five/hbrdd/dbf/dbf.go

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

// DBFArea — the core DBF file driver.
// Byte-compatible with Harbour/Clipper DBF files.
//
// Harbour equivalent: DBFAREA in dbf1.c
// Inherits from BaseArea (WAAREA), implements Area + RecordManager + Locker.
//
// Reference:
//   /mnt/d/harbour-core/src/rdd/dbf1.c
//   docs/dbf-engine-spec.md
package dbf

import (
	"five/hbrt"
	"five/hbrdd"
	"fmt"
	"os"
	"strings"
	"sync/atomic"
)

// DBFArea implements the DBF database driver.
// Harbour: struct DBFAREA in dbf1.c
type DBFArea struct {
	hbrdd.BaseArea // embed WAAREA defaults

	// File handles
	dataFile *os.File
	filePath string
	shared   bool
	readOnly bool

	// Header
	header     Header
	fieldDescs []FieldDesc
	offsets    []uint16 // field byte offsets within record

	// Record buffer — COW: recBuf may point into mmap (read-only) or ownBuf (writable)
	recBuf   []byte // current record view (mmap slice or ownBuf)
	ownBuf   []byte // owned writable buffer (allocated once)
	recNo    uint32 // current record number (1-based)
	dirty    bool   // record buffer modified
	recOwned bool   // true = recBuf is ownBuf (writable), false = mmap slice (read-only)

	// State
	recCount  uint32
	ghost     bool // at phantom record (after APPEND)
	recLoaded bool // false = recBuf stale, need loadRecord()

	// RecCount cache — skip the Seek-to-end syscall when nothing this
	// process did has changed and no external invalidation has fired.
	// See RecCount() + InvalidateRecCountCache().
	recCountCached bool
	recCountGen    uint64

	// Append batch buffer — accumulates records for single write at flush
	appendBuf   []byte // buffered appended records (not yet written to disk)
	appendStart uint32 // first recNo in appendBuf (1-based)

	// Pending index inserts for records that were appended but not
	// yet indexed. flushRecord walks this set after the body bytes
	// reach disk and calls InsertKey on every open index that
	// implements IndexWriter — so a follow-up dbSeek finds the new
	// record without a manual REINDEX. The set is populated by
	// Append() and drained by flushRecord(); typed as a slice (not
	// map) because append order matches the desired index walk.
	pendingIdxInserts []uint32

	// mmap for zero-copy record reads
	mmapData []byte

	// Memo file (FPT)
	memoFile *FPTFile

	// Index integration (NTX/CDX)
	idxState *indexState

	// File locking state (byte-range locks via fcntl)
	fileLocked   bool            // FLOCK() held
	lockedRecs   map[uint32]bool // records locked by DBRLOCK()

	// Field position cache — UPPER(name) → 1-based index.
	// Built lazily on first FieldPosCache() call.
	// SQLite: "column affinity binding" — O(1) vs O(n) linear scan.
	fieldPosMap  map[string]int

	// SQL NULL bitmap (VFP/Harbour _NullFlags convention).
	// nullFieldsIdx: descriptor index of the hidden _NullFlags field,
	//                or -1 if the table has no nullable columns.
	// nullBitOf:     user-field descriptor index → bit position within
	//                the _NullFlags byte range.
	nullFieldsIdx int
	nullBitOf     map[int]int
}

// DBFDriver is the driver factory for DBF files.
type DBFDriver struct{}

func (d *DBFDriver) Name() string { return "DBF" }

func (d *DBFDriver) Open(params hbrdd.OpenParams) (hbrdd.Area, error) {
	return openDBF(d, params)
}

func (d *DBFDriver) Create(params hbrdd.CreateParams) (hbrdd.Area, error) {
	return createDBF(d, params)
}

func init() {
	hbrdd.RegisterDriver(&DBFDriver{})
	// Register aliases used by Harbour
	hbrdd.RegisterDriver(&dbfAliasDriver{name: "DBFNTX"})
	hbrdd.RegisterDriver(&dbfAliasDriver{name: "DBFCDX"})
	hbrdd.RegisterDriver(&dbfAliasDriver{name: "DBFFPT"})
	// SIX compatible drivers — same DBF engine, different semantics handled at higher level
	hbrdd.RegisterDriver(&dbfAliasDriver{name: "SIXCDX"})
	hbrdd.RegisterDriver(&dbfAliasDriver{name: "DBFNSX"})
	hbrdd.RegisterDriver(&dbfAliasDriver{name: "DBFSIX"})
	// Transfer format aliases
	hbrdd.RegisterDriver(&dbfAliasDriver{name: "DBFDBT"})
	// Bitmap/Rushmore RDD variants
	hbrdd.RegisterDriver(&dbfAliasDriver{name: "BMDBFNTX"})
	hbrdd.RegisterDriver(&dbfAliasDriver{name: "BMDBFCDX"})
	hbrdd.RegisterDriver(&dbfAliasDriver{name: "BMDBFNSX"})
}

