five/hbrtl/database.go

// Copyright (c) 2026 Charles KWON OhJun (charleskwonohjun@gmail.com)
// All rights reserved.

// Database callable functions: FIELDPUT, ALIAS, DBEVAL, DBUSEAREA, DBCLOSEAREA,
// DBGOTO, DBSKIP, DBAPPEND, DBDELETE, DBRECALL, DBCOMMIT, DBSEEK,
// DBGOTOP, DBGOBOTTOM, DBRLOCKLIST, DBSETFILTER, DBCLEARFILTER

package hbrtl

import (
	"fmt"
	"strings"

	"five/hbrt"
	"five/hbrdd"
	"five/hbrdd/dbf"
)

// FIELDPUT(nField, xValue) → xValue
func rtlFieldPut(t *hbrt.Thread) {
	t.Frame(2, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area == nil {
		t.RetNil()
		return
	}
	nField := t.Local(1).AsInt()
	val := t.Local(2)
	area.PutValue(nField-1, val) // 1-based to 0-based
	t.RetVal(val)
}

// ALIAS([nWorkArea]) → cAlias
func rtlAlias(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetString("")
		return
	}
	area := wam.Current()
	if area != nil {
		t.RetString(area.Alias())
	} else {
		t.RetString("")
	}
}

// DBEVAL(bBlock [, bFor [, bWhile [, nCount [, nRecord [, lRest]]]]]) → NIL
func rtlDbEval(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()

	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area == nil {
		t.RetNil()
		return
	}

	block := t.Local(1)
	if !block.IsBlock() {
		t.RetNil()
		return
	}

	var bFor, bWhile hbrt.Value
	nCount := -1
	lRest := false

	if nParams >= 2 {
		bFor = t.Local(2)
	}
	if nParams >= 3 {
		bWhile = t.Local(3)
	}
	if nParams >= 4 && !t.Local(4).IsNil() {
		nCount = t.Local(4).AsInt()
	}
	if nParams >= 5 && !t.Local(5).IsNil() {
		nRec := t.Local(5).AsInt()
		area.GoTo(uint32(nRec))
	}
	if nParams >= 6 && !t.Local(6).IsNil() {
		lRest = t.Local(6).AsBool()
	}

	// If not lRest and no record specified, go top
	if !lRest && (nParams < 5 || t.Local(5).IsNil()) {
		area.GoTop()
	}

	count := 0
	for !area.EOF() {
		if nCount >= 0 && count >= nCount {
			break
		}

		// While condition
		if !bWhile.IsNil() && bWhile.IsBlock() {
			blk := bWhile.AsBlock()
			t.PendingParams2(0)
			blk.Fn(t)
			if !t.GetRetValue().AsBool() {
				break
			}
		}

		// For condition
		doBlock := true
		if !bFor.IsNil() && bFor.IsBlock() {
			blk := bFor.AsBlock()
			t.PendingParams2(0)
			blk.Fn(t)
			doBlock = t.GetRetValue().AsBool()
		}

		if doBlock {
			blk := block.AsBlock()
			t.PendingParams2(0)
			blk.Fn(t)
		}

		area.Skip(1)
		count++
	}

	t.RetNil()
}

// DBUSEAREA([lNewArea], [cDriver], cName, [cAlias], [lShared], [lReadOnly]) → NIL
func rtlDbUseArea(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	cName := ""
	cAlias := ""
	cDriver := "DBFNTX"
	if nParams >= 3 && !t.Local(3).IsNil() {
		cName = t.Local(3).AsString()
	}
	if nParams >= 4 && !t.Local(4).IsNil() {
		cAlias = t.Local(4).AsString()
	}
	if nParams >= 2 && !t.Local(2).IsNil() {
		cDriver = t.Local(2).AsString()
	}
	shared := false
	readOnly := false
	if nParams >= 5 && !t.Local(5).IsNil() {
		shared = t.Local(5).AsBool()
	}
	if nParams >= 6 && !t.Local(6).IsNil() {
		readOnly = t.Local(6).AsBool()
	}
	_, err := wam.Open(cDriver, cName, cAlias, shared, readOnly)
	if err != nil {
		panic(&hbrt.HbError{
			Description: err.Error(),
			Operation:   "DBUSEAREA",
			SubSystem:   "BASE",
		})
	}
	t.RetNil()
}

// DBCLOSEALL() → NIL — closes all open work areas
func rtlDbCloseAll(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam != nil {
		wam.CloseAll()
	}
	t.RetNil()
}

// DBCLOSEAREA() → NIL
func rtlDbCloseArea(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam != nil {
		wam.Close()
	}
	t.RetNil()
}

// DBGOTO(nRecNo) → NIL
func rtlDbGoTo(t *hbrt.Thread) {
	t.Frame(1, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area != nil {
		area.GoTo(uint32(t.Local(1).AsLong()))
	}
	t.RetNil()
}

// DBSKIP([nRecords]) → NIL
func rtlDbSkip(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area == nil {
		t.RetNil()
		return
	}
	n := int64(1)
	if nParams >= 1 && !t.Local(1).IsNil() {
		n = t.Local(1).AsLong()
	}
	area.Skip(n)
	t.RetNil()
}

// DBGOTOP() → NIL
func rtlDbGoTop(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area != nil {
		area.GoTop()
	}
	t.RetNil()
}

// DBGOBOTTOM() → NIL
func rtlDbGoBottom(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area != nil {
		area.GoBottom()
	}
	t.RetNil()
}

// DBAPPEND([lUnlock]) → NIL
func rtlDbAppend(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area != nil {
		area.Append()
	}
	t.RetNil()
}

// DBDELETE() → NIL
func rtlDbDelete(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area != nil {
		area.Delete()
	}
	t.RetNil()
}

// DBRECALL() → NIL
func rtlDbRecall(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area != nil {
		area.Recall()
	}
	t.RetNil()
}

