// 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.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeFixes;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Editing;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Text;
 
namespace Microsoft.CodeAnalysis.CSharp.ReplaceDefaultLiteral;
 
[ExportCodeFixProvider(LanguageNames.CSharp, Name = PredefinedCodeFixProviderNames.ReplaceDefaultLiteral), 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 CSharpReplaceDefaultLiteralCodeFixProvider() : CodeFixProvider
{
    private const string CS8313 = nameof(CS8313); // A default literal 'default' is not valid as a case constant. Use another literal (e.g. '0' or 'null') as appropriate. If you intended to write the default label, use 'default:' without 'case'.
    private const string CS8505 = nameof(CS8505); // A default literal 'default' is not valid as a pattern. Use another literal (e.g. '0' or 'null') as appropriate. To match everything, use a discard pattern 'var _'.
 
    public override ImmutableArray<string> FixableDiagnosticIds { get; } = [CS8313, CS8505];
 
    public override FixAllProvider? GetFixAllProvider()
    {
        // This code fix addresses very specific compiler errors. It's unlikely there will be more than 1 of them at a time.
        return null;
    }
 
    public override async Task RegisterCodeFixesAsync(CodeFixContext context)
    {
        var syntaxRoot = await context.Document.GetRequiredSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
        var token = syntaxRoot.FindToken(context.Span.Start);
 
        if (token.Span == context.Span &&
            token.IsKind(SyntaxKind.DefaultKeyword) &&
            token.Parent is LiteralExpressionSyntax(SyntaxKind.DefaultLiteralExpression) defaultLiteral)
        {
            var semanticModel = await context.Document.GetRequiredSemanticModelAsync(context.CancellationToken).ConfigureAwait(false);
 
            var (newExpression, displayText) = GetReplacementExpressionAndText(
                context.Document, semanticModel, defaultLiteral, context.CancellationToken);
 
            if (newExpression != null)
            {
                context.RegisterCodeFix(
                    CodeAction.Create(
                        string.Format(CSharpCodeFixesResources.Use_0, displayText),
                        c => ReplaceAsync(context.Document, context.Span, newExpression, c),
                        nameof(CSharpCodeFixesResources.Use_0)),
                    context.Diagnostics);
            }
        }
    }
 
    private static async Task<Document> ReplaceAsync(
        Document document, TextSpan span, SyntaxNode newExpression, CancellationToken cancellationToken)
    {
        var syntaxRoot = await document.GetRequiredSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
 
        var defaultToken = syntaxRoot.FindToken(span.Start);
        var defaultLiteral = (LiteralExpressionSyntax)defaultToken.GetRequiredParent();
 
        var newRoot = syntaxRoot.ReplaceNode(defaultLiteral, newExpression.WithTriviaFrom(defaultLiteral));
        return document.WithSyntaxRoot(newRoot);
    }
 
    private static (SyntaxNode newExpression, string displayText) GetReplacementExpressionAndText(
        Document document,
        SemanticModel semanticModel,
        LiteralExpressionSyntax defaultLiteral,
        CancellationToken cancellationToken)
    {
        var generator = SyntaxGenerator.GetGenerator(document);
 
        var type = semanticModel.GetTypeInfo(defaultLiteral, cancellationToken).ConvertedType;
        if (type != null && type.TypeKind != TypeKind.Error)
        {
            if (IsFlagsEnum(type, semanticModel.Compilation) &&
                type.GetMembers("None").FirstOrDefault() is IFieldSymbol field && IsZero(field.ConstantValue))
            {
                return GenerateMemberAccess("None");
            }
            else if (type.Equals(semanticModel.Compilation.GetTypeByMetadataName(typeof(CancellationToken).FullName!)))
            {
                return GenerateMemberAccess(nameof(CancellationToken.None));
            }
            else if (type.SpecialType is SpecialType.System_IntPtr or SpecialType.System_UIntPtr)
            {
                return GenerateMemberAccess(nameof(IntPtr.Zero));
            }
            else if (semanticModel.GetConstantValue(defaultLiteral, cancellationToken) is var constant && constant.HasValue)
            {
                var newLiteral = generator.LiteralExpression(constant.Value);
                return (newLiteral, newLiteral.ToString());
            }
            else if (!type.ContainsAnonymousType())
            {
                var defaultExpression = generator.DefaultExpression(type);
                return (defaultExpression, $"default({type.ToDisplayString(SymbolDisplayFormat.MinimallyQualifiedFormat)})");
            }
        }
 
        return default;
 
        (SyntaxNode newExpression, string displayText) GenerateMemberAccess(string memberName)
        {
            var memberAccess = generator.MemberAccessExpression(generator.TypeExpression(type), memberName);
            return (memberAccess, $"{type.ToDisplayString(SymbolDisplayFormat.MinimallyQualifiedFormat)}.{memberName}");
        }
    }
 
    private static bool IsFlagsEnum(ITypeSymbol type, Compilation compilation)
    {
        var flagsAttribute = compilation.GetTypeByMetadataName(typeof(FlagsAttribute).FullName!);
        return type.TypeKind == TypeKind.Enum &&
               flagsAttribute != null &&
               type.HasAttribute(flagsAttribute);
    }
 
    private static bool IsZero(object? o)
    {
        switch (o)
        {
            case default(int):
            case default(uint):
            case default(byte):
            case default(sbyte):
            case default(short):
            case default(ushort):
            case default(long):
            case default(ulong):
                return true;
            default:
                return false;
        }
    }
}