// dbfAliasDriver wraps DBFDriver with a different name.
type dbfAliasDriver struct {
	name string
}

func (d *dbfAliasDriver) Name() string { return d.name }
func (d *dbfAliasDriver) Open(params hbrdd.OpenParams) (hbrdd.Area, error) {
	return openDBF(&DBFDriver{}, params)
}
func (d *dbfAliasDriver) Create(params hbrdd.CreateParams) (hbrdd.Area, error) {
	return createDBF(&DBFDriver{}, params)
}

// fptPathFromDBF returns the FPT memo file path for a given DBF path.
func fptPathFromDBF(dbfPath string) string {
	base := dbfPath
	if idx := strings.LastIndex(base, "."); idx >= 0 {
		base = base[:idx]
	}
	return base + ".fpt"
}

// hasMemoField checks if any field descriptor is a MEMO type.
func hasMemoField(fields []FieldDesc) bool {
	for _, f := range fields {
		if f.Type == 'M' || f.Type == 'm' {
			return true
		}
	}
	return false
}

// --- Open ---
// Harbour: hb_dbfOpen in dbf1.c
func openDBF(drv *DBFDriver, params hbrdd.OpenParams) (*DBFArea, error) {
	path := params.Path
	if !hasExtension(path) {
		path += ".dbf"
	}

	flag := os.O_RDWR
	if params.ReadOnly {
		flag = os.O_RDONLY
	}

	f, err := os.OpenFile(path, flag, 0)
	if err != nil {
		return nil, fmt.Errorf("open %s: %w", path, err)
	}

	area := &DBFArea{
		dataFile: f,
		filePath: path,
		shared:   params.Shared,
		readOnly: params.ReadOnly,
	}
	area.BaseArea = hbrdd.BaseArea{}

	// Step 1: Read header (32 bytes)
	hdr, err := ReadHeader(f)
	if err != nil {
		f.Close()
		return nil, err
	}
	area.header = *hdr

	// Step 2: Read field descriptors
	fieldCount := hdr.FieldCount()
	if fieldCount <= 0 {
		f.Close()
		return nil, fmt.Errorf("invalid field count: %d", fieldCount)
	}

	fields, err := ReadFieldDescs(f, fieldCount)
	if err != nil {
		f.Close()
		return nil, err
	}
	area.fieldDescs = fields

	// Step 3: Build field offsets
	area.offsets = BuildFieldOffsets(fields)

	// Step 4: Validate record length
	expectedRecLen := area.offsets[len(fields)]
	if uint16(expectedRecLen) != hdr.RecordLen {
		// Allow minor discrepancy (some DBF writers add extra bytes)
		if uint16(expectedRecLen) > hdr.RecordLen {
			f.Close()
			return nil, fmt.Errorf("field offsets (%d) exceed record length (%d)",
				expectedRecLen, hdr.RecordLen)
		}
	}

	// Step 5: Allocate record buffer
	area.ownBuf = make([]byte, hdr.RecordLen)
	area.recBuf = area.ownBuf
	area.recOwned = true

	// Step 6: Set record count (shared mode: recalculate from file size)
	if params.Shared {
		fileSize, _ := f.Seek(0, 2)
		area.recCount = uint32((fileSize - int64(hdr.HeaderLen)) / int64(hdr.RecordLen))
	} else {
		area.recCount = hdr.RecCount
	}

	// Step 7: Build FieldInfo for BaseArea. System fields (notably
	// the hidden _NullFlags column carrying the SQL NULL bitmap) are
	// held in fieldDescs for storage but filtered out of the public
	// FieldInfo slice — user-visible counts stay stable.
	fieldInfos := make([]hbrdd.FieldInfo, 0, fieldCount)
	for _, fd := range fields {
		if fd.Flags&FieldFlagSystem != 0 {
			continue
		}
		fieldInfos = append(fieldInfos, hbrdd.FieldInfo{
			Name:  fd.GetName(),
			Type:  fd.Type,
			Len:   int(fd.Len),
			Dec:   int(fd.Dec),
			Flags: fd.Flags,
		})
	}
	area.InitFields(fieldInfos)
	area.buildNullIndex()

	// Step 8: Auto-open FPT if memo fields exist
	if hasMemoField(fields) {
		fptPath := fptPathFromDBF(path)
		if fpt, err := OpenFPT(fptPath); err == nil {
			area.memoFile = fpt
		}
		// If FPT doesn't exist, memo reads return empty string
	}

	// Step 9: mmap DBF for zero-copy record reads
	area.mmapDBF()

	// Step 10: Position at first record
	area.FEof = (area.recCount == 0)
	if area.recCount > 0 {
		area.GoTo(1)
	}

	return area, nil
}

// --- Create ---
func createDBF(drv *DBFDriver, params hbrdd.CreateParams) (*DBFArea, error) {
	path := params.Path
	if !hasExtension(path) {
		path += ".dbf"
	}

	f, err := os.Create(path)
	if err != nil {
		return nil, fmt.Errorf("create %s: %w", path, err)
	}