// DBRLOCK([nRecNo]) → lSuccess
// Acquires an advisory byte-range lock on a single record via fcntl(F_SETLK).
// Non-blocking: returns .F. if another process already holds the lock.
// Harbour: SELF_LOCK(a, &lockInfo) with DBLM_EXCLUSIVE.
func rtlDbRLock(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetBool(false)
		return
	}
	area := wam.Current()
	if area == nil {
		t.RetBool(false)
		return
	}
	da, ok := area.(*dbf.DBFArea)
	if !ok {
		// Non-DBF drivers: assume success (in-memory, etc.)
		t.RetBool(true)
		return
	}
	var recNo uint32
	if nParams >= 1 && !t.Local(1).IsNil() {
		recNo = uint32(t.Local(1).AsNumInt())
	}
	locked, err := da.LockRecord(recNo)
	if err != nil {
		t.RetBool(false)
		return
	}
	t.RetBool(locked)
}

// DBRUNLOCK([nRecNo]) → NIL
// Releases a specific record lock, or all record locks held by this
// workarea if called without arguments. Harbour: SELF_UNLOCK.
func rtlDbRUnlock(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area == nil {
		t.RetNil()
		return
	}
	da, ok := area.(*dbf.DBFArea)
	if !ok {
		t.RetNil()
		return
	}
	var recNo uint32
	if nParams >= 1 && !t.Local(1).IsNil() {
		recNo = uint32(t.Local(1).AsNumInt())
	}
	_ = da.UnlockRecord(recNo)
	t.RetNil()
}

// FLOCK() → lSuccess
// Acquires an exclusive file-wide lock via fcntl. Non-blocking: returns .F.
// if another process holds the file lock. Harbour: SELF_LOCK with DBLM_FILE.
func rtlFLock(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetBool(false)
		return
	}
	area := wam.Current()
	if area == nil {
		t.RetBool(false)
		return
	}
	da, ok := area.(*dbf.DBFArea)
	if !ok {
		t.RetBool(true) // in-memory etc.
		return
	}
	locked, err := da.LockFile()
	if err != nil {
		t.RetBool(false)
		return
	}
	t.RetBool(locked)
}

// DBUNLOCK() → NIL
// Releases all locks (file + record) held by the current workarea.
// Harbour: SELF_UNLOCK with no record number.
func rtlDbUnlock(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area == nil {
		t.RetNil()
		return
	}
	if da, ok := area.(*dbf.DBFArea); ok {
		_ = da.UnlockRecord(0)
		_ = da.UnlockFile()
	}
	t.RetNil()
}

// DBCOMMIT() → NIL
func rtlDbCommit(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area != nil {
		area.Flush()
	}
	t.RetNil()
}

// DBSEEK(xValue [, lSoftSeek [, lLast]]) → lFound
func rtlDbSeek(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetBool(false)
		return
	}
	area := wam.Current()
	if area == nil {
		t.RetBool(false)
		return
	}
	val := t.Local(1)
	softSeek := GetSetSoftSeek() // default: check SET SOFTSEEK
	findLast := false
	if nParams >= 2 && !t.Local(2).IsNil() {
		softSeek = t.Local(2).AsBool()
	}
	if nParams >= 3 && !t.Local(3).IsNil() {
		findLast = t.Local(3).AsBool()
	}
	// Check if area implements Indexer
	if idx, ok := area.(hbrdd.Indexer); ok {
		found, _ := idx.Seek(val, softSeek, findLast)
		t.RetBool(found)
	} else {
		t.RetBool(false)
	}
}

// DBSELECTAREA(nArea | cAlias) → NIL
func rtlDbSelectArea(t *hbrt.Thread) {
	t.Frame(1, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	v := t.Local(1)
	if v.IsString() {
		wam.Select(v.AsString())
	} else {
		wam.Select(uint16(v.AsInt()))
	}
	t.RetNil()
}

// DBPACK() → NIL
func rtlDbPack(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area != nil {
		area.Pack()
	}
	t.RetNil()
}

// DBZAP() → NIL
func rtlDbZap(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProcFast()
	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area != nil {
		area.Zap()
	}
	t.RetNil()
}

// --- LOCATE / CONTINUE ---
// Harbour: DBLOCATE(bFor, bWhile, nNext, nRec, lRest) → .T./.F.
// Searches from current position for record matching condition.

func rtlDbLocate(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()

	wam := getWA(t)
	if wam == nil {
		t.RetBool(false)
		return
	}
	area := wam.Current()
	if area == nil {
		t.RetBool(false)
		return
	}

	// param 1: bFor condition block
	var bFor hbrt.Value
	if nParams >= 1 && !t.Local(1).IsNil() {
		bFor = t.Local(1)
	}
	// param 2: bWhile condition block
	var bWhile hbrt.Value
	if nParams >= 2 && !t.Local(2).IsNil() {
		bWhile = t.Local(2)
	}
	// param 3: nNext — max records to scan
	nNext := int64(0) // 0 = all
	if nParams >= 3 && !t.Local(3).IsNil() {
		nNext = t.Local(3).AsNumInt()
	}
	// param 4: nRec — specific record number
	if nParams >= 4 && !t.Local(4).IsNil() {
		nRec := uint32(t.Local(4).AsNumInt())
		area.GoTo(nRec)
		if bFor.IsBlock() {
			t.PendingParams2(0)
			bFor.AsBlock().Fn(t)
			result := t.Pop2()
			area.SetFound(result.AsBool())
		} else {
			area.SetFound(true)
		}
		t.RetBool(area.Found())
		return
	}
	// param 5: lRest — .T. = continue from current, .F. = from top
	lRest := false
	if nParams >= 5 && !t.Local(5).IsNil() {
		lRest = t.Local(5).AsBool()
	}

	if !lRest && nNext == 0 {
		area.GoTop()
	}

	// Store locate block for __dbContinue
	if bFor.IsBlock() {
		area.SetLocate("", func(lt *hbrt.Thread) bool {
			lt.PendingParams2(0)
			bFor.AsBlock().Fn(lt)
			return lt.Pop2().AsBool()
		})
	}

	found := false
	count := int64(0)
	for !area.EOF() {
		if nNext > 0 && count >= nNext {
			break
		}
		// Check WHILE condition
		if bWhile.IsBlock() {
			t.PendingParams2(0)
			bWhile.AsBlock().Fn(t)
			if !t.Pop2().AsBool() {
				break
			}
		}
		// Check FOR condition
		if bFor.IsBlock() {
			t.PendingParams2(0)
			bFor.AsBlock().Fn(t)
			if t.Pop2().AsBool() {
				found = true
				break
			}
		} else {
			found = true
			break
		}
		area.Skip(1)
		count++
	}
	area.SetFound(found)
	t.RetBool(found)
}

