codebase-memory-mcp/internal/cypher/executor.go

package cypher

import (
	"database/sql"
	"fmt"
	"regexp"
	"sort"
	"strconv"
	"strings"

	"github.com/DeusData/codebase-memory-mcp/internal/store"
)

const maxResultRows = 200

// Executor runs Cypher execution plans against a store.
type Executor struct {
	Store      *store.Store
	regexCache map[string]*regexp.Regexp
}

// Result holds the tabular output of a query.
type Result struct {
	Columns []string         `json:"columns"`
	Rows    []map[string]any `json:"rows"`
}

// binding maps variable names to matched nodes and edges.
type binding struct {
	nodes map[string]*store.Node
	edges map[string]*store.Edge
}

func newBinding() binding {
	return binding{
		nodes: make(map[string]*store.Node),
		edges: make(map[string]*store.Edge),
	}
}

// Execute parses, plans, and executes a Cypher query across all projects.
func (e *Executor) Execute(query string) (*Result, error) {
	q, err := Parse(query)
	if err != nil {
		return nil, fmt.Errorf("parse: %w", err)
	}
	plan, err := BuildPlan(q)
	if err != nil {
		return nil, fmt.Errorf("plan: %w", err)
	}
	return e.executePlan(plan)
}

func (e *Executor) executePlan(plan *Plan) (*Result, error) {
	// Fast path: push COUNT aggregation to SQL when pattern is fusible.
	if result, ok := e.tryAggregateSQL(plan); ok {
		return result, nil
	}

	projects, err := e.Store.ListProjects()
	if err != nil {
		return nil, fmt.Errorf("list projects: %w", err)
	}

	var allBindings []binding
	for _, proj := range projects {
		bindings, err := e.executeStepsForProject(proj.Name, plan.Steps)
		if err != nil {
			continue // skip projects that error
		}
		allBindings = append(allBindings, bindings...)
		if len(allBindings) > maxResultRows*2 {
			allBindings = allBindings[:maxResultRows*2]
			break
		}
	}

	return e.projectResults(allBindings, plan.ReturnSpec)
}

// tryAggregateSQL attempts to push a COUNT aggregation query entirely to SQL.
// Returns (result, true) if the pattern is fusible, (nil, false) otherwise.
// Fusible pattern: ScanNodes + ExpandRelationship (fixed-length 1 hop) with
// RETURN containing COUNT and group-by items that map to SQL columns.
func (e *Executor) tryAggregateSQL(plan *Plan) (*Result, bool) {
	if plan.ReturnSpec == nil {
		return nil, false
	}

	// Must have COUNT in return
	var countItem *ReturnItem
	var groupItems []ReturnItem
	for i := range plan.ReturnSpec.Items {
		item := &plan.ReturnSpec.Items[i]
		if item.Func == "COUNT" {
			countItem = item
		} else {
			groupItems = append(groupItems, *item)
		}
	}
	if countItem == nil {
		return nil, false
	}

	// Identify the fusible step pattern: optional FilterWhere between Scan and Expand
	steps := plan.Steps
	var scan *ScanNodes
	var expand *ExpandRelationship
	var filter *FilterWhere

	switch len(steps) {
	case 2:
		s, ok1 := steps[0].(*ScanNodes)
		ex, ok2 := steps[1].(*ExpandRelationship)
		if !ok1 || !ok2 {
			return nil, false
		}
		scan, expand = s, ex
	case 3:
		s, ok1 := steps[0].(*ScanNodes)
		f, ok2 := steps[1].(*FilterWhere)
		ex, ok3 := steps[2].(*ExpandRelationship)
		if !ok1 || !ok3 {
			return nil, false
		}
		scan, expand = s, ex
		if ok2 {
			filter = f
		}
	default:
		return nil, false
	}

	// Must be fixed-length (1 hop)
	if expand.MinHops != 1 || expand.MaxHops != 1 {
		return nil, false
	}
	if len(expand.EdgeTypes) == 0 {
		return nil, false
	}
	if len(scan.Props) > 0 || len(expand.ToProps) > 0 {
		return nil, false // inline property filters not supported in SQL push-down
	}

	// All group-by items must reference SQL-pushable columns
	for _, gi := range groupItems {
		if gi.Property == "" {
			return nil, false
		}
		if _, ok := sqlPushableColumns[gi.Property]; !ok {
			return nil, false
		}
	}

	// Filter conditions must all be pushable
	if filter != nil {
		for _, c := range filter.Conditions {
			if _, ok := sqlPushableColumns[c.Property]; !ok {
				return nil, false
			}
			switch c.Operator {
			case "=", "CONTAINS", "STARTS WITH":
				// OK
			default:
				return nil, false // regex, numeric not pushable
			}
		}
	}

	// Build the SQL query
	projects, err := e.Store.ListProjects()
	if err != nil {
		return nil, false
	}

	dir := expand.Direction
	if dir == "" {
		dir = "outbound"
	}
	var srcCol, tgtCol string
	if dir == "outbound" {
		srcCol, tgtCol = "source_id", "target_id"
	} else {
		srcCol, tgtCol = "target_id", "source_id"
	}

