metatrondelivery/widget-src/datetime-widget/datetime-widget.ts

// Storefront widget for the Theme App Extension. Vanilla TS, no framework
// (IMPLEMENTATION_PLAN.md §1 sanctions "Preact or vanilla TS" — vanilla
// keeps the bundle tiny and avoids a runtime dependency for something this
// small). Bundled to ../assets/datetime-widget.js via esbuild
// (`npm run build:widget` at the repo root) — Theme App Extensions ship
// static assets as-is, there's no CLI build step for this extension type.
//
// The widget only *collects* a selection and writes it to cart attributes.
// It never enforces anything — that's the Validation Function's job
// (Phase 4), per CLAUDE.md's non-negotiable that enforcement is
// server-side. Losing network, JS, or an ad-blocker here should degrade to
// "no slot picked" (which the Function then rejects at checkout), not to a
// bypass.

type Method = "SHIPPING" | "LOCAL_DELIVERY" | "PICKUP";

interface SlotDto {
  date: string;
  startMin: number;
  endMin: number;
  capacity: number;
  remainingCapacity: number;
  // SHIPPING-only "date range" parity item (PRODUCT_STRATEGY.md §2): present
  // only when the merchant configured transit days on this slot's template.
  // ISO date-time strings (Luxon's DateTime.toJSON()), same shape as
  // start/end elsewhere in this response.
  arrivalRangeStart?: string;
  arrivalRangeEnd?: string;
}

interface RateDto {
  name: string;
  priceCents: number;
  label: string;
}

interface AvailabilityResponse {
  locationId: string | null;
  locationName?: string;
  locationLat?: number | null;
  locationLng?: number | null;
  timezone?: string;
  method: Method;
  dates: Record<string, SlotDto[]>;
  zoneId?: string | null;
  distanceKm?: number | null;
  rate?: RateDto | null;
  error?: string;
}

interface WidgetConfig {
  root: HTMLElement;
  heading: string;
  locationId: string | null;
  googleMapsApiKey: string | null;
  /**
   * "full" (default): the interactive picker that reserves a hold and writes
   * cart attributes. "preview": a read-only "earliest available date" line
   * for the product page (study §3.7 "Delivery/availability information can
   * surface at the product level") — it collects nothing.
   */
  mode: "full" | "preview";
  methods: Array<{ value: Method; label: string; attrLabel: string }>;
  labels: {
    chooseDate: string;
    chooseTime: string;
    noDates: string;
    confirmed: string;
    change: string;
    loading: string;
    error: string;
    postalCodeLabel: string;
    postalCodeSubmit: string;
    outOfArea: string;
    earliestPrefix: string;
    deliveryAtCheckout: string;
  };
}

const PROXY_BASE = "/apps/scheduling";

function minutesToDisplayTime(minutes: number): string {
  const h24 = Math.floor(minutes / 60);
  const m = minutes % 60;
  const period = h24 < 12 ? "AM" : "PM";
  const h12 = h24 % 12 === 0 ? 12 : h24 % 12;
  return `${h12}:${m.toString().padStart(2, "0")} ${period}`;
}

/** Formats the date portion of a full ISO date-time string (arrivalRangeStart/End) using the same weekday/month/day style as formatDateLabel. */
function formatArrivalDateLabel(dateTimeIso: string): string {
  return formatDateLabel(dateTimeIso.slice(0, 10));
}

/**
 * SHIPPING-only "date range" parity item (PRODUCT_STRATEGY.md §2): a
 * shipping slot's start/end time is a ship-out window the shopper doesn't
 * care about — when the merchant configured transit days, show the
 * estimated ARRIVAL range instead. Falls back to the normal time-of-day
 * label for every other slot (PICKUP/LOCAL_DELIVERY, or SHIPPING with no
 * transit days set).
 */
function slotTimeLabel(slot: SlotDto): string {
  if (slot.arrivalRangeStart && slot.arrivalRangeEnd) {
    return `Arrives ${formatArrivalDateLabel(slot.arrivalRangeStart)}–${formatArrivalDateLabel(slot.arrivalRangeEnd)}`;
  }
  if (slot.arrivalRangeStart) {
    return `Arrives from ${formatArrivalDateLabel(slot.arrivalRangeStart)}`;
  }
  if (slot.arrivalRangeEnd) {
    return `Arrives by ${formatArrivalDateLabel(slot.arrivalRangeEnd)}`;
  }
  return `${minutesToDisplayTime(slot.startMin)}–${minutesToDisplayTime(slot.endMin)}`;
}

