OpenApiTransformerGenerator.cs

using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Text;

namespace ErrorOr.Generators;

/// <summary>
///     Generates OpenAPI transformers from XML documentation on ErrorOr endpoints.
/// </summary>
[Generator(LanguageNames.CSharp)]
public sealed class OpenApiTransformerGenerator : IIncrementalGenerator
{
    /// <inheritdoc />
    public void Initialize(IncrementalGeneratorInitializationContext context)
    {
        // Attributes are emitted by ErrorOrEndpointGenerator (shared across both generators)
        var endpoints = CombineHttpMethodProviders(context);

        var typeMetadata = context.SyntaxProvider
            .CreateSyntaxProvider(
                static (node, _) => node is TypeDeclarationSyntax,
                static (ctx, ct) => ExtractTypeMetadata(ctx, ct))
            .WhereNotNull()
            .CollectAsEquatableArray();

        context.RegisterSourceOutput(
            endpoints.Combine(typeMetadata),
            static (spc, data) => Emit(spc, data.Left.AsImmutableArray(), data.Right.AsImmutableArray()));
    }

    private static IncrementalValueProvider<EquatableArray<OpenApiEndpointInfo>> CombineHttpMethodProviders(
        IncrementalGeneratorInitializationContext context)
    {
        return IncrementalProviderExtensions.CombineAll(
            CreateEndpointProvider(context, WellKnownTypes.GetAttribute),
            CreateEndpointProvider(context, WellKnownTypes.PostAttribute),
            CreateEndpointProvider(context, WellKnownTypes.PutAttribute),
            CreateEndpointProvider(context, WellKnownTypes.DeleteAttribute),
            CreateEndpointProvider(context, WellKnownTypes.PatchAttribute),
            CreateEndpointProvider(context, WellKnownTypes.HeadAttribute),
            CreateEndpointProvider(context, WellKnownTypes.OptionsAttribute),
            CreateEndpointProvider(context, WellKnownTypes.TraceAttribute),
            CreateEndpointProvider(context, WellKnownTypes.ErrorOrEndpointAttribute));
    }

    private static IncrementalValuesProvider<OpenApiEndpointInfo> CreateEndpointProvider(
        IncrementalGeneratorInitializationContext context,
        string attributeName)
    {
        return context.SyntaxProvider
            .ForAttributeWithMetadataName(
                attributeName,
                static (node, _) => node is MethodDeclarationSyntax,
                static (ctx, ct) => ExtractOpenApiMetadata(ctx, ct))
            .WhereNotNull();
    }

    private static OpenApiEndpointInfo? ExtractOpenApiMetadata(
        GeneratorAttributeSyntaxContext ctx,
        CancellationToken ct)
    {
        ct.ThrowIfCancellationRequested();

        if (ctx.TargetSymbol is not IMethodSymbol { IsStatic: true } method) return null;

        // Extract HTTP method and pattern from attribute
        // Combined null check: attr exists AND has a valid AttributeClass
        if (ctx.Attributes.FirstOrDefault() is not { AttributeClass: { } attrClass } attr) return null;

        var attrClassName = attrClass.ToDisplayString();

        var (httpMethod, pattern) = attrClassName switch
        {
            WellKnownTypes.GetAttribute => (WellKnownTypes.HttpMethod.Get, GetPattern(attr)),
            WellKnownTypes.PostAttribute => (WellKnownTypes.HttpMethod.Post, GetPattern(attr)),
            WellKnownTypes.PutAttribute => (WellKnownTypes.HttpMethod.Put, GetPattern(attr)),
            WellKnownTypes.DeleteAttribute => (WellKnownTypes.HttpMethod.Delete, GetPattern(attr)),
            WellKnownTypes.PatchAttribute => (WellKnownTypes.HttpMethod.Patch, GetPattern(attr)),
            WellKnownTypes.HeadAttribute => (WellKnownTypes.HttpMethod.Head, GetPattern(attr)),
            WellKnownTypes.OptionsAttribute => (WellKnownTypes.HttpMethod.Options, GetPattern(attr)),
            WellKnownTypes.TraceAttribute => (WellKnownTypes.HttpMethod.Trace, GetPattern(attr)),
            WellKnownTypes.ErrorOrEndpointAttribute => GetBaseAttributeInfo(attr),
            _ => (null, null)
        };

        if (httpMethod is null || pattern is null) return null;