	// Build field descriptors
	fieldDescs := make([]FieldDesc, len(params.Fields))
	for i, fi := range params.Fields {
		fieldDescs[i].SetName(fi.Name)
		fieldDescs[i].Type = fi.Type
		fieldDescs[i].Len = byte(fi.Len)
		fieldDescs[i].Dec = byte(fi.Dec)
		fieldDescs[i].Flags = fi.Flags
	}

	// If any user field is nullable, append the hidden _NullFlags
	// system column. Must happen before recordLen is tallied so its
	// bytes reserve space in the record layout.
	fieldDescs = appendNullFlagsField(fieldDescs)

	recordLen := uint16(1) // deletion flag
	for i := range fieldDescs {
		recordLen += uint16(fieldDescs[i].Len)
	}

	// Build header
	hasMemo := hasMemoField(fieldDescs)
	headerLen := uint16(HeaderSize + len(fieldDescs)*FieldDescSize + 1) // +1 for terminator
	version := byte(VersionDBF3)
	if hasMemo {
		version = VersionFPT
	}
	hdr := Header{
		Version:   version,
		RecCount:  0,
		HeaderLen: headerLen,
		RecordLen: recordLen,
	}
	hdr.UpdateDate()

	// Write header
	if err := WriteHeader(f, &hdr); err != nil {
		f.Close()
		return nil, err
	}

	// Write field descriptors
	if err := WriteFieldDescs(f, fieldDescs); err != nil {
		f.Close()
		return nil, err
	}

	// Write header terminator
	f.Write([]byte{HeaderTerminator})

	// Write EOF marker
	f.Write([]byte{EOFMarker})

	f.Seek(0, 0)

	area := &DBFArea{
		dataFile:   f,
		filePath:   path,
		header:     hdr,
		fieldDescs: fieldDescs,
		offsets:    BuildFieldOffsets(fieldDescs),
		ownBuf:     make([]byte, recordLen),
		recOwned:   true,
		recCount:   0,
	}
	area.recBuf = area.ownBuf

	fieldInfos := make([]hbrdd.FieldInfo, len(params.Fields))
	copy(fieldInfos, params.Fields)
	area.InitFields(fieldInfos)
	area.buildNullIndex()
	area.FEof = true

	// Auto-create FPT if memo fields exist
	if hasMemo {
		fptPath := fptPathFromDBF(path)
		fpt, err := CreateFPT(fptPath, FPTDefaultBlock)
		if err != nil {
			f.Close()
			return nil, fmt.Errorf("create memo file: %w", err)
		}
		area.memoFile = fpt
	}

	return area, nil
}

// --- Area interface ---

func (a *DBFArea) Driver() hbrdd.Driver { return &DBFDriver{} }

func (a *DBFArea) Close() error {
	a.unmapDBF() // unmap before writing
	if a.dirty {
		a.flushRecord()
	}
	a.dataFile.WriteAt([]byte{EOFMarker}, a.header.EOFOffset())
	a.updateHeader()
	// Release any held byte-range locks before closing the fd — POSIX
	// drops them implicitly on close, but being explicit avoids races
	// with other workareas sharing the same underlying file.
	a.releaseAllLocks()
	if a.memoFile != nil {
		a.memoFile.Close()
		a.memoFile = nil
	}
	err := a.dataFile.Close()
	a.BaseArea.Close()
	return err
}

// MemoFile returns the FPT memo file, or nil if no memo fields.
func (a *DBFArea) MemoFile() *FPTFile { return a.memoFile }

// FullPath returns the on-disk path of the DBF. For dbInfo(DBI_FULLPATH).
func (a *DBFArea) FullPath() string { return a.filePath }

// IsShared returns true if the area was opened shared.
// For dbInfo(DBI_SHARED).
func (a *DBFArea) IsShared() bool { return a.shared }

// IsReadOnly returns true if the area was opened read-only.
// For dbInfo(DBI_ISREADONLY).
func (a *DBFArea) IsReadOnly() bool { return a.readOnly }

// FieldPosCache returns the 1-based field position for a field name.
// Uses a lazily-built hash map for O(1) lookup instead of O(n) linear scan.
// SQLite: "column affinity binding" — critical for SQL engines that call
// FieldPos() hundreds of thousands of times per query.
func (a *DBFArea) FieldPosCache(name string) int {
	if a.fieldPosMap == nil {
		a.fieldPosMap = make(map[string]int, len(a.fieldDescs))
		for i, fd := range a.fieldDescs {
			// Trim null bytes + spaces from the [11]byte field name
			n := 0
			for n < 11 && fd.Name[n] != 0 {
				n++
			}
			fname := strings.ToUpper(strings.TrimSpace(string(fd.Name[:n])))
			a.fieldPosMap[fname] = i + 1
		}
	}
	if pos, ok := a.fieldPosMap[name]; ok {
		return pos
	}
	return 0
}

func (a *DBFArea) Flush() error {
	if a.dirty {
		if err := a.flushRecord(); err != nil {
			return err
		}
	}
	a.unmapDBF()
	a.dataFile.WriteAt([]byte{EOFMarker}, a.header.EOFOffset())
	a.updateHeader()
	err := a.dataFile.Sync()
	a.mmapDBF() // re-mmap after flush
	return err
}