function formatDateLabel(dateIso: string): string {
  // Parsed as a plain calendar date (no timezone conversion) — this string
  // already represents the location-local calendar day from the API.
  const [year, month, day] = dateIso.split("-").map(Number);
  const date = new Date(Date.UTC(year, month - 1, day));
  return date.toLocaleDateString(undefined, { weekday: "short", month: "short", day: "numeric", timeZone: "UTC" });
}

function readConfig(root: HTMLElement): WidgetConfig {
  const d = root.dataset;
  const methods: WidgetConfig["methods"] = [];
  if (d.showShipping === "true") {
    methods.push({ value: "SHIPPING", label: d.labelShipping || "Shipping", attrLabel: d.attrLabelShipping || "Shipping date" });
  }
  if (d.showLocalDelivery === "true") {
    methods.push({
      value: "LOCAL_DELIVERY",
      label: d.labelLocalDelivery || "Local delivery",
      attrLabel: d.attrLabelLocalDelivery || "Delivery date",
    });
  }
  if (d.showPickup === "true") {
    methods.push({ value: "PICKUP", label: d.labelPickup || "Pickup", attrLabel: d.attrLabelPickup || "Pickup date" });
  }

  return {
    root,
    heading: d.heading || "",
    locationId: d.locationId || null,
    googleMapsApiKey: d.googleMapsApiKey || null,
    mode: d.mode === "preview" ? "preview" : "full",
    methods,
    labels: {
      chooseDate: d.labelChooseDate || "Choose a date",
      chooseTime: d.labelChooseTime || "Choose a time",
      noDates: d.labelNoDates || "No dates are available right now.",
      confirmed: d.labelConfirmed || "Confirmed for",
      change: d.labelChange || "Change",
      loading: d.labelLoading || "Loading available dates…",
      error: d.labelError || "Couldn't load available dates. Please try again.",
      postalCodeLabel: d.labelPostalCode || "Enter your postal/ZIP code",
      postalCodeSubmit: d.labelPostalCodeSubmit || "Check availability",
      outOfArea: d.labelOutOfArea || "Sorry, we don't deliver to this address.",
      earliestPrefix: d.labelEarliestPrefix || "Earliest",
      deliveryAtCheckout: d.labelDeliveryAtCheckout || "Enter your address at checkout to see local delivery dates.",
    },
  };
}

// ProductRule scoping (PRODUCT_STRATEGY.md §2): vendor/productType come
// straight off /cart.js with no extra round trip; productId lets the backend
// additionally resolve collection/tag-scoped rules via one Admin API call.
// Fetched fresh on every availability/hold request so it always reflects the
// shopper's *current* cart, not a stale snapshot from an earlier step.
interface CartLineInfo {
  vendor: string;
  productType: string;
  productId: string;
  variantId: string;
}

interface CartInfo {
  token: string;
  lines: CartLineInfo[];
}

async function fetchCartInfo(): Promise<CartInfo> {
  const res = await fetch("/cart.js", { headers: { Accept: "application/json" } });
  const cart = (await res.json()) as {
    token: string;
    items?: Array<{ vendor?: string; product_type?: string; product_id: number; id: number; variant_id?: number }>;
  };
  return {
    token: cart.token,
    lines: (cart.items ?? []).map((item) => ({
      vendor: item.vendor ?? "",
      productType: item.product_type ?? "",
      productId: `gid://shopify/Product/${item.product_id}`,
      // /cart.js line `id` is the variant id; `variant_id` is present on some
      // theme payloads too — prefer whichever we get.
      variantId: `gid://shopify/ProductVariant/${item.variant_id ?? item.id}`,
    })),
  };
}

async function fetchAvailability(
  method: Method,
  locationId: string | null,
  cart: CartInfo,
  postalCode?: string,
): Promise<AvailabilityResponse> {
  const params = new URLSearchParams({ method, days: "14" });
  if (locationId) params.set("locationId", locationId);
  if (postalCode) params.set("postalCode", postalCode);
  if (cart.lines.length > 0) {
    params.set("cartLines", JSON.stringify(cart.lines.map((l) => ({ vendor: l.vendor, productType: l.productType }))));
    params.set("productIds", cart.lines.map((l) => l.productId).join(","));
    params.set("variantIds", cart.lines.map((l) => l.variantId).join(","));
  }
  const res = await fetch(`${PROXY_BASE}/availability?${params.toString()}`, {
    headers: { Accept: "application/json" },
  });
  const body = (await res.json()) as AvailabilityResponse;
  if (!res.ok) throw new Error(body.error || `Request failed (${res.status})`);
  return body;
}