        // Extract XML documentation
        var xmlDoc = method.GetDocumentationCommentXml(cancellationToken: ct);
        var (summary, description) = ParseXmlDoc(xmlDoc);
        var parameterDocs = ParseParamTags(xmlDoc);

        // Extract containing type info for tag generation
        var containingType = method.ContainingType;
        var containingTypeFqn = containingType.GetFullyQualifiedName();
        var (tagName, operationId) = EndpointNameHelper.GetEndpointIdentity(containingTypeFqn, method.Name);

        var parameters = ExtractParameterDefinitions(method, pattern);

        return new OpenApiEndpointInfo(
            operationId,
            tagName,
            summary,
            description,
            httpMethod.ToUpperInvariant(),
            pattern,
            new EquatableArray<(string, string)>(parameterDocs),
            new EquatableArray<OpenApiParameterInfo>(parameters));
    }

    private static string GetPattern(AttributeData attr)
    {
        if (attr.ConstructorArguments.Length > 0 &&
            attr.ConstructorArguments[0].Value is string p &&
            !string.IsNullOrWhiteSpace(p))
        {
            return p;
        }

        return "/";
    }

    private static (string? httpMethod, string? pattern) GetBaseAttributeInfo(AttributeData attr)
    {
        if (attr.ConstructorArguments.Length < 2) return (null, null);

        var method = attr.ConstructorArguments[0].Value as string;
        var pattern = attr.ConstructorArguments[1].Value as string;

        return string.IsNullOrWhiteSpace(method)
            ? (null, null)
            : (method, string.IsNullOrWhiteSpace(pattern) ? "/" : pattern);
    }

    private static (string? summary, string? description) ParseXmlDoc(string? xml)
    {
        if (xml is null || string.IsNullOrWhiteSpace(xml)) return (null, null);

        string? summary = null;
        string? description = null;

        // Simple XML parsing for summary and remarks
        var summaryStart = xml.IndexOfOrdinal("<summary>");
        var summaryEnd = xml.IndexOfOrdinal("</summary>");
        if (summaryStart >= 0 && summaryEnd > summaryStart)
        {
            summary = xml.Substring(summaryStart + 9, summaryEnd - summaryStart - 9)
                .Trim()
                .Replace("\r\n", " ")
                .Replace('\n', ' ')
                .Trim();
        }

        var remarksStart = xml.IndexOfOrdinal("<remarks>");
        var remarksEnd = xml.IndexOfOrdinal("</remarks>");
        if (remarksStart >= 0 && remarksEnd > remarksStart)
        {
            description = xml.Substring(remarksStart + 9, remarksEnd - remarksStart - 9)
                .Trim()
                .Replace("\r\n", " ")
                .Replace('\n', ' ')
                .Trim();
        }

        return (summary, description);
    }

    private static ImmutableArray<(string ParamName, string Description)> ParseParamTags(string? xml)
    {
        if (xml is null || string.IsNullOrWhiteSpace(xml)) return ImmutableArray<(string, string)>.Empty;

        var parameters = new List<(string, string)>();
        var searchPos = 0;

        while (true)
        {
            var paramStart = xml.IndexOf("<param name=\"", searchPos, StringComparison.Ordinal);
            if (paramStart < 0) break;

            var nameStart = paramStart + 13;
            var nameEnd = xml.IndexOf('"', nameStart);
            if (nameEnd < 0) break;

            var paramName = xml.Substring(nameStart, nameEnd - nameStart);

            var contentStart = xml.IndexOf(">", nameEnd, StringComparison.Ordinal);
            if (contentStart < 0) break;

            contentStart++;

            var contentEnd = xml.IndexOf("</param>", contentStart, StringComparison.Ordinal);
            if (contentEnd < 0) break;

            var description = xml.Substring(contentStart, contentEnd - contentStart)
                .Trim()
                .Replace("\r\n", " ")
                .Replace("\n", " ")
                .Trim();
            if (!string.IsNullOrWhiteSpace(description)) parameters.Add((paramName, description));

            searchPos = contentEnd + 8;
        }

        return [.. parameters];
    }

    private static ImmutableArray<OpenApiParameterInfo> ExtractParameterDefinitions(
        IMethodSymbol method, string pattern)
    {
        var routeParams = RouteValidator.ExtractRouteParameters(pattern);
        var routeParamNames = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        foreach (var rp in routeParams)
            routeParamNames.Add(rp.Name);

        var parameters = new List<OpenApiParameterInfo>();

        foreach (var param in method.Parameters)
        {
            var typeFqn = param.Type.ToDisplayString();