// --- Movement ---

func (a *DBFArea) RecNo() uint32 { return a.recNo }

func (a *DBFArea) RecCount() (uint32, error) {
	if a.shared {
		// Shared-mode recount — file size may have grown from another
		// process's Append. Skip the syscall on an opt-in cache window
		// controlled by recCountCacheGen: callers that don't need
		// cross-process freshness (e.g. SqlScan's one-shot row-count
		// estimate on a workarea we opened this session) can leave the
		// cache warm. Invalidate on our own Append and dbCloseAll.
		gen := atomic.LoadUint64(&recCountCacheGen)
		if a.recCountCached && a.recCountGen == gen {
			return a.recCount, nil
		}
		size, err := a.dataFile.Seek(0, 2)
		if err != nil {
			return a.recCount, err
		}
		a.recCount = uint32((size - int64(a.header.HeaderLen)) / int64(a.header.RecordLen))
		a.recCountCached = true
		a.recCountGen = gen
	}
	return a.recCount, nil
}

// recCountCacheGen — monotonic generation counter. Bumped by
// InvalidateRecCountCache() so callers that know they've performed
// cross-process-visible writes (or want a fresh sample) can force
// the next RecCount() to re-stat. Default semantics are "fresh is
// not required"; the cache is a hot-path optimization for workloads
// that don't share the file with another writer.
var recCountCacheGen uint64 = 1

// InvalidateRecCountCache bumps the generation counter so every DBFArea's
// cached count becomes stale and the next RecCount() call re-queries the
// filesystem. Atomic so it can be called from any goroutine without a
// lock — the only invariant readers care about is "if I see a value > X,
// my cache is stale", and atomic.LoadUint64 is sufficient.
func InvalidateRecCountCache() {
	atomic.AddUint64(&recCountCacheGen, 1)
}

func (a *DBFArea) Deleted() bool {
	a.loadRecord()
	if len(a.recBuf) > 0 {
		return a.recBuf[0] == RecordDeleted
	}
	return false
}

// GoTo positions the cursor at a specific record number.
// Harbour: hb_dbfGoTo in dbf1.c — lazy read: record loaded on first access.
func (a *DBFArea) GoTo(recNo uint32) error {
	if a.dirty {
		a.flushRecord()
	}

	a.FFound = false

	if recNo == 0 || recNo > a.recCount {
		a.recNo = a.recCount + 1
		a.FEof = true
		a.FBof = (recNo == 0)
		a.recLoaded = false
		a.recBuf = a.ownBuf
		a.recOwned = true
		for i := range a.recBuf {
			a.recBuf[i] = ' '
		}
		return nil
	}

	// Read record — COW: mmap slice reference (zero-copy), fallback to file read
	offset := a.header.RecordOffset(recNo)
	recLen := int(a.header.RecordLen)
	if a.mmapData != nil && int(offset)+recLen <= len(a.mmapData) {
		// Zero-copy: recBuf points into mmap (read-only until PutValue)
		a.recBuf = a.mmapData[offset : offset+int64(recLen)]
		a.recOwned = false
	} else if _, err := a.dataFile.ReadAt(a.ownBuf, offset); err != nil {
		a.FEof = true
		return fmt.Errorf("read record %d: %w", recNo, err)
	} else {
		a.recBuf = a.ownBuf
		a.recOwned = true
	}

	a.recNo = recNo
	a.recLoaded = true
	a.FEof = false
	a.FBof = false
	a.dirty = false
	a.ghost = false
	return nil
}

// GoTop positions at the first record.
// Harbour: hb_dbfGoTop
func (a *DBFArea) GoTop() error {
	// Use index order if active
	if a.idxState != nil && a.idxState.current >= 0 {
		a.FTop = true
		a.FBottom = false
		return a.GoTopIndexed()
	}

	a.FTop = true
	a.FBottom = false

	if a.recCount == 0 {
		a.FEof = true
		a.recNo = 1
		return nil
	}

	if err := a.GoTo(1); err != nil {
		return err
	}

	// Skip filtered/deleted records
	return a.skipFilter(1)
}

// GoBottom positions at the last record.
// Harbour: hb_dbfGoBottom
func (a *DBFArea) GoBottom() error {
	// Use index order if active
	if a.idxState != nil && a.idxState.current >= 0 {
		a.FTop = false
		a.FBottom = true
		return a.GoBottomIndexed()
	}

