Technical Documentation

Tech Stack

Kotlin Jetpack Compose for Wear OS Room Database Retrofit 2 Coroutines & Flow WorkManager Google OAuth 2.0 Google Tasks REST API DataStore Preferences

Architecture Overview

GTasksWear follows a layered architecture pattern with clear separation between data, domain, and presentation concerns.

Google Tasks API Integration

GTasksWear communicates with the Google Tasks REST API v1 via Retrofit 2. The base URL is https://www.googleapis.com/tasks/v1/.

API Endpoints Used

Authentication Flow

Authentication uses Google OAuth 2.0 with the https://www.googleapis.com/auth/tasks scope. An AuthInterceptor automatically injects the Bearer token into every Retrofit request. Token refresh is handled transparently.

Local Database (Room)

GTasksWear uses Room (version 2) as the local persistence layer, enabling offline-first functionality.

Database Schema

Offline Sync Tracking

Each TaskEntity has two fields for offline support:

• isPendingSync: Boolean — Marks tasks that have been modified locally but not yet pushed to the server.
• deleted: Boolean — Soft-delete flag. Tasks are marked for deletion locally and removed from the server on the next sync.

Locally created tasks use an ID prefixed with local_ to distinguish them from server-assigned IDs.

Synchronization Engine

The SyncManager is the core orchestrator for keeping local and remote data in sync.

Sync Flow

1. PUSH LOCAL CHANGES
   ├── For each task list:
   │   ├── Find tasks with isPendingSync = true
   │   ├── If deleted & local_ → delete from Room
   │   ├── If deleted & remote → DELETE via API, then delete from Room
   │   ├── If local_ (new) → POST via API, replace with server entity
   │   └── If remote (updated) → PATCH via API, update entity
   │
2. FETCH REMOTE STATE
   ├── GET all task lists
   └── For each list → GET all tasks
   │
3. ATOMIC DATABASE UPDATE (Room Transaction)
   ├── Clear all task lists (cascades to tasks)
   ├── Insert all fetched task lists
   └── Insert all fetched tasks

Sync Intervals

UI Layer (Jetpack Compose for Wear OS)

The entire UI is built with Jetpack Compose for Wear OS — no XML layouts.

Key Screens

Task Tree Rendering

Tasks support parent-child relationships. The UI builds a flattened tree using a recursive algorithm:

fun addWithChildren(task: Task) {
    orderedList.add(task)
    if (!collapsed[task.id]) {
        childrenMap[task.id]?.forEach { child ->
            addWithChildren(child)
        }
    }
}

This is wrapped in a remember(tasks, sortOption, collapsedParents) block with a TaskTreeResult data class to avoid unnecessary recomputations.

Design Principles

• AMOLED-optimized: True black backgrounds to save battery on OLED displays.
• High contrast: White text on dark backgrounds for outdoor readability.
• Touch-friendly: All interactive elements sized ≥ 48dp for easy tapping on small screens.
• Rotary input: ScalingLazyColumn natively supports crown/bezel scrolling.

Build & Optimization

Dependencies

Security

• No server infrastructure: All data flows directly between the device and Google's APIs. There is no intermediary server.
• OAuth 2.0: No passwords are ever stored. Authentication is handled entirely via Google's token-based system.
significantly harder.
• HTTPS only: All API communication uses TLS encryption.