            // Skip special types (services, context, etc.)
            if (IsSkippedParameterType(param, typeFqn)) continue;

            // Check explicit binding attributes
            var (explicitLocation, explicitName) = GetExplicitBinding(param);

            string name;
            string location;
            bool required;

            if (explicitLocation is not null)
            {
                // Explicit attribute wins
                name = explicitName ?? param.Name;
                location = explicitLocation;
                required = location == "path" ||
                           (param.Type.NullableAnnotation != NullableAnnotation.Annotated &&
                            !param.HasExplicitDefaultValue);
            }
            else if (routeParamNames.Contains(param.Name))
            {
                // Route parameter
                name = param.Name;
                location = "path";
                required = true;

                // Check if optional in route template
                foreach (var rp in routeParams)
                {
                    if (string.Equals(rp.Name, param.Name, StringComparison.OrdinalIgnoreCase) && rp.IsOptional)
                    {
                        required = false;
                        break;
                    }
                }
            }
            else if (IsPrimitiveType(typeFqn))
            {
                // Primitive not in route = query
                name = param.Name;
                location = "query";
                required = param.Type.NullableAnnotation != NullableAnnotation.Annotated &&
                           !param.HasExplicitDefaultValue;
            }
            else
            {
                // Complex type without explicit binding - skip (it's body or service)
                continue;
            }

            var (schemaType, schemaFormat) = GetOpenApiSchema(typeFqn);
            parameters.Add(new OpenApiParameterInfo(name, location, required, schemaType, schemaFormat));
        }

        return [.. parameters];
    }

    private static bool IsSkippedParameterType(IParameterSymbol param, string typeFqn)
    {
        // Skip special framework types
        if (typeFqn is WellKnownTypes.HttpContext or WellKnownTypes.CancellationToken
            or WellKnownTypes.FormFile or WellKnownTypes.FormFileCollection
            or WellKnownTypes.Stream or WellKnownTypes.PipeReader or WellKnownTypes.FormCollection)
        {
            return true;
        }

        // Skip interface types (services)
        if (param.Type.TypeKind == TypeKind.Interface) return true;

        // Skip abstract types (services)
        if (param.Type is { IsAbstract: true, TypeKind: TypeKind.Class }) return true;

        // Skip [FromServices] / [FromKeyedServices] / [FromBody] / [FromForm]
        foreach (var attr in param.GetAttributes())
        {
            var attrName = attr.AttributeClass?.ToDisplayString();
            if (attrName is WellKnownTypes.FromServicesAttribute or WellKnownTypes.FromBodyAttribute
                or WellKnownTypes.FromFormAttribute or WellKnownTypes.FromKeyedServicesAttribute)
            {
                return true;
            }
        }

        return false;
    }

    private static (string? Location, string? Name) GetExplicitBinding(ISymbol param)
    {
        foreach (var attr in param.GetAttributes())
        {
            var attrName = attr.AttributeClass?.ToDisplayString();
            switch (attrName)
            {
                case WellKnownTypes.FromRouteAttribute:
                {
                    var name = GetAttributeStringArg(attr, "Name");
                    return ("path", name);
                }
                case WellKnownTypes.FromQueryAttribute:
                {
                    var name = GetAttributeStringArg(attr, "Name");
                    return ("query", name);
                }
                case WellKnownTypes.FromHeaderAttribute:
                {
                    var name = GetAttributeStringArg(attr, "Name");
                    return ("header", name);
                }
            }
        }

        return (null, null);
    }

    private static string? GetAttributeStringArg(AttributeData attr, string propName)
    {
        foreach (var kvp in attr.NamedArguments)
        {
            if (kvp.Key == propName && kvp.Value.Value is string s && !string.IsNullOrWhiteSpace(s))
                return s;
        }