// __DBCONTINUE — continue previous LOCATE search.
// Harbour: __dbContinue()
func rtlDbContinue(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProcFast()

	wam := getWA(t)
	if wam == nil {
		t.RetBool(false)
		return
	}
	area := wam.Current()
	if area == nil {
		t.RetBool(false)
		return
	}

	blk := area.LocateBlock()
	if blk == nil {
		area.SetFound(false)
		t.RetBool(false)
		return
	}

	// Skip past current record
	area.Skip(1)

	found := false
	for !area.EOF() {
		if blk(t) {
			found = true
			break
		}
		area.Skip(1)
	}
	area.SetFound(found)
	t.RetBool(found)
}

// rtlDbAverage implements __dbAverage(bExpr, bFor, bWhile, nNext, nRec,
// lRest) — sum the expression over visible records and return the
// arithmetic mean. Returns 0 when the loop visits no records (mirrors
// Harbour's idiom of avoiding a divide-by-zero in the expansion).
//
// Used by `AVERAGE <x> TO <v>` in std.ch.
func rtlDbAverage(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()

	wam := getWA(t)
	if wam == nil {
		t.RetDouble(0, 10, 2)
		return
	}
	area := wam.Current()
	if area == nil {
		t.RetDouble(0, 10, 2)
		return
	}

	bExpr := t.Local(1)
	if !bExpr.IsBlock() {
		t.RetDouble(0, 10, 2)
		return
	}
	var bFor, bWhile hbrt.Value
	if nParams >= 2 {
		bFor = t.Local(2)
	}
	if nParams >= 3 {
		bWhile = t.Local(3)
	}
	nCount := -1
	if nParams >= 4 && !t.Local(4).IsNil() {
		nCount = t.Local(4).AsInt()
	}
	if nParams >= 5 && !t.Local(5).IsNil() {
		area.GoTo(uint32(t.Local(5).AsInt()))
	}
	lRest := false
	if nParams >= 6 && !t.Local(6).IsNil() {
		lRest = t.Local(6).AsBool()
	}
	if !lRest && (nParams < 5 || t.Local(5).IsNil()) {
		area.GoTop()
	}

	sum := 0.0
	n := 0
	scanned := 0
	for !area.EOF() {
		if nCount >= 0 && scanned >= nCount {
			break
		}
		// WHILE
		if bWhile.IsBlock() {
			t.PendingParams2(0)
			bWhile.AsBlock().Fn(t)
			if !t.GetRetValue().AsBool() {
				break
			}
		}
		// FOR
		eval := true
		if bFor.IsBlock() {
			t.PendingParams2(0)
			bFor.AsBlock().Fn(t)
			eval = t.GetRetValue().AsBool()
		}
		if eval {
			t.PendingParams2(0)
			bExpr.AsBlock().Fn(t)
			sum += t.GetRetValue().AsNumDouble()
			n++
		}
		area.Skip(1)
		scanned++
	}
	if n == 0 {
		t.RetDouble(0, 10, 2)
		return
	}
	t.RetDouble(sum/float64(n), 10, 2)
}

// rtlDbCopy implements __dbCopy(cFile, aFields, bFor, bWhile, nNext,
// xRec, lRest) — copy visible records from the current workarea into a
// freshly created DBF. Field projection: an empty/missing aFields
// copies the whole structure; otherwise only fields whose names match
// (case-insensitive) are carried over. Used by `COPY TO <f> [FIELDS]
// [FOR] [WHILE] [NEXT] [RECORD] [REST] [ALL]` in std.ch.
//
// Harbour's __dbCopy also accepts cRDD / nConnection / cCodepage / xDelim
// (params 8..11). Five only supports DBFNTX→DBFNTX for now; SDF/DELIMITED
// copies stay parser no-ops until that backend lands.
func rtlDbCopy(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()

	wam := getWA(t)
	if wam == nil {
		t.RetBool(false)
		return
	}
	srcArea := wam.Current()
	if srcArea == nil {
		t.RetBool(false)
		return
	}

	if nParams < 1 || t.Local(1).IsNil() {
		t.RetBool(false)
		return
	}
	cFile := t.Local(1).AsString()
	if cFile == "" {
		t.RetBool(false)
		return
	}

	// Field projection. Harbour passes `{ <(fields)> }` so each entry
	// is a string literal already; uppercase for case-insensitive
	// matching against the source's field names.
	var srcIdx []int
	var dstFields []hbrdd.FieldInfo
	nSrcFields := srcArea.FieldCount()
	useAll := true
	if nParams >= 2 && t.Local(2).IsArray() {
		arr := t.Local(2).AsArray()
		if arr != nil && len(arr.Items) > 0 {
			useAll = false
			wanted := make(map[string]struct{}, len(arr.Items))
			for _, it := range arr.Items {
				s := strings.ToUpper(strings.TrimSpace(it.AsString()))
				if s != "" {
					wanted[s] = struct{}{}
				}
			}
			for i := 0; i < nSrcFields; i++ {
				fi := srcArea.GetFieldInfo(i)
				if _, ok := wanted[strings.ToUpper(fi.Name)]; ok {
					srcIdx = append(srcIdx, i)
					dstFields = append(dstFields, fi)
				}
			}
		}
	}
	if useAll {
		srcIdx = make([]int, nSrcFields)
		dstFields = make([]hbrdd.FieldInfo, nSrcFields)
		for i := 0; i < nSrcFields; i++ {
			srcIdx[i] = i
			dstFields[i] = srcArea.GetFieldInfo(i)
		}
	}
	if len(dstFields) == 0 {
		// Nothing to copy — empty FIELDS list with no matches.
		t.RetBool(false)
		return
	}