interface HoldResponse {
  success: boolean;
  expiresAt?: number;
  error?: string;
}

async function requestHold(params: {
  intent: "create" | "release";
  locationId: string;
  method: Method;
  date: string;
  startMin: number;
  cartToken: string;
  cartLines?: Array<{ vendor: string; productType: string }>;
  productIds?: string[];
}): Promise<HoldResponse> {
  const res = await fetch(`${PROXY_BASE}/hold`, {
    method: "POST",
    headers: { "Content-Type": "application/json", Accept: "application/json" },
    body: JSON.stringify(params),
  });
  const body = (await res.json()) as HoldResponse;
  if (!res.ok && params.intent === "create") return { success: false, error: body.error || "Slot unavailable" };
  return body;
}

async function writeCartAttribute(key: string, machine: Record<string, string>, display: string): Promise<void> {
  await fetch("/cart/update.js", {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ attributes: { [key]: display, ...machine } }),
  });
}

// Google Maps JS API loads once per page and calls a global callback — the
// callback name has to be unique-ish and reachable on `window`.
let mapsLoadPromise: Promise<void> | null = null;
function loadGoogleMaps(apiKey: string): Promise<void> {
  if (mapsLoadPromise) return mapsLoadPromise;

  mapsLoadPromise = new Promise((resolve, reject) => {
    const callbackName = "__ddMapsReady";
    (window as unknown as Record<string, () => void>)[callbackName] = () => resolve();

    const script = document.createElement("script");
    script.src = `https://maps.googleapis.com/maps/api/js?key=${encodeURIComponent(apiKey)}&callback=${callbackName}`;
    script.async = true;
    script.onerror = () => reject(new Error("Failed to load Google Maps"));
    document.head.appendChild(script);
  });

  return mapsLoadPromise;
}

interface GoogleMapsGlobal {
  maps: {
    Map: new (el: HTMLElement, options: { center: { lat: number; lng: number }; zoom: number }) => unknown;
    Marker: new (options: { position: { lat: number; lng: number }; map: unknown; title?: string }) => unknown;
  };
}

async function renderPickupMap(container: HTMLElement, apiKey: string, lat: number, lng: number, title: string) {
  try {
    await loadGoogleMaps(apiKey);
    const google = (window as unknown as { google: GoogleMapsGlobal }).google;
    const map = new google.maps.Map(container, { center: { lat, lng }, zoom: 13 });
    new google.maps.Marker({ position: { lat, lng }, map, title });
  } catch {
    container.hidden = true; // no map, no crash — the date/time picker still works fine without it
  }
}

class DateTimeWidget {
  private config: WidgetConfig;
  private el = {
    heading: document.createElement("h3"),
    methodRow: document.createElement("div"),
    postalRow: document.createElement("div"),
    mapContainer: document.createElement("div"),
    dateRow: document.createElement("div"),
    timeRow: document.createElement("div"),
    status: document.createElement("p"),
    confirmation: document.createElement("div"),
  };
  private selectedMethod: WidgetConfig["methods"][number] | null = null;
  private selectedDate: string | null = null;
  private availability: AvailabilityResponse | null = null;
  private heldSlot:
    | { locationId: string; method: Method; date: string; startMin: number; cartToken: string; zoneId: string | null }
    | null = null;

  constructor(config: WidgetConfig) {
    this.config = config;
  }

  mount() {
    const { root, heading, methods } = this.config;
    root.classList.add("dd-widget--ready");
    root.innerHTML = "";

    if (methods.length === 0) return; // merchant disabled every method — render nothing

    if (this.config.mode === "preview") {
      void this.mountPreview();
      return;
    }

    if (heading) {
      this.el.heading.className = "dd-widget__heading";
      this.el.heading.textContent = heading;
      root.appendChild(this.el.heading);
    }

    this.el.methodRow.className = "dd-widget__row dd-widget__methods";
    this.el.postalRow.className = "dd-widget__row dd-widget__postal";
    this.el.postalRow.hidden = true;
    this.el.mapContainer.className = "dd-widget__map";
    this.el.mapContainer.hidden = true;
    this.el.dateRow.className = "dd-widget__row dd-widget__dates";
    this.el.timeRow.className = "dd-widget__row dd-widget__times";
    this.el.status.className = "dd-widget__status";
    this.el.confirmation.className = "dd-widget__confirmation";
    this.el.confirmation.hidden = true;

    root.append(
      this.el.confirmation,
      this.el.methodRow,
      this.el.postalRow,
      this.el.mapContainer,
      this.el.dateRow,
      this.el.timeRow,
      this.el.status,
    );

    if (methods.length === 1) {
      this.selectMethod(methods[0]);
    } else {
      this.renderMethods();
    }
  }