        return null;
    }

    private static bool IsPrimitiveType(string typeFqn)
    {
        // Strip nullable wrapper
        var type = typeFqn.EndsWithOrdinal("?") ? typeFqn.Substring(0, typeFqn.Length - 1) : typeFqn;

        return type is "int" or "System.Int32"
            or "long" or "System.Int64"
            or "short" or "System.Int16"
            or "uint" or "System.UInt32"
            or "ulong" or "System.UInt64"
            or "ushort" or "System.UInt16"
            or "byte" or "System.Byte"
            or "sbyte" or "System.SByte"
            or "bool" or "System.Boolean"
            or "decimal" or "System.Decimal"
            or "double" or "System.Double"
            or "float" or "System.Single"
            or "string" or "System.String"
            or "System.Guid"
            or "System.DateTime"
            or "System.DateTimeOffset"
            or "System.DateOnly"
            or "System.TimeOnly"
            or "System.TimeSpan";
    }

    private static (string SchemaType, string? SchemaFormat) GetOpenApiSchema(string typeFqn)
    {
        // Strip nullable wrapper
        var type = typeFqn.EndsWithOrdinal("?") ? typeFqn.Substring(0, typeFqn.Length - 1) : typeFqn;

        return type switch
        {
            "int" or "System.Int32" => ("integer", "int32"),
            "long" or "System.Int64" => ("integer", "int64"),
            "short" or "System.Int16" => ("integer", "int16"),
            "uint" or "System.UInt32" => ("integer", "int32"),
            "ulong" or "System.UInt64" => ("integer", "int64"),
            "ushort" or "System.UInt16" => ("integer", "int16"),
            "byte" or "System.Byte" => ("integer", "int32"),
            "sbyte" or "System.SByte" => ("integer", "int32"),
            "bool" or "System.Boolean" => ("boolean", null),
            "decimal" or "System.Decimal" => ("number", "double"),
            "double" or "System.Double" => ("number", "double"),
            "float" or "System.Single" => ("number", "float"),
            "System.Guid" => ("string", "uuid"),
            "System.DateTime" => ("string", "date-time"),
            "System.DateTimeOffset" => ("string", "date-time"),
            "System.DateOnly" => ("string", "date"),
            "System.TimeOnly" => ("string", "time"),
            "System.TimeSpan" => ("string", "duration"),
            _ => ("string", null)
        };
    }

    /// <summary>
    ///     Maps internal schema type string to OpenApi v2.0 JsonSchemaType enum name for emission.
    /// </summary>
    private static string ToJsonSchemaTypeEnum(string schemaType)
    {
        return schemaType switch
        {
            "integer" => "JsonSchemaType.Integer",
            "number" => "JsonSchemaType.Number",
            "boolean" => "JsonSchemaType.Boolean",
            _ => "JsonSchemaType.String"
        };
    }

    private static string GetReflectionFullName(ISymbol symbol)
    {
        var fqn = ((ITypeSymbol)symbol).GetFullyQualifiedName();
        return fqn.StartsWithOrdinal("global::") ? fqn.Substring("global::".Length) : fqn;
    }

    private static TypeMetadataInfo? ExtractTypeMetadata(
        GeneratorSyntaxContext ctx,
        CancellationToken ct)
    {
        if (ctx.Node is not TypeDeclarationSyntax typeDecl) return null;

        // Skip null symbols and compiler-generated types
        if (ctx.SemanticModel.GetDeclaredSymbol(typeDecl, ct) is not INamedTypeSymbol symbol ||
            symbol.IsImplicitlyDeclared)
        {
            return null;
        }

        // Skip types without XML docs
        var xmlDoc = symbol.GetDocumentationCommentXml(cancellationToken: ct);
        if (string.IsNullOrWhiteSpace(xmlDoc)) return null;

        var (summary, _) = ParseXmlDoc(xmlDoc);
        if (summary is null) return null;

        var typeKey = GetReflectionFullName(symbol);

        return new TypeMetadataInfo(typeKey, summary);
    }

    private static void Emit(
        SourceProductionContext spc,
        ImmutableArray<OpenApiEndpointInfo> endpoints,
        ImmutableArray<TypeMetadataInfo> types)
    {
        if (endpoints.IsDefaultOrEmpty) return;

