// Copyright IHY.
#pragma once

#include "CoreMinimal.h"
#include "EditorSubsystem.h"
#include "OptimizerTypes.h"
#include "OptimizerSubsystem.generated.h"

class UStaticMesh;
class UStaticMeshComponent;

/**
 * Editor subsystem driving the Mesh Optimizer pipeline. The Editor Utility Widget calls these:
 *   1. ScanLevel  -> dry-run plan (sibling groups + per-placement corrected transforms)
 *   2. ApplyUnify -> reassign every sibling placement to its canonical mesh with the fixed transform
 *   3. BuildHISM  -> collapse each group into one HierarchicalInstancedStaticMesh
 * Steps 2 and 3 each run inside a single undoable transaction. BuildHISM is independent of ApplyUnify
 * (it uses the canonical mesh + planned transforms directly).
 */
UCLASS()
class OPTIMIZEREDITOR_API UOptimizerSubsystem : public UEditorSubsystem
{
	GENERATED_BODY()

public:
	/** Dry run: scan the level, group sibling meshes, plan corrected transforms. Mutates nothing. */
	UFUNCTION(BlueprintCallable, Category = "Optimizer")
	FOptimizerScanResult ScanLevel(const FOptimizerScanSettings& Settings);

	/** Reassign all non-instanced sibling placements to their canonical mesh + corrected transform. Returns count changed. */
	UFUNCTION(BlueprintCallable, Category = "Optimizer")
	int32 ApplyUnify();

	/** Build one HISM actor per group from the planned transforms. Returns number of HISM actors created. */
	UFUNCTION(BlueprintCallable, Category = "Optimizer")
	int32 BuildHISM(bool bDestroyOriginals = true);

	/** Discard the current plan. */
	UFUNCTION(BlueprintCallable, Category = "Optimizer")
	void ClearPlan();

	UFUNCTION(BlueprintCallable, Category = "Optimizer")
	bool HasPlan() const;

private:
	/** One placement of a mesh in the level (a component, or one instance inside an ISM/HISM). */
	struct FPlacement
	{
		TWeakObjectPtr<UStaticMeshComponent> Component;
		int32 InstanceIndex = INDEX_NONE;   // >= 0 when this is an instance inside an ISM/HISM
		TWeakObjectPtr<UStaticMesh> Mesh;
		FTransform World = FTransform::Identity;
		FTransform PlannedWorld = FTransform::Identity;
		bool bNeedsTransformFix = false;
		bool bShearRejected = false;
		bool bInstanced = false;            // inside an ISM/HISM -> ApplyUnify can't swap it (HISM-only)
	};

	/** A sibling group: distinct meshes that share geometry, collapsed onto one canonical. */
	struct FGroup
	{
		TArray<TWeakObjectPtr<UStaticMesh>> Members;
		TWeakObjectPtr<UStaticMesh> Canonical;
		TArray<FPlacement> Placements;
		float MaxDeviation = 0.0f;
		bool bHasMirrored = false;
		bool bHasScaled = false;
		bool bMaterialMismatch = false;
		int32 ShearRejected = 0;
	};

	TArray<FGroup> Groups;
	FOptimizerScanSettings LastSettings;

	FOptimizerScanResult BuildResultView() const;
};