  /**
   * Product-page preview (study §3.7): a read-only "earliest available
   * <method> date" line per method. Collects nothing, reserves nothing —
   * the real picker on the cart page does that.
   */
  private async mountPreview() {
    const { root, heading, methods } = this.config;

    if (heading) {
      this.el.heading.className = "dd-widget__heading";
      this.el.heading.textContent = heading;
      root.appendChild(this.el.heading);
    }

    const list = document.createElement("ul");
    list.className = "dd-widget__preview";
    root.appendChild(list);

    const cart = await fetchCartInfo().catch(() => ({ token: "", lines: [] as CartLineInfo[] }));

    await Promise.all(
      methods.map(async (method) => {
        const li = document.createElement("li");
        li.className = "dd-widget__preview-item";

        if (method.value === "LOCAL_DELIVERY") {
          li.textContent = this.config.labels.deliveryAtCheckout;
          list.appendChild(li);
          return;
        }

        li.textContent = this.config.labels.loading;
        list.appendChild(li);

        try {
          const availability = await fetchAvailability(method.value, this.config.locationId, cart);
          const earliest = Object.keys(availability.dates ?? {}).sort()[0];
          li.textContent = earliest
            ? `${this.config.labels.earliestPrefix} ${method.label.toLowerCase()}: ${formatDateLabel(earliest)}`
            : `${method.label}: ${this.config.labels.noDates}`;
        } catch {
          li.textContent = `${method.label}: ${this.config.labels.error}`;
        }
      }),
    );
  }

  private renderMethods() {
    this.el.methodRow.innerHTML = "";
    for (const method of this.config.methods) {
      const button = document.createElement("button");
      button.type = "button";
      button.className = "dd-widget__pill";
      button.textContent = method.label;
      button.setAttribute("aria-pressed", String(this.selectedMethod?.value === method.value));
      button.addEventListener("click", () => this.selectMethod(method));
      this.el.methodRow.appendChild(button);
    }
  }

  private async selectMethod(method: WidgetConfig["methods"][number]) {
    this.selectedMethod = method;
    this.selectedDate = null;
    this.el.timeRow.innerHTML = "";
    this.el.dateRow.innerHTML = "";
    this.el.mapContainer.hidden = true;
    this.el.confirmation.hidden = false;
    this.el.confirmation.hidden = true;
    if (this.config.methods.length > 1) this.renderMethods();

    // Local delivery needs a postal/ZIP code first — availability depends
    // on which zone (if any) the address falls into, and which location
    // that zone routes to (PRODUCT_STRATEGY.md §2 "Auto location assignment").
    if (method.value === "LOCAL_DELIVERY") {
      this.renderPostalCodeInput(method);
      return;
    }

    this.el.postalRow.hidden = true;
    await this.loadAvailability(method);
  }

  private renderPostalCodeInput(method: WidgetConfig["methods"][number]) {
    this.el.postalRow.hidden = false;
    this.el.postalRow.innerHTML = "";
    this.el.status.textContent = "";

    const input = document.createElement("input");
    input.type = "text";
    input.className = "dd-widget__input";
    input.placeholder = this.config.labels.postalCodeLabel;
    input.setAttribute("aria-label", this.config.labels.postalCodeLabel);

    const button = document.createElement("button");
    button.type = "button";
    button.className = "dd-widget__pill";
    button.textContent = this.config.labels.postalCodeSubmit;
    button.addEventListener("click", async () => {
      const postalCode = input.value.trim();
      if (!postalCode) return;
      await this.loadAvailability(method, postalCode);
    });
    input.addEventListener("keydown", (e) => {
      if (e.key === "Enter") button.click();
    });

    this.el.postalRow.append(input, button);
  }

  private async loadAvailability(method: WidgetConfig["methods"][number], postalCode?: string) {
    this.el.status.textContent = this.config.labels.loading;
    this.el.dateRow.innerHTML = "";

