#pragma once

#include "CoreMinimal.h"
#include "Components/ActorComponent.h"
#include "Core/DescentHandle.h"
#include "Core/DescentWorldSubsystem.h"
#include "UObject/Interface.h"
#include "DescentInteraction.generated.h"

class ADescentCharacter;

UINTERFACE(MinimalAPI, NotBlueprintable)
class UDescentInteractable : public UInterface
{
	GENERATED_BODY()
};

/** Anything the player can use with E (DESIGN_UE.md section 5.4). Collision is not involved: the same result with blockout or real meshes. */
class THEDESCENT_API IDescentInteractable
{
	GENERATED_BODY()

public:
	/** The label after "[E]", e.g. "Take the helm - pilot the CANTICLE". */
	virtual FString GetPrompt() const = 0;
	/** World position (Unreal units) the prompt aims at. */
	virtual FVector GetFocusPointUU() const = 0;
	virtual double GetRangeM() const;
	virtual double GetMinDot() const;
	virtual bool CanUse(const ADescentCharacter* User) const { return true; }
	virtual void Use(ADescentCharacter* User) = 0;
};

/** Every interactable registers here; the character's component searches it. */
UCLASS()
class THEDESCENT_API UDescentInteractionRegistry : public UDescentWorldSubsystem
{
	GENERATED_BODY()

public:
	static UDescentInteractionRegistry* Get(const UWorld* World);
	void Register(UObject* Interactable);
	void Unregister(UObject* Interactable);
	const TArray<TWeakObjectPtr<UObject>>& All() const { return Items; }

private:
	TArray<TWeakObjectPtr<UObject>> Items;
};

/** Keeps the current focus: the v2 rule, within range of the eye and dot(view, toTarget) >= min dot, score = dot - 0.05 * distance. */
UCLASS(ClassGroup = (Descent))
class THEDESCENT_API UDescentInteractionComponent : public UActorComponent
{
	GENERATED_BODY()

public:
	UDescentInteractionComponent();

	/** Recomputes the focus from the eye and view direction (world, uu / unit). Called once per late step. */
	void UpdateFocus(const FVector& EyeUU, const FVector& ViewDir);
	void ClearFocus() { Focus.Reset(); FocusLabel.Reset(); }

	UObject* GetFocus() const { return Focus.Get(); }
	const FString& GetFocusLabel() const { return FocusLabel; }
	/** E: uses the focus if it is still valid and usable. Returns whether something was used. */
	bool UseFocus(ADescentCharacter* User);

private:
	TWeakObjectPtr<UObject> Focus;
	FString FocusLabel;
};