	// Loop bounds — same shape as dbEval.
	var bFor, bWhile hbrt.Value
	if nParams >= 3 {
		bFor = t.Local(3)
	}
	if nParams >= 4 {
		bWhile = t.Local(4)
	}
	nCount := -1
	if nParams >= 5 && !t.Local(5).IsNil() {
		nCount = t.Local(5).AsInt()
	}
	if nParams >= 6 && !t.Local(6).IsNil() {
		srcArea.GoTo(uint32(t.Local(6).AsInt()))
	}
	lRest := false
	if nParams >= 7 && !t.Local(7).IsNil() {
		lRest = t.Local(7).AsBool()
	}
	if !lRest && (nParams < 6 || t.Local(6).IsNil()) {
		srcArea.GoTop()
	}

	// Create + open the destination. Use a temp alias so we don't
	// clash with whatever the caller may have open under a name
	// matching the file's basename.
	drv, err := hbrdd.GetDriver("DBFNTX")
	if err != nil {
		t.RetBool(false)
		return
	}
	if _, err := drv.Create(hbrdd.CreateParams{Path: cFile, Fields: dstFields}); err != nil {
		t.RetBool(false)
		return
	}
	srcSel := wam.CurrentNum()
	dstSel, err := wam.Open("DBFNTX", cFile, "__copytmp", false, false)
	if err != nil {
		t.RetBool(false)
		return
	}
	dstArea := wam.AreaAt(dstSel)
	wam.SelectByNum(srcSel)

	scanned := 0
	for !srcArea.EOF() {
		if nCount >= 0 && scanned >= nCount {
			break
		}
		if bWhile.IsBlock() {
			t.PendingParams2(0)
			bWhile.AsBlock().Fn(t)
			if !t.GetRetValue().AsBool() {
				break
			}
		}
		emit := true
		if bFor.IsBlock() {
			t.PendingParams2(0)
			bFor.AsBlock().Fn(t)
			emit = t.GetRetValue().AsBool()
		}
		if emit {
			vals := make([]hbrt.Value, len(srcIdx))
			for i, idx := range srcIdx {
				v, _ := srcArea.GetValue(idx)
				vals[i] = v
			}
			wam.SelectByNum(dstSel)
			dstArea.Append()
			for i, v := range vals {
				dstArea.PutValue(i, v)
			}
			wam.SelectByNum(srcSel)
		}
		srcArea.Skip(1)
		scanned++
	}

	// Close the destination, leaving the source selected as on entry.
	wam.SelectByNum(dstSel)
	wam.Close()
	wam.SelectByNum(srcSel)
	t.RetBool(true)
}

// rtlDbSort implements __dbSort(cFile, aFields, bFor, bWhile, nNext,
// xRec, lRest) — same loop semantics as __dbCopy but the visible
// records are buffered, sorted by the named keys, and written in
// order. Each entry of aFields may be a plain field name (ascending)
// or `name/D` for descending. Unrecognized suffixes are ignored.
//
// Used by `SORT TO <f> [ON <field-list>] [FOR/WHILE/NEXT/...]` in
// std.ch.
func rtlDbSort(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()

	wam := getWA(t)
	if wam == nil {
		t.RetBool(false)
		return
	}
	srcArea := wam.Current()
	if srcArea == nil {
		t.RetBool(false)
		return
	}

	if nParams < 1 || t.Local(1).IsNil() {
		t.RetBool(false)
		return
	}
	cFile := t.Local(1).AsString()
	if cFile == "" {
		t.RetBool(false)
		return
	}

	nSrcFields := srcArea.FieldCount()
	dstFields := make([]hbrdd.FieldInfo, nSrcFields)
	for i := 0; i < nSrcFields; i++ {
		dstFields[i] = srcArea.GetFieldInfo(i)
	}
	if nSrcFields == 0 {
		t.RetBool(false)
		return
	}

	// Parse sort-key spec: name[/D] entries → (fieldIdx, descending).
	type sortKey struct {
		idx  int
		desc bool
	}
	var keys []sortKey
	if nParams >= 2 && t.Local(2).IsArray() {
		for _, item := range t.Local(2).AsArray().Items {
			s := strings.TrimSpace(item.AsString())
			if s == "" {
				continue
			}
			desc := false
			// Suffix `/D` (descending), `/A` (ascending), `/C`
			// (case-insensitive — treated as ascending).
			if i := strings.LastIndexByte(s, '/'); i > 0 {
				suffix := strings.ToUpper(strings.TrimSpace(s[i+1:]))
				switch suffix {
				case "D":
					desc = true
				}
				s = strings.TrimSpace(s[:i])
			}
			upper := strings.ToUpper(s)
			idx := -1
			for k := 0; k < nSrcFields; k++ {
				if strings.EqualFold(dstFields[k].Name, upper) {
					idx = k
					break
				}
			}
			if idx >= 0 {
				keys = append(keys, sortKey{idx: idx, desc: desc})
			}
		}
	}

