const MAX_STEPS = 100;

export class ComputerUseSession {
  constructor({ stepsMax = 20, grantMinutes = 3, mode = 'act', clock = () => Date.now(), audit } = {}) {
    this.clock = clock;
    this.mode = mode;
    this.grantMinutes = grantMinutes;
    this.stepsMax = Math.min(MAX_STEPS, Math.max(1, stepsMax));
    this.active = false;
    this.stepsUsed = 0;
    this.sessionId = null;
    this.backend = 'none';
    this.expiresAt = null;
    this.audit = audit;
  }

  grant({ persist = false, monitors = 'focused' } = {}) {
    if (this.mode === 'off') throw new Error('Desktop access is disabled in Settings');
    this.active = true;
    this.stepsUsed = 0;
    this.sessionId = `cu_${this.clock().toString(36)}`;
    this.expiresAt = this.clock() + this.grantMinutes * 60 * 1000;
    return { session_id: this.sessionId, restore_token_present: Boolean(persist), monitors, backend: this.backend };
  }

  setBackend(backend) { this.backend = ['portal-ei', 'portal-notify', 'ydotool', 'none'].includes(backend) ? backend : 'none'; return this.backend; }

  revoke() {
    this.active = false;
    this.sessionId = null;
    this.expiresAt = null;
    this.backend = 'none';
    Promise.resolve(this.audit?.wipeTemp?.()).catch(() => {});
  }

  status() {
    if (this.active && this.expiresAt != null && this.clock() >= this.expiresAt) this.revoke();
    return {
      active: this.active,
      mode: this.mode,
      steps_used: this.stepsUsed,
      steps_max: this.stepsMax,
      grant_expires_at: this.expiresAt,
      backend: this.backend,
    };
  }

  assertActive() {
    if (!this.active) throw new Error('computer-use grant is inactive');
    if (this.expiresAt && this.clock() >= this.expiresAt) {
      this.revoke();
      throw new Error('computer-use grant expired');
    }
  }

  beginStep() {
    this.assertActive();
    if (this.mode !== 'act') throw new Error('Desktop access is observe-only');
    if (this.stepsUsed >= this.stepsMax) throw new Error('computer-use step budget exhausted');
    this.stepsUsed += 1;
  }
}