	a.FTop = false
	a.FBottom = true

	if a.recCount == 0 {
		a.FEof = true
		a.recNo = 1
		return nil
	}

	if err := a.GoTo(a.recCount); err != nil {
		return err
	}

	return a.skipFilter(-1)
}

// Skip moves the cursor by count records.
// Harbour: hb_dbfSkip
func (a *DBFArea) Skip(count int64) error {
	// Use index order if active
	if a.idxState != nil && a.idxState.current >= 0 {
		a.FTop = false
		a.FBottom = false
		return a.SkipIndexed(count)
	}

	a.FTop = false
	a.FBottom = false

	if count == 0 {
		// Skip 0 = re-evaluate filter at current position
		return a.skipFilter(1)
	}

	if count > 0 {
		for i := int64(0); i < count; i++ {
			if a.FEof {
				break
			}
			newRec := a.recNo + 1
			if newRec > a.recCount {
				if a.dirty {
					a.flushRecord()
				}
				a.FEof = true
				a.recNo = a.recCount + 1
				break
			}
			if err := a.GoTo(newRec); err != nil {
				return err
			}
			if err := a.skipFilter(1); err != nil {
				return err
			}
		}
	} else {
		for i := int64(0); i > count; i-- {
			if a.recNo <= 1 {
				a.FBof = true
				break
			}
			if err := a.GoTo(a.recNo - 1); err != nil {
				return err
			}
			if err := a.skipFilter(-1); err != nil {
				return err
			}
		}
	}

	return nil
}

// mmapDBF / unmapDBF live in mmap_posix.go (Linux/Darwin, syscall.Mmap)
// and mmap_windows.go (CreateFileMapping / MapViewOfFile). Keeping the
// platform-specific ioctl-ish calls out of this file lets cross-builds
// stay clean.

// loadRecord reads the current record — from mmap or file fallback.
func (a *DBFArea) loadRecord() {
	if a.recLoaded || a.FEof || a.recNo == 0 || a.recNo > a.recCount {
		return
	}
	offset := a.header.RecordOffset(a.recNo)
	a.dataFile.ReadAt(a.recBuf, offset)
	a.recLoaded = true
}

// --- Field access ---

func (a *DBFArea) GetValue(fieldIndex int) (hbrt.Value, error) {
	a.loadRecord()
	if fieldIndex < 0 || fieldIndex >= len(a.fieldDescs) {
		return hbrt.MakeNil(), fmt.Errorf("field index out of range: %d", fieldIndex)
	}
	if a.FEof {
		return hbrt.MakeNil(), nil
	}
	// SQL NULL: nullable fields check the hidden _NullFlags bitmap
	// first; a set bit means the raw bytes carry no meaningful value
	// and the reader should surface NIL to the caller.
	if a.isFieldNull(fieldIndex) {
		return hbrt.MakeNil(), nil
	}
	fd := &a.fieldDescs[fieldIndex]
	// MEMO field: read from FPT and return string
	if (fd.Type == 'M' || fd.Type == 'm') && a.memoFile != nil {
		blockVal := GetFieldValue(a.recBuf, a.offsets[fieldIndex], fd)
		blockNo := uint32(blockVal.AsNumInt())
		if blockNo == 0 {
			return hbrt.MakeString(""), nil
		}
		data, err := a.memoFile.ReadMemo(blockNo)
		if err != nil {
			return hbrt.MakeString(""), nil
		}
		return hbrt.MakeString(string(data)), nil
	}
	return GetFieldValue(a.recBuf, a.offsets[fieldIndex], fd), nil
}

func (a *DBFArea) PutValue(fieldIndex int, val hbrt.Value) error {
	a.loadRecord()
	// COW: promote read-only mmap slice to writable owned buffer
	if !a.recOwned {
		copy(a.ownBuf, a.recBuf)
		a.recBuf = a.ownBuf
		a.recOwned = true
	}
	if a.readOnly {
		return fmt.Errorf("table is read-only")
	}
	if fieldIndex < 0 || fieldIndex >= len(a.fieldDescs) {
		return fmt.Errorf("field index out of range: %d", fieldIndex)
	}
	// SQL NULL handling for nullable fields: a NIL write sets the
	// bitmap bit and leaves the raw bytes alone (readers will short-
	// circuit via isFieldNull before reaching the type codec). A
	// non-NIL write clears the bit so the raw value surfaces again.
	if _, nullable := a.nullBitOf[fieldIndex]; nullable {
		if val.IsNil() {
			a.setFieldNull(fieldIndex, true)
			a.dirty = true
			return nil
		}
		a.setFieldNull(fieldIndex, false)
	}
	fd := &a.fieldDescs[fieldIndex]
	// MEMO field: write string to FPT, store block number in DBF
	if (fd.Type == 'M' || fd.Type == 'm') && a.memoFile != nil && val.IsString() {
		data := []byte(val.AsString())
		blockNo, err := a.memoFile.WriteMemo(data)
		if err != nil {
			return fmt.Errorf("write memo: %w", err)
		}
		putMemoRef(a.recBuf[a.offsets[fieldIndex]:a.offsets[fieldIndex]+uint16(fd.Len)], fd.Len, blockNo)
		a.dirty = true
		return nil
	}
	PutFieldValue(a.recBuf, a.offsets[fieldIndex], fd, val)
	a.dirty = true
	return nil
}

