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@@ -1,121 +1,135 @@
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package fit
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import (
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"bytes"
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"encoding/binary"
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"time"
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"io"
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)
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// FitBaseType represents FIT base type definitions
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type FitBaseType struct {
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ID int
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Name string
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Size int
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Invalid uint64
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Field byte
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}
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// Base types definitions
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var (
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FitEnum = FitBaseType{0, "enum", 1, 0xFF, 0x00}
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FitUint8 = FitBaseType{2, "uint8", 1, 0xFF, 0x02}
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FitUint16 = FitBaseType{4, "uint16", 2, 0xFFFF, 0x84}
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FitUint32 = FitBaseType{6, "uint32", 4, 0xFFFFFFFF, 0x86}
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FitString = FitBaseType{7, "string", 1, 0x00, 0x07}
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FitFloat32 = FitBaseType{8, "float32", 4, 0xFFFFFFFF, 0x88}
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FitByte = FitBaseType{13, "byte", 1, 0xFF, 0x0D}
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)
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// FitEncoder encodes FIT activity files
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// FitEncoder encodes FIT activity files using streaming writes with optimized CRC calculation
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type FitEncoder struct {
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buf bytes.Buffer
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w io.WriteSeeker
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crc uint16
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dataSize int
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headerSize int
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activityDefined bool
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startPos int64 // position after header
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}
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const (
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FitHeaderSize = 12
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FileTypeActivity = 4
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GarminEpochOffset = 631065600 // UTC 00:00 Dec 31 1989
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)
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// NewFitEncoder creates a new streaming FIT encoder
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func NewFitEncoder(w io.WriteSeeker) (*FitEncoder, error) {
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encoder := &FitEncoder{
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w: w,
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crc: 0,
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dataSize: 0,
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headerSize: 14, // Standard header size with CRC
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}
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// NewFitEncoder creates a new FIT encoder
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func NewFitEncoder() *FitEncoder {
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e := &FitEncoder{headerSize: FitHeaderSize}
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e.writeHeader(0) // Initial header with 0 data size
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return e
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}
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// Get current position for header
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var err error
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if encoder.startPos, err = w.Seek(0, io.SeekCurrent); err != nil {
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return nil, err
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}
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// writeHeader writes the FIT file header
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func (e *FitEncoder) writeHeader(dataSize int) {
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e.buf.Reset()
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// Write header placeholder
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header := []byte{
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byte(e.headerSize), // Header size
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16, // Protocol version
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0, 0, 0, 108, // Profile version (108.0)
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14, // Header size
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0x10, // Protocol version
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0x00, 0x2D, // Profile version (little endian 45)
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0x00, 0x00, 0x00, 0x00, // Data size (4 bytes, will be updated later)
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'.', 'F', 'I', 'T', // ".FIT" data type
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0x00, 0x00, // Header CRC (will be calculated later)
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}
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e.buf.Write(header)
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// Write data size (4 bytes, little-endian)
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sizeBytes := make([]byte, 4)
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binary.LittleEndian.PutUint32(sizeBytes, uint32(dataSize))
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e.buf.Write(sizeBytes)
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// Write file type signature
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e.buf.Write([]byte(".FIT"))
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}
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// AddActivity adds activity data to the FIT file
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func (e *FitEncoder) AddActivity(activity FitActivity) error {
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// TODO: Implement activity message encoding
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return nil
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}
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// Encode returns the encoded FIT file bytes
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func (e *FitEncoder) Encode() ([]byte, error) {
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dataSize := e.buf.Len() - e.headerSize
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e.writeHeader(dataSize)
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e.writeCRC()
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return e.buf.Bytes(), nil
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}
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// writeCRC calculates and appends the FIT CRC
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func (e *FitEncoder) writeCRC() {
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data := e.buf.Bytes()
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crc := uint16(0)
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for _, b := range data {
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crc = calcCRC(crc, b)
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// Write header and calculate CRC
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if _, err := w.Write(header); err != nil {
