private static void ApplyEdit(
        SyntaxEditor editor, SemanticModel semanticModel, INamedTypeSymbol? expressionTypeOpt,
        ISyntaxFactsService syntaxFacts, ISemanticFactsService semanticFacts,
        Diagnostic diagnostic, CancellationToken cancellationToken)
    {
        var root = editor.OriginalRoot;
        var conditionalExpression = root.FindNode(diagnostic.AdditionalLocations[0].SourceSpan, getInnermostNodeForTie: true);
        var conditionalPartHigh = root.FindNode(diagnostic.AdditionalLocations[1].SourceSpan);
        var whenPart = root.FindNode(diagnostic.AdditionalLocations[2].SourceSpan);
        syntaxFacts.GetPartsOfConditionalExpression(
            conditionalExpression, out var condition, out var whenTrue, out var whenFalse);
 
        var conditionalPartLow = syntaxFacts.WalkDownParentheses(conditionalPartHigh);
        editor.ReplaceNode(conditionalExpression,
            (c, g) =>
            {
                syntaxFacts.GetPartsOfConditionalExpression(
                    c, out var currentCondition, out var currentWhenTrue, out var currentWhenFalse);
 
                var coalesceExpression = GetCoalesceExpression(
                    syntaxFacts, g, whenPart, whenTrue, conditionalPartLow,
                    currentWhenTrue, currentWhenFalse)
                    .WithTrailingTrivia(conditionalExpression.GetTrailingTrivia());
 
                if (semanticFacts.IsInExpressionTree(
                        semanticModel, conditionalExpression, expressionTypeOpt, cancellationToken))
                {
                    coalesceExpression = coalesceExpression.WithAdditionalAnnotations(
                        WarningAnnotation.Create(AnalyzersResources.Changes_to_expression_trees_may_result_in_behavior_changes_at_runtime));
                }
 
                return coalesceExpression.WithAdditionalAnnotations(Formatter.Annotation);
            });
    }
 
    private static SyntaxNode GetCoalesceExpression(
        ISyntaxFactsService syntaxFacts, SyntaxGenerator generator,
        SyntaxNode whenPart, SyntaxNode whenTrue,
        SyntaxNode conditionalPartLow,
        SyntaxNode currentWhenTrue, SyntaxNode currentWhenFalse)
    {
        return whenPart == whenTrue
            ? generator.CoalesceExpression(conditionalPartLow, syntaxFacts.WalkDownParentheses(currentWhenTrue))
            : generator.CoalesceExpression(conditionalPartLow, syntaxFacts.WalkDownParentheses(currentWhenFalse));
    }
}