import type { ChannelConfig } from "../lib/channelConfig";
import type { SyncSchedulerSettings } from "../lib/settings";

// Pure cadence logic for the sync FULL SWEEP — the periodic deep pass that
// re-enumerates a channel's entire listing in one yt-dlp spawn and derives three
// outputs from it: a refreshed `playlist` file, the maybe-missing (upstream
// deletion) diff, and the same newest-first download set the paged walk would
// have picked. A full enumeration on a 5,000-VOD channel is far more expensive
// than one 50-entry page, so it runs at most once per interval per channel while
// ordinary syncs stay on the cheap paged walk.
//
// Mirrors resolveIntervalMinutes / overdueAmount in syncScheduler.ts: kept pure
// and side-effect-free so the due rules are unit-testable without a server.

// Resolve a channel's effective full-sweep interval in minutes. undefined
// inherits the global default; 0 means the full sweep is disabled for the
// channel (every sync stays a cheap paged walk).
export function resolveFullSweepIntervalMinutes(
  config: ChannelConfig,
  scheduler: SyncSchedulerSettings,
): number {
  if (config.fullSweepIntervalMinutes === undefined) {
    return scheduler.fullSweepIntervalMinutes;
  }
  return config.fullSweepIntervalMinutes;
}

// Whether a sync starting at `now` should pay for the full enumeration. A
// channel that has never swept is due immediately (that first sweep is what
// seeds `playlist` and maybe-missing.json); an unparseable timestamp is treated
// the same rather than wedging the channel out of sweeps forever. An interval of
// 0 (or less) disables the sweep outright and always wins.
export function isFullSweepDue(
  lastFullSweepAt: string | undefined,
  intervalMinutes: number,
  now: number,
): boolean {
  if (intervalMinutes <= 0) return false;
  if (!lastFullSweepAt) return true;
  const last = Date.parse(lastFullSweepAt);
  if (Number.isNaN(last)) return true;
  return now - last >= intervalMinutes * 60_000;
}