// --- Record operations ---

// Append adds a new blank record.
// Harbour: hb_dbfAppend — writes are deferred until Flush/Close/GoTo.
func (a *DBFArea) Append() error {
	if a.readOnly {
		return fmt.Errorf("table is read-only")
	}

	// Batch consecutive APPENDs: save current dirty record to appendBuf instead of writing to disk.
	if a.dirty && a.ghost {
		// Previous was also an APPEND — accumulate in batch buffer (no syscall)
		recLen := int(a.header.RecordLen)
		if a.appendBuf == nil {
			a.appendStart = a.recNo
			a.appendBuf = make([]byte, 0, recLen*256) // pre-alloc for ~256 records
		}
		a.appendBuf = append(a.appendBuf, a.recBuf[:recLen]...)
	} else if a.dirty {
		a.flushRecord()
	}

	// Unmap — file will grow
	if a.mmapData != nil {
		a.unmapDBF()
	}

	// Shared mode: serialize concurrent appends across processes and
	// re-read the header so we increment past whatever any peer has
	// already committed. Without this, two processes racing
	// `dbAppend` both bumped their *local* recCount from the stale
	// value they cached at Open time and wrote to the same byte
	// range — one record silently overwrote the other.
	//
	// We also immediately write the updated header to disk *inside*
	// the locked region so the next peer to acquire the lock sees
	// our reservation. The record body itself is still flushed
	// lazily by flushRecord; subsequent peers will pick up the
	// reserved slot via the bumped RecCount before our record body
	// reaches disk.
	if a.shared {
		if err := a.lockAppendIntent(); err != nil {
			return err
		}
		defer a.unlockAppendIntent()
		if _, err := a.dataFile.Seek(0, 0); err == nil {
			if hdr, err := ReadHeader(a.dataFile); err == nil {
				if hdr.RecCount > a.recCount {
					a.recCount = hdr.RecCount
				}
			}
		}
	}

	a.recCount++
	a.recNo = a.recCount
	a.header.RecCount = a.recCount

	if a.shared {
		// Persist the bumped RecCount immediately so a concurrent
		// appender refreshes past our slot in its own locked region.
		a.header.UpdateDate()
		if _, err := a.dataFile.Seek(0, 0); err == nil {
			_ = WriteHeader(a.dataFile, &a.header)
		}
		// Bump the global recCount-cache generation so every peer
		// DBFArea on this file re-stats on its next RecCount() call.
		// Without this, a pgserver connection that holds a cached
		// count from before our APPEND keeps seeing the pre-Append
		// row total — its SELECT misses the row we just inserted,
		// even though loadRecord()'s mmap-fallback path can read
		// the record bytes fine. Cheap (single atomic increment);
		// the cost is one Seek+stat per peer's next RecCount call,
		// which is exactly what cross-connection freshness needs.
		InvalidateRecCountCache()
	}

	// Promote to owned buffer for writing
	a.recBuf = a.ownBuf
	a.recOwned = true
	for i := range a.recBuf {
		a.recBuf[i] = ' '
	}

	a.FEof = false
	a.FBof = false
	a.dirty = true
	a.ghost = true
	a.recLoaded = true

	// Queue the new record for index maintenance. flushRecord drains
	// the queue after the body bytes are durable — by that point the
	// user has had a chance to PutValue into the appended record
	// (the common APPEND BLANK → REPLACE → dbSeek pattern), and the
	// key expression resolves against the final field values.
	if a.idxState != nil && len(a.idxState.indexes) > 0 {
		a.pendingIdxInserts = append(a.pendingIdxInserts, a.recNo)
	}
	return nil
}

// Delete marks the current record as deleted.
func (a *DBFArea) Delete() error {
	if a.readOnly || a.FEof {
		return nil
	}
	if !a.recOwned {
		copy(a.ownBuf, a.recBuf)
		a.recBuf = a.ownBuf
		a.recOwned = true
	}
	a.recBuf[0] = RecordDeleted
	a.dirty = true
	return nil
}

// Recall undeletes the current record.
func (a *DBFArea) Recall() error {
	if a.readOnly || a.FEof {
		return nil
	}
	if !a.recOwned {
		copy(a.ownBuf, a.recBuf)
		a.recBuf = a.ownBuf
		a.recOwned = true
	}
	a.recBuf[0] = RecordActive
	a.dirty = true
	return nil
}

