// 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 Microsoft.CodeAnalysis.CodeQuality;
using Microsoft.CodeAnalysis.CodeStyle;
using Microsoft.CodeAnalysis.Diagnostics;
using Microsoft.DotNet.FileBasedPrograms;
 
namespace Microsoft.CodeAnalysis.FileBasedPrograms;
 
[DiagnosticAnalyzer(LanguageNames.CSharp)]
internal sealed class FileLevelDirectiveDiagnosticAnalyzer()
    : AbstractCodeQualityDiagnosticAnalyzer(
        descriptors: [s_descriptor],
        generatedCodeAnalysisFlags: GeneratedCodeAnalysisFlags.Analyze | GeneratedCodeAnalysisFlags.ReportDiagnostics)
{
    public const string DiagnosticId = "FileBasedPrograms";
 
    private static readonly DiagnosticDescriptor s_descriptor = CreateDescriptor(
                id: DiagnosticId,
                enforceOnBuild: EnforceOnBuild.Never,
                title: DiagnosticId,
                messageFormat: "{0}",
                hasAnyCodeStyleOption: false,
                isUnnecessary: false,
                isEnabledByDefault: true,
                isConfigurable: false,
                defaultSeverity: DiagnosticSeverity.Error,
                helpLinkUri: "https://learn.microsoft.com/dotnet/csharp/language-reference/preprocessor-directives#file-based-apps");
 
    public override DiagnosticAnalyzerCategory GetAnalyzerCategory()
        => DiagnosticAnalyzerCategory.SyntaxTreeWithoutSemanticsAnalysis;
 
    protected override void InitializeWorker(AnalysisContext context)
    {
        context.RegisterSyntaxTreeAction(context =>
        {
            var cancellationToken = context.CancellationToken;
            var tree = context.Tree;
            if (!tree.Options.Features.ContainsKey("FileBasedProgram"))
                return;
 
            var root = tree.GetRoot(cancellationToken);
            if (!root.ContainsDirectives)
                return;
 
            // The compiler already reports an error on all the directives past the first token in the file.
            // Therefore, the analyzer only deals with the directives on the first token.
            //     Console.WriteLine("Hello World!");
            //     #:property foo=bar // error CS9297: '#:' directives cannot be after first token in file
            var diagnosticBag = DiagnosticBag.Collect(out var diagnosticsBuilder);
            FileLevelDirectiveHelpers.FindLeadingDirectives(
                new SourceFile(tree.FilePath, tree.GetText(cancellationToken)),
                root.GetLeadingTrivia(),
                diagnosticBag,
                builder: null);
 
            foreach (var simpleDiagnostic in diagnosticsBuilder)
            {
                context.ReportDiagnostic(Diagnostic.Create(
                    s_descriptor,
                    location: Location.Create(tree, simpleDiagnostic.Location.TextSpan),
                    simpleDiagnostic.Message));
            }
        });
    }
}