spb/earth-now Public License

1/**2 * earth-now.co3 * Author:  Simon-Pierre Boucher4 * Contact: contact@spboucher.ai5 * File:    packages/counter/src/windows.ts6 * Purpose: Reset-window helpers (today UTC / this year UTC / session) computed from the same model — pure, time is a parameter7 */89import type { CounterModel } from "./counter-model.js";10import { counterValue } from "./value.js";1112export type CounterWindow = "today" | "ytd" | "session" | "total";1314/** Start of the UTC day containing t (ms). */15export function startOfUtcDay(tMs: number): number {16  const d = new Date(tMs);17  return Date.UTC(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate());18}1920/** Start of the UTC year containing t (ms). */21export function startOfUtcYear(tMs: number): number {22  return Date.UTC(new Date(tMs).getUTCFullYear(), 0, 1);23}2425/**26 * Value of a cumulative counter over a display window, derived from the SAME27 * model (same function server/client/badge): v(t) − v(windowStart).28 * "session" needs the caller-provided session start (user arrival time).29 */30export function windowValue(31  model: CounterModel,32  tMs: number,33  window: CounterWindow,34  sessionStartMs?: number,35): number {36  switch (window) {37    case "total":38      return counterValue(model, tMs);39    case "today":40      return counterValue(model, tMs) - counterValue(model, startOfUtcDay(tMs));41    case "ytd":42      return counterValue(model, tMs) - counterValue(model, startOfUtcYear(tMs));43    case "session": {44      if (sessionStartMs === undefined)45        throw new Error("windowValue: 'session' window requires sessionStartMs");46      return counterValue(model, tMs) - counterValue(model, sessionStartMs);47    }48  }49}50