// Pack removes all deleted records.
// Harbour: hb_dbfPack — requires exclusive access.
//
// Crash-safe: writes the surviving records into `<file>.pack.tmp`,
// fsyncs, then atomic-renames over the original. Power loss /
// kill -9 between Reads and Writes of the old in-place rewrite
// could leave the file with overwritten prefix and a tail that
// looked legitimate but contained no original copies of the
// records we'd already advanced past — silent data loss.
func (a *DBFArea) Pack() error {
	if a.readOnly {
		return fmt.Errorf("table is read-only")
	}
	if a.shared {
		return fmt.Errorf("PACK requires exclusive access")
	}

	if a.dirty {
		a.flushRecord()
	}

	// Temporarily disable index to avoid indexed navigation during PACK
	var savedIdx *indexState
	if a.idxState != nil {
		savedIdx = a.idxState
		a.idxState = nil
	}

	// Drop mmap so we can do clean reads + so the source file can
	// be replaced atomically below.
	if a.mmapData != nil {
		a.unmapDBF()
	}

	origPath := a.dataFile.Name()
	tmpPath := origPath + ".pack.tmp"

	// Best-effort cleanup of any leftover tmp from a prior crash.
	_ = os.Remove(tmpPath)

	tmpFile, err := os.OpenFile(tmpPath, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
	if err != nil {
		return fmt.Errorf("PACK: create temp: %w", err)
	}

	// Write the same header to the temp; RecCount is patched at the
	// end once we know the survivor count.
	if _, err := tmpFile.Seek(0, 0); err == nil {
		_ = WriteHeader(tmpFile, &a.header)
	}
	// Pad up to HeaderLen with the original header bytes (field
	// descriptors etc.) so the new file has a structurally
	// identical envelope. We replay from the source.
	hdrBytes := make([]byte, a.header.HeaderLen)
	if _, err := a.dataFile.ReadAt(hdrBytes, 0); err == nil {
		_, _ = tmpFile.WriteAt(hdrBytes, 0)
	}

	outRec := uint32(0)
	buf := make([]byte, a.header.RecordLen)

	for recNo := uint32(1); recNo <= a.recCount; recNo++ {
		offset := a.header.RecordOffset(recNo)
		if _, err := a.dataFile.ReadAt(buf, offset); err != nil {
			tmpFile.Close()
			os.Remove(tmpPath)
			return err
		}
		if buf[0] != RecordDeleted {
			outRec++
			outOffset := a.header.RecordOffset(outRec)
			if _, err := tmpFile.WriteAt(buf, outOffset); err != nil {
				tmpFile.Close()
				os.Remove(tmpPath)
				return err
			}
		}
	}

	a.recCount = outRec
	a.header.RecCount = outRec

	// Write EOF marker on the temp.
	eofOff := int64(a.header.HeaderLen) + int64(outRec)*int64(a.header.RecordLen)
	if _, err := tmpFile.WriteAt([]byte{EOFMarker}, eofOff); err != nil {
		tmpFile.Close()
		os.Remove(tmpPath)
		return err
	}

	// Patch the survivor count + date into the temp header.
	a.header.UpdateDate()
	if _, err := tmpFile.Seek(0, 0); err == nil {
		_ = WriteHeader(tmpFile, &a.header)
	}

	// Make the survivor durable before the rename so a crash between
	// rename and process exit doesn't leave a truncated temp.
	if err := tmpFile.Sync(); err != nil {
		tmpFile.Close()
		os.Remove(tmpPath)
		return err
	}
	tmpFile.Close()

	// Close the current handle, then atomic-rename. POSIX rename
	// guarantees readers/writers observe either the old or the
	// new contents — never an in-progress half-state.
	a.dataFile.Close()
	if err := os.Rename(tmpPath, origPath); err != nil {
		os.Remove(tmpPath)
		return fmt.Errorf("PACK: rename temp: %w", err)
	}

	// Reopen the (now repacked) file in the same mode and re-mmap.
	flag := os.O_RDWR
	if a.readOnly {
		flag = os.O_RDONLY
	}
	newF, err := os.OpenFile(origPath, flag, 0644)
	if err != nil {
		return fmt.Errorf("PACK: reopen: %w", err)
	}
	a.dataFile = newF
	a.mmapDBF()

	// Reposition (natural order, no index yet)
	if a.recCount > 0 {
		a.GoTo(1)
	} else {
		a.FEof = true
		a.recNo = 1
	}

	// Rebuild indexes (record numbers changed after PACK)
	if savedIdx != nil {
		a.idxState = savedIdx
		if err := a.OrderListRebuild(); err != nil {
			return err
		}
	}

	return nil
}

// Zap removes all records.
func (a *DBFArea) Zap() error {
	if a.readOnly || a.shared {
		return fmt.Errorf("ZAP requires exclusive access")
	}

