/**
 * Free low-stock "Only N left" text under the variation form.
 *
 * Reads the single-source b3wvs_low_stock count that StockState adds to the
 * WooCommerce variation payload and renders a plain, theme-styled line when a
 * variation is at/under its low-stock threshold. The Pro feature is a distinctly
 * styled badge (color/shape/pulse); this free version is plain text only and
 * imports nothing from src/frontend/extension/.
 *
 * @package B3VariationSwatches
 */

const VARIATION_FORM_SELECTOR = "form.variations_form";
const TEXT_CLASS = "b3-wvs-low-stock-text";

export interface LowStockSettings {
  enabled: boolean;
  format: string;
  hideOnBackorder: boolean;
}

export interface WooVariationStock {
  b3wvs_low_stock?: number | false;
  /** WooCommerce's native flag from get_available_variation(). */
  backorders_allowed?: boolean | number | string;
  /** Legacy/custom payload flag; still honored when present. */
  is_on_backorder?: boolean | number | string;
}

/**
 * Normalize a PHP/JSON boolean-ish flag. Only genuine "true" shapes count, so
 * `false`, `"false"`, `"0"`, `0`, `""`, `null` and `undefined` are all false.
 */
const isTruthyFlag = (value: unknown): boolean => {
  if (value === true || value === 1) return true;
  if (typeof value === "string") {
    const normalized = value.trim().toLowerCase();
    return normalized === "1" || normalized === "true" || normalized === "yes";
  }
  return false;
};

/** Whether the variation is available on backorder (native or legacy flag). */
export const isVariationOnBackorder = (variation: WooVariationStock): boolean =>
  isTruthyFlag(variation.backorders_allowed) ||
  isTruthyFlag(variation.is_on_backorder);

/** Read the low-stock settings from the localized payload (with safe defaults). */
export const readLowStockSettings = (): LowStockSettings => {
  const settings =
    typeof b3WvsData !== "undefined" && b3WvsData?.settings
      ? b3WvsData.settings
      : null;
  const rawFormat = settings?.low_stock_text_format;
  const format =
    typeof rawFormat === "string" && rawFormat.includes("{qty}")
      ? rawFormat
      : "Only {qty} left";
  return {
    enabled: Boolean(settings?.low_stock_text_enabled),
    format,
    hideOnBackorder: settings?.low_stock_text_hide_on_backorder !== false,
  };
};

/** Resolve the low-stock count to display, or null when nothing should show. */
export const resolveLowStockCount = (
  variation: WooVariationStock | undefined,
  settings: LowStockSettings,
): number | null => {
  if (!settings.enabled || !variation) return null;
  const count = variation.b3wvs_low_stock;
  if (typeof count !== "number" || !Number.isFinite(count) || count <= 0) {
    return null;
  }
  if (settings.hideOnBackorder && isVariationOnBackorder(variation)) {
    return null;
  }
  return Math.floor(count);
};

/** Build the display string. Plain text only (rendered via textContent). */
export const formatLowStockText = (format: string, qty: number): string =>
  (format && format.includes("{qty}") ? format : "Only {qty} left").replace(
    /\{qty\}/g,
    String(qty),
  );

const getTextElement = (
  form: HTMLElement,
): { element: HTMLElement; created: boolean } => {
  const existing = form.querySelector<HTMLElement>(`.${TEXT_CLASS}`);
  if (existing) return { element: existing, created: false };

  // WooCommerce replaces `.single_variation` while resolving selections. Mount
  // the live region in its stable wrapper so announcements survive that update.
  const host =
    form.querySelector<HTMLElement>(".single_variation_wrap") ||
    form.querySelector<HTMLElement>(".woocommerce-variation") ||
    form;
  const element = form.ownerDocument.createElement("p");
  element.className = TEXT_CLASS;
  element.setAttribute("role", "status");
  element.setAttribute("aria-live", "polite");
  host.appendChild(element);
  return { element, created: true };
};

export const updateLowStockTextForForm = (
  form: HTMLElement,
  variation?: WooVariationStock,
): void => {
  const settings = readLowStockSettings();
  const qty = resolveLowStockCount(variation, settings);
  if (qty == null) {
    const existing = form.querySelector<HTMLElement>(`.${TEXT_CLASS}`);
    if (existing) existing.textContent = "";
    return;
  }
  const { element, created } = getTextElement(form);
  const text = formatLowStockText(settings.format, qty);
  if (!created) {
    element.textContent = text;
    return;
  }

  // Give assistive technology a chance to observe the empty live region before
  // its first message is inserted.
  window.setTimeout(() => {
    if (element.isConnected) element.textContent = text;
  }, 0);
};

let listenersBound = false;

/** Bind the WooCommerce variation listeners (idempotent). */
export const initLowStockText = (): void => {
  if (listenersBound) return;
  const jq =
    typeof window !== "undefined"
      ? (window as { jQuery?: unknown }).jQuery
      : undefined;
  if (typeof jq !== "function") return;
  listenersBound = true;

  document
    .querySelectorAll<HTMLElement>(VARIATION_FORM_SELECTOR)
    .forEach((form) => getTextElement(form));

  const $ = jq as (el: unknown) => {
    on: (
      events: string,
      selector: string,
      handler: (this: HTMLElement, ...args: unknown[]) => void,
    ) => void;
  };

  $(document.body).on(
    "found_variation",
    VARIATION_FORM_SELECTOR,
    function (this: HTMLElement, _event: unknown, variation: unknown) {
      updateLowStockTextForForm(
        this,
        variation as WooVariationStock | undefined,
      );
    },
  );

  $(document.body).on(
    "reset_data hide_variation",
    VARIATION_FORM_SELECTOR,
    function (this: HTMLElement) {
      const existing = this.querySelector<HTMLElement>(`.${TEXT_CLASS}`);
      if (existing) existing.textContent = "";
    },
  );
};