Add NewSector function

fmp/fmp_dict.go

@@ -42,7 +42,7 @@ func (dict *FmpDict) GetChildren(path ...uint64) *FmpDict {
 	return &FmpDict{}
 }
 
-func (dict *FmpDict) SetValue(path []uint64, value []byte) {
+func (dict *FmpDict) set(path []uint64, value []byte) {
 	for i, key := range path {
 		_, ok := (*dict)[key]
 		if !ok {

fmp/fmp_file.go

@@ -32,7 +32,7 @@ type FmpFile struct {
 	numSectors      uint64 // Excludes the header sector
 	currentSectorID uint64
 
-	stream io.ReadSeeker
+	stream *os.File
 }
 
 func OpenFile(path string) (*FmpFile, error) {
@@ -41,11 +41,10 @@ func OpenFile(path string) (*FmpFile, error) {
 		return nil, err
 	}
 
-	stream, err := os.Open(path)
+	stream, err := os.OpenFile(path, os.O_RDWR, 0)
 	if err != nil {
 		return nil, err
 	}
-	defer stream.Close()
 
 	ctx := &FmpFile{stream: stream, Dictionary: &FmpDict{}}
 	if err := ctx.readHeader(); err != nil {
@@ -90,6 +89,10 @@ func OpenFile(path string) (*FmpFile, error) {
 	return ctx, nil
 }
 
+func (ctx *FmpFile) Close() {
+	ctx.stream.Close()
+}
+
 func (ctx *FmpFile) readHeader() error {
 	buf := make([]byte, headerSize)
 	_, err := ctx.stream.Read(buf)
@@ -208,3 +211,43 @@ func (ctx *FmpFile) readTables() {
 
 	ctx.tables = tables
 }
+
+func (ctx *FmpFile) NewSector() (*FmpSector, error) {
+	id := uint64(len(ctx.Sectors)) + 1
+	prevID := id - 2
+
+	ctx.Sectors[prevID].NextID = uint64(id)
+	_, err := ctx.stream.WriteAt(encodeUint(4, int(id)), int64((id-1)*sectorSize)+4)
+
+	if err != nil {
+		return nil, err
+	}
+
+	sector := &FmpSector{
+		ID:      uint64(id),
+		Deleted: false,
+		Level:   0,
+		PrevID:  prevID,
+		NextID:  0,
+		Chunks:  make([]*FmpChunk, 0),
+	}
+
+	ctx.Sectors = append(ctx.Sectors, sector)
+
+	sectorBuf := make([]byte, sectorSize)
+	sectorBuf[0] = 0 // deleted
+	sectorBuf[1] = 0 // level
+	writeToSlice(sectorBuf, 4, encodeUint(4, int(prevID))...)
+	writeToSlice(sectorBuf, 8, encodeUint(4, int(id))...)
+
+	_, err = ctx.stream.WriteAt(sectorBuf, int64((id+1)*sectorSize))
+	if err != nil {
+		return nil, err
+	}
+	return sector, nil
+}
+
+func (ctx *FmpFile) setValue(path []uint64, value []byte) {
+	// ctx.Dictionary.set(path, value)
+
+}

fmp/fmp_sector.go

@@ -79,23 +79,23 @@ func (sect *FmpSector) processChunks(dict *FmpDict) error {
 			}
 
 		case FmpChunkSimpleData:
-			dict.SetValue(currentPath, chunk.Value)
+			dict.set(currentPath, chunk.Value)
 
 		case FmpChunkSegmentedData:
 			// Todo: take index into account
-			dict.SetValue(
+			dict.set(
 				currentPath,
 				append(dict.GetValue(currentPath...), chunk.Value...),
 			)
 
 		case FmpChunkSimpleKeyValue:
-			dict.SetValue(
+			dict.set(
 				append(currentPath, uint64(chunk.Key)),
 				chunk.Value,
 			)
 
 		case FmpChunkLongKeyValue:
-			dict.SetValue(
+			dict.set(
 				append(currentPath, uint64(chunk.Key)), // todo: ??
 				chunk.Value,
 			)

fmp/fmp_test.go

@@ -10,8 +10,10 @@ func TestOpenFile(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+	defer f.Close()
+
 	if f.FileSize != 229376 {
-		t.Errorf("expected file size to be 393216, got %d", f.FileSize)
+		t.Errorf("expected file size to be 229376, got %d", f.FileSize)
 	}
 	if f.numSectors != 55 {
 		t.Errorf("expected number of sectors to be 55, got %d", f.numSectors)
@@ -22,6 +24,7 @@ func TestOpenFile(t *testing.T) {
 	if f.VersionDate.Format("2006-01-02") != "2025-01-11" {
 		t.Errorf("expected version date to be '2025-01-11', got '%s'", f.VersionDate.Format("2006-01-02"))
 	}
+
 	f.ToDebugFile("../private/output")
 }
 
@@ -30,6 +33,7 @@ func TestTables(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+	defer f.Close()
 
 	expectedNames := []string{"Untitled"}
 	tableNames := []string{}

fmp/fmp_util.go

@@ -24,3 +24,18 @@ func decodeString(payload []byte) string {
 	}
 	return result
 }
+
+func encodeUint(size uint, value int) []byte {
+	result := make([]byte, size)
+	for i := range size {
+		result[i] = byte(value & 0xFF)
+		value >>= 8
+	}
+	return result
+}
+
+func writeToSlice(slice []byte, start int, payload ...byte) {
+	for i := range payload {
+		slice[start+i] = payload[i]
+	}
+}