// Copyright 2025 https://yuewu.dev/en  All Rights Reserved.

#pragma once

#include "Kismet/BlueprintFunctionLibrary.h"
#include "GMS_Math.generated.h"

UCLASS(Meta = (BlueprintThreadSafe))
class GENERICMOVEMENTSYSTEM_API UGMS_Math : public UBlueprintFunctionLibrary
{
	GENERATED_BODY()

public:
	static constexpr auto Ln2{0.6931471805599453f}; // FMath::Loge(2.0f).

public:
	UFUNCTION(BlueprintCallable, BlueprintPure, Category = "GMS|Math Utility", Meta = (ReturnDisplayName = "Value"))
	static float Clamp01(float Value);

	UFUNCTION(BlueprintCallable, BlueprintPure, Category = "GMS|Math Utility", Meta = (ReturnDisplayName = "Value"))
	static float LerpClamped(float From, float To, float Ratio);

	//Output the frame-rate stable alpha used for smoothly lerp current to target.
	UFUNCTION(BlueprintCallable, BlueprintPure, Category = "GMS|Math Utility", Meta = (ReturnDisplayName = "Alpha"))
	static float DamperExactAlpha(float DeltaTime, float HalfLife);

	// HalfLife is the time it takes for the distance to the target to be reduced by half.
	template <typename ValueType>
	static ValueType DamperExact(const ValueType& Current, const ValueType& Target, float DeltaTime, float HalfLife);
};

inline float UGMS_Math::Clamp01(const float Value)
{
	return Value > 0.0f
		       ? Value < 1.0f
			         ? Value
			         : 1.0f
		       : 0.0f;
}

inline float UGMS_Math::LerpClamped(const float From, const float To, const float Ratio)
{
	return From + (To - From) * Clamp01(Ratio);
}

inline float UGMS_Math::DamperExactAlpha(const float DeltaTime, const float HalfLife)
{
	// https://theorangeduck.com/page/spring-roll-call#exactdamper

	return 1.0f - FMath::InvExpApprox(Ln2 / (HalfLife + UE_SMALL_NUMBER) * DeltaTime);
}

template <typename ValueType>
ValueType UGMS_Math::DamperExact(const ValueType& Current, const ValueType& Target, const float DeltaTime, const float HalfLife)
{
	return FMath::Lerp(Current, Target, DamperExactAlpha(DeltaTime, HalfLife));
}