export type RuntimeReceiptHeartbeatOutcome = 'active' | 'terminal';

export type RuntimeReceiptHeartbeatSupervisor = {
  start(): void;
  stop(): void;
};

export function createRuntimeReceiptHeartbeatSupervisor(input: {
  intervalMs: number;
  heartbeat: () => Promise<RuntimeReceiptHeartbeatOutcome>;
  isLeaseLost: (error: unknown) => boolean;
  onLeaseLost: (error: unknown) => void;
  onTransientFailure?: (error: unknown) => void;
  onTerminal?: () => void;
}): RuntimeReceiptHeartbeatSupervisor {
  if (!Number.isFinite(input.intervalMs) || input.intervalMs <= 0) {
    throw new Error('Runtime receipt heartbeat interval must be positive.');
  }

  let stopped = false;
  let timer: ReturnType<typeof setTimeout> | null = null;

  const stop = () => {
    stopped = true;
    if (timer !== null) {
      clearTimeout(timer);
      timer = null;
    }
  };

  const schedule = () => {
    if (stopped || timer !== null) return;
    timer = setTimeout(() => {
      timer = null;
      void input
        .heartbeat()
        .then((outcome) => {
          if (outcome === 'terminal') {
            stop();
            input.onTerminal?.();
            return;
          }
          schedule();
        })
        .catch((error) => {
          if (input.isLeaseLost(error)) {
            stop();
            input.onLeaseLost(error);
            return;
          }
          input.onTransientFailure?.(error);
          schedule();
        });
    }, input.intervalMs);
  };

  return {
    start() {
      if (stopped) return;
      schedule();
    },
    stop,
  };
}