⚡ The Lore

USDx is the stable settlement currency of the Interchained network — the financial bloodstream that connects creators, node operators, traders, and builders.

On the server, interchained-usdx guards every balance with atomic Lua scripts running inside Redis. No locks. No races. No double-spends.

This package is the client side of that contract — a zero-dependency TypeScript SDK that speaks fluent HTTP to any server built on the Python package. Fully typed. Strict. Runs in every JavaScript runtime that ships native fetch.

Whether you're building a Next.js dashboard, a React Native wallet, or a serverless Cloudflare Worker — this is how you talk to USDx.

📦 Install

# npm
npm install @interchained/usdx

# pnpm
pnpm add @interchained/usdx

# yarn
yarn add @interchained/usdx

# bun
bun add @interchained/usdx

🏗️ How it fits together

┌──────────────────────────────────────────────────────────────┐
│  Your TypeScript / Next.js / React Native / Cloudflare app   │
│                                                              │
│    import { USDxClient } from "@interchained/usdx"           │
│                                                              │
│    ✓ zero production deps     ✓ native fetch                 │
│    ✓ strict TypeScript        ✓ Node • Browser • Deno • Bun  │
└──────────────────────┬───────────────────────────────────────┘
                       │  HTTP / REST
                       │  (JSON, standard HTTP status codes)
┌──────────────────────▼───────────────────────────────────────┐
│  FastAPI wallet server  (interchained-usdx Python package)   │
│                                                              │
│    from usdx import USDxWallet, NowPaymentsService, …        │
│                                                              │
│    ✓ Lua atomic scripts    ✓ NowPayments IPN handler         │
│    ✓ PSBT payout builder   ✓ OTC rate engine                 │
└──────────────────────┬───────────────────────────────────────┘
                       │
               ┌───────▼────────┐
               │   Redis 6+     │
               │ (the source    │
               │  of truth)     │
               └────────────────┘

🚀 Quick start

import { USDxClient } from "@interchained/usdx";

const client = new USDxClient({
  baseUrl:   "https://api.yourapp.com",
  apiKey:    "your-api-key",    // optional — sent as X-Api-Key
  timeoutMs: 10_000,
});

// ── Balance ───────────────────────────────────────────────────
const { balance } = await client.getBalance("alice");
console.log(balance);                  // 20.74

const info = await client.getInfo("alice");
console.log(info.is_frozen);           // false
console.log(info.total_credited);      // 50.00

const history = await client.getHistory("alice", { limit: 10 });
// → Transaction[]

// ── Credit / Debit ────────────────────────────────────────────
const tx = await client.credit({
  userId:      "alice",
  amount:      10.00,
  description: "Article view earnings",
  txType:      "view_reward",
  multiplier:  1.5,    // 1.5× for premium — applied atomically server-side
});
console.log(tx.amount);          // 15.0
console.log(tx.balance_after);   // 35.74

// Both InsufficientBalance and AccountFrozen are first-class error types
try {
  await client.debit({ userId: "alice", amount: 3.99, description: "Subscription" });
} catch (e) {
  if (e instanceof InsufficientBalance) console.log("Not enough funds");
  if (e instanceof AccountFrozen)       console.log("Account is locked");
}

// ── Transfer ──────────────────────────────────────────────────
const { debit, credit } = await client.transfer({
  fromUser:    "alice",
  toUser:      "bob",
  amount:      5.00,
  description: "Tip",
});
console.log(debit.balance_after, credit.balance_after);

// ── Freeze / Unfreeze (fraud protection) ─────────────────────
await client.freeze("alice");
await client.unfreeze("alice");

// ── NowPayments crypto deposits ───────────────────────────────
const invoice = await client.createDeposit({
  userId:   "alice",
  amount:   25.00,
  currency: "usdttrc20",    // any of 22 supported coins
});
console.log(invoice.payment_url);    // Redirect user here ↗

const status = await client.checkPayment("payment_id_here");
console.log(status.status);          // "waiting" | "confirming" | "finished" | "failed"

const result = await client.claimPayment("payment_id_here");
// result.already_processed === true if already claimed (idempotent)

// ── OTC rate engine ───────────────────────────────────────────
const rate  = await client.getOtcRate();   // ITC per 1 USDx (e.g. 10.5)
const stats = await client.getOtcStats();  // { itc_reserve, usdx_supply, current_rate, … }

📚 Full API reference

new USDxClient(options)

new USDxClient({
  baseUrl:   string,                         // required — your wallet server URL
  apiKey?:   string,                         // sent as X-Api-Key header
  headers?:  Record<string, string>,         // merged into every request
  timeoutMs?: number,                        // default: 30_000 ms
  fetch?:    typeof fetch,                   // swap in a polyfill or test mock
})

