Modules.h

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/** @noop License Comment
 *  @file
 *  @copyright
 *  This Source Code is subject to the terms of the Mozilla Public License, v2.0.
 *  If a copy of the MPL was not distributed with this file You can obtain one at
 *  https://mozilla.org/MPL/2.0/
 *  
 *  @author David Mórász
 *  @date 2025
 */
 
#pragma once
#include "CoreMinimal.h"
#include "Mcro/TypeName.h"
#include "Mcro/Delegates/EventDelegate.h"
 
/** Namespace for utilities handling Unreal modules */
namespace Mcro::Modules
{
    using namespace Mcro::Delegates;
    using namespace Mcro::Concepts;
    using namespace Mcro::TypeName;
 
    /** Add this interface to your module class if other things can listen to module startup or shutdown */
    class MCRO_API IObservableModule : public IModuleInterface
    {
    public:
        
        /**
         * Event broadcasted on module startup or immediately executed upon subscription if module has already been
         * started up.
         */
        TBelatedEventDelegate<void()> OnStartupModule;
        
        /**
         * Event broadcasted on module shutdown or immediately executed upon subscription if module has already been
         * shut down.
         */
        TBelatedEventDelegate<void()> OnShutdownModule;
 
        virtual void StartupModule() override;
        virtual void ShutdownModule() override;
    };
 
    /** Use this in global variables to automatically do things on module startup or shutdown */
    template <CDerivedFrom<IObservableModule> M>
    struct TObserveModule
    {
        /**
         * Default constructor will try to infer module name from type name. Given convention
         * `(F|I)Foobar(Module(Interface)?)? the extracted name will be Foobar. If your module doesn't follow this
         * naming use the constructor accepting an FName
         */
        TObserveModule()
        {
            auto moduleName = TTypeString<M>.Mid(1);
            moduleName.RemoveFromEnd(TEXT("Module"));
            moduleName.RemoveFromEnd(TEXT("ModuleInterface"));
            ObserveModule(moduleName);
        }
 
        /** This constructor provides an explicit FName for getting the module */
        TObserveModule(FName const& moduleName)
        {
            ObserveModule(moduleName);
        }
 
        /**
         * Event broadcasted on module startup or immediately executed upon subscription if module has already been
         * started up.
         */
        TBelatedEventDelegate<void()> OnStartupModule;
 
        /**
         * Event broadcasted on module shutdown or immediately executed upon subscription if module has already been
         * shut down.
         */
        TBelatedEventDelegate<void()> OnShutdownModule;
 
        /** Specify function to be executed on startup */
        TObserveModule& OnStartup(TFunction<void()>&& func)
        {
            OnStartupModule.Add(From(func));
            return *this;
        }
        
        /** Specify function to be executed on shutdown */
        TObserveModule& OnShutdown(TFunction<void()>&& func)
        {
            OnShutdownModule.Add(From(func));
            return *this;
        }
        
    private:
        M* Module = nullptr;
 
        void ObserveModule(FName const& moduleName)
        {
            decltype(auto) manager = FModuleManager::Get();
            M* module = static_cast<M*>(manager.GetModule(moduleName));
            if (!module)
            {
                manager.OnModulesChanged().AddLambda([this, moduleName](FName name, EModuleChangeReason changeReason)
                {
                    if (changeReason == EModuleChangeReason::ModuleLoaded && moduleName == name)
                        ObserveModule(moduleName);
                });
            }
            else
            {
                Module = module;
                module->OnStartupModule.Add(OnStartupModule.Delegation());
                module->OnShutdownModule.Add(OnShutdownModule.Delegation());
            }
        }
    };
}