Add oracle rates

src/utils/rates/base-rates.ts

@@ -0,0 +1,56 @@
+import { EventEmitter } from '../event-emitter.js';
+
+/**
+ * Events emitted by our Rates Adapters
+ */
+export type RatesEventMap = {
+  rateUpdated: {
+    numeratorUnitCode: string;
+    denominatorUnitCode: string;
+    price: number;
+  };
+};
+
+export abstract class BaseRates<
+  T extends RatesEventMap = RatesEventMap,
+> extends EventEmitter<T> {
+  /** Starts the given rates adapter so that it will emit events on price updates. */
+  public abstract start(): Promise<void>;
+
+  /** Stops the given rates adapter so that it will stop checking for price updates. */
+  public abstract stop(): Promise<void>;
+
+  /**
+   * List all available market products (pairs).
+   * @returns A set of strings in the format "NUMERATOR/DENOMINATOR"
+   */
+  public abstract listPairs(): Promise<Set<string>>;
+
+  // TODO: Consider whether we actually want the below.
+  //       Ideally, we will want to replace this with something like the Units class:
+  //       See: https://gitlab.com/GeneralProtocols/xo/stack/-/issues/44
+  /**
+   * Format the amount in the target currency to the correct number of decimal places.
+   *
+   * @param {number} amount - The amount to format.
+   * @param {string} targetCurrency - The target currency.
+   *
+   * @returns The formatted amount.
+   */
+  public formatCurrency(amount: number, targetCurrency: string): string {
+    const minimumFractionDigitsMap: { [currency: string]: number } = {
+      AUD: 2,
+      BCH: 8,
+      USD: 2,
+    };
+
+    const formatter = new Intl.NumberFormat('en-US', {
+      style: 'currency',
+      currency: targetCurrency,
+      currencyDisplay: 'narrowSymbol',
+      minimumFractionDigits: minimumFractionDigitsMap[targetCurrency] || 0,
+    });
+
+    return formatter.format(amount);
+  }
+}