// Copyright UShaderLab. All Rights Reserved.

#pragma once

#include "CoreMinimal.h"

class UMaterial;
struct FShaderLabModel;

/**
 * Turns a parsed FShaderLabModel into a UMaterial expression graph: property parameter nodes + a Custom
 * HLSL node for the Surface body wired into a Substrate Slab BSDF (-> FrontMaterial), plus an optional
 * Vertex Custom node for WPO/displacement/UVs. Lives in the UncookedOnly UShaderLabBuilder module, so it
 * runs in the editor AND under `-game` on uncooked data (not in cooked builds — see AIDoc §2.9).
 *
 * The build is fully deterministic for a given model (node creation order, input/output order,
 * generated HLSL) so the cook-time and editor-time graphs — and therefore the baked uniform
 * expression set — match.
 */
class USHADERLABBUILDER_API FShaderLabGraphBuilder
{
public:
	/**
	 * Clear `Material`'s expression graph and rebuild it from `Model`, applying settings
	 * (domain/blend/two-sided) and updating cached expression data. Does NOT trigger shader
	 * compilation — callers decide when to compile. Returns false with diagnostics on failure.
	 */
	static bool BuildInto(UMaterial& Material, const FShaderLabModel& Model, TArray<FString>& OutErrors);

	/**
	 * Replace `Material`'s graph with a minimal Substrate material whose single Custom node emits a
	 * `#line`-mapped `#error` for `Diagnostics`, so it deliberately fails to compile with those messages
	 * mapped back to `SrcPath` (an absolute, forward-slashed .usl path). This routes .usl parse/build
	 * errors through the standard shader-compile path — MIC editor red text, GetCompileErrors, cook —
	 * instead of dropping them. The graph itself is always valid; the failure is intentional and happens
	 * at shader compile. Does NOT trigger compilation (the caller decides when).
	 */
	static void BuildPoisonInto(UMaterial& Material, const TArray<FString>& Diagnostics, const FString& SrcPath);

	/**
	 * Resolve a virtual shader path ("/Project/Lib/X.uslfunc", "/Plugin/ShaderLab/...", "/Engine/...") to an
	 * absolute disk path via the registered shader-source directory mappings (longest-prefix match, exact-root
	 * allowed). Returns false if no mapping root contains the path. The single canonical reversal of the
	 * shader-source mappings — used to load `.uslfunc` imports, by the editor hot-reload loader, and by the
	 * VSCode button. (Forward direction: FShaderLabMaterialRegistry::MakeVirtualShaderPath.)
	 */
	static bool ResolveVirtualShaderFile(const FString& VirtualPath, FString& OutDiskPath);

	/**
	 * Virtual shader root under which per-shader generated local-code headers live
	 * (e.g. "/UShaderLabGen"). The editor module maps it to GetGeneratedShaderDir() at startup.
	 */
	static const TCHAR* GetGeneratedVirtualRoot();

	/**
	 * Absolute disk directory backing GetGeneratedVirtualRoot(): the plugin's
	 * `Intermediate/ShaderLabGen`. A build-time artifact only (never staged into a pak); the cooked
	 * runtime never builds graphs and skips the mapping. Empty string if the plugin can't be found.
	 */
	static FString GetGeneratedShaderDir();
};