	// Map variable names to table aliases
	srcAlias := "src" // scan variable
	tgtAlias := "tgt" // expand target variable

	// Build SELECT columns for group-by items
	selectParts := make([]string, 0, len(groupItems)+1)
	groupByParts := make([]string, 0, len(groupItems))
	for _, gi := range groupItems {
		col := sqlPushableColumns[gi.Property]
		var alias string
		if gi.Variable == scan.Variable {
			alias = srcAlias
		} else {
			alias = tgtAlias
		}
		selectParts = append(selectParts, alias+"."+col)
		groupByParts = append(groupByParts, alias+"."+col)
	}
	selectParts = append(selectParts, "COUNT(*) as cnt")

	// Accumulate results across all projects
	cols := buildColumnNames(plan.ReturnSpec.Items)
	countCol := cols[len(cols)-1] // COUNT column is last

	allRows := make([]map[string]any, 0)

	for _, proj := range projects {
		var sb strings.Builder
		args := make([]any, 0, 10)

		sb.WriteString("SELECT ")
		sb.WriteString(strings.Join(selectParts, ", "))
		sb.WriteString(" FROM edges e")
		sb.WriteString(fmt.Sprintf(" JOIN nodes %s ON %s.id = e.%s", srcAlias, srcAlias, srcCol))
		sb.WriteString(fmt.Sprintf(" JOIN nodes %s ON %s.id = e.%s", tgtAlias, tgtAlias, tgtCol))
		sb.WriteString(" WHERE e.project = ?")
		args = append(args, proj.Name)

		// Edge type filter
		typePlaceholders := make([]string, len(expand.EdgeTypes))
		for i, et := range expand.EdgeTypes {
			typePlaceholders[i] = "?"
			args = append(args, et)
		}
		sb.WriteString(" AND e.type IN (" + strings.Join(typePlaceholders, ",") + ")")

		// Label filters
		if scan.Label != "" {
			sb.WriteString(fmt.Sprintf(" AND %s.label = ?", srcAlias))
			args = append(args, scan.Label)
		}
		if expand.ToLabel != "" {
			sb.WriteString(fmt.Sprintf(" AND %s.label = ?", tgtAlias))
			args = append(args, expand.ToLabel)
		}

		// Push-down WHERE conditions
		if filter != nil {
			for _, c := range filter.Conditions {
				col := sqlPushableColumns[c.Property]
				var alias string
				if c.Variable == scan.Variable {
					alias = srcAlias
				} else {
					alias = tgtAlias
				}
				switch c.Operator {
				case "=":
					sb.WriteString(fmt.Sprintf(" AND %s.%s = ?", alias, col))
					args = append(args, c.Value)
				case "CONTAINS":
					sb.WriteString(fmt.Sprintf(" AND %s.%s LIKE ?", alias, col))
					args = append(args, "%"+c.Value+"%")
				case "STARTS WITH":
					sb.WriteString(fmt.Sprintf(" AND %s.%s LIKE ?", alias, col))
					args = append(args, c.Value+"%")
				}
			}
		}

		sb.WriteString(" GROUP BY " + strings.Join(groupByParts, ", "))

		rows, qErr := e.Store.DB().Query(sb.String(), args...)
		if qErr != nil {
			continue
		}

		for rows.Next() {
			// Scan group-by values + count
			vals := make([]any, len(groupItems)+1)
			ptrs := make([]any, len(groupItems)+1)
			for i := range vals {
				ptrs[i] = &vals[i]
			}
			if sErr := rows.Scan(ptrs...); sErr != nil {
				rows.Close()
				continue
			}
			row := make(map[string]any)
			for i, gi := range groupItems {
				col := gi.Variable + "." + gi.Property
				if gi.Alias != "" {
					col = gi.Alias
				}
				// Normalize []byte to string (mattn returns []byte for TEXT cols)
				if b, ok := vals[i].([]byte); ok {
					row[col] = string(b)
				} else {
					row[col] = vals[i]
				}
			}
			// Normalize COUNT to int for consistency with Go-side aggregation
			switch v := vals[len(vals)-1].(type) {
			case int64:
				row[countCol] = int(v)
			default:
				row[countCol] = v
			}
			allRows = append(allRows, row)
		}
		rows.Close()
	}

	// ORDER BY
	if plan.ReturnSpec.OrderBy != "" {
		orderCol := resolveOrderColumn(plan.ReturnSpec.OrderBy, plan.ReturnSpec.Items, cols)
		sortRows(allRows, orderCol, plan.ReturnSpec.OrderDir)
	}

