using System.Linq;
using System.Text;
using GFramework.SourceGenerators.Common.diagnostics;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;

namespace GFramework.SourceGenerators.rule;

[Generator]
public sealed class ContextAwareGenerator : IIncrementalGenerator
{
    private const string AttributeMetadataName =
        "GFramework.SourceGenerators.Attributes.rule.ContextAwareAttribute";

    public void Initialize(IncrementalGeneratorInitializationContext context)
    {
        // 1. 找到所有 class 声明
        var classDeclarations = context.SyntaxProvider
            .CreateSyntaxProvider(
                predicate: static (node, _) => node is ClassDeclarationSyntax,
                transform: static (ctx, _) => GetCandidate(ctx)
            )
            .Where(static s => s is not null);

        // 2. 生成代码
        context.RegisterSourceOutput(
            classDeclarations,
            static (spc, source) => Generate(spc, source!)
        );
    }

    private static INamedTypeSymbol? GetCandidate(GeneratorSyntaxContext context)
    {
        var classDecl = (ClassDeclarationSyntax)context.Node;

        if (classDecl.AttributeLists.Count == 0)
            return null;

        if (context.SemanticModel.GetDeclaredSymbol(classDecl)
            is not { } symbol)
            return null;

        return Enumerable.Any(symbol.GetAttributes(),
            attr => attr.AttributeClass?.ToDisplayString() == AttributeMetadataName)
            ? symbol
            : null;
    }


    private static void Generate(
        SourceProductionContext context,
        INamedTypeSymbol symbol)
    {
        var syntax = symbol.DeclaringSyntaxReferences
            .FirstOrDefault()?
            .GetSyntax() as ClassDeclarationSyntax;

        if (syntax is null || !syntax.Modifiers.Any(SyntaxKind.PartialKeyword))
        {
            context.ReportDiagnostic(
                Diagnostic.Create(
                    CommonDiagnostics.ClassMustBePartial,
                    syntax?.Identifier.GetLocation(),
                    symbol.Name
                )
            );
            return;
        }

        var ns = symbol.ContainingNamespace.IsGlobalNamespace
            ? null
            : symbol.ContainingNamespace.ToDisplayString();

        var source = GenerateSource(ns, symbol);

        context.AddSource(
            $"{symbol.Name}.ContextAware.g.cs",
            source
        );
    }

    private static string GenerateSource(string? ns, INamedTypeSymbol symbol)
    {
        var sb = new StringBuilder();

        sb.AppendLine("// <auto-generated/>");
        sb.AppendLine("#nullable enable");

        if (ns is not null)
        {
            sb.AppendLine($"namespace {ns};");
            sb.AppendLine();
        }

        sb.AppendLine($"partial class {symbol.Name} : GFramework.Core.rule.IContextAware");
        sb.AppendLine("{");

        sb.AppendLine(
            "    protected GFramework.Core.architecture.IArchitectureContext Context { get; private set; } = null!;");

        sb.AppendLine("""
                          void GFramework.Core.rule.IContextAware.SetContext(
                              GFramework.Core.architecture.IArchitectureContext context)
                          {
                              Context = context;
                          }
                      """);

        sb.AppendLine("}");

        return sb.ToString();
    }
}