        var code = new StringBuilder();
        code.AppendLine("// <auto-generated/>");
        code.AppendLine("#nullable enable");
        code.AppendLine();
        code.AppendLine("using System;");
        code.AppendLine("using System.Collections.Frozen;");
        code.AppendLine("using System.Collections.Generic;");
        code.AppendLine("using System.Threading;");
        code.AppendLine("using System.Threading.Tasks;");
        code.AppendLine("using Microsoft.AspNetCore.OpenApi;");
        code.AppendLine("using Microsoft.AspNetCore.Routing;");
        code.AppendLine("using Microsoft.Extensions.DependencyInjection;");
        code.AppendLine("using Microsoft.OpenApi;");
        code.AppendLine();
        code.AppendLine("namespace ErrorOr.Generated;");
        code.AppendLine();

        // Collect unique tags (1 attribute → 1 transformer)
        var tags = endpoints.Select(static e => e.TagName).Distinct(StringComparer.Ordinal)
            .OrderBy(static t => t, StringComparer.Ordinal).ToList();

        // Emit tag transformers (strict 1:1 - one transformer per unique tag)
        foreach (var tag in tags) EmitTagTransformer(code, tag);

        // Emit operation transformer (applies XML doc summaries)
        var hasOperationDocs = EmitOperationTransformer(code, endpoints);

        // Emit schema transformer (applies type descriptions)
        var hasTypeDocs = false;
        if (!types.IsDefaultOrEmpty) hasTypeDocs = EmitSchemaTransformer(code, types);

        // Emit registration extension
        EmitRegistrationExtension(code, tags, hasOperationDocs, hasTypeDocs);

        spc.AddSource("OpenApiTransformers.g.cs", SourceText.From(code.ToString(), Encoding.UTF8));
    }

    private static void EmitTagTransformer(StringBuilder code, string tagName)
    {
        var safeTagName = tagName.SanitizeIdentifier();
        code.AppendLine("/// <summary>");
        code.AppendLine($"/// Document transformer for tag: {tagName}");
        code.AppendLine($"/// Generated from: [ErrorOrEndpoint] attribute on *{tagName}Endpoints class");
        code.AppendLine("/// </summary>");
        code.AppendLine($"file sealed class Tag_{safeTagName}_Transformer : IOpenApiDocumentTransformer");
        code.AppendLine("{");
        code.AppendLine("    public Task TransformAsync(");
        code.AppendLine("        OpenApiDocument document,");
        code.AppendLine("        OpenApiDocumentTransformerContext context,");
        code.AppendLine("        CancellationToken cancellationToken)");
        code.AppendLine("    {");
        // OpenApiDocument.Tags setter auto-wraps with OpenApiTagComparer.Instance
        // which handles deduplication by Name - no manual .Any() check needed
        code.AppendLine("        document.Tags ??= new HashSet<OpenApiTag>();");
        code.AppendLine($"        document.Tags.Add(new OpenApiTag {{ Name = \"{tagName}\" }});");
        code.AppendLine("        return Task.CompletedTask;");
        code.AppendLine("    }");
        code.AppendLine("}");
        code.AppendLine();
    }

    private static bool EmitOperationTransformer(StringBuilder code, ImmutableArray<OpenApiEndpointInfo> endpoints)
    {
        // Collect operations with XML docs (summary/description OR parameter docs)
        var opsWithDocs = endpoints
            .Where(static e => !string.IsNullOrEmpty(e.Summary) || !string.IsNullOrEmpty(e.Description) ||
                               !e.ParameterDocs.IsDefaultOrEmpty)
            .OrderBy(static e => e.Pattern, StringComparer.Ordinal)
            .ThenBy(static e => e.HttpMethod, StringComparer.Ordinal).ToList();

        // Collect operations with OpenAPI parameter definitions
        var opsWithParams = endpoints
            .Where(static e => !e.Parameters.IsDefaultOrEmpty)
            .OrderBy(static e => e.OperationId, StringComparer.Ordinal)
            .ToList();

        if (opsWithDocs.Count is 0 && opsWithParams.Count is 0) return false;