	// Loop bounds.
	var bFor, bWhile hbrt.Value
	if nParams >= 3 {
		bFor = t.Local(3)
	}
	if nParams >= 4 {
		bWhile = t.Local(4)
	}
	nCount := -1
	if nParams >= 5 && !t.Local(5).IsNil() {
		nCount = t.Local(5).AsInt()
	}
	if nParams >= 6 && !t.Local(6).IsNil() {
		srcArea.GoTo(uint32(t.Local(6).AsInt()))
	}
	lRest := false
	if nParams >= 7 && !t.Local(7).IsNil() {
		lRest = t.Local(7).AsBool()
	}
	if !lRest && (nParams < 6 || t.Local(6).IsNil()) {
		srcArea.GoTop()
	}

	// Buffer visible records' field values.
	var rows [][]hbrt.Value
	scanned := 0
	for !srcArea.EOF() {
		if nCount >= 0 && scanned >= nCount {
			break
		}
		if bWhile.IsBlock() {
			t.PendingParams2(0)
			bWhile.AsBlock().Fn(t)
			if !t.GetRetValue().AsBool() {
				break
			}
		}
		emit := true
		if bFor.IsBlock() {
			t.PendingParams2(0)
			bFor.AsBlock().Fn(t)
			emit = t.GetRetValue().AsBool()
		}
		if emit {
			row := make([]hbrt.Value, nSrcFields)
			for i := 0; i < nSrcFields; i++ {
				v, _ := srcArea.GetValue(i)
				row[i] = v
			}
			rows = append(rows, row)
		}
		srcArea.Skip(1)
		scanned++
	}

	// Sort if any keys were given. Stable so equal keys keep input
	// order. Comparison is type-aware: numeric by AsNumDouble, date by
	// AsNumInt julian, logical by truth, otherwise string.
	if len(keys) > 0 && len(rows) > 1 {
		less := func(i, j int) bool {
			for _, k := range keys {
				a := rows[i][k.idx]
				b := rows[j][k.idx]
				cmp := compareValues(a, b)
				if cmp == 0 {
					continue
				}
				if k.desc {
					cmp = -cmp
				}
				return cmp < 0
			}
			return false
		}
		stableSort(rows, less)
	}

	// Create + open destination, then append in order.
	drv, err := hbrdd.GetDriver("DBFNTX")
	if err != nil {
		t.RetBool(false)
		return
	}
	if _, err := drv.Create(hbrdd.CreateParams{Path: cFile, Fields: dstFields}); err != nil {
		t.RetBool(false)
		return
	}
	srcSel := wam.CurrentNum()
	dstSel, err := wam.Open("DBFNTX", cFile, "__sorttmp", false, false)
	if err != nil {
		t.RetBool(false)
		return
	}
	dstArea := wam.AreaAt(dstSel)
	for _, row := range rows {
		dstArea.Append()
		for i, v := range row {
			dstArea.PutValue(i, v)
		}
	}
	wam.Close()
	wam.SelectByNum(srcSel)
	t.RetBool(true)
}

// rtlDbList implements __dbList(lOff, aBlocks, lAll, bFor, bWhile,
// nNext, nRec, lRest, lPrn, cFile) — output visible records to
// stdout. aBlocks is an array of column-evaluation code blocks (one
// per LIST / DISPLAY column expression). If aBlocks is empty or
// contains only NIL placeholders, every field of the current
// workarea is emitted.
//
// Used by both `LIST [<v,...>]` and `DISPLAY [<v,...>]` in std.ch.
// lAll distinguishes them: LIST always passes .T. (all matching
// records); DISPLAY passes .T. only for `DISPLAY ALL`, otherwise .F.
// (just the current record).
//
// TO PRINTER / TO FILE redirection (lPrn / cFile) is accepted but
// not yet implemented — both paths still write to stdout. OFF (lOff)
// suppresses the record-number prefix.
func rtlDbList(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()

	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	srcArea := wam.Current()
	if srcArea == nil {
		t.RetNil()
		return
	}

	lOff := false
	if nParams >= 1 && !t.Local(1).IsNil() {
		lOff = t.Local(1).AsBool()
	}

	// Decode column blocks. Empty / `{ NIL }` → fall back to "all fields".
	var blocks []hbrt.Value
	useAllFields := true
	if nParams >= 2 && t.Local(2).IsArray() {
		arr := t.Local(2).AsArray()
		if arr != nil {
			for _, it := range arr.Items {
				if it.IsBlock() {
					blocks = append(blocks, it)
					useAllFields = false
				}
			}
		}
	}

	lAll := true
	if nParams >= 3 && !t.Local(3).IsNil() {
		lAll = t.Local(3).AsBool()
	}

	// Loop bounds — same shape as dbEval.
	var bFor, bWhile hbrt.Value
	if nParams >= 4 {
		bFor = t.Local(4)
	}
	if nParams >= 5 {
		bWhile = t.Local(5)
	}
	nCount := -1
	if nParams >= 6 && !t.Local(6).IsNil() {
		nCount = t.Local(6).AsInt()
	}
	if nParams >= 7 && !t.Local(7).IsNil() {
		srcArea.GoTo(uint32(t.Local(7).AsInt()))
	}
	lRest := false
	if nParams >= 8 && !t.Local(8).IsNil() {
		lRest = t.Local(8).AsBool()
	}
	// DISPLAY without ALL emits exactly one record; LIST always emits
	// the full filtered range. Encode the difference by clamping
	// nCount to 1 when lAll is false and no explicit NEXT was given.
	if !lAll && nCount < 0 {
		nCount = 1
	}
	if !lRest && lAll && (nParams < 7 || t.Local(7).IsNil()) {
		srcArea.GoTop()
	}

	nFields := srcArea.FieldCount()
	scanned := 0
	for !srcArea.EOF() {
		if nCount >= 0 && scanned >= nCount {
			break
		}
		if bWhile.IsBlock() {
			t.PendingParams2(0)
			bWhile.AsBlock().Fn(t)
			if !t.GetRetValue().AsBool() {
				break
			}
		}
		emit := true
		if bFor.IsBlock() {
			t.PendingParams2(0)
			bFor.AsBlock().Fn(t)
			emit = t.GetRetValue().AsBool()
		}
		if emit {
			parts := []string{}
			if !lOff {
				parts = append(parts, fmt.Sprintf("%6d", srcArea.RecNo()))
			}
			if useAllFields {
				for i := 0; i < nFields; i++ {
					v, _ := srcArea.GetValue(i)
					parts = append(parts, valueToDisplay(v))
				}
			} else {
				for _, blk := range blocks {
					t.PendingParams2(0)
					blk.AsBlock().Fn(t)
					parts = append(parts, valueToDisplay(t.GetRetValue()))
				}
			}
			fmt.Print("\r\n" + strings.Join(parts, " "))
		}
		srcArea.Skip(1)
		scanned++
	}
	t.RetNil()
}

