/**
 * Translation session management (background).
 *
 * Only one translation may be active at a time (SEC-14 / Design.md §9).
 * Starting a new request aborts the previous one. Chunks belonging to a
 * stale requestId are discarded.
 */

import { ERROR_CODES } from '../shared/constants.js';

export class TranslationSession {
  constructor() {
    /** @type {{requestId: string, controller: AbortController, port: object}|null} */
    this.active = null;
  }

  /**
   * @returns {boolean}
   */
  hasActive() {
    return this.active !== null;
  }

  /**
   * Abort the active request, if any. Notifies its port so the UI can reset.
   * @returns {void}
   */
  abortActive() {
    if (!this.active) return;
    const { controller, port, requestId } = this.active;
    this.active = null;
    try {
      controller.abort();
    } catch {
      // ignore abort errors
    }
    if (port) {
      try {
        port.postMessage({ type: 'error', requestId, code: ERROR_CODES.REQUEST_ABORTED, message: 'Superseded by a newer request' });
      } catch {
        // port may be gone
      }
    }
  }

  /**
   * Register a new active request, aborting any previous one.
   * @param {string} requestId
   * @param {object} port runtime.Port owning the request
   * @returns {AbortController} the controller for the new request
   */
  start(requestId, port) {
    this.abortActive();
    const controller = new AbortController();
    this.active = { requestId, controller, port };
    return controller;
  }

  /**
   * @param {string} requestId
   * @returns {boolean} true when the given id is the active request.
   */
  isActive(requestId) {
    return this.active !== null && this.active.requestId === requestId;
  }

  /**
   * Clear the active session when it matches the id.
   * @param {string} requestId
   */
  clear(requestId) {
    if (this.isActive(requestId)) {
      this.active = null;
    }
  }
}