# Architecture — Social Proximity

## System Overview

Social Proximity er bygget som et minimal monorepo med tre separate komponenter:

```
┌────────────────────────────────────────────────────────┐
│                    Mobile App (Flutter)                 │
│                                                        │
│   BLE Scanner ──► Match Screen ──► "Say hello" nudge  │
└───────────────────────┬────────────────────────────────┘
                        │ HTTPS + WebSocket
                        ▼
┌────────────────────────────────────────────────────────┐
│                  Backend (FastAPI)                     │
│                                                        │
│   Match Engine ──► Session Store (Redis) ──► DB (PG)  │
└───────────┬────────────────────────────────────────────┘
            │ Internal API
            ▼
┌────────────────────────────────────────────────────────┐
│              Admin Dashboard (Next.js)                 │
│                                                        │
│   Anonymised stats — pings, sessions, interest counts │
└────────────────────────────────────────────────────────┘
```

## Components

### Mobile App
- **Technology:** Flutter (Dart) — cross-platform Android + iOS
- **BLE library:** `flutter_blue_plus`
- **Responsibility:** BLE scanning and advertisement, interest profile, consent toggle, nudge display
- **Does NOT:** store data persistently, track location, communicate with other users directly

### Backend
- **Technology:** FastAPI (Python) + WebSockets
- **Session store:** Redis — ephemeral sessions, no long-term identity storage
- **Database:** PostgreSQL — anonymised aggregate stats only
- **Responsibility:** receive BLE advertisement tokens, match users, push nudge via WebSocket, aggregate stats

### Admin Dashboard
- **Technology:** Next.js (TypeScript)
- **Responsibility:** display anonymised platform stats — no PII, no user-level data
- **Access:** Internal only (no public-facing auth in MVP)

## Data Flow

### Happy path — two users nudged to talk

```
User A opens app, selects interests, enables "open to talk"
  └─► App generates ephemeral BLE token
  └─► App advertises token via BLE
  └─► App registers token + interests with backend (POST /session)

User B nearby detects User A's BLE token
  └─► App sends token to backend (POST /match)
  └─► Backend checks: does B's interest list overlap with A's?
  └─► If overlap + both consent: backend sends WebSocket nudge to both
        "Someone nearby also works with DevOps and enjoys hardstyle"
  └─► Users see nudge, put phones down, say hello
  └─► Session expires automatically (Redis TTL: 2 hours)
```

### Privacy properties
- BLE tokens are ephemeral — regenerated every session
- Backend never stores exact location or movement history
- Interest matching happens server-side — apps never see each other's raw profile
- After session expiry, all session data is deleted from Redis

## Infrastructure

| Environment | Platform |
|---|---|
| Local dev | Docker Compose (backend + PostgreSQL + Redis) |
| Production | Azure Container Apps or Kubernetes (i80.dk) |

## Repository Structure

```
SigHej/
├── README.md
├── Docs/              ← Technical documentation (this folder)
├── backend/           ← FastAPI application
├── app/               ← Flutter mobile app
├── admin/             ← Next.js admin dashboard
└── docker-compose.yml
```

See individual docs for each component:
- [BACKEND.md](./BACKEND.md)
- [APP.md](./APP.md)
- [ADMIN.md](./ADMIN.md)
- [TESTING.md](./TESTING.md)
- [DECISIONS.md](./DECISIONS.md)