// 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 Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.Diagnostics;
using Analyzer.Utilities;
using Analyzer.Utilities.Extensions;

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

    /// <summary>
    /// CA1028: <inheritdoc cref="EnumStorageShouldBeInt32Title"/>
    /// Implementation slightly modified from original FxCop after discussing with Nick Guerrera
    /// FxCop implementation used 2 distinct diagnostic messages depending on the underlying type of the enum
    /// In this implementation, we have only 1 diagnostic message - "If possible, make the underlying type of '{0}'  System.Int32 instead of {1}."
    /// </summary>
    [DiagnosticAnalyzer(LanguageNames.CSharp, LanguageNames.VisualBasic)]
    public sealed class EnumStorageShouldBeInt32Analyzer : DiagnosticAnalyzer
    {
        internal const string RuleId = "CA1028";

        internal static readonly DiagnosticDescriptor Rule = DiagnosticDescriptorHelper.Create(
            RuleId,
            CreateLocalizableResourceString(nameof(EnumStorageShouldBeInt32Title)),
            CreateLocalizableResourceString(nameof(EnumStorageShouldBeInt32Message)),
            DiagnosticCategory.Design,
            RuleLevel.CandidateForRemoval,
            description: CreateLocalizableResourceString(nameof(EnumStorageShouldBeInt32Description)),
            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(compilationContext =>
            {
                INamedTypeSymbol? flagsAttribute = compilationContext.Compilation.GetOrCreateTypeByMetadataName(WellKnownTypeNames.SystemFlagsAttribute);
                if (flagsAttribute == null)
                {
                    return;
                }

                compilationContext.RegisterSymbolAction(symbolContext => AnalyzeSymbol(symbolContext, flagsAttribute), SymbolKind.NamedType);
            });
        }

        private static void AnalyzeSymbol(SymbolAnalysisContext context, INamedTypeSymbol flagsAttribute)
        {
            var symbol = (INamedTypeSymbol)context.Symbol;

            if (symbol.TypeKind != TypeKind.Enum)
            {
                return;
            }

            SpecialType underlyingType = symbol.EnumUnderlyingType!.SpecialType;
            if (underlyingType == SpecialType.System_Int32)
            {
                return;
            }

            // Check accessibility of enum matches configuration or is public if not configured
            if (!context.Options.MatchesConfiguredVisibility(Rule, symbol, context.Compilation))
            {
                return;
            }

            // If enum is Int64 and has Flags attributes then exit
            if (underlyingType == SpecialType.System_Int64 && symbol.HasAnyAttribute(flagsAttribute))
            {
                return;
            }

            context.ReportDiagnostic(symbol.CreateDiagnostic(Rule, symbol.Name, symbol.EnumUnderlyingType));
        }
    }
}