	// LIMIT
	allRows = applyLimit(allRows, plan.ReturnSpec.Limit)

	return &Result{Columns: cols, Rows: allRows}, true
}

//nolint:gocognit // step dispatch with fusion/push-down is inherently branchy
func (e *Executor) executeStepsForProject(project string, steps []PlanStep) ([]binding, error) {
	var bindings []binding

	for i, step := range steps {
		var err error
		switch s := step.(type) {
		case *ScanNodes:
			// Fast path: ScanNodes followed by ExpandRelationship can be fused
			// into a single SQL JOIN, avoiding N+1 queries.
			if i+1 < len(steps) {
				if expand, ok := steps[i+1].(*ExpandRelationship); ok && canFuseJoin(s, expand) {
					bindings, err = e.execJoinScanExpand(project, s, expand)
					if err != nil {
						return nil, err
					}
					// Mark next step as consumed by incrementing i via a skip flag
					// We'll handle this below.
					steps[i+1] = &fusedExpandMarker{}
					break
				}
			}

			// Check if the next step is a FilterWhere that can be pushed down
			var pushDown *FilterWhere
			if i+1 < len(steps) {
				if fw, ok := steps[i+1].(*FilterWhere); ok {
					pushDown = fw
				}
			}
			bindings, err = e.execScan(project, s, pushDown)
		case *ExpandRelationship:
			bindings, err = e.execExpand(s, bindings)
		case *fusedExpandMarker:
			continue // already handled by JOIN fusion
		case *FilterWhere:
			// Skip if this was already consumed by push-down
			if i > 0 {
				if _, wasScan := steps[i-1].(*ScanNodes); wasScan {
					continue // already handled in execScan
				}
			}
			bindings, err = e.execFilter(s, bindings)
		default:
			return nil, fmt.Errorf("unknown step type: %T", step)
		}
		if err != nil {
			return nil, err
		}
		isLastStep := i == len(steps)-1
		_, isExpand := step.(*ExpandRelationship)
		if isLastStep || isExpand {
			if len(bindings) > maxResultRows*2 {
				bindings = bindings[:maxResultRows*2]
			}
		}
	}

	return bindings, nil
}

// fusedExpandMarker is a placeholder step marking an ExpandRelationship
// that was already handled by JOIN fusion with the preceding ScanNodes.
type fusedExpandMarker struct{}

func (*fusedExpandMarker) stepType() string { return "fused" }

// canFuseJoin returns true if a ScanNodes + ExpandRelationship pair can be
// replaced by a single SQL JOIN. Requirements: fixed-length (1 hop), known
// edge types, standard direction, no inline property filters on source.
func canFuseJoin(scan *ScanNodes, expand *ExpandRelationship) bool {
	if expand.MinHops != 1 || expand.MaxHops != 1 {
		return false // variable-length paths need BFS
	}
	if len(expand.EdgeTypes) == 0 {
		return false // untyped edges: keep generic path
	}
	if len(scan.Props) > 0 {
		return false // inline property filters on source not supported in JOIN
	}
	if expand.Direction != "outbound" && expand.Direction != "inbound" && expand.Direction != "" {
		return false
	}
	return true
}

// execJoinScanExpand executes a fused ScanNodes→ExpandRelationship step using
// a single SQL JOIN, avoiding N+1 queries.
func (e *Executor) execJoinScanExpand(project string, scan *ScanNodes, expand *ExpandRelationship) ([]binding, error) {
	// Build type filter: type IN (?, ?, ...)
	typePlaceholders := make([]string, len(expand.EdgeTypes))
	args := make([]any, 0, len(expand.EdgeTypes)+2)
	args = append(args, project)
	for i, et := range expand.EdgeTypes {
		typePlaceholders[i] = "?"
		args = append(args, et)
	}
	typeFilter := strings.Join(typePlaceholders, ",")

	// Determine join direction
	var srcCol, tgtCol string
	dir := expand.Direction
	if dir == "" {
		dir = "outbound"
	}
	if dir == "outbound" {
		srcCol, tgtCol = "source_id", "target_id"
	} else {
		srcCol, tgtCol = "target_id", "source_id"
	}

	// Build label filters
	var srcLabelClause, tgtLabelClause string
	if scan.Label != "" {
		srcLabelClause = " AND src.label = ?"
		args = append(args, scan.Label)
	}
	if expand.ToLabel != "" {
		tgtLabelClause = " AND tgt.label = ?"
		args = append(args, expand.ToLabel)
	}

	query := fmt.Sprintf(`
		SELECT
			src.id, src.project, src.label, src.name, src.qualified_name, src.file_path, src.start_line, src.end_line, src.properties,
			tgt.id, tgt.project, tgt.label, tgt.name, tgt.qualified_name, tgt.file_path, tgt.start_line, tgt.end_line, tgt.properties,
			e.id, e.project, e.source_id, e.target_id, e.type, e.properties
		FROM edges e
		JOIN nodes src ON src.id = e.%s
		JOIN nodes tgt ON tgt.id = e.%s
		WHERE e.project = ? AND e.type IN (%s)%s%s
		LIMIT ?`,
		srcCol, tgtCol, typeFilter, srcLabelClause, tgtLabelClause)

	args = append(args, maxResultRows*2)

	rows, err := e.Store.DB().Query(query, args...)
	if err != nil {
		return nil, fmt.Errorf("join scan+expand: %w", err)
	}
	defer rows.Close()

