This project aims to provide a TypeScript implementation of the Garmin FIT protocol. The current code base only contains a handful of utility classes and a partial FileEncoder. Below is a roadmap describing every task required to reach a publishable SDK.

• Basic utilities (CRC16, Fit, ProtocolVersion)
• Basic FileEncoder skeleton
• FileDecoder implementation
• Streaming classes (InputStream, OutputStream, DataInputStream, DataOutputStream, OutputStreamWriter)
• Numeric helpers (BigInteger, BigDecimal)
• Field helpers (FieldComponent, DeveloperField, DeveloperFieldDefinition, DeveloperDataIdMesg)
• Complete message class implementations (see list below)
• Tests for each component
• Continuous integration & npm packaging

The repository currently lacks many classes required by the FIT specification. Below is an exhaustive list extracted from the protocol documentation and code references.

• FileDecoder (implemented)
• BigInteger (implemented)
• BigDecimal (implemented)
• FieldComponent (implemented)
• DeveloperField (implemented)
• DeveloperDataIdMesg (implemented)
• FitBaseType (implemented)
• FitBaseUnit (implemented)

The following FIT messages require dedicated classes. All of them are present in the repository:

• FileIdMesg
• CapabilitiesMesg
• DeviceSettingsMesg
• UserProfileMesg
• HrmProfileMesg
• SdmProfileMesg
• BikeProfileMesg
• ZonesTargetMesg
• HrZoneMesg
• PowerZoneMesg
• MetZoneMesg
• SportMesg
• GoalMesg
• SessionMesg
• LapMesg
• RecordMesg
• EventMesg
• DeviceInfoMesg
• WorkoutMesg
• WorkoutStepMesg
• ScheduleMesg
• WeightScaleMesg
• CourseMesg
• CoursePointMesg
• TotalsMesg
• ActivityMesg
• SoftwareMesg
• FileCapabilitiesMesg
• MesgCapabilitiesMesg
• FieldCapabilitiesMesg
• FileCreatorMesg
• BloodPressureMesg
• SpeedZoneMesg
• MonitoringMesg
• TrainingFileMesg
• HrvMesg
• AntRxMesg
• AntTxMesg
• AntChannelIdMesg
• LengthMesg
• MonitoringInfoMesg
• PadMesg
• SlaveDeviceMesg
• ConnectivityMesg
• WeatherConditionsMesg
• WeatherAlertMesg
• CadenceZoneMesg
• HrMesg
• SegmentLapMesg
• MemoGlobMesg
• SegmentIdMesg
• SegmentLeaderboardEntryMesg
• SegmentPointMesg
• SegmentFileMesg
• WorkoutSessionMesg
• WatchfaceSettingsMesg
• GpsMetadataMesg
• CameraEventMesg
• TimestampCorrelationMesg
• GyroscopeDataMesg
• AccelerometerDataMesg
• ThreeDSensorCalibrationMesg
• VideoFrameMesg
• ObdiiDataMesg
• NmeaSentenceMesg
• AviationAttitudeMesg
• VideoMesg
• VideoTitleMesg
• VideoDescriptionMesg
• VideoClipMesg
• OhrSettingsMesg
• ExdScreenConfigurationMesg
• ExdDataFieldConfigurationMesg
• ExdDataConceptConfigurationMesg
• FieldDescriptionMesg
• DeveloperDataIdMesg
• MagnetometerDataMesg
• BarometerDataMesg
• OneDSensorCalibrationMesg
• MonitoringHrDataMesg
• TimeInZoneMesg
• SetMesg
• StressLevelMesg
• MaxMetDataMesg
• DiveSettingsMesg
• DiveGasMesg
• DiveAlarmMesg
• ExerciseTitleMesg
• DiveSummaryMesg
• SleepLevelMesg
• JumpMesg
• BeatIntervalsMesg
• RespirationRateMesg
• SplitMesg
• ClimbProMesg
• TankUpdateMesg
• TankSummaryMesg
• SleepAssessmentMesg
• HrvStatusSummaryMesg
• HrvValueMesg
• DeviceAuxBatteryInfoMesg
• DiveApneaAlarmMesg
• MfgRangeMinMesg
• MfgRangeMaxMesg

Each item below describes a self-contained Codex task. When all boxes are checked, the SDK can be published to npm.

1. Stream Abstractions
   • Implement InputStream and OutputStream wrappers using Node streams.
   • Implement DataInputStream, DataOutputStream and OutputStreamWriter helpers.
   • Integrate BigInteger and BigDecimal utilities for large numeric values
2. File Handling
   • Write basic FileEncoder (already present).
   • Finish FileEncoder (record CRC during writes, manage message definitions).
   • Create FileDecoder able to parse FIT headers and message records.
3. Field and Message Structure
   • Base Field, SubField and definition classes.
   • Add FieldComponent logic.
   • Add DeveloperField and DeveloperFieldDefinition with support for DeveloperDataIdMesg.
4. Message Classes
   • Implement each message type listed above under Message Types.
   • Populate Factory with a mesgs array describing field layouts for every message.
5. Profile Information
   • Add enums (FitBaseType, FitBaseUnit, Profile.Type or equivalent) following the FIT profile.
   • Provide helpers to access profile version and message numbers.
6. Testing and Validation
   • Unit tests for FileEncoder and FileDecoder.
   • Unit tests for every message class (creation, encoding, decoding).
   • Protocol validation via ProtocolValidator against all versions.
7. Continuous Integration
   • Set up GitHub Actions to run npm test and TypeScript build on each pull request.
   • Enforce linting and code formatting.
8. Packaging
   • Generate dist/ with compiled JavaScript and type declarations.

• Publish the package to npm with semantic versioning.

graph TD
  FileEncoder --> OutputStream
  DataOutputStream --> OutputStream
  OutputStreamWriter --> OutputStream
  FieldBase --> DataOutputStream
  FieldBase --> DataInputStream
  DataInputStream --> InputStream
  FileDecoder --> InputStream
  FieldBase --> BigInteger
  FieldBase --> BigDecimal
  OutputStream -->|wraps| Writable
  InputStream -->|wraps| Readable
  Factory --> Mesg
  Mesg -->|extends| MessageTypes
  Mesg --> DeveloperField
  MesgDefinition --> DeveloperFieldDefinition
  Profile --> MesgNum

Contributions are welcome. Each unchecked item in the roadmap can be tackled as a standalone pull request. Please include unit tests for new functionality and keep code style consistent with the existing files.