Medusa-CS/Medusa.Core/Services/HandlerService.cs

using Medusa.Core.Attributes;
using Medusa.Core.Handlers;
using System.Reflection;
using System.Xml.Linq;

namespace Medusa.Core.Services
{
    public class HandlerService(IServiceProvider serviceProvider, ILogger<HandlerService> logger) : IHandlerService
    {
        private readonly IServiceProvider _serviceProvider = serviceProvider;
        private readonly ILogger<HandlerService> _logger = logger;

        public List<Type> Handlers { get; set; } = [];

        public async Task<XDocument> Handle(string model, string module, string method, XDocument body)
        {
            foreach(var handler in Handlers)
            {
                //Module and service are on the attribute
                var handlerAttribute = handler.CustomAttributes.FirstOrDefault(x => x.AttributeType == typeof(HandlerAttribute));

                if(handlerAttribute is null)
                {
                    var response = await HandleInheritanceClass(handler, model, module, method, body);

                    if(response is not null)
                    {
                        return response;
                    }

                    continue;
                }

                var attributeModule = handlerAttribute.ConstructorArguments[0].Value.ToString();
                var attributeMethod = handlerAttribute.ConstructorArguments[1].Value.ToString();

                if(attributeModule == module && attributeMethod == method)
                {
                    // Body param is optional so check for it
                    bool requiresXDocumentConstructor = handler.GetConstructors()
                        .Any(c => c.GetParameters().Any(p => p.ParameterType == typeof(XDocument)));

                    IHandler handlerInstance = requiresXDocumentConstructor
                        ? (IHandler)ActivatorUtilities.CreateInstance(_serviceProvider, handler, body)
                        : (IHandler)ActivatorUtilities.CreateInstance(_serviceProvider, handler);

                    return await handlerInstance.HandleAsync(model);
                }
            }

            //If no handler is found return an empty document
            _logger.LogWarning($"No handler found for {model}/{module}/{method}");

            return new XDocument();
        }

        private async Task<XDocument?> HandleInheritanceClass(Type handler, string model, string module, string method, XDocument body)
        {
            bool requiredXdocumentConstructor = handler.GetConstructors()
                .Any(c => c.GetParameters().Any(p => p.ParameterType == typeof(XDocument)));

            Handler handlerInstance = requiredXdocumentConstructor
                ? (Handler)ActivatorUtilities.CreateInstance(_serviceProvider, handler, body)
                : (Handler)ActivatorUtilities.CreateInstance(_serviceProvider, handler);

            try
            {
                var configureMethod = handler.GetMethod("Configure");
                configureMethod?.Invoke(handlerInstance, null);
            }
            catch(NotImplementedException e)
            {
                _logger.LogError(e, "Configure method not implemented for {Handler}", handler.Name);
                return null;
            }

            var handlerModule = handlerInstance.HandlerModule;
            var handlerMethod = handlerInstance.HandlerMethod;

            if(string.IsNullOrEmpty(handlerModule))
            {
                _logger.LogError("Module not set for {Handler}", handler.Name);
                return null;
            }

            if(string.IsNullOrEmpty(handlerMethod))
            {
                _logger.LogError("Method not set for {Handler}", handler.Name);
                return null;
            }

            if(handlerModule != module && handlerMethod != method)
                return null;

            var handleMethod = handlerInstance.GetType().GetMethod("Handle", [typeof(string)]);
            var handleAsyncMethod = handlerInstance.GetType().GetMethod("HandleAsync", [typeof(string)]);

            var response = new XDocument();

            response = handleMethod?.DeclaringType != typeof(Handler)
                ? handlerInstance.Handle(model)
                : handleAsyncMethod?.DeclaringType != typeof(Handler)
                    ? await handlerInstance.HandleAsync(model)
                    : null;

            if(response is null)
            {
                _logger.LogError("Handle and HandleAsync not implemented for {Handler}", handler.Name);
                return null;
            }

            return response;
        }
    }
}