// 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.Collections.Immutable;
using System.Composition;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CodeRefactorings;
using Microsoft.CodeAnalysis.CodeRefactorings.SyncNamespace;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Text;

namespace Microsoft.CodeAnalysis.CSharp.CodeRefactorings.SyncNamespace;

[ExportCodeRefactoringProvider(LanguageNames.CSharp, Name = PredefinedCodeRefactoringProviderNames.SyncNamespace), 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 CSharpSyncNamespaceCodeRefactoringProvider()
        : AbstractSyncNamespaceCodeRefactoringProvider<BaseNamespaceDeclarationSyntax, CompilationUnitSyntax, MemberDeclarationSyntax>
{
    protected override async Task<SyntaxNode?> TryGetApplicableInvocationNodeAsync(Document document, TextSpan span, CancellationToken cancellationToken)
    {
        if (!span.IsEmpty)
            return null;

        if (await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false) is not CompilationUnitSyntax compilationUnit)
            return null;

        var position = span.Start;
        var namespaceDecls = compilationUnit.DescendantNodes(n => n is CompilationUnitSyntax or BaseNamespaceDeclarationSyntax)
            .OfType<BaseNamespaceDeclarationSyntax>().ToImmutableArray();

        if (namespaceDecls.Length == 1 && compilationUnit.Members.Count == 1)
        {
            var namespaceDeclaration = namespaceDecls[0];
            if (namespaceDeclaration.Name.Span.IntersectsWith(position))
                return namespaceDeclaration;
        }

        if (namespaceDecls.Length == 0)
        {
            var firstMemberDeclarationName = compilationUnit.Members.FirstOrDefault().GetNameToken();

            if (firstMemberDeclarationName != default
                && firstMemberDeclarationName.Span.IntersectsWith(position))
            {
                return compilationUnit;
            }
        }

        return null;
    }
}