Show a dispatch estimate at checkout

import { createServer } from 'node:http';
import { pathToFileURL } from 'node:url';
// example:imports
import { parseAPI } from '@parseapi/sdk';
// /example:imports

class InputError extends Error {}
const escape = value => String(value).replace(/[&<>"']/g, char => ({ '&': '&amp;', '<': '&lt;', '>': '&gt;', '"': '&quot;', "'": '&#39;' }[char]));
const text = (value, max = 160) => typeof value === 'string' && value.length > 0 && value.length <= max && !/[\u0000-\u001f\u007f]/u.test(value);
const DAY = 86400000;
function civilDay(value) {
  const time = typeof value === 'string' && /^\d{4}-\d{2}-\d{2}$/.test(value) ? Date.parse(`${value}T00:00:00Z`) : NaN;
  if (!Number.isFinite(time) || value.startsWith('0000') || new Date(time).toISOString().slice(0, 10) !== value) throw new InputError('Choose a real date.');
  return time / DAY;
}
const isoDay = day => new Date(day * DAY).toISOString().slice(0, 10);
function businessClock(now) {
  if (!(now instanceof Date) || !Number.isFinite(now.getTime())) throw new Error('Clock unavailable.');
  const parts = Object.fromEntries(new Intl.DateTimeFormat('en-CA', {
    timeZone: 'America/New_York', year: 'numeric', month: '2-digit', day: '2-digit',
    hour: '2-digit', minute: '2-digit', hourCycle: 'h23'
  }).formatToParts(now).map(part => [part.type, part.value]));
  return { date: `${parts.year}-${parts.month}-${parts.day}`, minutes: Number(parts.hour) * 60 + Number(parts.minute) };
}
function readHoliday(holiday, date) {
  if (!holiday || holiday.date !== date || !text(holiday.name) || !['public', 'observance'].includes(holiday.type) ||
      typeof holiday.substitute !== 'boolean' || !(holiday.regions === null || Array.isArray(holiday.regions) && holiday.regions.length <= 100 && holiday.regions.every(region => text(region, 20)))) throw new Error('Unexpected holiday.');
  civilDay(holiday.date);
  // This example's policy is US federal only, without state-specific holidays.
  if (holiday.type === 'public' && holiday.regions !== null) throw new Error('Calendar scope does not match the policy.');
  return holiday;
}

export const POLICY = { country: 'US', zone: 'America/New_York', cutoffMinutes: 14 * 60, closedDates: ['2026-12-24'] };
const SERVICES = { standard: { label: 'Standard', days: 2 }, priority: { label: 'Priority', days: 1 } };
const TITLE = 'Estimate your dispatch date';
const INTRO = 'Your order is prepared on weekdays, excluding US federal holidays and our closed dates. Orders received before 2pm New York time can begin that day.';
const FAILURE = 'A required holiday calendar could not be checked. No dispatch estimate is available. Try again.';
const FIELDS = ['service'];
export async function estimateDispatch(service, parse, signal, now = new Date()) {
  if (!Object.hasOwn(SERVICES, service)) throw new InputError('Choose Standard or Priority preparation.');
  const clock = businessClock(now), calendars = new Map();
  const start = civilDay(clock.date);
  let remaining = SERVICES[service].days;
  for (let day = start; day <= start + 45; day++) {
    const date = isoDay(day), year = Number(date.slice(0, 4));
    if (!calendars.has(year)) {
      // example:request
      const calendar = await parse.holiday('US', { year, signal });
      // /example:request
      if (!calendar || calendar.country !== 'US' || calendar.year !== year || !Array.isArray(calendar.holidays) || !calendar.holidays.length || calendar.holidays.length > 1000) throw new Error('Unexpected calendar response.');
      for (const holiday of calendar.holidays) {
        if (!holiday || typeof holiday.date !== 'string' || !holiday.date.startsWith(`${year}-`)) throw new Error('Unexpected holiday year.');
        readHoliday(holiday, holiday.date);
      }
      // example:result
      const holidays = new Set(calendar.holidays
        .filter(holiday => holiday.type === 'public')
        .map(holiday => holiday.date));
      // /example:result
      if (!holidays.size) throw new Error('US federal calendar has no public dates.');
      calendars.set(year, holidays);
    }
    // example:calculate
    const weekday = ![0, 6].includes(new Date(day * DAY).getUTCDay());
    const working = weekday && !calendars.get(year).has(date)
      && !POLICY.closedDates.includes(date);
    const beforeCutoff = day !== start || clock.minutes < POLICY.cutoffMinutes;
    if (working && beforeCutoff && --remaining === 0) {
      return {
        date, orderDate: clock.date, service: SERVICES[service].label,
        processingDays: SERVICES[service].days
      };
    }
    // /example:calculate
  }
  throw new Error('No estimate within the bounded processing window.');
}
function renderForm(fields = {}) {
  // example:form
  const form = `<section class="account"><h2>Your basket</h2><p>Studio notebook · Quantity 1</p></section>
  <form method="post" action="/">
    <label for="service">Order preparation</label>
    <select id="service" name="service" aria-describedby="policy">
      <option value="standard"${fields.service !== 'priority' ? ' selected' : ''}>
        Standard - 2 business days
      </option>
      <option value="priority"${fields.service === 'priority' ? ' selected' : ''}>
        Priority - 1 business day
      </option>
    </select>
    <p id="policy" class="note">A working day before 2pm counts as day one.
      Weekends, US federal holidays, and December 24, 2026 are closed.</p>
    <button type="submit">Estimate dispatch</button>
  </form>`;
  // /example:form
  return form;
}
async function submit(fields, parse, signal, now) {
  const estimate = await estimateDispatch(fields.service, parse, signal, now);
  // example:integration
  return `<section class="result"><h2>Estimated dispatch:
    <time datetime="${escape(estimate.date)}">${escape(estimate.date)}</time></h2>
    <p>${escape(estimate.service)} preparation, ${estimate.processingDays}
      business ${estimate.processingDays === 1 ? 'day' : 'days'}.</p>
    <p class="note">Based on the server's order time in America/New_York.
      Dispatch is when preparation finishes, not the arrival date.</p></section>`;
  // /example:integration
}