	var bindings []binding
	for rows.Next() {
		var srcN, tgtN store.Node
		var srcProps, tgtProps string
		var edge store.Edge
		var edgeProps string

		if err := rows.Scan(
			&srcN.ID, &srcN.Project, &srcN.Label, &srcN.Name, &srcN.QualifiedName, &srcN.FilePath, &srcN.StartLine, &srcN.EndLine, &srcProps,
			&tgtN.ID, &tgtN.Project, &tgtN.Label, &tgtN.Name, &tgtN.QualifiedName, &tgtN.FilePath, &tgtN.StartLine, &tgtN.EndLine, &tgtProps,
			&edge.ID, &edge.Project, &edge.SourceID, &edge.TargetID, &edge.Type, &edgeProps,
		); err != nil {
			return nil, err
		}
		srcN.Properties = store.UnmarshalProps(srcProps)
		tgtN.Properties = store.UnmarshalProps(tgtProps)
		edge.Properties = store.UnmarshalProps(edgeProps)

		// Apply target inline property filters
		if len(expand.ToProps) > 0 && !nodeMatchesProps(&tgtN, expand.ToProps) {
			continue
		}

		b := newBinding()
		if scan.Variable != "" {
			b.nodes[scan.Variable] = &srcN
		}
		if expand.ToVar != "" {
			b.nodes[expand.ToVar] = &tgtN
		}
		if expand.RelVar != "" {
			b.edges[expand.RelVar] = &edge
		}
		bindings = append(bindings, b)
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}

	return bindings, nil
}

// sqlPushableColumns are node properties that map directly to SQL columns.
var sqlPushableColumns = map[string]string{
	"name":           "name",
	"qualified_name": "qualified_name",
	"label":          "label",
	"file_path":      "file_path",
}

func (e *Executor) execScan(project string, s *ScanNodes, pushDown *FilterWhere) ([]binding, error) {
	// Build dynamic SQL query with optional push-down conditions
	query := `SELECT id, project, label, name, qualified_name, file_path, start_line, end_line, properties FROM nodes WHERE project=?`
	args := []any{project}

	if s.Label != "" {
		query += " AND label=?"
		args = append(args, s.Label)
	}

	// Push down WHERE conditions into SQL where possible
	var unpushedConditions []Condition
	if pushDown != nil {
		for _, c := range pushDown.Conditions {
			col, canPush := sqlPushableColumns[c.Property]
			if !canPush {
				unpushedConditions = append(unpushedConditions, c)
				continue
			}
			switch c.Operator {
			case "=":
				query += " AND " + col + "=?"
				args = append(args, c.Value)
			case "CONTAINS":
				query += " AND " + col + " LIKE ?"
				args = append(args, "%"+c.Value+"%")
			case "STARTS WITH":
				query += " AND " + col + " LIKE ?"
				args = append(args, c.Value+"%")
			default:
				// =~, numeric comparisons: can't push to SQL easily
				unpushedConditions = append(unpushedConditions, c)
			}
		}
	}

	rows, err := e.Store.DB().Query(query, args...)
	if err != nil {
		return nil, fmt.Errorf("scan nodes: %w", err)
	}
	defer rows.Close()

	var nodes []*store.Node
	for rows.Next() {
		n, scanErr := scanNodeFromRows(rows)
		if scanErr != nil {
			return nil, scanErr
		}
		nodes = append(nodes, n)
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}

	// Apply inline property filters
	if len(s.Props) > 0 {
		nodes = filterNodesByProps(nodes, s.Props)
	}

	bindings := make([]binding, 0, len(nodes))
	for _, n := range nodes {
		// Apply unpushed conditions in Go
		if len(unpushedConditions) > 0 {
			b := newBinding()
			b.nodes[s.Variable] = n
			match, evalErr := e.evaluateConditions(b, unpushedConditions, "AND")
			if evalErr != nil {
				return nil, evalErr
			}
			if !match {
				continue
			}
		}
		b := newBinding()
		if s.Variable != "" {
			b.nodes[s.Variable] = n
		}
		bindings = append(bindings, b)
	}
	return bindings, nil
}

// scanNodeFromRows scans a single node from sql.Rows.
func scanNodeFromRows(rows *sql.Rows) (*store.Node, error) {
	var n store.Node
	var props string
	if err := rows.Scan(&n.ID, &n.Project, &n.Label, &n.Name, &n.QualifiedName, &n.FilePath, &n.StartLine, &n.EndLine, &props); err != nil {
		return nil, err
	}
	n.Properties = store.UnmarshalProps(props)
	return &n, nil
}

func (e *Executor) execExpand(s *ExpandRelationship, bindings []binding) ([]binding, error) {
	if len(bindings) == 0 {
		return nil, nil
	}

	isVariableLength := s.MinHops != 1 || s.MaxHops != 1

	if isVariableLength {
		// Variable-length: use BFS per binding (already uses recursive CTE)
		result := make([]binding, 0, len(bindings))
		for _, b := range bindings {
			fromNode, ok := b.nodes[s.FromVar]
			if !ok {
				continue
			}
			expanded, err := e.expandVariableLength(b, fromNode, s)
			if err != nil {
				return nil, err
			}
			result = append(result, expanded...)
			if len(result) > maxResultRows*2 {
				result = result[:maxResultRows*2]
				break
			}
		}
		return result, nil
	}

