#pragma once

#include "CoreMinimal.h"

class UClass;

/**
 * Which pawn / controller / HUD class ADescentGameMode uses, chosen by registration instead of by editing the game
 * mode: the track that owns a class registers it from its own .cpp with a priority, the highest priority wins.
 *
 *   // Player/DescentCharacter.cpp (M2): replaces the M0 fly pawn without touching Core/DescentGameMode.cpp
 *   DESCENT_REGISTER_GAME_CLASS(Pawn, 100, ADescentCharacter)
 *   // Player/DescentPlayerController.cpp
 *   DESCENT_REGISTER_GAME_CLASS(PlayerController, 100, ADescentPlayerController)
 *
 * The placeholder fly pawn registers at priority 0 (Core/DescentFlyPawn.cpp). Registration stores a getter, not a
 * UClass: StaticClass() must not be called while static initialisers run. The game mode resolves the slots in its
 * constructor, which the engine runs after every module has loaded.
 */
enum class EDescentGameClassSlot : uint8
{
	Pawn,
	PlayerController,
	HUD,
	GameState,
	PlayerState,
	Count
};

class THEDESCENT_API FDescentGameClassRegistry
{
public:
	using FClassGetter = TFunction<UClass*()>;

	/** The registry the game mode reads. Tests make their own instance instead. */
	static FDescentGameClassRegistry& Get();

	void Register(EDescentGameClassSlot Slot, int32 Priority, FName Owner, FClassGetter Getter);
	void Unregister(EDescentGameClassSlot Slot, FName Owner);

	/** The class of the highest-priority registration of the slot (ties: the owner name that sorts first), or null if none. */
	UClass* Resolve(EDescentGameClassSlot Slot) const;

	/** Owner of the registration Resolve would pick, NAME_None if none. */
	FName ResolveOwner(EDescentGameClassSlot Slot) const;

private:
	struct FEntry
	{
		EDescentGameClassSlot Slot = EDescentGameClassSlot::Pawn;
		int32 Priority = 0;
		FName Owner;
		FClassGetter Getter;
	};
	const FEntry* Pick(EDescentGameClassSlot Slot) const;
	TArray<FEntry> Entries;
};

struct THEDESCENT_API FDescentGameClassRegistrar
{
	FDescentGameClassRegistrar(EDescentGameClassSlot InSlot, int32 Priority, const TCHAR* Owner, FDescentGameClassRegistry::FClassGetter Getter)
		: Slot(InSlot), OwnerName(Owner)
	{
		FDescentGameClassRegistry::Get().Register(Slot, Priority, OwnerName, MoveTemp(Getter));
	}
	~FDescentGameClassRegistrar()
	{
		FDescentGameClassRegistry::Get().Unregister(Slot, OwnerName);
	}
	EDescentGameClassSlot Slot;
	FName OwnerName;
};

/** Registers ClassName (a UCLASS already declared) for a slot: DESCENT_REGISTER_GAME_CLASS(Pawn, 100, ADescentCharacter). */
#define DESCENT_REGISTER_GAME_CLASS(SlotName, Priority, ClassName) \
	static FDescentGameClassRegistrar GDescentGameClass_##SlotName##_##ClassName( \
		EDescentGameClassSlot::SlotName, (Priority), TEXT(#ClassName), []() -> UClass* { return ClassName::StaticClass(); });