Balance operations

| Method | Signature | Returns | |---|---|---| | getBalance | (userId: string) | Promise<{ user_id: string; balance: number }> | | getInfo | (userId: string) | Promise<BalanceInfo> | | getHistory | (userId: string, opts?: { limit?, offset? }) | Promise<Transaction[]> | | credit | (opts: CreditOptions) | Promise<Transaction> | | debit | (opts: DebitOptions) | Promise<Transaction> | | transfer | (opts: TransferOptions) | Promise<TransferResult> | | freeze | (userId: string) | Promise<void> | | unfreeze | (userId: string) | Promise<void> |

Deposits

| Method | Signature | Returns | |---|---|---| | createDeposit | (opts: DepositOptions) | Promise<DepositInvoice> | | checkPayment | (paymentId: string) | Promise<PaymentStatus> | | claimPayment | (paymentId: string) | Promise<ClaimResult> |

OTC rate engine

| Method | Signature | Returns | |---|---|---| | getOtcRate | () | Promise<number> | | getOtcStats | () | Promise<OtcStats> |

🔷 TypeScript types

All types are exported from the package root. Import only what you need.

import type {
  // Core wallet
  Transaction,
  BalanceInfo,
  TransferResult,

  // Deposits
  DepositInvoice,
  PaymentStatus,
  ClaimResult,

  // OTC
  OtcStats,

  // Request option shapes
  CreditOptions,
  DebitOptions,
  TransferOptions,
  DepositOptions,
} from "@interchained/usdx";

Key type shapes

interface Transaction {
  id:            string;
  user_id:       string;
  direction:     "credit" | "debit";
  tx_type:       string;
  amount:        number;
  balance_after: number;
  description:   string;
  metadata:      Record<string, unknown> | null;
  created_at:    string;   // ISO 8601
}

interface BalanceInfo {
  user_id:        string;
  balance:        number;
  total_credited: number;
  total_debited:  number;
  is_frozen:      boolean;
  created_at:     string | null;
  last_updated:   string | null;
}

🚨 Error handling

All SDK errors extend USDxError. Each is a concrete class you can instanceof against.

import { USDxError, InsufficientBalance, AccountFrozen, HttpError } from "@interchained/usdx";

try {
  await client.debit({ userId: "alice", amount: 999_999, description: "YOLO" });
} catch (e) {
  if (e instanceof InsufficientBalance) {
    // HTTP 422 — balance too low
    console.log("Not enough funds:", e.message);
  }
  else if (e instanceof AccountFrozen) {
    // HTTP 403 — account is locked by fraud protection
    console.log("Account locked:", e.message);
  }
  else if (e instanceof HttpError) {
    // Any other non-2xx response
    console.log(`HTTP ${e.statusCode}:`, e.message);
  }
  else if (e instanceof USDxError) {
    // Network timeout, DNS failure, etc.
    console.log("SDK error:", e.message);
  }
}

🔬 Bring your own fetch

The client accepts a custom fetch function — useful for testing, polyfilling, or logging every request.

// ── Test mocking ──────────────────────────────────────────────
const client = new USDxClient({
  baseUrl: "http://localhost:8000",
  fetch: async (url, init) => {
    // intercept, inspect, or stub any request
    return mockFetch(url, init);
  },
});

// ── Node.js < 18 polyfill ────────────────────────────────────
import nodeFetch from "node-fetch";
const client = new USDxClient({ baseUrl: "...", fetch: nodeFetch as typeof fetch });

// ── Request logging middleware ────────────────────────────────
const client = new USDxClient({
  baseUrl: "...",
  fetch: async (url, init) => {
    console.log("→", init?.method, url);
    const res = await fetch(url, init);
    console.log("←", res.status);
    return res;
  },
});

📁 Examples

See examples/ for runnable code:

| Example | Description | |---|---| | quickstart.ts | End-to-end Node.js script covering every USDxClient method | | express-wallet-app/ | Express skeleton that uses USDxClient as a proxy layer — add your auth, validation, and business logic on top |

🔨 Building from source

npm install
npm run build     # compiles to dist/ (ESM .js + .d.ts)
npm run check     # tsc --noEmit (strict, zero warnings)

🐍 Server-side companion

This SDK is the client half of the USDx stack. The server half is built with the Python package:

pip install interchained-usdx

See interchained-usdx on PyPI and the usdx-py repo for the full wallet engine, NowPayments IPN handler, PSBT builder, and OTC rate engine.

🤝 Contributing

1. Fork → branch → make your changes
2. npm run check — zero TypeScript errors
3. npm run build — clean build with no new .js artifacts committed
4. Open a PR with a clear description of what changed and why

Please report security issues via private message, not public issues.

📜 License

GNU General Public License v3.0 or later. See LICENSE for the full text.

@interchained/usdx  Copyright (C) 2024  Interchained
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under the terms of the GPLv3.