// rtlDbTotal implements __dbTotal(cFile, bKey, aFields, bFor, bWhile,
// nNext, xRec, lRest) — emit one record per *consecutive* run of
// equal key values from the current workarea, summing the named
// numeric fields and copying every other field from the run's first
// record. The source must already be sorted/indexed on the key for
// the grouping to produce one row per distinct value (Harbour's
// dbtotal.prg has the same precondition).
//
// Used by `TOTAL TO <f> ON <key> [FIELDS <list>] [FOR/WHILE/...]` in
// std.ch.
func rtlDbTotal(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()

	wam := getWA(t)
	if wam == nil {
		t.RetBool(false)
		return
	}
	srcArea := wam.Current()
	if srcArea == nil {
		t.RetBool(false)
		return
	}

	if nParams < 1 || t.Local(1).IsNil() {
		t.RetBool(false)
		return
	}
	cFile := t.Local(1).AsString()
	if cFile == "" {
		t.RetBool(false)
		return
	}

	bKey := t.Local(2)
	if !bKey.IsBlock() {
		t.RetBool(false)
		return
	}

	// Build dst struct — drop memos like Harbour does.
	nFields := srcArea.FieldCount()
	var dstFields []hbrdd.FieldInfo
	var keptIdx []int
	for i := 0; i < nFields; i++ {
		fi := srcArea.GetFieldInfo(i)
		if fi.Type == 'M' {
			continue
		}
		dstFields = append(dstFields, fi)
		keptIdx = append(keptIdx, i)
	}
	if len(dstFields) == 0 {
		t.RetBool(false)
		return
	}

	// Resolve sum-fields → list of (dstIdx, srcIdx) pairs preserving
	// declaration order.
	type sumPair struct{ dst, src int }
	var sums []sumPair
	if nParams >= 3 && t.Local(3).IsArray() {
		arr := t.Local(3).AsArray()
		if arr != nil {
			wanted := map[string]struct{}{}
			for _, it := range arr.Items {
				s := strings.ToUpper(strings.TrimSpace(it.AsString()))
				if s != "" {
					wanted[s] = struct{}{}
				}
			}
			for di, si := range keptIdx {
				if _, ok := wanted[strings.ToUpper(dstFields[di].Name)]; ok {
					sums = append(sums, sumPair{dst: di, src: si})
				}
			}
		}
	}

	// Loop bounds.
	var bFor, bWhile hbrt.Value
	if nParams >= 4 {
		bFor = t.Local(4)
	}
	if nParams >= 5 {
		bWhile = t.Local(5)
	}
	nCount := -1
	if nParams >= 6 && !t.Local(6).IsNil() {
		nCount = t.Local(6).AsInt()
	}
	if nParams >= 7 && !t.Local(7).IsNil() {
		srcArea.GoTo(uint32(t.Local(7).AsInt()))
	}
	lRest := false
	if nParams >= 8 && !t.Local(8).IsNil() {
		lRest = t.Local(8).AsBool()
	}
	if !lRest && (nParams < 7 || t.Local(7).IsNil()) {
		srcArea.GoTop()
	}

	// Create + open destination.
	drv, err := hbrdd.GetDriver("DBFNTX")
	if err != nil {
		t.RetBool(false)
		return
	}
	if _, err := drv.Create(hbrdd.CreateParams{Path: cFile, Fields: dstFields}); err != nil {
		t.RetBool(false)
		return
	}
	srcSel := wam.CurrentNum()
	dstSel, err := wam.Open("DBFNTX", cFile, "__totaltmp", false, false)
	if err != nil {
		t.RetBool(false)
		return
	}
	dstArea := wam.AreaAt(dstSel)
	wam.SelectByNum(srcSel)

	// Group walk.
	var prevKey hbrt.Value
	haveGroup := false
	running := make([]float64, len(sums))

	flush := func() {
		if !haveGroup {
			return
		}
		wam.SelectByNum(dstSel)
		// The dst row for this group is the most recent append.
		// Overwrite the sum-field positions with the accumulated total,
		// preserving the field's declared length/decimals.
		for i, sp := range sums {
			fi := dstFields[sp.dst]
			dstArea.PutValue(sp.dst, hbrt.MakeDouble(running[i], uint16(fi.Len), uint16(fi.Dec)))
		}
		wam.SelectByNum(srcSel)
		for i := range running {
			running[i] = 0
		}
		haveGroup = false
	}

	scanned := 0
	for !srcArea.EOF() {
		if nCount >= 0 && scanned >= nCount {
			break
		}
		if bWhile.IsBlock() {
			t.PendingParams2(0)
			bWhile.AsBlock().Fn(t)
			if !t.GetRetValue().AsBool() {
				break
			}
		}
		match := true
		if bFor.IsBlock() {
			t.PendingParams2(0)
			bFor.AsBlock().Fn(t)
			match = t.GetRetValue().AsBool()
		}
		if match {
			t.PendingParams2(0)
			bKey.AsBlock().Fn(t)
			curKey := t.GetRetValue()

			if !haveGroup || compareValues(prevKey, curKey) != 0 {
				flush()
				// Append a fresh dst row and copy this first-of-group
				// record's non-memo fields into it.
				wam.SelectByNum(dstSel)
				dstArea.Append()
				wam.SelectByNum(srcSel)
				for di, si := range keptIdx {
					v, _ := srcArea.GetValue(si)
					wam.SelectByNum(dstSel)
					dstArea.PutValue(di, v)
					wam.SelectByNum(srcSel)
				}
				prevKey = curKey
				haveGroup = true
			}

