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

using Analyzer.Utilities;
using Analyzer.Utilities.Extensions;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.Diagnostics;
using Microsoft.NetCore.Analyzers.Usage;

namespace Microsoft.NetCore.CSharp.Analyzers.Usage
{
    [DiagnosticAnalyzer(LanguageNames.CSharp)]
    public sealed class CSharpMissingShebangInFileBasedProgram : MissingShebangInFileBasedProgram
    {
        public override void Initialize(AnalysisContext context)
        {
            context.EnableConcurrentExecution();
            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);

            context.RegisterCompilationStartAction(context =>
            {
                var entryPointFilePath = context.Options.GetMSBuildPropertyValue(
                    MSBuildPropertyOptionNames.EntryPointFilePath, context.Compilation);
                if (string.IsNullOrEmpty(entryPointFilePath))
                {
                    return;
                }

                // Count non-generated trees upfront so we can report directly
                // from a SyntaxTreeAction without needing CompilationEnd.
                // We avoid CompilationEnd so diagnostics appear as live IDE diagnostics.
                // We replicate Roslyn's generated code detection here because
                // Compilation.SyntaxTrees is the raw set (unlike RegisterSyntaxTreeAction
                // which gets automatic filtering via ConfigureGeneratedCodeAnalysis).
                int nonGeneratedTreeCount = 0;
                foreach (var tree in context.Compilation.SyntaxTrees)
                {
                    if (IsGeneratedCode(tree, context.Options.AnalyzerConfigOptionsProvider))
                    {
                        continue;
                    }

                    nonGeneratedTreeCount++;
                }

                // Only report when there are multiple non-generated files
                // (i.e., #:include directives are used).
                // Single-file programs don't need a shebang to distinguish the entry point.
                if (nonGeneratedTreeCount <= 1)
                {
                    return;
                }

                context.RegisterSyntaxTreeAction(context =>
                {
                    if (!context.Tree.FilePath.Equals(entryPointFilePath, StringComparison.Ordinal))
                    {
                        return;
                    }

                    var root = context.Tree.GetRoot(context.CancellationToken);
                    if (root.GetLeadingTrivia().Any(SyntaxKind.ShebangDirectiveTrivia))
                    {
                        return;
                    }

                    var location = root.GetFirstToken(includeZeroWidth: true).GetLocation();
                    context.ReportDiagnostic(location.CreateDiagnostic(Rule));
                });
            });
        }

        /// <summary>
        /// Replicates Roslyn's generated code detection which checks:
        /// the <c>generated_code</c> analyzer config option,
        /// common file name patterns, and <c>&lt;auto-generated&gt;</c> comment headers.
        /// Based on <see href="https://github.com/dotnet/roslyn/blob/0504782ef845507260874f2efc253b36d1775685/src/Compilers/Core/Portable/SourceGeneration/GeneratedCodeUtilities.cs">GeneratedCodeUtilities</see>.
        /// </summary>
        private static bool IsGeneratedCode(SyntaxTree tree, AnalyzerConfigOptionsProvider optionsProvider)
        {
            if (optionsProvider.GetOptions(tree)
                    .TryGetValue("generated_code", out var generatedValue) &&
                generatedValue.Equals("true", StringComparison.OrdinalIgnoreCase))
            {
                return true;
            }

            var filePath = tree.FilePath;
            if (!string.IsNullOrEmpty(filePath))
            {
                var fileName = Path.GetFileName(filePath);
                if (fileName.StartsWith("TemporaryGeneratedFile_", StringComparison.OrdinalIgnoreCase))
                {
                    return true;
                }

                var nameWithoutExtension = Path.GetFileNameWithoutExtension(fileName);
                if (nameWithoutExtension.EndsWith(".designer", StringComparison.OrdinalIgnoreCase) ||
                    nameWithoutExtension.EndsWith(".generated", StringComparison.OrdinalIgnoreCase) ||
                    nameWithoutExtension.EndsWith(".g", StringComparison.OrdinalIgnoreCase) ||
                    nameWithoutExtension.EndsWith(".g.i", StringComparison.OrdinalIgnoreCase))
                {
                    return true;
                }
            }

            // Check for <auto-generated> or <autogenerated> comment at the top of the file.
            foreach (var trivia in tree.GetRoot().GetLeadingTrivia())
            {
                switch (trivia.Kind())
                {
                    case SyntaxKind.SingleLineCommentTrivia:
                    case SyntaxKind.MultiLineCommentTrivia:
                        var text = trivia.ToString();
                        if (text.Contains("<auto-generated") || text.Contains("<autogenerated"))
                        {
                            return true;
                        }
                        break;
                    case SyntaxKind.WhitespaceTrivia:
                    case SyntaxKind.EndOfLineTrivia:
                        continue;
                    default:
                        return false;
                }
            }

            return false;
        }
    }
}