// Copyright IHY. Vertical Partition Streaming plugin.
//
// Pure cell math shared by the editor builder and the runtime streamer. No state.
#pragma once

#include "CoreMinimal.h"
#include "Kismet/BlueprintFunctionLibrary.h"
#include "VerticalPartitionTypes.h"
#include "VerticalPartitionStatics.generated.h"

/** Context the desired-state policy needs beyond the raw cell index. */
struct FVerticalStreamingContext
{
	int32 PlayerCellZ = 0;
	int32 PlayerCellX = 0;
	int32 PlayerCellY = 0;
	float PlayerVelocityZ = 0.f;   // cm/s, +up
	float PlayerWorldZ = 0.f;      // cm, exact (for hysteresis at boundaries)
	float CameraPitchDeg = 0.f;    // +looking up
	bool bUseXY = false;
};

UCLASS()
class VERTICALPARTITION_API UVerticalPartitionStatics : public UBlueprintFunctionLibrary
{
	GENERATED_BODY()

public:
	/** Z index of a world Z (cm) relative to the volume floor. */
	UFUNCTION(BlueprintPure, Category="VerticalPartition")
	static int32 GetCellZFromWorldZ(float WorldZ, float VolumeMinZ, float CellHeight);

	UFUNCTION(BlueprintPure, Category="VerticalPartition")
	static int32 GetCellXFromWorldX(float WorldX, float VolumeMinX, float XYCellSize);
	UFUNCTION(BlueprintPure, Category="VerticalPartition")
	static int32 GetCellYFromWorldY(float WorldY, float VolumeMinY, float XYCellSize);

	/** Cell id for a single point (actor origin). */
	static FVerticalCellId GetCellIdFromPoint(const FVector& Point, const FBox& VolumeBounds, const FVerticalPartitionSettings& S);

	/** Cell id for a bounds box. Uses the dominant-overlap cell (center of the
	 *  clamped intersection) so a box straddling a boundary lands deterministically.
	 *  bOutCrossesMultiple reports whether the box spans more than one cell. */
	static FVerticalCellId GetCellIdFromBounds(const FBox& ActorBounds, const FBox& VolumeBounds, const FVerticalPartitionSettings& S, bool& bOutCrossesMultiple);

	/** World-space bounds of a cell, clamped to the volume when requested. */
	static FBox GetCellBounds(const FVerticalCellId& Cell, const FBox& VolumeBounds, const FVerticalPartitionSettings& S);

	/** Number of Z cells the volume spans (>=1). */
	static int32 GetNumZCells(const FBox& VolumeBounds, const FVerticalPartitionSettings& S);

	/** THE policy. Maps a cell relative to the player to its desired representation,
	 *  honouring full/preload/HLOD/unload bands, hysteresis, velocity prediction,
	 *  fall-risk-below, camera direction and the above-player priority bias.
	 *  CurrentState is the cell's live state and is what makes hysteresis sticky. */
	static EVerticalCellDesiredState GetDesiredStateForCell(
		const FVerticalCellId& Cell,
		const FVerticalStreamingContext& Ctx,
		const FVerticalPartitionSettings& S,
		EVerticalCellState CurrentState = EVerticalCellState::Unloaded);

	/** True when a cell sits in the preload band (load full data, keep it hidden). */
	static bool ShouldPreloadFull(const FVerticalCellId& Cell, const FVerticalStreamingContext& Ctx, const FVerticalPartitionSettings& S);

	/** Human-readable colour for a runtime state (debug draw / overlay). */
	UFUNCTION(BlueprintPure, Category="VerticalPartition")
	static FLinearColor GetStateColor(EVerticalCellState State);

	UFUNCTION(BlueprintPure, Category="VerticalPartition")
	static FString WarningTypeToString(EVerticalWarningType Type);
};