# Bincio Mobile App — Design Document

## Philosophy

The Bincio mobile app follows a **local-first** model:

- All activity data lives on the device. The app works fully offline — no account or internet connection required.
- An online instance (bincio.org or a self-hosted server) is an optional upgrade, not a prerequisite.
- Activities are stored in the open **BAS format** (the same JSON schema the server uses), so data is always portable and readable without the app.
- Sync is explicit and user-initiated — the app never silently overwrites local data.

The goal is a personal activity log that you own. The cloud is a backup and a sharing mechanism, not the source of truth.

---

## What already exists

Several pieces of the mobile app are already implemented or proven:

| Piece | Where | Notes |
|---|---|---|
| BAS schema | `docs/schema.md` | The on-device data format — identical to the server format |
| In-browser FIT/GPX/TCX parsing | `site/src/pages/convert/` | Pyodide + the Python extractor running in a browser tab. Proves the extraction works without a server. Not suitable for mobile (Pyodide is 30 MB, browser-only). |
| Local activity storage | `site/src/pages/convert/` | IndexedDB + service worker serving local activities in the feed. Proves the concept; needs a native equivalent. |
| Content-addressed dedup | `bincio/extract/dedup.py` | `source_hash` (SHA-256 of raw file) already prevents duplicates on upload |
| Sync-ready REST API | `bincio/serve/server.py` | Login, upload, activity detail, index.json — the sync primitives are already there |
| Settings persistence | `bincio/serve/db.py` | `settings` table (key/value) in the multi-user SQLite DB; the mobile_app branch added this |
| Elevation algorithms | `bincio/extract/metrics.py`, `bincio/extract/dem.py` | Hysteresis accumulation and DEM correction — need a TypeScript port |

---

## Technology choice

### Cross-platform framework: Expo (React Native)

**Expo** (React Native + the Expo SDK) is the recommended platform:

- TypeScript-first, large ecosystem
- `expo-sqlite` (v2+) provides a fast on-device SQLite database with WAL mode — good fit for BAS-style JSON blobs
- File picking and sharing: `expo-document-picker`, `expo-sharing`
- Maps: MapLibre React Native (`@maplibre/maplibre-react-native`) — same tile standard as the web app, self-hostable
- Background tasks: `expo-background-fetch` / `expo-task-manager`
- OTA updates via Expo's update service
- Expo Go app for rapid development without a build step
- Builds for iOS and Android from a single codebase via EAS Build

**Why not alternatives:**

| Option | Reason for skipping |
|---|---|
| Capacitor + Svelte | Reuses web components but WebView performance is poor for map-heavy activities; Pyodide can't run on mobile |
| Flutter | Dart is unfamiliar, requires rewriting all logic; no advantage over RN for this use case |
| PWA | iOS severely limits background sync, local storage quotas, and file access — not viable for an activity logger |

### Extraction engine: TypeScript port

The Python extractor (`bincio/extract/`) cannot run on mobile. It must be re-implemented in TypeScript. The math is straightforward:

- **FIT parsing**: `@garmin/fitsdk` or `fit-file-parser` (existing JS libraries)
- **GPX/TCX parsing**: standard XML parsing (`DOMParser` or `fast-xml-parser`)
- **Metrics**: distance (Haversine), speed, HR/power averages, lap splits — all simple loops
- **Elevation**: direct port of the hysteresis algorithm from `metrics.py` and `dem.py`
- **DEM correction**: same HTTP API call to Open-Elevation, works from mobile

The TypeScript extraction library (`bincio-extract-ts` or similar) should produce BAS-compatible JSON — the same schema that the server writes. This makes the output directly uploadable.

---

## Architecture

```
Bincio Mobile
├── UI Layer (React Native / Expo)
│   ├── Feed screen        — list of local activities
│   ├── Activity detail    — map + chart + stats
│   ├── Import screen      — pick FIT/GPX/TCX from device or cloud storage
│   ├── Sync screen        — configure instance, push/pull
│   └── Settings screen    — instance URL, account, preferences
│
├── Extraction Engine (TypeScript)
│   ├── FIT parser         — wraps @garmin/fitsdk
│   ├── GPX parser         — XML → BAS points
│   ├── TCX parser         — XML → BAS points
│   ├── Metrics            — port of metrics.py (distance, elevation, HR, power)
│   └── Hysteresis         — port of dem.py _hysteresis_gain_loss + _moving_average
│
├── Local Store (expo-sqlite)
│   ├── activities         — BAS detail JSON + summary fields as columns
│   ├── timeseries         — 1 Hz arrays stored as JSON blobs per activity
│   ├── geojson            — simplified GPS track per activity
│   └── settings           — instance_url, auth_token, sync preferences
│
└── Sync Layer
    ├── Auth               — POST /api/auth/login → session cookie or token
    ├── Manifest fetch     — GET /{handle}/index.json → list of remote IDs
    ├── Push               — POST /api/upload (multipart, original file)
    └── Pull               — GET /api/activity/{id} + timeseries + geojson
```

