#pragma once

#include "CoreMinimal.h"
#include "Dom/JsonObject.h"
#include "Dom/JsonValue.h"

class UWorld;

/**
 * Registry of named snapshot providers. `Descent.DumpState <name>` calls every registered provider and
 * writes the result to Saved/State/<name>.json:
 *
 *   { "schema": 1, "name": "<name>", "<section>": { ... }, "<section>": { ... } }
 *
 * A system adds its own section with one object at file scope:
 *
 *   static FDescentStateProviderRegistrar GMySection(TEXT("fuel"), [](UWorld* World, FJsonObject& Out)
 *   {
 *       Out.SetNumberField(TEXT("litres"), 12.5);
 *   });
 *
 * Several systems can share ONE section by each owning a named part of it (the design's `ui` section is
 * {hud, widgets, window, cargo_display} written by different files). A part provider fills its own object, which
 * appears as a field named after the part:
 *
 *   static FDescentStatePartRegistrar GHudPart(TEXT("ui"), TEXT("hud"), [](UWorld* World, FJsonObject& Out) { ... });
 *
 * A section may have a whole-section provider, parts, or both (the provider writes first, then the parts).
 *
 * Positions are always written in metres (see DescentUnits.h) so a dump can be compared with the design
 * numbers directly. Providers run on the game thread, may be called with a null World (in the editor with
 * no game running) and must tolerate that.
 */
class THEDESCENT_API FDescentStateRegistry
{
public:
	using FProvider = TFunction<void(UWorld* World, FJsonObject& Section)>;

	static FDescentStateRegistry& Get();

	/** Registers (or replaces) the provider for a section. */
	void Register(FName Section, FProvider Provider);
	bool Unregister(FName Section);

	/** Registers (or replaces) one named part of a section; see the class comment. */
	void RegisterPart(FName Section, FName Part, FProvider Provider);
	bool UnregisterPart(FName Section, FName Part);
	TArray<FName> GetSectionNames() const;

	/** Builds the whole snapshot object. Sections appear in alphabetical order so dumps diff cleanly. */
	TSharedRef<FJsonObject> BuildSnapshot(UWorld* World, const FString& SnapshotName) const;

	/** Saved/State and Saved/Shots as absolute paths. */
	static FString GetStateDir();
	static FString GetShotDir();

	/**
	 * Accepts a bare file stem like "boot" or "kazah_showcase_front" (letters, digits, '_', '-', '.').
	 * Rejects anything with a path separator or "..", so a console argument cannot write outside Saved/.
	 */
	static bool IsValidFileStem(const FString& Stem);

	/** Serialises the object (pretty-printed) to the given absolute path. */
	static bool WriteJsonFile(const TSharedRef<FJsonObject>& Object, const FString& AbsPath, FString& OutError);

	/** meta, camera, pawn, world. Called by the module. */
	static void RegisterBuiltInProviders();
	static void UnregisterBuiltInProviders();

private:
	TMap<FName, FProvider> Providers;
	TMap<FName, TMap<FName, FProvider>> Parts;
};

/** RAII helper for registering a provider at file scope or as a member of a long-lived object. */
struct THEDESCENT_API FDescentStateProviderRegistrar
{
	FDescentStateProviderRegistrar(FName InSection, FDescentStateRegistry::FProvider Provider)
		: Section(InSection)
	{
		FDescentStateRegistry::Get().Register(Section, MoveTemp(Provider));
	}
	~FDescentStateProviderRegistrar()
	{
		FDescentStateRegistry::Get().Unregister(Section);
	}
	FName Section;
};

/** RAII helper for registering one part of a shared section at file scope. */
struct THEDESCENT_API FDescentStatePartRegistrar
{
	FDescentStatePartRegistrar(FName InSection, FName InPart, FDescentStateRegistry::FProvider Provider)
		: Section(InSection), Part(InPart)
	{
		FDescentStateRegistry::Get().RegisterPart(Section, Part, MoveTemp(Provider));
	}
	~FDescentStatePartRegistrar()
	{
		FDescentStateRegistry::Get().UnregisterPart(Section, Part);
	}
	FName Section;
	FName Part;
};

namespace Descent::Json
{
	/** Rounds to 4 decimals so dumps stay readable and stable across runs. */
	FORCEINLINE double Round(double V) { return FMath::RoundToDouble(V * 10000.0) / 10000.0; }

	THEDESCENT_API TSharedRef<FJsonValue> Vec3(const FVector& V);
	THEDESCENT_API TSharedRef<FJsonValue> Rot3(const FRotator& R); // [pitch, yaw, roll] in degrees
}