UnrealEngineUWP/Engine/Plugins/Runtime/Metasound/Source/MetasoundFrontend/Public/MetasoundEnum.h

// Copyright Epic Games, Inc. All Rights Reserved.

#pragma once

#include "CoreMinimal.h"

#include <type_traits>

// NOTE: Metasound Enum types are defined outside of Engine so can't use the UENUM type reflection here.
// Basic reflection is provides using template specialization and Macros defined below.

// Example usage:
//
// 1. Declare an Enum class. 
// enum class EMyOtherTestEnum : int32
// {
//		Alpha = 500,
//		Beta = -666,
//		Gamma = 333
// };

// 2. Declare its wrapper types using the DECLARE_METASOUND_ENUM macro.
// DECLARE_METASOUND_ENUM(EMyOtherTestEnum, EMyOtherTestEnum::Gamma, METASOUNDSTANDARDNODES_API, FMyOtherTestEnumTypeInfo, FMyOtherTestEnumReadRef, FMyOtherTestEnumWriteRef)

// 3. Define it using the BEGIN/ENTRY/END macros
// DEFINE_METASOUND_ENUM_BEGIN(EMyOtherTestEnum)
// 		DEFINE_METASOUND_ENUM_ENTRY(EMyOtherTestEnum::Alpha, LOCTEXT("AlphaDescription", "Alpha"), LOCTEXT("AlphaDescriptionTT", "Alpha tooltip")),
// 		DEFINE_METASOUND_ENUM_ENTRY(EMyOtherTestEnum::Beta, LOCTEXT("BetaDescription", "Beta"), LOCTEXT("BetaDescriptioTT", "Beta tooltip")),
// 		DEFINE_METASOUND_ENUM_ENTRY(EMyOtherTestEnum::Gamma, LOCTEXT("GammaDescription", "Gamma", LOCTEXT("GammaDescriptionTT", "Gamma tooltip"))
// DEFINE_METASOUND_ENUM_END()

namespace Metasound
{
	// Struct to hold each of the entries of the Enum.
	template<typename T>
	struct TEnumEntry
	{
		T Value;
		FName Name;
		FText DisplayName;		// TODO: Remove this from runtime.
		FText Tooltip;			// TODO: Remove this from runtime.

		// Allow implicit conversion to int32 entry
		operator TEnumEntry<int32>() const
		{
			return TEnumEntry<int32>{ static_cast<int32>(Value), Name, DisplayName, Tooltip };
		}	
	};

	/** CRTP base class for Enum String Helper type.
	 *  Provides common code for all specializations.
	 */ 
	template<typename Derived, typename EnumType>
	struct TEnumStringHelperBase
	{
		// Give a enum value e.g. 'EMyEnum::One', convert that to a Name (if its valid)
		static TOptional<FName> ToName(EnumType InValue)
		{
			for (const TEnumEntry<EnumType>& i : Derived::GetAllEntries())
			{
				if (i.Value == InValue)
				{
					return i.Name;
				}
			}
			return {};
		}
		// Give a Name "EMyEnum::One", convert that to a Enum Value
		static TOptional<EnumType> FromName(const FName	InName)
		{
			for (const TEnumEntry<EnumType>& i : Derived::GetAllEntries())
			{
				if (i.Name == InName)
				{
					return i.Value;
				}
			}
			return {};
		}
		// Return all possible names.
		static TArray<FName> GetAllNames()
		{
			TArray<FName> Names;
			for (const TEnumEntry<EnumType>& i : Derived::GetAllEntries())
			{
				Names.Emplace(i.Name);
			}
			return Names;
		}	
	};

	/** Metasound Enum String Helper
	 */
	template<typename T>
	struct METASOUNDFRONTEND_API TEnumStringHelper : TEnumStringHelperBase<TEnumStringHelper<T>, T>
	{
		static_assert(TIsEnum<T>::Value, "Please define a specialization of this class. The DECLARE_METASOUND_ENUM macros will do this for you");
	};

	/** Metasound Enum Wrapper
	 */
	template<typename EnumType, EnumType DefaultValue>
	class TEnum final
	{
	public:
		using InnerType = EnumType;
	
		static_assert(TIsEnum<EnumType>::Value, "Expecting an Enum type");
		
		// Allow Non-enum class Enum or Enum class that's are derived from int32
		static_assert(TIsSame<typename std::underlying_type<EnumType>::type, int32>::Value || 
			!TIsEnumClass<EnumType>::Value, "We serialize to int32, so limit to that for now");

		// Default.
		explicit TEnum(EnumType InValue = DefaultValue)
		{
			// Try and convert to validate this is a valid value.
			TOptional<FName> Converted = ToName(InValue);
			if (ensure(Converted))
			{
				EnumValue = InValue;
			}
		}

		// From Int32 (this is the common path from a Literal).
		explicit TEnum(int32 InIntValue)
			: TEnum(static_cast<EnumType>(InIntValue))
		{
		}

		// From Name
		explicit TEnum(FName InValueName)		
		{
			// Try and convert from Name to Value and ensure that we succeed
			TOptional<EnumType> Converted = NameToEnum(InValueName);
			if (ensure(Converted))
			{
				EnumValue = *Converted;
			}
		}

		// Slow, construct from FString to FName.
		explicit TEnum(const FString& InString)
			: TEnum(FName(*InString))
		{
		}

		EnumType Get() const
		{
			return EnumValue;
		}

		int32 ToInt() const
		{
			return static_cast<int32>(EnumValue);
		}

		// Convert to its FName (if possible).
		TOptional<FName> ToName() const 
		{
			return ToName(EnumValue);
		}

		// Conversion operator to automatically convert this to its underlying enum type.
		operator EnumType() const
		{
			return EnumValue;
		}

		// Convert from EnumValue to FName (if possible).
		static TOptional<FName> ToName(EnumType InValue)
		{
			return TEnumStringHelper<EnumType>::ToName(InValue);
		}

		// Convert from Name to EnumValue (if possible).
		static TOptional<EnumType> NameToEnum(FName InValue)
		{
			return TEnumStringHelper<EnumType>::FromName(InValue);
		}

		// Return all possible Names
		static TArray<FName> GetAllNames()
		{
			return TEnumStringHelper<EnumType>::GetAllNames();
		}
				
	private:
		// Keep the type in its fully typed form for debugging.
		EnumType EnumValue = DefaultValue;
	};

	template<typename T>
	struct TEnumTraits
	{
		static constexpr bool bIsEnum = false;
		using InnerType = int32;
		static constexpr int32 DefaultValue = 0;
	};

	template<typename T, T D>
	struct TEnumTraits<TEnum<T, D>>
	{
		static constexpr bool bIsEnum = true;
		using InnerType = T;
		static constexpr T DefaultValue = D;		
	};	
}