	// Fixed-length (1 hop): batch all source IDs, 2 queries total
	return e.expandFixedLengthBatch(s, bindings)
}

// expandFixedLengthBatch performs fixed-length (1 hop) expansion for all bindings
// in just 2 SQL queries: one for edges, one for target nodes.
func (e *Executor) expandFixedLengthBatch(s *ExpandRelationship, bindings []binding) ([]binding, error) {
	// Collect all unique source node IDs
	sourceIDs := make([]int64, 0, len(bindings))
	idSeen := make(map[int64]bool, len(bindings))
	for _, b := range bindings {
		fromNode, ok := b.nodes[s.FromVar]
		if !ok {
			continue
		}
		if !idSeen[fromNode.ID] {
			idSeen[fromNode.ID] = true
			sourceIDs = append(sourceIDs, fromNode.ID)
		}
	}

	if len(sourceIDs) == 0 {
		return nil, nil
	}

	direction := s.Direction
	if direction == "" {
		direction = "outbound"
	}

	// Batch 1: fetch all edges for all source IDs
	var edgesByNode map[int64][]*store.Edge
	var err error
	switch direction {
	case "outbound":
		edgesByNode, err = e.Store.FindEdgesBySourceIDs(sourceIDs, s.EdgeTypes)
	case "inbound":
		edgesByNode, err = e.Store.FindEdgesByTargetIDs(sourceIDs, s.EdgeTypes)
	case "any":
		outEdges, outErr := e.Store.FindEdgesBySourceIDs(sourceIDs, s.EdgeTypes)
		if outErr != nil {
			return nil, outErr
		}
		inEdges, inErr := e.Store.FindEdgesByTargetIDs(sourceIDs, s.EdgeTypes)
		if inErr != nil {
			return nil, inErr
		}
		edgesByNode = outEdges
		for id, edges := range inEdges {
			edgesByNode[id] = append(edgesByNode[id], edges...)
		}
	default:
		edgesByNode, err = e.Store.FindEdgesBySourceIDs(sourceIDs, s.EdgeTypes)
	}
	if err != nil {
		return nil, err
	}

	// Collect all target node IDs
	targetIDSet := make(map[int64]bool)
	for _, edges := range edgesByNode {
		for _, edge := range edges {
			tid := edgeTargetID(edge, 0, direction)
			if direction == "any" {
				// For "any", we need to check per-source
				targetIDSet[edge.SourceID] = true
				targetIDSet[edge.TargetID] = true
			} else {
				targetIDSet[tid] = true
			}
		}
	}
	targetIDs := make([]int64, 0, len(targetIDSet))
	for id := range targetIDSet {
		targetIDs = append(targetIDs, id)
	}

	// Batch 2: fetch all target nodes
	nodeMap, err := e.Store.FindNodesByIDs(targetIDs)
	if err != nil {
		return nil, err
	}

	// Build results per binding
	result := make([]binding, 0, len(bindings))
	for _, b := range bindings {
		fromNode, ok := b.nodes[s.FromVar]
		if !ok {
			continue
		}
		edges := edgesByNode[fromNode.ID]
		seen := make(map[int64]bool)

		for _, edge := range edges {
			targetID := edgeTargetID(edge, fromNode.ID, direction)
			if seen[targetID] {
				continue
			}
			seen[targetID] = true

			node, exists := nodeMap[targetID]
			if !exists {
				continue
			}
			if s.ToLabel != "" && node.Label != s.ToLabel {
				continue
			}
			if len(s.ToProps) > 0 && !nodeMatchesProps(node, s.ToProps) {
				continue
			}
			newB := copyBinding(b)
			if s.ToVar != "" {
				newB.nodes[s.ToVar] = node
			}
			if s.RelVar != "" {
				newB.edges[s.RelVar] = edge
			}
			result = append(result, newB)
		}

		if len(result) > maxResultRows*2 {
			result = result[:maxResultRows*2]
			break
		}
	}
	return result, nil
}

func (e *Executor) expandVariableLength(b binding, fromNode *store.Node, s *ExpandRelationship) ([]binding, error) {
	maxDepth := s.MaxHops
	if maxDepth == 0 {
		maxDepth = 10 // cap unbounded at 10
	}

	direction := s.Direction
	if direction == "" {
		direction = "outbound"
	}

	edgeTypes := s.EdgeTypes
	if len(edgeTypes) == 0 {
		edgeTypes = []string{"CALLS"} // default
	}

	bfsResult, err := e.Store.BFS(fromNode.ID, direction, edgeTypes, maxDepth, maxResultRows)
	if err != nil {
		return nil, fmt.Errorf("bfs: %w", err)
	}

	result := make([]binding, 0, len(bfsResult.Visited))
	for _, nh := range bfsResult.Visited {
		if nh.Hop < s.MinHops {
			continue
		}
		if s.MaxHops > 0 && nh.Hop > s.MaxHops {
			continue
		}
		if s.ToLabel != "" && nh.Node.Label != s.ToLabel {
			continue
		}
		if len(s.ToProps) > 0 && !nodeMatchesProps(nh.Node, s.ToProps) {
			continue
		}
		newB := copyBinding(b)
		if s.ToVar != "" {
			newB.nodes[s.ToVar] = nh.Node
		}
		// Note: variable-length BFS doesn't bind individual edges
		result = append(result, newB)
	}
	return result, nil
}


