/**
 * Monitor sweep scheduling.
 *
 * The sweep rides the event bus's existing `timer.tick.5m` rather than
 * introducing a scheduler: the bus's timer menu is deliberately fixed
 * (packages/event-bus/src/timer.ts), and a five-minute grid is accurate enough
 * for home-lab monitoring cadences. Consequence, accepted: a monitor's real
 * period is its configured interval rounded up to the next sweep.
 *
 * See openspec/changes/add-alerting/design.md D2.
 */

const MINUTE_MS = 60_000;

export interface SchedulableMonitor {
  id: string;
  intervalMinutes: number;
  enabled: boolean;
  /** Null when the monitor has never run. */
  lastRunAt: Date | null;
}

/**
 * Select the monitors due to run at `now`.
 *
 * A monitor that has never run is due immediately — otherwise a newly created
 * monitor would stay silent for a full interval, which reads as "monitoring is
 * broken" precisely when someone has just switched it on and is watching.
 *
 * Disabled monitors are never due. Their alerts are resolved when they are
 * disabled rather than left to hang, so skipping them here cannot strand a
 * firing alert.
 */
export function selectDueMonitors<T extends SchedulableMonitor>(monitors: T[], now: Date): T[] {
  return monitors.filter((monitor) => {
    if (!monitor.enabled) return false;
    if (monitor.lastRunAt === null) return true;
    const elapsed = now.getTime() - monitor.lastRunAt.getTime();
    return elapsed >= monitor.intervalMinutes * MINUTE_MS;
  });
}