			// Sum this record's contribution.
			for i, sp := range sums {
				v, _ := srcArea.GetValue(sp.src)
				running[i] += v.AsNumDouble()
			}
		}
		srcArea.Skip(1)
		scanned++
	}
	flush()

	wam.SelectByNum(dstSel)
	wam.Close()
	wam.SelectByNum(srcSel)
	t.RetBool(true)
}

// rtlDbJoin implements __dbJoin(cAlias, cFile, aFields, bFor) — emit
// the cartesian product of the current ("master") workarea and the
// named "detail" workarea, filtered by bFor. Output structure:
//
//   * No FIELDS clause: master's fields followed by detail's fields,
//     dropping detail-side names that clash with master.
//   * FIELDS list: in declaration order, each name is resolved
//     against master first then detail.
//
// Same shape as harbour-core/src/rdd/dbjoin.prg. Five-specific
// simplifications: alias->name FIELD notation isn't supported yet
// (bare names with master-precedence lookup); RDD/codepage args
// dropped.
func rtlDbJoin(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()

	wam := getWA(t)
	if wam == nil {
		t.RetBool(false)
		return
	}
	master := wam.Current()
	if master == nil {
		t.RetBool(false)
		return
	}
	masterSel := wam.CurrentNum()

	// param 1: detail workarea alias
	if nParams < 1 || t.Local(1).IsNil() {
		t.RetBool(false)
		return
	}
	cAlias := strings.TrimSpace(t.Local(1).AsString())
	if cAlias == "" {
		t.RetBool(false)
		return
	}
	detailSel := wam.FindByAlias(cAlias)
	if detailSel == 0 {
		t.RetBool(false)
		return
	}
	detail := wam.AreaAt(detailSel)
	if detail == nil {
		t.RetBool(false)
		return
	}

	// param 2: destination file name
	if nParams < 2 || t.Local(2).IsNil() {
		t.RetBool(false)
		return
	}
	cFile := t.Local(2).AsString()
	if cFile == "" {
		t.RetBool(false)
		return
	}

	// Build dst struct + a per-dst-field source descriptor (which
	// area to read from at output time).
	type srcRef struct {
		isMaster bool
		idx      int
	}
	var dstFields []hbrdd.FieldInfo
	var srcRefs []srcRef
	addField := func(fi hbrdd.FieldInfo, isMaster bool, srcIdx int) {
		// Skip if name already present (master wins).
		for _, e := range dstFields {
			if strings.EqualFold(e.Name, fi.Name) {
				return
			}
		}
		dstFields = append(dstFields, fi)
		srcRefs = append(srcRefs, srcRef{isMaster: isMaster, idx: srcIdx})
	}

	// FIELDS list — empty means union of all fields.
	var wanted []string
	if nParams >= 3 && t.Local(3).IsArray() {
		arr := t.Local(3).AsArray()
		if arr != nil {
			for _, it := range arr.Items {
				s := strings.TrimSpace(it.AsString())
				if s != "" {
					wanted = append(wanted, strings.ToUpper(s))
				}
			}
		}
	}
	if len(wanted) == 0 {
		// All master fields, then detail fields with master-name precedence.
		for i := 0; i < master.FieldCount(); i++ {
			addField(master.GetFieldInfo(i), true, i)
		}
		for i := 0; i < detail.FieldCount(); i++ {
			addField(detail.GetFieldInfo(i), false, i)
		}
	} else {
		// User-specified order: master first, then detail.
		for _, n := range wanted {
			found := false
			for i := 0; i < master.FieldCount(); i++ {
				fi := master.GetFieldInfo(i)
				if strings.EqualFold(fi.Name, n) {
					addField(fi, true, i)
					found = true
					break
				}
			}
			if !found {
				for i := 0; i < detail.FieldCount(); i++ {
					fi := detail.GetFieldInfo(i)
					if strings.EqualFold(fi.Name, n) {
						addField(fi, false, i)
						break
					}
				}
			}
		}
	}
	if len(dstFields) == 0 {
		t.RetBool(false)
		return
	}

	// param 4: FOR block. Empty std.ch rule wraps it as `{|| .T. }`,
	// so a missing block here means "always true". Treat NIL-block
	// the same way for direct callers.
	bFor := hbrt.Value{}
	if nParams >= 4 {
		bFor = t.Local(4)
	}

	// Create + open destination.
	drv, err := hbrdd.GetDriver("DBFNTX")
	if err != nil {
		t.RetBool(false)
		return
	}
	if _, err := drv.Create(hbrdd.CreateParams{Path: cFile, Fields: dstFields}); err != nil {
		t.RetBool(false)
		return
	}
	dstSel, err := wam.Open("DBFNTX", cFile, "__jointmp", false, false)
	if err != nil {
		t.RetBool(false)
		return
	}
	dstArea := wam.AreaAt(dstSel)

	wam.SelectByNum(masterSel)
	master.GoTop()
	for !master.EOF() {
		wam.SelectByNum(detailSel)
		detail.GoTop()
		for !detail.EOF() {
			wam.SelectByNum(masterSel)
			match := true
			if bFor.IsBlock() {
				t.PendingParams2(0)
				bFor.AsBlock().Fn(t)
				match = t.GetRetValue().AsBool()
			}
			if match {
				vals := make([]hbrt.Value, len(srcRefs))
				for k, r := range srcRefs {
					if r.isMaster {
						v, _ := master.GetValue(r.idx)
						vals[k] = v
					} else {
						v, _ := detail.GetValue(r.idx)
						vals[k] = v
					}
				}
				wam.SelectByNum(dstSel)
				dstArea.Append()
				for k, v := range vals {
					dstArea.PutValue(k, v)
				}
				wam.SelectByNum(masterSel)
			}
			wam.SelectByNum(detailSel)
			detail.Skip(1)
		}
		wam.SelectByNum(masterSel)
		master.Skip(1)
	}

	wam.SelectByNum(dstSel)
	wam.Close()
	wam.SelectByNum(masterSel)
	t.RetBool(true)
}