    try {
      const cart = await fetchCartInfo();
      this.availability = await fetchAvailability(method.value, this.config.locationId, cart, postalCode);

      if (!this.availability.locationId) {
        this.el.status.textContent = this.availability.error || this.config.labels.outOfArea;
        return;
      }

      if (method.value === "PICKUP" && this.config.googleMapsApiKey) {
        this.showPickupMap();
      }

      this.renderDates();
    } catch {
      this.el.status.textContent = this.config.labels.error;
    }
  }

  private showPickupMap() {
    const a = this.availability;
    if (!a?.locationLat || !a?.locationLng || !this.config.googleMapsApiKey) return;
    this.el.mapContainer.hidden = false;
    void renderPickupMap(this.el.mapContainer, this.config.googleMapsApiKey, a.locationLat, a.locationLng, a.locationName ?? "");
  }

  private renderDates() {
    const dates = Object.keys(this.availability?.dates ?? {}).sort();
    this.el.dateRow.innerHTML = "";

    if (dates.length === 0) {
      this.el.status.textContent = this.config.labels.noDates;
      return;
    }

    this.el.status.textContent = this.config.labels.chooseDate;
    for (const date of dates) {
      const button = document.createElement("button");
      button.type = "button";
      button.className = "dd-widget__pill";
      button.textContent = formatDateLabel(date);
      button.setAttribute("aria-pressed", String(this.selectedDate === date));
      button.addEventListener("click", () => this.selectDate(date));
      this.el.dateRow.appendChild(button);
    }
  }

  private selectDate(date: string) {
    this.selectedDate = date;
    for (const child of Array.from(this.el.dateRow.children)) {
      child.setAttribute("aria-pressed", String(child.textContent === formatDateLabel(date)));
    }

    const slots = this.availability?.dates[date] ?? [];
    this.el.timeRow.innerHTML = "";
    this.el.status.textContent = this.config.labels.chooseTime;

    for (const slot of slots) {
      const button = document.createElement("button");
      button.type = "button";
      button.className = "dd-widget__pill";
      button.textContent = slotTimeLabel(slot);
      button.addEventListener("click", () => this.selectSlot(date, slot));
      this.el.timeRow.appendChild(button);
    }
  }

  private async selectSlot(date: string, slot: SlotDto) {
    const method = this.selectedMethod!;
    const availability = this.availability!;
    const rateLabel = availability.rate ? ` (${availability.rate.label})` : "";
    const display =
      slot.arrivalRangeStart || slot.arrivalRangeEnd
        ? `Ships ${formatDateLabel(date)}, ${slotTimeLabel(slot)}${rateLabel}`
        : `${formatDateLabel(date)}, ${slotTimeLabel(slot)}${rateLabel}`;

    this.el.status.textContent = this.config.labels.loading;

    try {
      const cart = await fetchCartInfo();

      // Reserve capacity FIRST. Writing the cart attribute alone would just
      // be two shoppers racing to write the same free-text field — nothing
      // would stop both checkouts from completing for the last slot. The
      // hold is what the Validation Function (Phase 4) actually enforces
      // against at checkout. It also re-checks ProductRule constraints
      // server-side (hold-request.server.ts) — the real enforcement point,
      // not just what this widget chose to display.
      const hold = await requestHold({
        intent: "create",
        locationId: availability.locationId!,
        method: method.value,
        date,
        startMin: slot.startMin,
        cartToken: cart.token,
        cartLines: cart.lines.map((l) => ({ vendor: l.vendor, productType: l.productType })),
        productIds: cart.lines.map((l) => l.productId),
      });

      if (!hold.success) {
        this.el.status.textContent = hold.error || this.config.labels.error;
        // The slot we just tried is gone (or a ProductRule now excludes it) — refresh so the list reflects reality.
        await this.selectMethod(method);
        return;
      }

      this.heldSlot = {
        locationId: availability.locationId!,
        method: method.value,
        date,
        startMin: slot.startMin,
        cartToken: cart.token,
        zoneId: availability.zoneId ?? null,
      };

