FitTrack_GarminSync/specs/001-create-from-initialspec/spec.md

# Feature Specification: Garmin Connect Synchronization Service

**Feature Branch**: `001-create-from-initialspec`  
**Created**: 2025-10-09  
**Status**: Draft  
**Input**: User description: "the feature description is in @initialspec.md"

## User Scenarios & Testing *(mandatory)*

### User Story 1 - Connect Garmin Account (Priority: P1)

As a single-app user, I want to securely connect my Garmin Connect account so that the application can access my fitness data.

**Why this priority**: This is the foundational step required for any data synchronization. Without it, no other feature can work.

**Independent Test**: Can be tested by initiating the connection process, authenticating with Garmin, and confirming the application shows a successful connection status. This delivers the core value of enabling data exchange.

**Acceptance Scenarios**:

1. **Given** I am not connected to Garmin, **When** I choose to connect my Garmin account, **Then** I am securely redirected to a Garmin authentication page.
2. **Given** I have successfully authenticated with Garmin, **When** I am redirected back to the application, **Then** the application shows that my account is successfully linked.
3. **Given** I deny the authentication request on the Garmin page, **When** I am redirected back to the application, **Then** the application shows that the connection failed and allows me to try again.

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### User Story 2 - Synchronize Activities (Priority: P1)

As a connected user, I want the application to automatically download my latest activities (like runs, rides) from Garmin so my fitness dashboard is always up-to-date.

**Why this priority**: This is the primary purpose of the synchronization service, providing users with their core fitness data.

**Independent Test**: Can be tested by having a connected Garmin account with recent activities, triggering a sync, and verifying that the new activities appear within the application's database.

**Acceptance Scenarios**:

1. **Given** my Garmin account is connected and has recent activities, **When** a synchronization event is triggered, **Then** the new activities are downloaded and stored by the application.
2. **Given** an activity has already been synchronized, **When** the sync runs again, **Then** the existing activity is not duplicated.
3. **Given** I manually trigger a sync, **When** the process starts, **Then** I can view the current status of the synchronization (e.g., "In Progress", "Completed", "Failed").

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### User Story 3 - Upload Workouts (Priority: P2)

As a connected user, I want to be able to upload a planned workout from the application to my Garmin Connect calendar so I can use it on my device.

**Why this priority**: This enables a two-way integration, allowing users to manage their training plans within the application and execute them on their Garmin devices.

**Independent Test**: Can be tested by creating a workout in the application, triggering the upload, and verifying the workout appears in the user's Garmin Connect calendar.

**Acceptance Scenarios**:

1. **Given** my Garmin account is connected, **When** I choose to upload a workout, **Then** the workout is sent to my Garmin Connect calendar.
2. **Given** the workout fails to upload due to a connection issue, **When** the process fails, **Then** I am notified of the failure with a clear error message.

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### Edge Cases

- What happens if the user revokes access to the application from their Garmin Connect account settings?
- How does the system handle rate limits imposed by the Garmin API to avoid being blocked?
- What happens if a synchronization job is interrupted midway (e.g., server restart)?
- How are data conflicts resolved if data is modified in both places between syncs?

## Requirements *(mandatory)*

### Functional Requirements

- **FR-001**: System MUST allow a user to securely connect their Garmin Connect account.
- **FR-002**: System MUST be able to store and manage authentication tokens for the connected Garmin account, including securely handling refresh tokens.
- **FR-003**: System MUST download and store a user's activities from their Garmin account.
- **FR-004**: System MUST provide a mechanism to manually trigger a data synchronization with Garmin.
- **FR-005**: System MUST provide a way for the user to check the status of an ongoing or completed synchronization.
- **FR-006**: System MUST be able to upload a user's planned workouts to their Garmin Connect calendar.
- **FR-007**: System MUST synchronize user health metrics from Garmin, including Daily Summary (Steps, Resting Heart Rate, Sleep), VO2 Max, Heart Rate Zones, FTP Zones, and Max Heart Rate.
- **FR-008**: All synchronization processes MUST run in the background to not block the user interface.
- **FR-009**: The system's interaction with the Garmin API MUST be rate-limited to prevent exceeding API quotas.
- **FR-010**: The system MUST include error handling and retry logic for failed API requests to Garmin.
- **FR-011**: The system MUST maintain a history of synchronization events and their outcomes.

### Key Entities *(include if feature involves data)*

- **User Account**: Represents the single user of the application.
- **Garmin Connection**: Stores the authentication tokens and connection status for a user's Garmin account.
- **Activity**: Represents a fitness activity (e.g., run, cycle) with its associated data (e.g., distance, time, location data).
- **Workout**: Represents a planned workout to be executed by the user.
- **Health Metric**: Represents a specific point-in-time or daily health measurement (e.g., daily steps, resting heart rate).
- **Sync Job**: Represents a single synchronization process, its status, and history.

## Success Criteria *(mandatory)*

### Measurable Outcomes

- **SC-001**: 99% of synchronization requests should be successfully processed within 5 minutes of being initiated.
- **SC-002**: Users can connect their Garmin account in under 60 seconds.
- **SC-003**: The system must be able to handle and store at least 10 years of activity data for a single user without performance degradation.
- **SC-004**: The synchronization process must accurately reflect the user's data from Garmin with a data discrepancy rate of less than 0.1%.
- **SC-005**: No user-facing errors should occur during the background synchronization process. The user should only see the final status (Success/Failure).