import { TIER_BASE_INTERVAL, TIER_MAX_INTERVAL, TIER_MIN_INTERVAL, type Tier } from "./taxonomy";

/**
 * Adaptive polling. The next interval depends on tier bounds, how recently the sensor
 * changed, how often it changes, error state and HTTP cache behaviour (304s are cheap
 * so we can afford to poll a bit faster).
 */
export interface ScheduleInput {
  tier: Tier;
  baseIntervalSeconds?: number | null;
  lastChangeAt?: Date | null;
  /** changes in the last 7 days */
  changes7d: number;
  /** meaningful events in the last 7 days */
  events7d: number;
  consecutiveErrors: number;
  /** last run served 304 Not Modified */
  lastWas304: boolean;
  now?: Date;
}

export function nextIntervalSeconds(i: ScheduleInput): number {
  const now = i.now ?? new Date();
  const base = i.baseIntervalSeconds ?? TIER_BASE_INTERVAL[i.tier];
  const min = TIER_MIN_INTERVAL[i.tier];
  const max = TIER_MAX_INTERVAL[i.tier];
  let interval = base;

  if (i.lastChangeAt) {
    const ageMin = (now.getTime() - i.lastChangeAt.getTime()) / 60000;
    if (ageMin < 15) interval = base / 6; // burst window
    else if (ageMin < 60) interval = base / 3;
    else if (ageMin < 24 * 60) interval = base / 1.5;
    else if (ageMin > 14 * 24 * 60) interval = base * 3;
    else if (ageMin > 7 * 24 * 60) interval = base * 2;
  } else {
    interval = base * 1.5;
  }

  // Frequent changers get tighter polling; the weight is bounded so the tier still rules.
  const perDay = i.changes7d / 7;
  if (perDay >= 3) interval *= 0.6;
  else if (perDay >= 1) interval *= 0.8;
  if (i.events7d >= 3) interval *= 0.8;

  if (i.lastWas304) interval *= 0.85;

  if (i.consecutiveErrors > 0) interval = Math.max(interval, base) * Math.min(16, 2 ** i.consecutiveErrors);

  // ±10 % jitter to avoid thundering herds
  const jitter = 1 + (Math.random() * 0.2 - 0.1);
  return Math.round(Math.max(min, Math.min(max * (i.consecutiveErrors ? 4 : 1), interval * jitter)));
}