// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Collections.Immutable;
using Analyzer.Utilities;
using Analyzer.Utilities.Extensions;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.Diagnostics;
using Microsoft.CodeAnalysis.Operations;

namespace Microsoft.CodeQuality.Analyzers.QualityGuidelines
{
    using static MicrosoftCodeQualityAnalyzersResources;

    /// <summary>
    /// CA1821: <inheritdoc cref="RemoveEmptyFinalizers"/>
    /// </summary>
    [DiagnosticAnalyzer(LanguageNames.CSharp, LanguageNames.VisualBasic)]
    public sealed class RemoveEmptyFinalizersAnalyzer : DiagnosticAnalyzer
    {
        public const string RuleId = "CA1821";

        internal static readonly DiagnosticDescriptor Rule = DiagnosticDescriptorHelper.Create(
            RuleId,
            CreateLocalizableResourceString(nameof(RemoveEmptyFinalizers)),
            CreateLocalizableResourceString(nameof(RemoveEmptyFinalizers)),
            DiagnosticCategory.Performance,
            RuleLevel.BuildWarningCandidate,
            description: CreateLocalizableResourceString(nameof(RemoveEmptyFinalizersDescription)),
            isPortedFxCopRule: true,
            isDataflowRule: false);

        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } = ImmutableArray.Create(Rule);

        public override void Initialize(AnalysisContext context)
        {
            context.EnableConcurrentExecution();
            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);

            context.RegisterCompilationStartAction(context =>
            {
                if (!context.Compilation.TryGetOrCreateTypeByMetadataName(WellKnownTypeNames.SystemDiagnosticsConditionalAttribute, out var conditionalAttributeType))
                {
                    return;
                }

                context.RegisterOperationBlockAction(context =>
                {
                    if (context.OperationBlocks.Length != 1 ||
                        context.OperationBlocks[0] is not IBlockOperation blockOperation ||
                        context.OwningSymbol is not IMethodSymbol methodSymbol ||
                        !methodSymbol.IsDestructor())
                    {
                        return;
                    }

                    var isMethodSurroundedWithDirective = blockOperation.Syntax.Parent?.ContainsDirectives ?? false;

                    if (!blockOperation.HasAnyExplicitDescendant(op => CanDescendIntoOperation(op, conditionalAttributeType, isMethodSurroundedWithDirective)))
                    {
                        context.ReportDiagnostic(methodSymbol.CreateDiagnostic(Rule));
                    }
                });
            });
        }

        private static bool CanDescendIntoOperation(IOperation operation, INamedTypeSymbol conditionalAttributeType, bool isMethodSurroundedWithDirective)
        {
            if (operation.Kind == OperationKind.Throw)
            {
                return false;
            }

            if (operation.Kind == OperationKind.Invocation)
            {
                return isMethodSurroundedWithDirective
                    || !((IInvocationOperation)operation).TargetMethod.HasAnyAttribute(conditionalAttributeType);
            }

            return true;
        }
    }
}