// Copyright UShaderLab. All Rights Reserved.

#pragma once

#include "CoreMinimal.h"
#include "MaterialValueType.h"
#include "Materials/MaterialExpressionCustomOutput.h"
#include "MaterialExpressionShaderLabParameterAnchor.generated.h"

/**
 * Internal ShaderLab node with two jobs, both keeping workaround machinery off the user's body nodes:
 *
 *  1. Anchors parameters so the Material Instance editor lists them. StaticBool parameters are consumed
 *     only inside HLSL `#if`, so they would otherwise be unconnected; the instance editor's visibility
 *     walk only reaches parameters connected to a material output or a CustomOutput. This is a
 *     CustomOutput, so it is always traversed; each anchored parameter reaches one of its inputs (via
 *     its static-switch selector).
 *
 *  2. Injects per-permutation static-switch `#define`s with ZERO engine modifications. Each input is a
 *     StaticSwitch over two `#define <Switch> 1` / `#define <Switch> 0` Custom nodes. This node returns
 *     ShouldCompileBeforeAttributes()==true, so FHLSLMaterialTranslator compiles it BEFORE the material
 *     attributes (FrontMaterial / body). Its Compile() compiles each input, so the selected `#define`
 *     (only the taken StaticSwitch branch is compiled) is emitted ahead of every body's `#if`. The
 *     `#define` leaks forward (preprocessor is global) and the body's `#if <Switch>` sees the current
 *     permutation's value — including a Material Instance's static override.
 *
 * It only ever lives in the editor graph (never serialized into a cooked package).
 */
UCLASS(MinimalAPI, collapsecategories, hidecategories = Object)
class UMaterialExpressionShaderLabParameterAnchor : public UMaterialExpressionCustomOutput
{
	GENERATED_UCLASS_BODY()

	/** One input per static-switch selector (a StaticSwitch over two `#define`-emitting Custom nodes). */
	UPROPERTY()
	TArray<FExpressionInput> Inputs;

	//~ Begin UMaterialExpressionCustomOutput Interface
	// One output so the translator actually compiles us (a zero-output CustomOutput is skipped). The
	// output value is unused; compiling us is purely to emit our inputs' `#define`s before attributes.
	virtual int32 GetNumOutputs() const override { return 1; }
	virtual FString GetFunctionName() const override { return TEXT("ShaderLabParameterAnchor"); }
#if WITH_EDITOR
	virtual bool NeedsCustomOutputDefines() override { return false; } // don't emit NUM_MATERIAL_OUTPUTS_*
	virtual bool ShouldCompileBeforeAttributes() override { return true; } // emit #defines ahead of body #if
#endif
	//~ End UMaterialExpressionCustomOutput Interface

#if WITH_EDITOR
	//~ Begin UMaterialExpression Interface
	virtual TArrayView<FExpressionInput*> GetInputsView() override;
	virtual FExpressionInput* GetInput(int32 InputIndex) override;
	virtual FName GetInputName(int32 InputIndex) const override;
	virtual EMaterialValueType GetInputValueType(int32 InputIndex) override { return MCT_Float1; }
	virtual int32 Compile(class FMaterialCompiler* Compiler, int32 OutputIndex) override;
	virtual void GetCaption(TArray<FString>& OutCaptions) const override;
	//~ End UMaterialExpression Interface
#endif

private:
	/** Scratch pointer view rebuilt by GetInputsView(). */
	TArray<FExpressionInput*> CachedInputs;
};