/** Raised on the window when a Recomaze service stops or starts answering. */
export const CONNECTION_EVENT = 'recomaze:connection';

/** What a call that never got an answer says, instead of axios's "Network Error". */
export const UNREACHABLE_MESSAGE =
  'Recomaze could not be reached. Check your connection, then try again.';

/** Gateway answers: the service behind them is down or restarting. */
const DOWN_STATUSES: ReadonlySet<number> = new Set([502, 503, 504]);

/** The part of an axios error this module reads. */
export interface FailedCall {
  code?: string;
  message?: string;
  response?: { status?: number; data?: unknown };
  config?: { url?: string; baseURL?: string };
}

/** Detail of {@link CONNECTION_EVENT}. */
export interface ConnectionChange {
  host: string;
  up: boolean;
}

/**
 * The Recomaze host a request went to, or '' for anything else: WordPress's
 * own REST API failing is not Recomaze being down.
 *
 * @param {string | undefined} url - The request URL, absolute or relative.
 * @param {string | undefined} baseURL - The base a relative URL resolves against.
 * @returns {string} The host, e.g. ``agent.recomaze.ai``.
 */
export const recomazeHost = (url?: string, baseURL?: string): string => {
  try {
    const host = new URL(url ?? '', baseURL || undefined).hostname;

    return /(^|\.)recomaze\.ai$/.test(host) ? host : '';
  } catch {
    return '';
  }
};

/**
 * Whether a failed call means the service did not answer at all: no response
 * (refused, offline, timed out) or a gateway error. A 4xx or a 500 is the
 * service answering, so the page's own message stands.
 *
 * @param {FailedCall} error - The failed call.
 * @returns {boolean} True when the service itself is unreachable.
 */
export const isUnreachable = (error: FailedCall): boolean => {
  if (error.code === 'ERR_CANCELED') return false;
  const status = error.response?.status;

  return status === undefined || DOWN_STATUSES.has(status);
};

/**
 * A failed call's message as a page can print it: on a refusal (4xx) the
 * service's own words, which are written for the merchant; on a server
 * error, what happened in plain words, since its text ("Internal Server
 * Error") is not. Never axios's "Request failed with status code 500".
 *
 * @param {FailedCall} error - The failed call.
 * @returns {string} The message.
 */
export const readableFailure = (error: FailedCall): string => {
  const status = error.response?.status;
  if (status === undefined) return UNREACHABLE_MESSAGE;
  const data = (error.response?.data ?? {}) as {
    detail?: unknown;
    message?: unknown;
  };
  if (status < 500) {
    if (typeof data.detail === 'string' && data.detail) return data.detail;
    if (typeof data.message === 'string' && data.message) return data.message;
  }

  return `Recomaze could not complete that (error ${status}). Try again in a moment.`;
};

/**
 * Tell the page a Recomaze service answered or did not.
 *
 * @param {ConnectionChange} change - The host and whether it answered.
 * @returns {void}
 */
export const reportConnection = (change: ConnectionChange): void => {
  if (!change.host || typeof window === 'undefined') return;
  window.dispatchEvent(
    new CustomEvent<ConnectionChange>(CONNECTION_EVENT, { detail: change })
  );
};