/** Injection token carrying the resolved {@link ExchangeOptions}. */
export const EXCHANGE_OPTIONS = Symbol("EXCHANGE_OPTIONS");

/** Configuration for the {@link ExchangeService} and its CBE provider. */
export interface ExchangeOptions {
  /**
   * CBE daily-exchange-rates JSON endpoint. Returns an array of daily records;
   * `_limit=1&_sort=Date%3ADESC` narrows it to the most recent day.
   * @default 'https://combanketh.et/cbeapi/daily-exchange-rates/?_limit=1&_sort=Date%3ADESC'
   */
  scrapeUrl?: string;

  /**
   * Last-resort USD→ETB rate, used only when the fetch fails, no cached rate
   * exists, and {@link loadFallbackRate} supplies nothing. The ETB→USD
   * direction is derived as its inverse.
   * @default 162
   */
  fallbackRate?: number;

  /**
   * Reads the persisted fallback rate — the last known good CBE rate, or one
   * set by an operator. Consulted only when the live fetch fails and no cached
   * rate is available; a `null` result falls through to {@link fallbackRate}.
   *
   * Optional: omit it and the provider uses the static `fallbackRate` alone.
   */
  loadFallbackRate?: () => Promise<number | null>;

  /**
   * Persists a freshly fetched live rate as the new fallback, so the stored
   * value is never more than one successful fetch stale. Called after every
   * successful fetch that produced a changed rate.
   *
   * Failures here are logged and swallowed — persisting the fallback must
   * never break the pricing call that triggered it.
   */
  saveFallbackRate?: (rate: number) => Promise<void>;

  /**
   * How long a successfully fetched rate is cached, in milliseconds.
   * @default 3_600_000 (1 hour)
   */
  cacheTtlMs?: number;

  /**
   * Timeout for the rate HTTP request, in milliseconds.
   * @default 8_000
   */
  requestTimeoutMs?: number;
}

/** The scalar options, all resolved — the callbacks stay genuinely optional. */
export type ResolvedExchangeOptions = Required<
  Omit<ExchangeOptions, "loadFallbackRate" | "saveFallbackRate">
> &
  Pick<ExchangeOptions, "loadFallbackRate" | "saveFallbackRate">;

/** Defaults applied to any unset scalar {@link ExchangeOptions} field. */
export const EXCHANGE_DEFAULTS: ResolvedExchangeOptions = {
  scrapeUrl:
    "https://combanketh.et/cbeapi/daily-exchange-rates/?_limit=1&_sort=Date%3ADESC",
  fallbackRate: 162,
  cacheTtlMs: 3_600_000,
  requestTimeoutMs: 8_000,
};

/** Factory contract for {@link ExchangeModule.forRootAsync}. */
export interface ExchangeAsyncOptions {
  /** Providers to inject into {@link useFactory} (e.g. `[ConfigService]`). */
  inject?: unknown[];
  /** Returns the options, possibly async. */
  useFactory: (...args: never[]) => ExchangeOptions | Promise<ExchangeOptions>;
}