---

## Data model on device

Each activity is stored in SQLite with:

- `id` — BAS activity ID (`2026-04-17T074238Z`)
- `source_hash` — SHA-256 of the original file (deduplication key)
- `detail_json` — full BAS detail JSON blob
- `timeseries_json` — 1 Hz arrays blob (nullable — loaded lazily)
- `geojson` — simplified GPS track (nullable)
- `synced_at` — timestamp of last successful push to remote instance (nullable = not yet synced)
- `origin` — `"local"` (parsed on device) | `"remote"` (pulled from instance)

The `settings` table stores:

| Key | Value |
|---|---|
| `instance_url` | `https://bincio.org` |
| `handle` | user's handle on the remote instance |
| `session_token` | auth cookie/token value |
| `last_sync_at` | ISO timestamp of last sync |

---

## Sync protocol

Sync is a two-way, hash-based diff — no custom server protocol needed:

### Push (local → server)

1. Fetch `{instance_url}/{handle}/index.json` to get remote activity IDs.
2. Find activities where `synced_at IS NULL` or `origin = "local"` and `id NOT IN remote_ids`.
3. For each unsynced activity, `POST /api/upload` with the original file (stored separately from the extracted JSON) or reconstruct a minimal file from the BAS JSON.
4. On 200, set `synced_at = now()`.

### Pull (server → local)

1. Fetch `{instance_url}/{handle}/index.json` (and yearly shards if present).
2. Find IDs in the remote list that are not in the local DB.
3. For each missing activity:
   - `GET {instance_url}/activities/{id}.json` → store as `detail_json`
   - `GET {instance_url}/activities/{id}.timeseries.json` → store as `timeseries_json` (lazy, on demand)
   - `GET {instance_url}/activities/{id}.geojson` → store as `geojson`
4. Insert with `origin = "remote"`, `synced_at = now()`.

### Conflict handling

Activities are immutable once created (same philosophy as the server). Conflicts only arise if the same source file is imported on two devices before sync. The `source_hash` prevents double-counting — whichever copy arrives at the server first wins; the duplicate is rejected silently.

---

## What's NOT in scope (v1)

- Live activity recording (GPS track + sensor recording during a ride) — this is a separate, harder problem
- Offline map tiles — initial version requires network for map rendering
- Photo sync — photos are not included in the BAS timeseries, sync deferred
- Watch / ANT+ / Bluetooth sensors — out of scope for v1
- Editing activities on mobile — read-only feed in v1; edits happen on the web

---

## Open questions

1. **Original file storage**: To push to the server, we need the original FIT/GPX/TCX file. Do we always keep it, or reconstruct a minimal file from extracted BAS JSON? The `POST /api/import-bas` endpoint already exists on the edit server for this use case (see `convert/` page).

2. **Auth model**: The multi-user server uses HTTP session cookies. React Native handles cookies but a token-based auth (`Authorization: Bearer …`) would be cleaner for a mobile client. A `POST /api/auth/token` endpoint may be worth adding.

3. **iOS file access**: FIT/GPX files from Garmin Connect, Komoot, etc. arrive via the share sheet or Files app. `expo-document-picker` handles this but needs testing with each source.

4. **Offline DEM**: DEM correction requires a network call. On mobile, the hysteresis method (offline) should be the default; DEM correction is opt-in when connected.

---

## Roadmap

| Phase | Scope |
|---|---|
| **0 — Foundation** | Expo project scaffold, local SQLite store, settings screen, BAS reader (load an existing `.json` file into the feed) |
| **1 — Import** | TypeScript FIT/GPX/TCX parser + metrics engine, local feed, activity detail with map and chart |
| **2 — Sync** | Auth, push/pull sync with bincio.org or a self-hosted instance |
| **3 — Polish** | Offline map tiles, share sheet integration, widgets, performance |