const CSS = `
:root{color-scheme:light dark;font:16px/1.55 system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;color:#202124;background:#f5f5f7}
*{box-sizing:border-box}body{margin:0}main{max-width:720px;margin:0 auto;padding:56px 20px 72px}h1{font-size:clamp(2rem,6vw,2.8rem);line-height:1.12;letter-spacing:-.045em;margin:0 0 16px}h2{font-size:1.35rem;line-height:1.3;letter-spacing:-.025em;margin:0 0 12px}h3{font-size:1rem;margin:0 0 8px}p{margin:0 0 16px}.intro,.note,small{color:#62646a}.intro{max-width:56ch}form,.result,.account{background:#fff;border:1px solid #e2e3e4;border-radius:18px;padding:24px;margin-top:24px}label{display:block;font-weight:600;margin-bottom:8px}input,select,button{font:inherit;min-height:44px;border-radius:8px}input,select{width:100%;border:1px solid #acafb5;background:#fff;color:inherit;padding:10px 12px}select{appearance:none;background-image:url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 16 16'%3E%3Cpath fill='none' stroke='%2371717a' stroke-width='1.5' d='m4 6 4 4 4-4'/%3E%3C/svg%3E");background-repeat:no-repeat;background-position:right 12px center;padding-right:36px}button{border:0;background:#087f9c;color:#fff;font-weight:600;padding:10px 18px;margin-top:20px;cursor:pointer}button:disabled{opacity:.65;cursor:wait}:focus-visible{outline:3px solid #0891b2;outline-offset:3px}.note{font-size:.875rem;margin-top:12px}.status{min-height:1.5em;margin-top:14px}ul{padding-left:20px}li{overflow-wrap:anywhere}.result{overflow-wrap:anywhere}.result p:last-child,.account p:last-child{margin-bottom:0}.grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:24px}.technology{display:block}time{font-variant-numeric:tabular-nums}
@media(max-width:480px){main{padding-top:32px}form,.result,.account{padding:20px}.grid{grid-template-columns:1fr}button{width:100%}}
@media(prefers-color-scheme:dark){:root{background:#000;color:#f5f5f7}form,.result,.account{background:#1d1d1f;border-color:#424245}input,select{background-color:#1d1d1f;border-color:#69696e}.intro,.note,small{color:#a1a1a6}button{background:#087f9c}}
`;
const CLIENT = `
const form = document.querySelector('form');
const result = document.querySelector('#result');
const status = document.querySelector('#status');
const button = form.querySelector('button');
let controller, revision = 0;
form.addEventListener('input', () => {
  revision++; controller?.abort(); result.replaceChildren(); status.textContent = ''; button.disabled = false;
});
form.addEventListener('submit', async event => {
  event.preventDefault(); controller?.abort(); controller = new AbortController();
  const current = ++revision, signal = controller.signal;
  result.replaceChildren(); status.textContent = 'Checking...'; button.disabled = true;
  try {
    const response = await fetch('/', { method: 'POST', signal, headers: {
      'Content-Type': 'application/x-www-form-urlencoded', 'X-Example-Fragment': '1'
    }, body: new URLSearchParams(new FormData(form)) });
    const html = await response.text();
    if (current !== revision || signal.aborted) return;
    if (!response.headers.get('content-type')?.startsWith('text/html')) throw new Error();
    result.innerHTML = html; status.textContent = '';
  } catch {
    if (current !== revision || signal.aborted) return;
    status.textContent = 'The check did not finish. Try again.';
  } finally { if (current === revision) button.disabled = false; }
});
`;
function page(form, result = '') {
  return `<!doctype html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1"><title>${TITLE}</title><style>${CSS}</style></head><body><main><h1>${TITLE}</h1><p class="intro">${INTRO}</p>${form}<p id="status" class="status" role="status"></p><div id="result" aria-live="polite">${result}</div></main><script>${CLIENT}</script></body></html>`;
}
function readForm(req, allowed) {
  if (req.headers['content-type']?.split(';')[0] !== 'application/x-www-form-urlencoded') return Promise.reject(new InputError('Submit this form again.'));
  return new Promise((resolve, reject) => {
    const chunks = []; let bytes = 0;