        // Collect operations with parameter docs
        var opsWithParamDocs = opsWithDocs
            .Where(static e => !e.ParameterDocs.IsDefaultOrEmpty)
            .ToList();

        code.AppendLine("/// <summary>");
        code.AppendLine(
            "/// Operation transformer that applies XML documentation and parameter definitions to operations.");
        code.AppendLine("/// Each entry is a strict 1:1 mapping from handler signature to operation metadata.");
        code.AppendLine("/// </summary>");
        code.AppendLine("file sealed class XmlDocOperationTransformer : IOpenApiOperationTransformer");
        code.AppendLine("{");
        code.AppendLine("    // Pre-computed metadata from XML docs (compile-time extraction)");
        code.AppendLine(
            "    private static readonly FrozenDictionary<string, (string? Summary, string? Description)> OperationDocs =");
        code.AppendLine("        new Dictionary<string, (string? Summary, string? Description)>");
        code.AppendLine("        {");

        foreach (var op in opsWithDocs.Where(static e =>
                     !string.IsNullOrEmpty(e.Summary) || !string.IsNullOrEmpty(e.Description)))
        {
            var summary = op.Summary is not null ? $"\"{op.Summary.EscapeCSharpString()}\"" : "null";
            var description = op.Description is not null ? $"\"{op.Description.EscapeCSharpString()}\"" : "null";
            code.AppendLine($"            [\"{op.OperationId}\"] = ({summary}, {description}),");
        }

        code.AppendLine("        }.ToFrozenDictionary(StringComparer.Ordinal);");
        code.AppendLine();

        // Emit parameter docs dictionary
        code.AppendLine("    // Pre-computed parameter descriptions from XML <param> tags");
        code.AppendLine(
            "    private static readonly FrozenDictionary<string, FrozenDictionary<string, string>> ParameterDocs =");
        code.AppendLine("        new Dictionary<string, FrozenDictionary<string, string>>");
        code.AppendLine("        {");

        foreach (var op in opsWithParamDocs)
        {
            code.AppendLine($"            [\"{op.OperationId}\"] = new Dictionary<string, string>");
            code.AppendLine("            {");
            foreach (var (paramName, paramDesc) in op.ParameterDocs.AsImmutableArray())
            {
                code.AppendLine(
                    $"                [\"{paramName.EscapeCSharpString()}\"] = \"{paramDesc.EscapeCSharpString()}\",");
            }

            code.AppendLine("            }.ToFrozenDictionary(StringComparer.Ordinal),");
        }

        code.AppendLine("        }.ToFrozenDictionary(StringComparer.Ordinal);");
        code.AppendLine();

        // Emit parameter definitions dictionary
        if (opsWithParams.Count > 0)
        {
            code.AppendLine("    // Pre-computed parameter definitions from handler signatures");
            code.AppendLine(
                "    private static readonly FrozenDictionary<string, (string Name, ParameterLocation Location, bool Required, JsonSchemaType SchemaType, string? SchemaFormat)[]> ParameterDefs =");
            code.AppendLine(
                "        new Dictionary<string, (string, ParameterLocation, bool, JsonSchemaType, string?)[]>");
            code.AppendLine("        {");

            foreach (var op in opsWithParams)
            {
                code.Append($"            [\"{op.OperationId}\"] = [(");
                var first = true;
                foreach (var p in op.Parameters.AsImmutableArray())
                {
                    if (!first) code.Append("), (");

                    var format = p.SchemaFormat is not null ? $"\"{p.SchemaFormat}\"" : "null";
                    var locationEnum = p.Location switch
                    {
                        "path" => "ParameterLocation.Path",
                        "header" => "ParameterLocation.Header",
                        _ => "ParameterLocation.Query"
                    };
                    var schemaTypeEnum = ToJsonSchemaTypeEnum(p.SchemaType);
                    code.Append(
                        $"\"{p.Name}\", {locationEnum}, {(p.Required ? "true" : "false")}, {schemaTypeEnum}, {format}");
                    first = false;
                }

                code.AppendLine(")],");
            }

            code.AppendLine("        }.ToFrozenDictionary(StringComparer.Ordinal);");
            code.AppendLine();
        }