// edgeTargetID returns the ID of the node on the "other end" of the edge relative to nodeID.
func edgeTargetID(edge *store.Edge, nodeID int64, direction string) int64 {
	switch direction {
	case "inbound":
		return edge.SourceID
	case "any":
		if edge.SourceID == nodeID {
			return edge.TargetID
		}
		return edge.SourceID
	default:
		return edge.TargetID
	}
}

func (e *Executor) execFilter(s *FilterWhere, bindings []binding) ([]binding, error) {
	var result []binding
	for _, b := range bindings {
		match, err := e.evaluateConditions(b, s.Conditions, s.Operator)
		if err != nil {
			return nil, err
		}
		if match {
			result = append(result, b)
		}
	}
	return result, nil
}

func (e *Executor) evaluateConditions(b binding, conditions []Condition, op string) (bool, error) {
	if op == "OR" {
		for _, c := range conditions {
			ok, err := e.evaluateCondition(b, c)
			if err != nil {
				return false, err
			}
			if ok {
				return true, nil
			}
		}
		return false, nil
	}
	// AND (default)
	for _, c := range conditions {
		ok, err := e.evaluateCondition(b, c)
		if err != nil {
			return false, err
		}
		if !ok {
			return false, nil
		}
	}
	return true, nil
}

// compiledRegex returns a compiled regex for the pattern, using a cache
// to avoid recompiling the same pattern on every binding.
func (e *Executor) compiledRegex(pattern string) (*regexp.Regexp, error) {
	if e.regexCache == nil {
		e.regexCache = make(map[string]*regexp.Regexp)
	}
	if re, ok := e.regexCache[pattern]; ok {
		return re, nil
	}
	re, err := regexp.Compile(pattern)
	if err != nil {
		return nil, err
	}
	e.regexCache[pattern] = re
	return re, nil
}

func (e *Executor) evaluateCondition(b binding, c Condition) (bool, error) {
	// Try node first, then edge
	var actual any
	if node, ok := b.nodes[c.Variable]; ok {
		actual = getNodeProperty(node, c.Property)
	} else if edge, ok := b.edges[c.Variable]; ok {
		actual = getEdgeProperty(edge, c.Property)
	} else {
		return false, nil
	}

	switch c.Operator {
	case "=":
		return fmt.Sprintf("%v", actual) == c.Value, nil
	case "=~":
		s, ok := actual.(string)
		if !ok {
			return false, nil
		}
		re, err := e.compiledRegex(c.Value)
		if err != nil {
			return false, fmt.Errorf("regex %q: %w", c.Value, err)
		}
		return re.MatchString(s), nil
	case "CONTAINS":
		s, ok := actual.(string)
		if !ok {
			return false, nil
		}
		return strings.Contains(s, c.Value), nil
	case "STARTS WITH":
		s, ok := actual.(string)
		if !ok {
			return false, nil
		}
		return strings.HasPrefix(s, c.Value), nil
	case ">", "<", ">=", "<=":
		return compareNumeric(actual, c.Value, c.Operator)
	default:
		return false, fmt.Errorf("unsupported operator: %s", c.Operator)
	}
}

func compareNumeric(actual any, expected, op string) (bool, error) {
	expectedNum, err := strconv.ParseFloat(expected, 64)
	if err != nil {
		return false, fmt.Errorf("invalid numeric value %q: %w", expected, err)
	}
	var actualNum float64
	switch v := actual.(type) {
	case int:
		actualNum = float64(v)
	case int64:
		actualNum = float64(v)
	case float64:
		actualNum = v
	case string:
		n, parseErr := strconv.ParseFloat(v, 64)
		if parseErr != nil {
			return false, fmt.Errorf("cannot compare %q as number: %w", v, parseErr)
		}
		actualNum = n
	default:
		return false, nil
	}

	switch op {
	case ">":
		return actualNum > expectedNum, nil
	case "<":
		return actualNum < expectedNum, nil
	case ">=":
		return actualNum >= expectedNum, nil
	case "<=":
		return actualNum <= expectedNum, nil
	default:
		return false, nil
	}
}

func getNodeProperty(n *store.Node, prop string) any {
	switch prop {
	case "name":
		return n.Name
	case "qualified_name":
		return n.QualifiedName
	case "label":
		return n.Label
	case "file_path":
		return n.FilePath
	case "start_line":
		return n.StartLine
	case "end_line":
		return n.EndLine
	case "id":
		return n.ID
	case "project":
		return n.Project
	default:
		if n.Properties != nil {
			if v, ok := n.Properties[prop]; ok {
				return v
			}
		}
		return nil
	}
}

