export function initProjectsCarousel() {
  const root = document.querySelector("[data-projects-carousel]");
  if (!root) return;

  const viewport = root.querySelector("[data-projects-viewport]");
  const prevBtn = root.parentElement?.querySelector("[data-projects-prev]");
  const nextBtn = root.parentElement?.querySelector("[data-projects-next]");
  if (!viewport || !prevBtn || !nextBtn) return;
  const edgePrevBtn = root.querySelector("[data-projects-edge-prev]");
  const edgeNextBtn = root.querySelector("[data-projects-edge-next]");

  let dragState = null;
  let suppressClick = false;

  function syncViewportWidthVar() {
    const visibleWidth = document.documentElement.clientWidth || window.innerWidth;
    root.style.setProperty("--projects-viewport-width", `${Math.max(visibleWidth, 0)}px`);
  }

  function getEdgeSpace() {
    const raw = getComputedStyle(root).getPropertyValue("--projects-edge-space");
    const value = Number.parseFloat(raw);
    return Number.isFinite(value) ? Math.max(value, 0) : 0;
  }

  function getMinScroll() {
    return getEdgeSpace();
  }

  function getMaxScroll() {
    const maxNative = Math.max(viewport.scrollWidth - viewport.clientWidth, 0);
    return Math.max(maxNative - getEdgeSpace(), getMinScroll());
  }

  function clampScroll(left) {
    return Math.min(Math.max(left, getMinScroll()), getMaxScroll());
  }

  function getStep() {
    const firstItem = viewport.querySelector(".projects-carousel__item");
    if (!(firstItem instanceof HTMLElement)) return viewport.clientWidth;
    const track = viewport.querySelector(".projects-carousel__track");
    const gapRaw = track ? getComputedStyle(track).columnGap : "0";
    const gap = Number.parseFloat(gapRaw) || 0;
    return firstItem.getBoundingClientRect().width + gap;
  }

  function getSnapIndex() {
    const step = getStep();
    if (!step) return 0;
    const min = getMinScroll();
    return Math.round((viewport.scrollLeft - min) / step);
  }

  function scrollToIndex(index, behavior = "smooth") {
    const step = getStep();
    const min = getMinScroll();
    const max = getMaxScroll();
    if (!step) {
      viewport.scrollTo({ left: clampScroll(viewport.scrollLeft), behavior });
      return;
    }
    const maxIndex = Math.max(Math.round((max - min) / step), 0);
    const nextIndex = Math.min(Math.max(index, 0), maxIndex);
    const target = clampScroll(min + nextIndex * step);
    viewport.scrollTo({ left: target, behavior });
  }

  function snapToNearest(behavior = "smooth") {
    scrollToIndex(getSnapIndex(), behavior);
  }

  function updateControls() {
    const x = viewport.scrollLeft;
    const min = getMinScroll();
    const max = getMaxScroll();
    prevBtn.disabled = x <= min + 2;
    nextBtn.disabled = x >= max - 2;
  }

  function scrollByStep(direction) {
    const currentIndex = getSnapIndex();
    scrollToIndex(currentIndex + direction, "smooth");
  }

  function getEdgeHitZone() {
    const sectionInner = root.closest(".section__inner");
    const sectionInnerWidth = sectionInner instanceof HTMLElement ? sectionInner.getBoundingClientRect().width : viewport.clientWidth;
    const viewportWidthWithScrollbar = window.innerWidth || document.documentElement.clientWidth || viewport.clientWidth;
    const track = viewport.querySelector(".projects-carousel__track");
    const gapRaw = track ? getComputedStyle(track).columnGap : "0";
    const gap = Number.parseFloat(gapRaw) || 0;
    const zone = (viewportWidthWithScrollbar - sectionInnerWidth) / 2 - gap;
    return Math.max(zone, 0);
  }

  prevBtn.addEventListener("click", () => scrollByStep(-1));
  nextBtn.addEventListener("click", () => scrollByStep(1));
  edgePrevBtn?.addEventListener("click", (e) => {
    e.preventDefault();
    e.stopPropagation();
    scrollByStep(-1);
  });
  edgeNextBtn?.addEventListener("click", (e) => {
    e.preventDefault();
    e.stopPropagation();
    scrollByStep(1);
  });

  viewport.addEventListener("scroll", updateControls, { passive: true });
  window.addEventListener("resize", updateControls, { passive: true });
  viewport.querySelectorAll("a, img").forEach((el) => {
    el.setAttribute("draggable", "false");
  });
  viewport.addEventListener("dragstart", (e) => {
    e.preventDefault();
  });

  viewport.addEventListener("pointerdown", (e) => {
    if (e.button !== 0) return;
    if (!(e.target instanceof Element)) return;
    suppressClick = false;
    dragState = {
      pointerId: e.pointerId,
      startX: e.clientX,
      startScrollLeft: viewport.scrollLeft,
      moved: false,
    };
    viewport.classList.add("is-dragging");
  });

  viewport.addEventListener("pointermove", (e) => {
    if (!dragState || dragState.pointerId !== e.pointerId) return;
    const dx = e.clientX - dragState.startX;
    if (Math.abs(dx) > 8) dragState.moved = true;
    if (dragState.moved) e.preventDefault();
    viewport.scrollLeft = clampScroll(dragState.startScrollLeft - dx);
  });

  function finishDrag(e) {
    if (!dragState || dragState.pointerId !== e.pointerId) return;
    if (dragState.moved) {
      e.preventDefault();
      suppressClick = true;
      snapToNearest("smooth");
    } else {
      suppressClick = false;
    }
    viewport.classList.remove("is-dragging");
    dragState = null;
  }

  viewport.addEventListener("pointerup", finishDrag);
  viewport.addEventListener("pointercancel", finishDrag);
  viewport.addEventListener("pointerleave", (e) => {
    if (!dragState) return;
    finishDrag(e);
  });

  viewport.addEventListener(
    "click",
    (e) => {
      if (suppressClick) {
        e.preventDefault();
        e.stopPropagation();
        suppressClick = false;
      }
    },
    true,
  );

  function alignToStart() {
    syncViewportWidthVar();
    const edgeZone = `${getEdgeHitZone()}px`;
    root.style.setProperty("--projects-edge-hit-zone", edgeZone);
    viewport.scrollLeft = getMinScroll();
    updateControls();
  }

  alignToStart();
  window.addEventListener("load", alignToStart, { once: true });
  window.addEventListener(
    "resize",
    () => {
      syncViewportWidthVar();
      snapToNearest("auto");
      updateControls();
    },
    { passive: true },
  );
}