#pragma once

#include "CoreMinimal.h"
#include "Core/DescentHandle.h"
#include "Core/DescentWorldSubsystem.h"
#include "Core/Tuning/DescentTune_Env.h"
#include "DescentEnvQuery.generated.h"

/**
 * The environment query seam (DESIGN_UE.md sections 3.3 and 7.4; requirements U5 and U6): "is this point dry, and
 * how warm is it". By default everything is water and the temperature is the water formula of section 2.7. A system
 * that owns dry space registers a dry-volume provider; the systems that only ask (look, fauna, HUD, dashboards)
 * never include the registering system:
 *
 *   // carrier (M2), in its own Initialize / BeginPlay:
 *   DryHandle = UDescentEnvQuerySubsystem::Get(World)->RegisterDryVolume(TEXT("Carrier"),
 *       [this](const FVector& WorldUU) { return IsDry(GetTransform().InverseTransformPosition(WorldUU) / 100.0); });
 *
 *   // look / fauna / HUD:
 *   if (Descent::IsDry(World, CameraUU)) { ... }               // free functions, null-safe
 *   const double TempC = Descent::AmbientTemperatureAt(World, RefPointUU);
 *
 * Positions are Unreal units (what GetActorLocation returns); the *Metres variants take metres.
 */
UCLASS()
class THEDESCENT_API UDescentEnvQuerySubsystem : public UDescentWorldSubsystem
{
	GENERATED_BODY()

public:
	/** Answers "is WorldUU inside my dry volume". Called often (every frame, per fauna spawn): keep it cheap and allocation-free. */
	using FDryVolumeFn = TFunction<bool(const FVector& WorldUU)>;

	static UDescentEnvQuerySubsystem* Get(const UWorld* World);

	/**
	 * Registers a dry volume. Any provider answering true makes the point dry. TemperatureC is what a point inside it
	 * reads (26 degrees by default, requirement U5); if several volumes contain a point the first by owner name wins.
	 */
	FDescentHandle RegisterDryVolume(FName Owner, FDryVolumeFn IsInside, double TemperatureC = Descent::Tune::Env::DryCabinTemperatureC);
	bool UnregisterDryVolume(FDescentHandle Handle);
	TArray<FName> GetDryVolumeOwners() const;

	/** True if some registered dry volume contains the point. False everywhere when nothing is registered. */
	bool IsDry(const FVector& WorldUU) const;
	bool IsDryAtMetres(const FVector& WorldM) const;

	/** Dry volume's temperature inside one, otherwise the water temperature at the point's depth. Degrees Celsius. */
	double AmbientTemperatureC(const FVector& WorldUU) const;
	double AmbientTemperatureAtMetres(const FVector& WorldM) const;

	/** Section 2.7: 4.2 + 9 clamp((Depth - 1740) / 1400, 0, 1) + (Depth > 2300 ? 6 : 0). Depth in metres. */
	static double WaterTemperatureC(double DepthM);

private:
	struct FVolume
	{
		uint32 Id = 0;
		FName Owner;
		FDryVolumeFn IsInside;
		double TemperatureC = 26.0;
	};
	/** Kept sorted by (owner name, id) so the answer never depends on registration order. */
	TArray<FVolume> Volumes;
	uint32 NextId = 1;
};

namespace Descent
{
	/** True if WorldUU is inside a registered dry volume (no world, no subsystem or no provider: false, i.e. water). */
	THEDESCENT_API bool IsDry(const UWorld* World, const FVector& WorldUU);

	/** Section 3.3: dry volume temperature (26.0 C) inside, the water formula outside. Every temperature readout calls this with its own reference point. */
	THEDESCENT_API double AmbientTemperatureAt(const UWorld* World, const FVector& WorldUU);
}