/**
 * RuntimeRegistry — Strict single-active-account enforcement
 *
 * Prevents concurrent accounts from running.
 * Registry.register() throws if another account is already active.
 * This replaces the old shared.js singleton pattern.
 *
 * See §1.1 of refactoring-plan.md.
 */

import { logger } from '../util/logger.js';
import type { AccountRuntime } from './account.js';

export class RuntimeRegistry {
  private _active: AccountRuntime | null = null;

  /**
   * Register an AccountRuntime as the active instance.
   * @throws Error if another account is already active
   */
  register(runtime: AccountRuntime): void {
    if (this._active && this._active !== runtime) {
      throw new Error(
        `Cannot start account '${runtime.accountId}': ` +
        `account '${this._active.accountId}' is already running. ` +
        `Stop it first.`
      );
    }
    this._active = runtime;
    logger.info(`[registry] Registered account '${runtime.accountId}'`);
  }

  /**
   * Unregister the active runtime.
   */
  unregister(runtime: AccountRuntime): void {
    if (this._active === runtime) {
      logger.info(`[registry] Unregistered account '${runtime.accountId}'`);
      this._active = null;
    }
  }

  /**
   * Get the currently active runtime.
   * Returns null if no account is running.
   */
  getActive(): AccountRuntime | null {
    return this._active;
  }

  /**
   * Get the default (only) runtime.
   * In single-active-account mode, this is the same as getActive().
   */
  getDefault(): AccountRuntime | null {
    return this._active;
  }

  /**
   * Check if any account is currently running.
   */
  hasActive(): boolean {
    return this._active !== null;
  }
}

/**
 * Global registry instance.
 * Shared by channel adapter, tools, and hooks.
 */
export const registry = new RuntimeRegistry();