        code.AppendLine("    public Task TransformAsync(");
        code.AppendLine("        OpenApiOperation operation,");
        code.AppendLine("        OpenApiOperationTransformerContext context,");
        code.AppendLine("        CancellationToken cancellationToken)");
        code.AppendLine("    {");
        code.AppendLine("        string? operationId = null;");
        code.AppendLine("        var metadata = context.Description.ActionDescriptor?.EndpointMetadata;");
        code.AppendLine("        if (metadata is not null)");
        code.AppendLine("        {");
        code.AppendLine("            for (var i = 0; i < metadata.Count; i++)");
        code.AppendLine("            {");
        code.AppendLine("                if (metadata[i] is IEndpointNameMetadata nameMetadata)");
        code.AppendLine("                {");
        code.AppendLine("                    operationId = nameMetadata.EndpointName;");
        code.AppendLine("                    break;");
        code.AppendLine("                }");
        code.AppendLine("            }");
        code.AppendLine("        }");
        code.AppendLine();
        code.AppendLine("        if (operationId is null)");
        code.AppendLine("            return Task.CompletedTask;");
        code.AppendLine();
        code.AppendLine("        // Apply summary and description");
        code.AppendLine("        if (OperationDocs.TryGetValue(operationId, out var docs))");
        code.AppendLine("        {");
        code.AppendLine("            if (docs.Summary is not null)");
        code.AppendLine("                operation.Summary ??= docs.Summary;");
        code.AppendLine("            if (docs.Description is not null)");
        code.AppendLine("                operation.Description ??= docs.Description;");
        code.AppendLine("        }");
        code.AppendLine();

        // Emit parameter definitions application code
        if (opsWithParams.Count > 0)
        {
            code.AppendLine("        // Add parameter definitions from handler signatures");
            code.AppendLine("        if (ParameterDefs.TryGetValue(operationId, out var paramDefs))");
            code.AppendLine("        {");
            code.AppendLine("            operation.Parameters ??= [];");
            code.AppendLine(
                "            foreach (var (pName, pLocation, pRequired, pSchemaType, pSchemaFormat) in paramDefs)");
            code.AppendLine("            {");
            code.AppendLine("                var schema = new OpenApiSchema { Type = pSchemaType };");
            code.AppendLine("                if (pSchemaFormat is not null) schema.Format = pSchemaFormat;");
            code.AppendLine("                operation.Parameters.Add(new OpenApiParameter");
            code.AppendLine("                {");
            code.AppendLine("                    Name = pName,");
            code.AppendLine("                    In = pLocation,");
            code.AppendLine("                    Required = pRequired,");
            code.AppendLine("                    Schema = schema");
            code.AppendLine("                });");
            code.AppendLine("            }");
            code.AppendLine("        }");
            code.AppendLine();
        }

        code.AppendLine("        // Apply parameter descriptions");
        code.AppendLine(
            "        if (ParameterDocs.TryGetValue(operationId, out var paramDocs) && operation.Parameters is not null)");
        code.AppendLine("        {");
        code.AppendLine("            foreach (var param in operation.Parameters)");
        code.AppendLine("            {");
        code.AppendLine(
            "                if (param.Name is not null && paramDocs.TryGetValue(param.Name, out var paramDesc))");
        code.AppendLine("                {");
        code.AppendLine("                    param.Description ??= paramDesc;");
        code.AppendLine("                }");
        code.AppendLine("            }");
        code.AppendLine("        }");
        code.AppendLine();
        code.AppendLine("        return Task.CompletedTask;");
        code.AppendLine("    }");
        code.AppendLine("}");
        code.AppendLine();

        return true;
    }

    private static bool EmitSchemaTransformer(StringBuilder code, ImmutableArray<TypeMetadataInfo> types)
    {
        var typesWithDocs = types.OrderBy(static t => t.TypeKey, StringComparer.Ordinal).ToList();

        if (typesWithDocs.Count is 0) return false;

        code.AppendLine("/// <summary>");
        code.AppendLine("/// Schema transformer that applies type XML documentation to schemas.");
        code.AppendLine("/// Each entry is a strict 1:1 mapping from XML doc to schema description.");
        code.AppendLine("/// AOT-safe: Uses Type as dictionary key (no runtime reflection).");
        code.AppendLine("/// </summary>");
        code.AppendLine("file sealed class XmlDocSchemaTransformer : IOpenApiSchemaTransformer");
        code.AppendLine("{");
        code.AppendLine(
            "    // Pre-computed type descriptions from XML docs (AOT-safe: Type keys resolved at compile-time)");
        code.AppendLine("    private static readonly FrozenDictionary<Type, string> TypeDescriptions =");
        code.AppendLine("        new Dictionary<Type, string>");
        code.AppendLine("        {");

