cloudflare-domain-manager/apps/api/src/services/routing/weighted.ts

import type { LbIpRow } from "./types.js";
import { isPoolMember } from "./health.js";

/** Slot length for time-sliced weighted DNS (one A at a time). */
export const WEIGHTED_SLOT_MS = 60_000;

/** Cloudflare DNS-only minimum TTL; Auto (1) is ~300s and would smear ratios. */
export const WEIGHTED_DNS_TTL = 60;

export function weightedDesired(rows: LbIpRow[], nowMs = Date.now()): string[] {
  if (rows.length === 0) return [];
  const live = rows.filter((r) => isPoolMember(r.health));
  const pool = live.length > 0 ? live : rows;
  if (pool.length === 1) return [pool[0]!.ip];

  const sorted = [...pool].sort((a, b) => a.ip.localeCompare(b.ip));
  const cycle: string[] = [];
  for (const row of sorted) {
    const weight = Math.max(1, Math.round(row.weight));
    for (let i = 0; i < weight; i++) cycle.push(row.ip);
  }
  const slot = Math.floor(nowMs / WEIGHTED_SLOT_MS) % cycle.length;
  return [cycle[slot]!];
}