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#pragma once
#include "Api.h"
#include "CursorManager.h"
#include "Types.h"
/**
* @file VM.h
* @brief Declares the logic execution boundary for relational and higher-order workloads.
*/
namespace nt
{
/**
* @class VM
* @brief Hosts the first-order logic (FOL) and second-order logic (SOL) cores.
*
* This partitioning exists to ensure retrieval terminates when execution is
* constrained to first-order logic.
*
* - Tarski runtime (FOL): a relational engine that implements Tarski's
* relational calculus. It uses a deterministic Volcano-iterator model to
* perform relational algebra operations such as joins, projections, and
* selects directly against the CursorManager and a prepared plan.
*
* - Karuta runtime (SOL): an isolated WAM-based environment for
* higher-order logic programming. It handles recursion, choice points, and
* other programming constructs that do not guarantee termination.
*
* @remark Lazy evaluation and paging strategy
*
* Both the Tarski first-order engine and the Karuta second-order engine are
* strictly pull-based. Data is streamed lazily from the CursorManager to
* preserve a constant memory footprint regardless of relation size.
*
* Pipeline dynamics:
* - Demand-driven: the Karuta WAM requests a fact only when a goal needs
* satisfaction. A request propagates down the algebra tree as a chain of
* Next() calls.
*
* - Short-circuiting: if the Karuta engine finds a solution or reaches a
* failure that invalidates a branch, the Tarski iterator is discarded or
* reset without materializing the remaining tuples.
*
* - Resource stewardship: by maintaining laziness up to the highest logical
* level, the runtime minimizes pressure on ObjectManager and keeps
* snapshots pinned through LifecycleManager::Monitor only for the minimum
* time required.
*/
/**
* @brief A node in the Volcano operator tree executed by the Tarski (FOL) runtime.
*
* Each node represents one relational algebra operator. The tree is demand-driven:
* VM::Next() propagates pull requests from root to leaves.
*
* TODO: Add FILTER, PROJECT, and JOIN operators as the query layer grows.
*/
struct NT_API PlanNode
{
enum class Op { SCAN };
Op op;
PlanNode* left = nullptr; /**< Left child (binary operators). */
PlanNode* right = nullptr; /**< Right child (binary operators). */
/** Cursor to scan. Set when op == SCAN. */
CursorManager::cursor* scan_cursor = nullptr;
};
class NT_API VM
{
public:
// TODO: CursorManager should be injected as a shared runtime instance,
// matching the pattern flagged for HandlerManager and LifecycleManager.
//
// A single CursorManager instance supports multiple simultaneous cursors —
// all iteration state lives in each cursor struct, not in the manager.
// A JOIN plan, for example, holds two independent cursors (one per SCAN leaf)
// and both are driven through the same CursorManager reference.
explicit VM(CursorManager& cursors);
/**
* @brief Pulls the next tuple from the plan tree (Tarski/FOL core).
*
* Propagates a Next() call down the operator tree. The call chain
* terminates at a SCAN node, which delegates to CursorManager.
*
* @param node Root of the plan subtree to evaluate.
* @return Next matching tuple, or nullptr when the plan is exhausted.
*/
Tuple* Next(PlanNode* node);
private:
CursorManager& cursors_;
};
}
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