integration/Plugins/BlueprintMCP/Source/BlueprintMCP/Public/MCPHandler.h

#pragma once

#include "CoreMinimal.h"
#include "UObject/Interface.h"
#include "UObject/Object.h"
#include "Dom/JsonObject.h"
#include "MCPHandler.generated.h"

// Marker struct for handler parameters that accept a JSON object.
// PopulateFromJson stashes the actual JSON object into the Json field.
USTRUCT()
struct FMCPJsonObject
{
	GENERATED_BODY()
	TSharedPtr<FJsonObject> Json;
};

// Marker struct for handler parameters that accept a JSON array.
// PopulateFromJson stashes the actual JSON array into the Array field.
USTRUCT()
struct FMCPJsonArray
{
	GENERATED_BODY()
	TArray<TSharedPtr<FJsonValue>> Array;
};

// Interface for self-registering MCP tool handlers.
//
// Implementing classes declare their parameters as UPROPERTY fields, which are
// automatically populated from the incoming JSON request and used to
// generate the tool's JSON Schema for MCP tools/list.
//
// Class metadata:
//   ToolName      - the MCP tool name (e.g. "spawn_node")
//
// Property metadata:
//   Optional      - marks a parameter as not required
//
UINTERFACE(MinimalAPI, meta=(CannotImplementInterfaceInBlueprint))
class UMCPHandler : public UInterface
{
	GENERATED_BODY()
};

class BLUEPRINTMCP_API IMCPHandler
{
	GENERATED_BODY()

public:
	// Human-readable tool description for MCP tools/list.
	virtual FString GetDescription() const = 0;

	// Called after parameter fields have been populated from JSON.
	// Override the FStringBuilderBase version for plain-text responses, or the
	// FJsonObject version for JSON responses. The dispatcher calls the text
	// version first; if the builder remains empty, it falls back to JSON.
	virtual void Handle(const FJsonObject* Json, FStringBuilderBase& Result) {}
	virtual void Handle(const FJsonObject* Json, FJsonObject* Result) {}
};