xo-cli/src/services/rates.ts

import { EventEmitter } from '../utils/event-emitter.js';
import {
  type RatesEventMap,
} from '../utils/rates/base-rates.js';
import { RatesOracle } from '../utils/rates/rates-oracles.js';

/**
 * Event map emitted by {@link RatesService}.
 */
export type RatesServiceEventMap = {
  'rate-updated': {
    numeratorUnitCode: string;
    denominatorUnitCode: string;
    price: number;
    pair: string;
    updatedAt: number;
  };
};

/**
 * In-memory representation of a market rate.
 */
type CachedRate = {
  price: number;
  updatedAt: number;
};

/**
 * Minimal adapter contract that RatesService depends on.
 *
 * Using a small interface keeps the service decoupled and avoids inheriting
 * implementation-specific type constraints from concrete adapters.
 */
export interface RatesAdapter {
  start(): Promise<void>;
  stop(): Promise<void>;
  listPairs(): Promise<Set<string>>;
  formatCurrency(amount: number, targetCurrency: string): string;
  on(
    type: 'rateUpdated',
    listener: (detail: RatesEventMap['rateUpdated']) => void,
  ): () => void;
}

/**
 * Orchestrates the rates adapter lifecycle and provides BCH -> fiat helpers
 * for the TUI.
 *
 * This service keeps a small in-memory snapshot of the latest prices and emits
 * a normalized event whenever a pair changes. React components can subscribe
 * through `useSyncExternalStore` for clean and predictable reactivity.
 */
export class RatesService extends EventEmitter<RatesServiceEventMap> {
  private readonly adapter: RatesAdapter;
  private readonly ratesByPair = new Map<string, CachedRate>();
  private unsubscribeFromAdapter: (() => void) | null = null;
  private started = false;

  constructor(adapter: RatesAdapter) {
    super();
    this.adapter = adapter;
  }

  /**
   * Creates a rates service.
   *
   * If no adapter is passed, this defaults to the Oracle-backed adapter.
   */
  public static async create(adapter?: RatesAdapter): Promise<RatesService> {
    const resolvedAdapter = adapter ?? (await RatesOracle.from());
    return new RatesService(resolvedAdapter);
  }

  /**
   * Starts the underlying adapter and begins collecting live updates.
   */
  public async start(): Promise<void> {
    if (this.started) {
      return;
    }
    this.started = true;

    this.unsubscribeFromAdapter = this.adapter.on('rateUpdated', (event) => {
      this.handleRateUpdated(event);
    });

    try {
      await this.adapter.start();
    } catch (error) {
      this.unsubscribeFromAdapter?.();
      this.unsubscribeFromAdapter = null;
      this.started = false;
      throw error;
    }
  }

  /**
   * Stops live rate collection.
   */
  public async stop(): Promise<void> {
    if (!this.started) {
      return;
    }
    this.started = false;

    this.unsubscribeFromAdapter?.();
    this.unsubscribeFromAdapter = null;

    await this.adapter.stop();
  }

  /**
   * Returns the latest price for a pair in NUMERATOR/DENOMINATOR form.
   *
   * Example: `getRate("USD", "BCH")`.
   */
  public getRate(
    numeratorUnitCode: string,
    denominatorUnitCode: string,
  ): number | null {
    const pair = this.getPairKey(numeratorUnitCode, denominatorUnitCode);
    return this.ratesByPair.get(pair)?.price ?? null;
  }

  /**
   * Converts satoshis to fiat using the latest BCH/fiat rate.
   *
   * Example: `convertBchToFiat(1234n, "USD")`.
   */
  public convertBchToFiat(
    satoshis: bigint,
    targetCurrency: string = 'USD',
  ): number | null {
    const rate = this.getRate(targetCurrency, 'BCH');
    if (rate === null) {
      return null;
    }

    const amountInBch = Number(satoshis) / 100_000_000;
    return amountInBch * rate;
  }

  /**
   * Formats a BCH -> fiat converted amount using the adapter formatter.
   */
  public formatBchToFiat(
    satoshis: bigint,
    targetCurrency: string = 'USD',
  ): string | null {
    const normalizedCurrency = targetCurrency.toUpperCase();
    const amount = this.convertBchToFiat(satoshis, normalizedCurrency);
    if (amount === null) {
      return null;
    }
    return this.adapter.formatCurrency(amount, normalizedCurrency);
  }

  /**
   * Formats an arbitrary fiat amount in a currency-aware way.
   */
  public formatCurrency(amount: number, currencyCode: string): string {
    return this.adapter.formatCurrency(amount, currencyCode.toUpperCase());
  }

  /**
   * Handles normalized updates from the underlying adapter.
   */
  private handleRateUpdated(event: RatesEventMap['rateUpdated']): void {
    const numeratorUnitCode = event.numeratorUnitCode.toUpperCase();
    const denominatorUnitCode = event.denominatorUnitCode.toUpperCase();
    const pair = this.getPairKey(numeratorUnitCode, denominatorUnitCode);
    const updatedAt = Date.now();

    this.ratesByPair.set(pair, {
      price: event.price,
      updatedAt,
    });

    this.emit('rate-updated', {
      numeratorUnitCode,
      denominatorUnitCode,
      price: event.price,
      pair,
      updatedAt,
    });
  }

  /**
   * Creates a stable key for pair lookups.
   */
  private getPairKey(
    numeratorUnitCode: string,
    denominatorUnitCode: string,
  ): string {
    return `${numeratorUnitCode.toUpperCase()}/${denominatorUnitCode.toUpperCase()}`;
  }
}