        foreach (var type in typesWithDocs)
        {
            // Convert reflection-style name (Namespace.Outer+Inner) to C# typeof expression (global::Namespace.Outer.Inner)
            var typeofExpr = ConvertToTypeofExpression(type.TypeKey);
            code.AppendLine($"            [typeof({typeofExpr})] = \"{type.Description.EscapeCSharpString()}\",");
        }

        code.AppendLine("        }.ToFrozenDictionary();");
        code.AppendLine();
        code.AppendLine("    public Task TransformAsync(");
        code.AppendLine("        OpenApiSchema schema,");
        code.AppendLine("        OpenApiSchemaTransformerContext context,");
        code.AppendLine("        CancellationToken cancellationToken)");
        code.AppendLine("    {");
        // AOT-safe: Direct Type lookup without reflection
        code.AppendLine("        var type = context.JsonTypeInfo.Type;");
        code.AppendLine("        // For generic types, lookup the generic type definition");
        code.AppendLine("        var lookupType = type.IsGenericType ? type.GetGenericTypeDefinition() : type;");
        code.AppendLine("        if (TypeDescriptions.TryGetValue(lookupType, out var description))");
        code.AppendLine("        {");
        code.AppendLine("            schema.Description ??= description;");
        code.AppendLine("        }");
        code.AppendLine("        return Task.CompletedTask;");
        code.AppendLine("    }");
        code.AppendLine("}");
        code.AppendLine();

        return true;
    }

    /// <summary>
    ///     Converts a reflection-style type name to a C# typeof expression.
    ///     Example: "Namespace.Outer+Inner" → "global::Namespace.Outer.Inner"
    /// </summary>
    private static string ConvertToTypeofExpression(string reflectionName)
    {
        // Replace nested type separator (+) with C# dot notation
        var csharpName = reflectionName.Replace('+', '.');
        return $"global::{csharpName}";
    }

    private static void EmitRegistrationExtension(
        StringBuilder code,
        List<string> tags,
        bool hasOperationDocs,
        bool hasTypeDocs)
    {
        code.AppendLine("/// <summary>");
        code.AppendLine("/// Extension methods for registering generated OpenAPI transformers.");
        code.AppendLine("/// </summary>");
        code.AppendLine("public static class GeneratedOpenApiExtensions");
        code.AppendLine("{");
        code.AppendLine("    /// <summary>");
        code.AppendLine("    /// Adds OpenAPI with generated transformers for ErrorOr endpoints.");
        code.AppendLine("    /// Each transformer is registered following the strict 1:1 mapping rule.");
        code.AppendLine("    /// </summary>");
        code.AppendLine("    public static IServiceCollection AddErrorOrOpenApi(");
        code.AppendLine("        this IServiceCollection services,");
        code.AppendLine("        string documentName = \"v1\")");
        code.AppendLine("    {");
        code.AppendLine("        services.AddOpenApi(documentName, options =>");
        code.AppendLine("        {");

        // Register tag transformers (1:1 - one per tag)
        foreach (var tag in tags)
        {
            var safeTagName = tag.SanitizeIdentifier();
            code.AppendLine($"            // Tag: {tag}");
            code.AppendLine($"            options.AddDocumentTransformer(new Tag_{safeTagName}_Transformer());");
        }

        // Register operation transformer if we have docs
        if (hasOperationDocs)
        {
            code.AppendLine();
            code.AppendLine("            // XML doc summaries → operation metadata");
            code.AppendLine("            options.AddOperationTransformer(new XmlDocOperationTransformer());");
        }

        // Register schema transformer if we have type docs
        if (hasTypeDocs)
        {
            code.AppendLine();
            code.AppendLine("            // XML doc summaries → schema descriptions");
            code.AppendLine("            options.AddSchemaTransformer(new XmlDocSchemaTransformer());");
        }

        code.AppendLine("        });");
        code.AppendLine();
        code.AppendLine("        return services;");
        code.AppendLine("    }");
        code.AppendLine("}");
    }
}