      const machineAttrs: Record<string, string> = {
        dd_method: method.value,
        dd_date: date,
        dd_start_min: String(slot.startMin),
        dd_end_min: String(slot.endMin),
        dd_location_id: availability.locationId!,
      };
      if (availability.zoneId) machineAttrs.dd_zone_id = availability.zoneId;
      if (availability.rate) machineAttrs.dd_rate_label = availability.rate.label;
      if (slot.arrivalRangeStart) machineAttrs.dd_arrival_range_start = slot.arrivalRangeStart;
      if (slot.arrivalRangeEnd) machineAttrs.dd_arrival_range_end = slot.arrivalRangeEnd;

      await writeCartAttribute(method.attrLabel, machineAttrs, display);

      this.el.status.textContent = "";
      this.el.methodRow.hidden = true;
      this.el.postalRow.hidden = true;
      this.el.mapContainer.hidden = true;
      this.el.dateRow.hidden = true;
      this.el.timeRow.hidden = true;
      this.el.confirmation.hidden = false;
      this.el.confirmation.innerHTML = "";

      const summary = document.createElement("p");
      summary.textContent = `${this.config.labels.confirmed} ${display}`;
      const changeButton = document.createElement("button");
      changeButton.type = "button";
      changeButton.className = "dd-widget__link";
      changeButton.textContent = this.config.labels.change;
      changeButton.addEventListener("click", () => {
        if (this.heldSlot) {
          void requestHold({ intent: "release", ...this.heldSlot });
          this.heldSlot = null;
        }
        this.el.methodRow.hidden = false;
        this.el.dateRow.hidden = false;
        this.el.timeRow.hidden = false;
        this.el.confirmation.hidden = true;
      });

      this.el.confirmation.append(summary, changeButton);
    } catch {
      this.el.status.textContent = this.config.labels.error;
    }
  }
}

// Cross-theme cart placement: a manually-placed app BLOCK only ever lands
// wherever the active theme's own section schema happens to declare an
// `@app` slot — many themes only expose "Add section" for the cart's
// checkout area, not "Add block" next to the actual Checkout button, which
// is what shows up as a disconnected standalone section. There's no
// Shopify-supported way for an app to inject a block into an arbitrary
// spot in a theme's own markup, so instead: the app embed (blocks/
// app-embed.liquid, loaded site-wide once merchants enable it, independent
// of any block placement) emits an inert <template id="dd-widget-cart-
// template"> carrying the widget's config as data-* attributes. If we're
// on the cart page, no block-placed widget already exists (avoids a
// double render), and a Checkout button can be found by one of these
// selectors, clone a live widget in immediately before it. Ordered
// roughly most-to-least specific/reliable across common theme markup
// patterns; the first match wins.
const CHECKOUT_BUTTON_SELECTORS = [
  'form[action*="/cart"] button[name="checkout"]',
  'form[action*="/cart"] input[name="checkout"]',
  '[name="checkout"]',
  '#checkout',
  'a[href="/checkout"]',
];

function findCheckoutButton(): HTMLElement | null {
  for (const selector of CHECKOUT_BUTTON_SELECTORS) {
    const el = document.querySelector<HTMLElement>(selector);
    if (el) return el;
  }
  return null;
}

function isCartPage(): boolean {
  // Matches /cart, /cart/, and locale-prefixed variants like /en/cart —
  // but not /cart/add or similar sub-paths that aren't the cart page itself.
  return window.location.pathname.replace(/\/+$/, "").endsWith("/cart");
}

function maybeAutoPlaceOnCart() {
  if (!isCartPage()) return;
  if (document.querySelector("[data-dd-widget]")) return; // a block is already placed manually — don't double up

  const template = document.getElementById("dd-widget-cart-template");
  if (!template) return; // merchant turned auto-placement off in the app embed's settings

  const checkoutButton = findCheckoutButton();
  if (!checkoutButton) return; // couldn't find a safe, theme-agnostic anchor — do nothing rather than guess

  const widget = document.createElement("div");
  widget.setAttribute("data-dd-widget", "");
  widget.classList.add("dd-widget--cart-injected");
  for (const attr of Array.from(template.attributes)) {
    if (attr.name === "id") continue;
    widget.setAttribute(attr.name, attr.value);
  }

  checkoutButton.insertAdjacentElement("beforebegin", widget);
  new DateTimeWidget(readConfig(widget)).mount();
}

function init() {
  const roots = document.querySelectorAll<HTMLElement>("[data-dd-widget]");
  roots.forEach((root) => {
    new DateTimeWidget(readConfig(root)).mount();
  });
  maybeAutoPlaceOnCart();
}

if (document.readyState === "loading") {
  document.addEventListener("DOMContentLoaded", init);
} else {
  init();
}