#pragma once

#include "Model/Workflow/Value.hpp"
#include "Utils/Vector.hpp"
#include "cplt_fwd.hpp"

#include <cstddef>
#include <cstdint>
#include <iosfwd>
#include <limits>
#include <memory>
#include <span>
#include <string>
#include <variant>
#include <vector>

class WorkflowConnection {
public:
	static constexpr auto kInvalidId = std::numeric_limits<size_t>::max();

	enum Direction {
		ManyToOne,
		OneToMany,
	};

	struct ConnectionPoint {
		size_t Node;
		int Pin;

		bool operator==(const ConnectionPoint&) const = default;
	};

	std::vector<ConnectionPoint> MultiConnections;
	ConnectionPoint SingleConnection;
	Direction ConnectionDirection;

public:
	WorkflowConnection();

	bool IsValid() const;
	std::span<ConnectionPoint> GetSourcePoints();
	std::span<const ConnectionPoint> GetSourcePoints() const;
	std::span<ConnectionPoint> GetDestinationPoints();
	std::span<const ConnectionPoint> GetDestinationPoints() const;

	void DrawDebugInfo() const;
	void ReadFrom(std::istream& stream);
	void WriteTo(std::ostream& stream);
};

class WorkflowNode {
public:
	static constexpr auto kInvalidId = std::numeric_limits<size_t>::max();

	enum Type {
		InputType,
		TransformType,
		OutputType,
	};

	enum Kind {
		KD_NumericAddition,
		KD_NumericSubtraction,
		KD_NumericMultiplication,
		KD_NumericDivision,
		KD_NumericExpression,
		KD_TextFormatting,
		KD_DocumentTemplateExpansion,
		KD_FormInput,
		KD_DatabaseRowsInput,

		InvalidKind,
		KindCount = InvalidKind,
	};

protected:
	struct InputPin {
		size_t Connection = WorkflowConnection::kInvalidId;
		BaseValue::Kind MatchingType = BaseValue::InvalidKind;
		bool ConnectionToConst = false;
		bool AllowsMultipleConnections = false;

		/// A constant connection connects from a user-specified constant value, feeding to a valid \c Destination and \c DestinationPin (i.e. input pins).
		bool IsConstantConnection() const;
		bool IsConnected() const;
		BaseValue::Kind GetMatchingType() const;
		WorkflowConnection::Direction GetSupportedDirection() const;
	};

	struct OutputPin {
		size_t Connection = WorkflowConnection::kInvalidId;
		BaseValue::Kind MatchingType = BaseValue::InvalidKind;
		bool AllowsMultipleConnections = false;

		bool IsConnected() const;
		BaseValue::Kind GetMatchingType() const;
		WorkflowConnection::Direction GetSupportedDirection() const;
	};

	friend class Workflow;
	friend class WorkflowEvaluationContext;

	Workflow* mWorkflow;
	size_t mId;
	std::vector<InputPin> mInputs;
	std::vector<OutputPin> mOutputs;
	Vec2i mPosition;
	Kind mKind;
	int mDepth;

public:
	static const char* FormatKind(Kind kind);
	static const char* FormatType(Type type);
	static std::unique_ptr<WorkflowNode> CreateByKind(Kind kind);

	WorkflowNode(Type type, Kind kind);
	virtual ~WorkflowNode() = default;

	WorkflowNode(const WorkflowNode&) = delete;
	WorkflowNode& operator=(const WorkflowNode&) = delete;
	WorkflowNode(WorkflowNode&&) = default;
	WorkflowNode& operator=(WorkflowNode&&) = default;

	void SetPosition(const Vec2i& position);
	Vec2i GetPosition() const;

	size_t GetId() const;
	Kind GetKind() const;
	int GetDepth() const;

	Type GetType() const;
	bool IsInputNode() const;
	bool IsOutputNode() const;

	void ConnectInput(int nodeId, WorkflowNode& output, int outputNodeId);
	void DisconnectInput(int nodeId);
	bool IsInputConnected(int nodeId) const;

	void ConnectOutput(int nodeId, WorkflowNode& input, int inputNodeId);
	void DisconnectOutput(int nodeId);
	bool IsOutputConnected(int nodeId) const;

	virtual void Evaluate(WorkflowEvaluationContext& ctx) = 0;

	void Draw();
	virtual void DrawExtra() {}

	void DrawDebugInfo() const;
	virtual void DrawExtraDebugInfo() const {}

	virtual void ReadFrom(std::istream& istream);
	virtual void WriteTo(std::ostream& ostream);

protected:
	InputPin& InsertInputPin(int atIdx);
	void RemoveInputPin(int pin);
	void SwapInputPin(int a, int b);
	OutputPin& InsertOutputPin(int atIdx);
	void RemoveOutputPin(int pin);
	void SwapOutputPin(int a, int b);

	/* For \c Workflow to invoke, override by implementations */

	void OnAttach(Workflow& workflow, size_t newId) {}
	void OnDetach() {}
};

class Workflow {
private:
	friend class WorkflowEvaluationContext;

	std::vector<WorkflowConnection> mConnections;
	std::vector<std::unique_ptr<WorkflowNode>> mNodes;
	std::vector<std::unique_ptr<BaseValue>> mConstants;
	std::vector<std::vector<size_t>> mDepthGroups;
	int mConnectionCount;
	int mNodeCount;
	int mConstantCount;
	bool mDepthsDirty = true;

public:
	WorkflowConnection* GetConnectionById(size_t id);
	WorkflowNode* GetStepById(size_t id);
	BaseValue* GetConstantById(size_t id);

	void AddStep(std::unique_ptr<WorkflowNode> step);
	void RemoveStep(size_t id);

	void RemoveConnection(size_t id);

	bool Connect(WorkflowNode& sourceNode, int sourcePin, WorkflowNode& destinationNode, int destinationPin);
	bool DisconnectBySource(WorkflowNode& sourceNode, int sourcePin);
	bool DisconnectByDestination(WorkflowNode& destinationNode, int destinationPin);

	const std::vector<std::vector<size_t>>& GetDepthGroups() const;
	bool DoesDepthNeedsUpdate() const;

	struct GraphUpdate_Success {};
	struct GraphUpdate_NoWorkToDo {};
	struct GraphUpdate_UnsatisfiedDependencies {
		std::vector<size_t> UnsatisfiedNodes;
	};
	struct GraphUpdate_UnreachableNodes {
		std::vector<size_t> UnreachableNodes;
	};

	using GraphUpdateResult = std::variant<
		GraphUpdate_Success,
		GraphUpdate_NoWorkToDo,
		GraphUpdate_UnsatisfiedDependencies,
		GraphUpdate_UnreachableNodes>;

	/// When `getInfo == false, the corresponding error code is returned but without/with empty payloads.
	GraphUpdateResult UpdateGraph(bool getInfo = true);

	enum ReadResult {
		ReadSuccess,
		ReadInvalidVersion,
	};
	ReadResult ReadFrom(std::istream& stream);
	void WriteTo(std::ostream& stream);

private:
	std::pair<WorkflowConnection&, size_t> AllocWorkflowConnection();
	std::pair<std::unique_ptr<WorkflowNode>&, size_t> AllocWorkflowStep();
};