// rtlDbUpdate implements __dbUpdate(cAlias, bKey, lRandom, bAssign) —
// for each record in the detail workarea, find the matching master
// record (by key equality) and apply bAssign in master's context.
// Same shape as harbour-core/src/rdd/dbupdat.prg:
//
//   * bKey runs in either context — typically a bare field name that
//     exists in both areas.
//   * bAssign runs in *master* context — Harbour's std.ch wraps each
//     `<f> WITH <x>` clause as `_FIELD-><f> := <x>` so the assignment
//     targets the master row while `<x>` is free to read detail->...
//   * lRandom .T.: scan master from top for each detail key. Otherwise
//     both areas must be sorted on the key; the master pointer just
//     walks forward through equal-or-greater keys (matches Harbour's
//     forward-walk semantics for the non-random branch).
//
// Used by `UPDATE FROM <alias> [ON <key>] [RANDOM] REPLACE ...`
// in std.ch.
func rtlDbUpdate(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()

	wam := getWA(t)
	if wam == nil {
		t.RetBool(false)
		return
	}
	master := wam.Current()
	if master == nil {
		t.RetBool(false)
		return
	}
	masterSel := wam.CurrentNum()

	if nParams < 1 || t.Local(1).IsNil() {
		t.RetBool(false)
		return
	}
	cAlias := strings.TrimSpace(t.Local(1).AsString())
	if cAlias == "" {
		t.RetBool(false)
		return
	}
	detailSel := wam.FindByAlias(cAlias)
	if detailSel == 0 {
		t.RetBool(false)
		return
	}
	detail := wam.AreaAt(detailSel)
	if detail == nil {
		t.RetBool(false)
		return
	}

	bKey := hbrt.Value{}
	if nParams >= 2 {
		bKey = t.Local(2)
	}
	if !bKey.IsBlock() {
		// No key block — nothing to drive the update by.
		t.RetBool(false)
		return
	}

	lRandom := false
	if nParams >= 3 && !t.Local(3).IsNil() {
		lRandom = t.Local(3).AsBool()
	}

	bAssign := hbrt.Value{}
	if nParams >= 4 {
		bAssign = t.Local(4)
	}
	if !bAssign.IsBlock() {
		t.RetBool(false)
		return
	}

	// Position both areas at top.
	master.GoTop()
	wam.SelectByNum(detailSel)
	detail.GoTop()
	wam.SelectByNum(masterSel)

	for {
		wam.SelectByNum(detailSel)
		if detail.EOF() {
			break
		}
		// Key from the detail row.
		t.PendingParams2(0)
		bKey.AsBlock().Fn(t)
		detailKey := t.GetRetValue()
		wam.SelectByNum(masterSel)

		if lRandom {
			// Linear scan from top — index-aware seek would be
			// faster but Five's seek API isn't part of the Area
			// interface yet.
			master.GoTop()
			for !master.EOF() {
				t.PendingParams2(0)
				bKey.AsBlock().Fn(t)
				if compareValues(t.GetRetValue(), detailKey) == 0 {
					break
				}
				master.Skip(1)
			}
		} else {
			// Walk forward while master's key < detail's key.
			for !master.EOF() {
				t.PendingParams2(0)
				bKey.AsBlock().Fn(t)
				if compareValues(t.GetRetValue(), detailKey) >= 0 {
					break
				}
				master.Skip(1)
			}
		}
		if !master.EOF() {
			// Match check (also covers the random branch's
			// "found something" outcome).
			t.PendingParams2(0)
			bKey.AsBlock().Fn(t)
			if compareValues(t.GetRetValue(), detailKey) == 0 {
				t.PendingParams2(0)
				bAssign.AsBlock().Fn(t)
			}
		}

		wam.SelectByNum(detailSel)
		detail.Skip(1)
	}

	wam.SelectByNum(masterSel)
	t.RetBool(true)
}

// stableSort is a tiny insertion sort for small N (typical DBF SORT
// targets are interactive datasets). Avoids a sort import dependency.
func stableSort(rows [][]hbrt.Value, less func(i, j int) bool) {
	for i := 1; i < len(rows); i++ {
		for j := i; j > 0 && less(j, j-1); j-- {
			rows[j], rows[j-1] = rows[j-1], rows[j]
		}
	}
}

// --- DBSETFILTER / DBCLEARFILTER / DBFILTER ---

// DBSETFILTER(bCondition [, cCondition])
func rtlDbSetFilter(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProcFast()

	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	area := wam.Current()
	if area == nil {
		t.RetNil()
		return
	}

	if nParams >= 1 && t.Local(1).IsBlock() {
		bFilter := t.Local(1)
		expr := ""
		if nParams >= 2 && t.Local(2).IsString() {
			expr = t.Local(2).AsString()
		}
		area.SetFilter(expr, func(lt *hbrt.Thread) bool {
			lt.PendingParams2(0)
			bFilter.AsBlock().Fn(lt)
			return lt.Pop2().AsBool()
		})
	}
	t.RetNil()
}

// DBCLEARFILTER()
func rtlDbClearFilter(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProcFast()

	wam := getWA(t)
	if wam == nil {
		t.RetNil()
		return
	}
	if area := wam.Current(); area != nil {
		area.ClearFilter()
	}
	t.RetNil()
}

// DBFILTER() → cFilterExpression
func rtlDbFilter(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProcFast()

	// TODO: return stored filter expression from area
	t.RetString("")
}