/**
 * Horizontal product rails with under-rail dots + 3s autoplay ([data-product-slider]).
 * RTL-safe scrollLeft (Chrome negative vs Firefox positive).
 */
export function initProductSliders() {
  document.querySelectorAll("[data-product-slider]").forEach((root) => {
    const rail = root.querySelector("[data-slider-rail]");
    const dotsHost = root.querySelector("[data-slider-dots]");
    if (!(rail instanceof HTMLElement)) return;

    const rtl =
      getComputedStyle(rail).direction === "rtl" ||
      document.documentElement.dir === "rtl";
    const AUTO_MS = 3000;

    // Chrome/Safari RTL: scrollLeft goes negative; Firefox RTL: positive.
    let rtlNegative = false;
    if (rtl) {
      const prevLeft = rail.scrollLeft;
      rail.scrollLeft = -1;
      rtlNegative = rail.scrollLeft < 0;
      rail.scrollLeft = prevLeft;
    }

    const step = () => {
      const card = rail.querySelector(".product-card");
      const w = card instanceof HTMLElement ? card.getBoundingClientRect().width : 200;
      const styles = getComputedStyle(rail);
      const gap = Number.parseFloat(styles.columnGap || styles.gap || "1") || 1;
      return Math.max(w + gap, 120);
    };

    function maxScroll() {
      return Math.max(0, rail.scrollWidth - rail.clientWidth);
    }

    function canScroll() {
      return maxScroll() > 4;
    }

    /** Absolute distance from the logical start (0…max), independent of engine sign. */
    function scrollPos() {
      return Math.abs(rail.scrollLeft);
    }

    function scrollToPos(pos, smooth) {
      const max = maxScroll();
      const target = Math.min(max, Math.max(0, pos));
      let left = target;
      if (rtl) left = rtlNegative ? -target : target;
      rail.scrollTo({ left, behavior: smooth ? "smooth" : "auto" });
    }

    function pageCount() {
      const max = maxScroll();
      if (max <= 4) return 1;
      return Math.floor(max / step()) + 1;
    }

    function currentPage() {
      const pages = pageCount();
      if (pages <= 1) return 0;
      const s = step();
      return Math.min(pages - 1, Math.round(scrollPos() / s));
    }

    function goToPage(index, smooth = true) {
      const pages = pageCount();
      const i = Math.max(0, Math.min(pages - 1, index));
      const max = maxScroll();
      if (i >= pages - 1) scrollToPos(max, smooth);
      else scrollToPos(i * step(), smooth);
    }

    function goNext() {
      const max = maxScroll();
      if (max <= 4) return;
      const pages = pageCount();
      const next = currentPage() + 1;
      if (next >= pages) goToPage(0, true);
      else goToPage(next, true);
    }

    function renderDots() {
      if (!(dotsHost instanceof HTMLElement)) return;
      const pages = pageCount();
      if (pages <= 1) {
        dotsHost.hidden = true;
        dotsHost.replaceChildren();
        return;
      }
      dotsHost.hidden = false;
      const active = currentPage();
      if (dotsHost.childElementCount !== pages) {
        const frag = document.createDocumentFragment();
        for (let i = 0; i < pages; i++) {
          const btn = document.createElement("button");
          btn.type = "button";
          btn.className = "slider-dot";
          btn.setAttribute("role", "tab");
          btn.setAttribute("aria-label", `صفحه ${i + 1}`);
          btn.addEventListener("click", (e) => {
            e.preventDefault();
            goToPage(i, true);
            startAuto();
          });
          frag.appendChild(btn);
        }
        dotsHost.replaceChildren(frag);
      }
      Array.from(dotsHost.children).forEach((el, i) => {
        if (!(el instanceof HTMLElement)) return;
        const on = i === active;
        el.classList.toggle("is-active", on);
        el.setAttribute("aria-selected", on ? "true" : "false");
        if (on) el.setAttribute("aria-current", "true");
        else el.removeAttribute("aria-current");
      });
    }

    let timer = 0;
    function stopAuto() {
      window.clearInterval(timer);
      timer = 0;
    }
    function startAuto() {
      stopAuto();
      if (!canScroll()) return;
      timer = window.setInterval(goNext, AUTO_MS);
    }

    root.addEventListener("mouseenter", stopAuto);
    root.addEventListener("mouseleave", startAuto);
    root.addEventListener(
      "focusin",
      (e) => {
        if (e.target instanceof Element && e.target.closest(".slider-dot")) {
          /* keep running */
        } else {
          stopAuto();
        }
      },
      true
    );
    root.addEventListener("focusout", () => {
      window.setTimeout(() => {
        if (!root.contains(document.activeElement)) startAuto();
      }, 0);
    });

    rail.addEventListener(
      "pointerdown",
      () => {
        stopAuto();
      },
      { passive: true }
    );
    rail.addEventListener(
      "pointerup",
      () => {
        startAuto();
      },
      { passive: true }
    );

    rail.addEventListener(
      "scroll",
      () => {
        renderDots();
      },
      { passive: true }
    );
    window.addEventListener(
      "resize",
      () => {
        renderDots();
        startAuto();
      },
      { passive: true }
    );

    // Layout may not be final on first paint (images / fonts).
    const kick = () => {
      renderDots();
      startAuto();
    };
    kick();
    window.requestAnimationFrame(kick);
    window.setTimeout(kick, 400);
    window.addEventListener("load", kick, { once: true });
  });
}