// getEdgeProperty returns a property value from an edge.
func getEdgeProperty(edge *store.Edge, prop string) any {
	switch prop {
	case "type":
		return edge.Type
	case "id":
		return edge.ID
	case "source_id":
		return edge.SourceID
	case "target_id":
		return edge.TargetID
	default:
		if edge.Properties != nil {
			if v, ok := edge.Properties[prop]; ok {
				return v
			}
		}
		return nil
	}
}

func (e *Executor) projectResults(bindings []binding, ret *ReturnClause) (*Result, error) {
	if ret == nil {
		return e.defaultProjection(bindings)
	}

	// Check if we have a COUNT aggregation
	hasCount := false
	for _, item := range ret.Items {
		if item.Func == "COUNT" {
			hasCount = true
			break
		}
	}

	if hasCount {
		return e.aggregateResults(bindings, ret)
	}

	return e.simpleProjection(bindings, ret)
}

func (e *Executor) defaultProjection(bindings []binding) (*Result, error) {
	if len(bindings) == 0 {
		return &Result{Columns: []string{}, Rows: []map[string]any{}}, nil
	}

	// Collect all variable names from nodes and edges
	varSet := make(map[string]bool)
	edgeVarSet := make(map[string]bool)
	for _, b := range bindings {
		for k := range b.nodes {
			varSet[k] = true
		}
		for k := range b.edges {
			edgeVarSet[k] = true
		}
	}
	cols := make([]string, 0, len(varSet)*3+len(edgeVarSet))
	for k := range varSet {
		cols = append(cols, k+".name", k+".qualified_name", k+".label")
	}
	for k := range edgeVarSet {
		cols = append(cols, k+".type")
	}
	sort.Strings(cols)

	rows := make([]map[string]any, 0, len(bindings))
	for _, b := range bindings {
		row := make(map[string]any)
		for varName, node := range b.nodes {
			row[varName+".name"] = node.Name
			row[varName+".qualified_name"] = node.QualifiedName
			row[varName+".label"] = node.Label
		}
		for varName, edge := range b.edges {
			row[varName+".type"] = edge.Type
		}
		rows = append(rows, row)
	}

	if len(rows) > maxResultRows {
		rows = rows[:maxResultRows]
	}

	return &Result{Columns: cols, Rows: rows}, nil
}

func (e *Executor) simpleProjection(bindings []binding, ret *ReturnClause) (*Result, error) {
	cols := buildColumnNames(ret.Items)

	seen := make(map[string]bool)
	rows := make([]map[string]any, 0, len(bindings))
	for _, b := range bindings {
		row := buildProjectionRow(b, ret.Items, cols)

		// DISTINCT check
		if ret.Distinct {
			key := fmt.Sprintf("%v", row)
			if seen[key] {
				continue
			}
			seen[key] = true
		}

		rows = append(rows, row)
	}

	// ORDER BY
	if ret.OrderBy != "" {
		orderCol := resolveOrderColumn(ret.OrderBy, ret.Items, cols)
		sortRows(rows, orderCol, ret.OrderDir)
	}

	// LIMIT
	rows = applyLimit(rows, ret.Limit)

	return &Result{Columns: cols, Rows: rows}, nil
}

// buildColumnNames builds column names from return items.
func buildColumnNames(items []ReturnItem) []string {
	cols := make([]string, 0, len(items))
	for _, item := range items {
		col := item.Variable
		if item.Property != "" {
			col = item.Variable + "." + item.Property
		}
		if item.Alias != "" {
			col = item.Alias
		}
		cols = append(cols, col)
	}
	return cols
}

// buildProjectionRow builds a single result row from a binding.
func buildProjectionRow(b binding, items []ReturnItem, cols []string) map[string]any {
	row := make(map[string]any)
	for i, item := range items {
		row[cols[i]] = resolveItemValue(b, item)
	}
	return row
}

// resolveItemValue resolves a return item value from a binding (node or edge).
func resolveItemValue(b binding, item ReturnItem) any {
	if node, ok := b.nodes[item.Variable]; ok {
		return resolveNodeItemValue(node, item.Property)
	}
	if edge, ok := b.edges[item.Variable]; ok {
		return resolveEdgeItemValue(edge, item.Property)
	}
	return nil
}

// resolveNodeItemValue resolves a node return item: full node map or single property.
func resolveNodeItemValue(node *store.Node, property string) any {
	if property == "" {
		return map[string]any{
			"name":           node.Name,
			"qualified_name": node.QualifiedName,
			"label":          node.Label,
			"file_path":      node.FilePath,
			"start_line":     node.StartLine,
			"end_line":       node.EndLine,
		}
	}
	return getNodeProperty(node, property)
}

