# DChain Messenger — React Native Client

E2E-encrypted mobile/desktop messenger built on the DChain blockchain stack.

**Stack:** React Native · Expo · NativeWind (Tailwind) · TweetNaCl · Zustand

## Quick Start

```bash
cd client-app
npm install
npx expo start          # opens Expo Dev Tools
# Press 'i' for iOS simulator, 'a' for Android, 'w' for web
```

## Requirements

- Node.js 18+
- [Expo Go](https://expo.dev/client) on your phone (for Expo tunnel), or iOS/Android emulator
- A running DChain node (see root README for `docker compose up --build -d`)

## Project Structure

```
client-app/
├── app/
│   ├── _layout.tsx           # Root layout — loads keys, sets up nav
│   ├── index.tsx             # Welcome / onboarding
│   ├── (auth)/
│   │   ├── create.tsx        # Generate new Ed25519 + X25519 keys
│   │   ├── created.tsx       # Key created — export reminder
│   │   └── import.tsx        # Import existing key.json
│   └── (app)/
│       ├── _layout.tsx       # Tab bar — Chats · Wallet · Settings
│       ├── chats/
│       │   ├── index.tsx     # Chat list with contacts
│       │   └── [id].tsx      # Individual chat with E2E encryption
│       ├── requests.tsx      # Incoming contact requests
│       ├── new-contact.tsx   # Add contact by @username or address
│       ├── wallet.tsx        # Balance + TX history + send
│       └── settings.tsx      # Node URL, key export, profile
├── components/ui/            # shadcn-style components (Button, Card, Input…)
├── hooks/
│   ├── useMessages.ts        # Poll relay inbox, decrypt messages
│   ├── useBalance.ts         # Poll token balance
│   └── useContacts.ts        # Load contacts + poll contact requests
└── lib/
    ├── api.ts                # REST client for all DChain endpoints
    ├── crypto.ts             # NaCl box encrypt/decrypt, Ed25519 sign
    ├── storage.ts            # SecureStore (keys) + AsyncStorage (data)
    ├── store.ts              # Zustand global state
    ├── types.ts              # TypeScript interfaces
    └── utils.ts              # cn(), formatAmount(), relativeTime()
```

## Cryptography

| Operation | Algorithm | Library |
|-----------|-----------|---------|
| Transaction signing | Ed25519 | TweetNaCl `sign` |
| Key exchange | X25519 (Curve25519) | TweetNaCl `box` |
| Message encryption | NaCl box (XSalsa20-Poly1305) | TweetNaCl `box` |
| Key storage | Device secure enclave | expo-secure-store |

Messages are encrypted as:
```
Envelope {
  sender_pub:    <X25519 hex>   // sender's public key
  recipient_pub: <X25519 hex>   // recipient's public key
  nonce:         <24-byte hex>  // random per message
  ciphertext:    <hex>          // NaCl box(plaintext, nonce, sender_priv, recipient_pub)
}
```

## Connect to your node

1. Start the DChain node: `docker compose up --build -d`
2. Open the app → Settings → Node URL → `http://YOUR_IP:8081`
3. If using Expo Go on physical device: your PC and phone must be on the same network, or use `npx expo start --tunnel`

## Key File Format

The `key.json` exported/imported by the app:
```json
{
  "pub_key":     "26018d40...",   // Ed25519 public key (64 hex chars)
  "priv_key":    "...",           // Ed25519 private key (128 hex chars)
  "x25519_pub":  "...",           // X25519 public key (64 hex chars)
  "x25519_priv": "..."            // X25519 private key (64 hex chars)
}
```

This is the same format as the Go node's `--key` flag.