	// Save index state
	var savedIdx *indexState
	if a.idxState != nil {
		savedIdx = a.idxState
		a.idxState = nil
	}

	a.recCount = 0
	a.header.RecCount = 0

	// Truncate to header + EOF
	a.dataFile.Truncate(int64(a.header.HeaderLen) + 1)
	a.dataFile.WriteAt([]byte{EOFMarker}, int64(a.header.HeaderLen))

	a.updateHeader()
	a.FEof = true
	a.recNo = 1

	// Rebuild indexes (empty after ZAP)
	if savedIdx != nil {
		a.idxState = savedIdx
		a.OrderListRebuild() // rebuilds empty indexes
	}

	return nil
}

// --- Internal ---

func (a *DBFArea) flushRecord() error {
	if !a.dirty || a.FEof {
		return nil
	}
	// Flush any accumulated append batch first (single write for all buffered records)
	if len(a.appendBuf) > 0 {
		offset := a.header.RecordOffset(a.appendStart)
		recLen := int(a.header.RecordLen)
		// Append current dirty record to batch too
		all := append(a.appendBuf, a.recBuf[:recLen]...)
		_, err := a.dataFile.WriteAt(all, offset)
		a.appendBuf = nil
		a.appendStart = 0
		if err == nil {
			a.dirty = false
			a.drainPendingIndexInserts()
		}
		return err
	}
	offset := a.header.RecordOffset(a.recNo)
	_, err := a.dataFile.WriteAt(a.recBuf, offset)
	if err == nil {
		a.dirty = false
		a.drainPendingIndexInserts()
	}
	return err
}

// drainPendingIndexInserts pushes any queued APPENDed records into
// every open IndexWriter so a follow-up dbSeek finds them. Engines
// that don't implement IndexWriter (CDX today) are skipped — those
// indexes remain stale and must be REINDEXed manually. Errors from
// InsertKey are swallowed because a partial index update is the
// strict-best worst case; reporting them up the flush stack would
// abort the user's transaction over a recoverable index issue.
func (a *DBFArea) drainPendingIndexInserts() {
	if len(a.pendingIdxInserts) == 0 || a.idxState == nil {
		a.pendingIdxInserts = nil
		return
	}
	for _, recNo := range a.pendingIdxInserts {
		for i, idx := range a.idxState.indexes {
			writer, ok := idx.(IndexWriter)
			if !ok {
				continue
			}
			if i >= len(a.idxState.keyExprs) {
				continue
			}
			key := a.evalKeyExpr(a.idxState.keyExprs[i], recNo)
			_ = writer.InsertKey(key, recNo)
		}
	}
	a.pendingIdxInserts = nil
}

func (a *DBFArea) updateHeader() {
	// Shared-mode max-merge. A pgserver-style multi-connection
	// scenario has every peer call Close → updateHeader in arbitrary
	// order. Each peer's `a.recCount` reflects its own view at the
	// time of its last Append; if the file has grown since (because
	// another peer's Append took the append-intent lock and bumped
	// the disk header), naively writing a.recCount back would
	// roll the on-disk count BACKWARDS — and subsequent peer SELECTs
	// would iterate only as far as our stale count, missing rows
	// that are demonstrably on disk.
	//
	// Re-read the disk header and pick the max. This is correct under
	// the append-intent lock invariant (the bumped count is always
	// monotonic) and cheap (one stat-sized read). Single-process /
	// EXCLUSIVE mode still writes its local count unconditionally,
	// since no peer can have bumped it.
	if a.shared {
		if _, err := a.dataFile.Seek(0, 0); err == nil {
			if hdr, err := ReadHeader(a.dataFile); err == nil {
				if hdr.RecCount > a.recCount {
					a.recCount = hdr.RecCount
				}
			}
		}
	}
	a.header.RecCount = a.recCount
	a.header.UpdateDate()

	a.dataFile.Seek(0, 0)
	WriteHeader(a.dataFile, &a.header)
}

// skipFilter advances cursor past deleted/filtered records.
// Harbour: hb_dbfSkipFilter in dbf1.c
// direction: 1 = forward, -1 = backward
func (a *DBFArea) skipFilter(direction int64) error {
	if direction == 0 {
		direction = 1
	}

	setDel := hbrdd.IsSetDeleted != nil && hbrdd.IsSetDeleted()

	if !setDel {
		return nil
	}

	for !a.FEof && !a.FBof {
		if !a.Deleted() {
			break
		}

		// Move to next/prev record
		if direction > 0 {
			newRec := a.recNo + 1
			if newRec > a.recCount {
				a.FEof = true
				a.recNo = a.recCount + 1
				break
			}
			if err := a.GoTo(newRec); err != nil {
				return err
			}
		} else {
			if a.recNo <= 1 {
				a.FBof = true
				if err := a.GoTo(1); err != nil {
					return err
				}
				break
			}
			if err := a.GoTo(a.recNo - 1); err != nil {
				return err
			}
		}
	}
	return nil
}

// --- Helpers ---

func hasExtension(path string) bool {
	for i := len(path) - 1; i >= 0; i-- {
		if path[i] == '.' {
			return true
		}
		if path[i] == '/' || path[i] == '\\' {
			return false
		}
	}
	return false
}