// resolveEdgeItemValue resolves an edge return item: full edge map or single property.
func resolveEdgeItemValue(edge *store.Edge, property string) any {
	if property == "" {
		return map[string]any{
			"type":      edge.Type,
			"source_id": edge.SourceID,
			"target_id": edge.TargetID,
		}
	}
	return getEdgeProperty(edge, property)
}

// resolveOrderColumn maps an ORDER BY field to the actual column name.
func resolveOrderColumn(orderBy string, items []ReturnItem, cols []string) string {
	for i, item := range items {
		if item.Alias == orderBy {
			return cols[i]
		}
	}
	return orderBy
}

// applyLimit enforces the LIMIT clause on result rows.
func applyLimit(rows []map[string]any, limit int) []map[string]any {
	if limit <= 0 || limit > maxResultRows {
		limit = maxResultRows
	}
	if len(rows) > limit {
		return rows[:limit]
	}
	return rows
}

func (e *Executor) aggregateResults(bindings []binding, ret *ReturnClause) (*Result, error) {
	groupItems, countItem := splitAggregateItems(ret.Items)
	groups, order := buildGroups(bindings, groupItems)

	// Build columns
	cols := buildColumnNames(ret.Items)

	// Build result rows
	countCol := countItem.Alias
	if countCol == "" {
		countCol = "COUNT(" + countItem.Variable + ")"
	}

	rows := make([]map[string]any, 0, len(order))
	for _, key := range order {
		g := groups[key]
		row := g.row
		row[countCol] = g.count
		rows = append(rows, row)
	}

	// ORDER BY
	if ret.OrderBy != "" {
		sortRows(rows, ret.OrderBy, ret.OrderDir)
	}

	// LIMIT
	rows = applyLimit(rows, ret.Limit)

	return &Result{Columns: cols, Rows: rows}, nil
}

// splitAggregateItems separates return items into group-by items and the COUNT item.
func splitAggregateItems(items []ReturnItem) (groupItems []ReturnItem, countItem ReturnItem) {
	for _, item := range items {
		if item.Func == "COUNT" {
			countItem = item
		} else {
			groupItems = append(groupItems, item)
		}
	}
	return groupItems, countItem
}

type groupEntry struct {
	key   string
	row   map[string]any
	count int
}

// buildGroups groups bindings by non-COUNT items and counts occurrences.
func buildGroups(bindings []binding, groupItems []ReturnItem) (groups map[string]*groupEntry, order []string) {
	groups = make(map[string]*groupEntry)

	for _, b := range bindings {
		row := make(map[string]any)
		var keyParts []string
		for _, item := range groupItems {
			col := item.Variable
			if item.Property != "" {
				col = item.Variable + "." + item.Property
			}
			if item.Alias != "" {
				col = item.Alias
			}
			val := resolveItemValue(b, item)
			row[col] = val
			keyParts = append(keyParts, fmt.Sprintf("%v", val))
		}
		key := strings.Join(keyParts, "\x00")
		if g, ok := groups[key]; ok {
			g.count++
		} else {
			groups[key] = &groupEntry{key: key, row: row, count: 1}
			order = append(order, key)
		}
	}
	return groups, order
}

// sortRows sorts rows by the given column.
func sortRows(rows []map[string]any, col, dir string) {
	sort.SliceStable(rows, func(i, j int) bool {
		a, b := rows[i][col], rows[j][col]
		cmp := compareValues(a, b)
		if dir == "DESC" {
			return cmp > 0
		}
		return cmp < 0
	})
}

func compareValues(a, b any) int {
	// Try numeric
	aNum, aOK := toFloat(a)
	bNum, bOK := toFloat(b)
	if aOK && bOK {
		if aNum < bNum {
			return -1
		}
		if aNum > bNum {
			return 1
		}
		return 0
	}
	// Fall back to string
	aStr := fmt.Sprintf("%v", a)
	bStr := fmt.Sprintf("%v", b)
	if aStr < bStr {
		return -1
	}
	if aStr > bStr {
		return 1
	}
	return 0
}

func toFloat(v any) (float64, bool) {
	switch n := v.(type) {
	case int:
		return float64(n), true
	case int64:
		return float64(n), true
	case float64:
		return n, true
	default:
		return 0, false
	}
}

// copyBinding makes a shallow copy of a binding.
func copyBinding(b binding) binding {
	c := newBinding()
	for k, v := range b.nodes {
		c.nodes[k] = v
	}
	for k, v := range b.edges {
		c.edges[k] = v
	}
	return c
}

// filterNodesByProps filters nodes by inline property key-value pairs.
func filterNodesByProps(nodes []*store.Node, props map[string]string) []*store.Node {
	var filtered []*store.Node
	for _, n := range nodes {
		if nodeMatchesProps(n, props) {
			filtered = append(filtered, n)
		}
	}
	return filtered
}

// nodeMatchesProps checks if a node matches all given property filters.
func nodeMatchesProps(n *store.Node, props map[string]string) bool {
	for key, val := range props {
		actual := getNodeProperty(n, key)
		if fmt.Sprintf("%v", actual) != val {
			return false
		}
	}
	return true
}