    const fail = error => { cleanup(); req.resume(); reject(error); };
    const chunk = value => {
      bytes += value.length;
      if (bytes > 4096) return fail(new InputError('The form is too large.'));
      chunks.push(value);
    };
    const finish = () => {
      cleanup(); const fields = new URLSearchParams(Buffer.concat(chunks).toString('utf8'));
      if ([...fields.keys()].some(key => !allowed.includes(key)) || allowed.some(key => fields.getAll(key).length !== 1)) return reject(new InputError('Submit one value for each field.'));
      resolve(Object.fromEntries(fields));
    };
    const aborted = () => fail(new Error('Request ended.'));
    const cleanup = () => { req.off('data', chunk); req.off('end', finish); req.off('aborted', aborted); req.off('error', fail); };
    req.on('data', chunk); req.once('end', finish); req.once('aborted', aborted); req.once('error', fail);
  });
}
export function createApp(parse, { now = () => new Date() } = {}) {
  const server = createServer(async (req, res) => {
    const controller = new AbortController();
    const disconnect = () => { if (!res.writableEnded) controller.abort(); };
    res.once('close', disconnect);
    const send = (status, html) => {
      if (controller.signal.aborted) return;
      res.writeHead(status, { 'Content-Type': 'text/html; charset=utf-8', 'Cache-Control': 'no-store',
        'X-Content-Type-Options': 'nosniff', 'Referrer-Policy': 'no-referrer',
        'Content-Security-Policy': "default-src 'none'; img-src data:; style-src 'unsafe-inline'; script-src 'unsafe-inline'; connect-src 'self'; form-action 'self'; base-uri 'none'; frame-ancestors 'none'" });
      res.end(html);
    };
    let fields = {};
    const fragment = req.headers['x-example-fragment'] === '1';
    try {
      const host = req.headers.host ?? '';
      if (!/^(?:127\.0\.0\.1|localhost)(?::[0-9]{1,5})?$/.test(host) ||
          req.headers.origin && req.headers.origin !== `http://${host}` || req.headers['sec-fetch-site'] === 'cross-site') return send(403, '<p>Open the app on 127.0.0.1 to use this form.</p>');
      if (req.url !== '/') return send(404, '<p>Page not found.</p>');
      if (req.method === 'GET') return send(200, page(renderForm({}, now())));
      if (req.method !== 'POST') return send(405, '<p>Use the form to submit a check.</p>');
      fields = await readForm(req, FIELDS);
      const result = await submit(fields, parse, controller.signal, now());
      send(200, fragment ? result : page(renderForm(fields, now()), result));
    } catch (error) {
      if (controller.signal.aborted) return;
      const message = error instanceof InputError ? error.message : FAILURE;
      const result = `<section class="result" role="alert"><h2>Check unavailable</h2><p>${escape(message)}</p></section>`;
      send(error instanceof InputError ? 400 : 502, fragment ? result : page(renderForm(fields, now()), result));
    }
  });
  server.requestTimeout = 10000; server.headersTimeout = 10000;
  return server;
}
function main() {
  const key = process.env.PARSEAPI_KEY?.trim();
  if (!key || key.startsWith('parse_public_') || key.startsWith('parse_app_') || /[\r\n]/.test(key)) throw new Error('Set PARSEAPI_KEY to a server secret key.');
  const port = process.env.PORT === undefined ? 8000 : Number(process.env.PORT);
  if (!Number.isInteger(port) || port < 1 || port > 65535) throw new Error('PORT must be from 1 to 65535.');
  // API 2.1.0 is selected by @parseapi/sdk 1.14.0. No automatic retry of a submitted form.
  // example:client
  const parse = parseAPI(key, { retries: 0 });
  // /example:client
  const server = createApp(parse);
  server.on('error', () => { console.error('The local app could not start. Check PORT.'); process.exitCode = 1; });
  server.listen(port, '127.0.0.1', () => console.log(`Open http://127.0.0.1:${port}`));
}
if (process.argv[1] && import.meta.url === pathToFileURL(process.argv[1]).href) {
  try { main(); } catch (error) { console.error(error.message); process.exitCode = 1; }
}

// The website embeds this same app; the standalone server remains unchanged.
export { page, renderForm, submit };