Added Rates Service: Base, Coinbase, Composite

packages/stack/src/rates/rates-composite.ts

@@ -0,0 +1,43 @@
+import { Satoshis } from "@xocash/primitives";
+
+import { BaseRates, type RateOptions } from "./base-rates.js";
+
+export type RatesCompositePolicy = (rates: number[]) => number;
+
+const ratesAveragePolicy: RatesCompositePolicy = (rates) => rates.reduce((acc, rate) => acc + rate, 0) / rates.length;
+
+/**
+ * A composite rate that averages the rates of multiple rates.
+ */
+export class RatesComposite extends BaseRates {
+  constructor(private rates: BaseRates[], private policy: RatesCompositePolicy = ratesAveragePolicy) {
+    super();
+  }
+
+  public async start(): Promise<void> {
+    await Promise.all(this.rates.map((rate) => rate.start()));
+  }
+
+  public async stop(): Promise<void> {
+    await Promise.all(this.rates.map((rate) => rate.stop()));
+  }
+
+  public async getRate(currency: string, options?: Partial<RateOptions>): Promise<number> {
+    const rates = await Promise.all(this.rates.map((rate) => rate.getRate(currency, options)));
+    return this.policy(rates);
+  }
+
+  public async toBCH(amount: number, fromCurrency: string): Promise<Satoshis> {
+    const rate = await this.getRate(fromCurrency);
+
+    const bchAmount = amount / rate;
+    return Satoshis.fromBCH(bchAmount);
+  }
+
+  public async fromBCH(amount: Satoshis, toCurrency: string): Promise<number> {
+    const rate = await this.getRate(toCurrency);
+
+    const result = amount.toBCH() * rate;
+    return result;
+  }
+}