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return nil, err
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}
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crcBytes := make([]byte, 2)
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binary.LittleEndian.PutUint16(crcBytes, crc)
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e.buf.Write(crcBytes)
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encoder.updateCRC(header)
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return encoder, nil
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}
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// calcCRC calculates FIT CRC
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func calcCRC(crc uint16, byteVal byte) uint16 {
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table := [...]uint16{
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// updateCRC calculates CRC-16 checksum without hash/crc16 dependency
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func (e *FitEncoder) updateCRC(data []byte) {
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crcTable := [...]uint16{
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0x0000, 0xCC01, 0xD801, 0x1400, 0xF001, 0x3C00, 0x2800, 0xE401,
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0xA001, 0x6C00, 0x7800, 0xB401, 0x5000, 0x9C01, 0x8801, 0x4400,
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}
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tmp := table[crc & 0xF]
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crc = (crc >> 4) & 0x0FFF
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crc = crc ^ tmp ^ table[byteVal & 0xF]
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currentCRC := e.crc
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for _, b := range data {
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// Compute checksum of lower four bits
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tmp := crcTable[currentCRC&0xF]
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currentCRC = (currentCRC >> 4) & 0x0FFF
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currentCRC = currentCRC ^ tmp ^ crcTable[b&0xF]
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// Compute checksum of upper four bits
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tmp = crcTable[currentCRC&0xF]
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currentCRC = (currentCRC >> 4) & 0x0FFF
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currentCRC = currentCRC ^ tmp ^ crcTable[(b>>4)&0xF]
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}
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e.crc = currentCRC
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}
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// Write writes activity data in chunks
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func (e *FitEncoder) Write(p []byte) (int, error) {
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n, err := e.w.Write(p)
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if err != nil {
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return n, err
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}
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e.updateCRC(p)
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e.dataSize += n
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return n, nil
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}
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// Close finalizes the FIT file
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func (e *FitEncoder) Close() error {
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// Save current position
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currentPos, err := e.w.Seek(0, io.SeekCurrent)
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if err != nil {
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return err
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}
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// Update data size in header
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if _, err := e.w.Seek(e.startPos+4, io.SeekStart); err != nil {
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return err
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}
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dataSizeBytes := make([]byte, 4)
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binary.LittleEndian.PutUint32(dataSizeBytes, uint32(e.dataSize))
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if _, err := e.w.Write(dataSizeBytes); err != nil {
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return err
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}
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// Recalculate header CRC with original data
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header := []byte{
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14, // Header size
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0x10, // Protocol version
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0x00, 0x2D, // Profile version
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dataSizeBytes[0], dataSizeBytes[1], dataSizeBytes[2], dataSizeBytes[3],
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'.', 'F', 'I', 'T', // ".FIT" data type
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}
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tmp = table[crc & 0xF]
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crc = (crc >> 4) & 0x0FFF
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return crc ^ tmp ^ table[(byteVal >> 4) & 0xF]
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}
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// Calculate header CRC with clean state
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e.crc = 0
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e.updateCRC(header)
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headerCRC := e.crc
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// timestamp converts Go time to FIT timestamp
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func timestamp(t time.Time) uint32 {
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return uint32(t.Unix() - GarminEpochOffset)
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}
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// Update header CRC
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if _, err := e.w.Seek(e.startPos+12, io.SeekStart); err != nil {
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return err
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}
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crcBytes := make([]byte, 2)
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binary.LittleEndian.PutUint16(crcBytes, headerCRC)
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if _, err := e.w.Write(crcBytes); err != nil {
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return err
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}
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// FitActivity represents basic activity data for FIT encoding
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type FitActivity struct {
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Name string
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Type string
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StartTime time.Time
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Duration time.Duration
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Distance float32 // in meters
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// Write final file CRC
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if _, err := e.w.Seek(currentPos, io.SeekStart); err != nil {
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return err
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}
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fileCRCBytes := make([]byte, 2)
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binary.LittleEndian.PutUint16(fileCRCBytes, e.crc)
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_, err = e.w.Write(fileCRCBytes)
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return err
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}
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