/**
 * 학습센터 / 뉴스레터 목록: 무한 스크롤·실시간 검색
 * (인라인 스크립트는 HTML 엔티티(&) 처리로 SyntaxError가 날 수 있어 외부 파일로 분리)
 */
(function () {
  var cfg = document.getElementById("lecture-page-config");
  var apiPath = (cfg && cfg.getAttribute("data-learning-api")) || "/api/learning/lectures";
  var viewerBasePath = (cfg && cfg.getAttribute("data-viewer-base")) || "/learning";

  var form = document.querySelector(".filter-panel form");
  var qInput = document.getElementById("learning-filter-q");
  var resultsRoot = document.getElementById("lecture-results-root");
  var countEl = document.getElementById("lecture-total-count");

  var radios = document.querySelectorAll('#category-filter input[name="category"]');
  if (form && radios.length) {
    radios.forEach(function (radio) {
      radio.addEventListener("change", function () {
        form.submit();
      });
    });
  }

  var scrollObserver = null;
  var scrollLoading = false;
  var scrollListener = null;
  var scrollRootsBound = [];
  var wheelHandler = null;
  var pollTimer = null;

  function disconnectInfiniteScroll() {
    if (scrollObserver) {
      scrollObserver.disconnect();
      scrollObserver = null;
    }
    if (scrollListener) {
      scrollRootsBound.forEach(function (t) {
        t.removeEventListener("scroll", scrollListener);
      });
      scrollRootsBound = [];
      window.removeEventListener("resize", scrollListener);
      scrollListener = null;
    }
    if (wheelHandler) {
      document.removeEventListener("wheel", wheelHandler, true);
      wheelHandler = null;
    }
    if (pollTimer) {
      clearInterval(pollTimer);
      pollTimer = null;
    }
  }

  function setupInfiniteScroll() {
    disconnectInfiniteScroll();
    var loadingEl = document.getElementById("infinite-scroll-loading");

    function shouldLoadMore() {
      var sentinel = document.getElementById("infinite-scroll-sentinel");
      if (!sentinel || sentinel.getAttribute("data-has-next") !== "true") return false;
      var rect = sentinel.getBoundingClientRect();
      var vh = window.innerHeight || document.documentElement.clientHeight;
      var margin = 3200;
      return rect.top <= vh + margin;
    }

    function loadNextPage() {
      if (scrollLoading) return;
      var sentinel = document.getElementById("infinite-scroll-sentinel");
      var grid = document.getElementById("lecture-grid");
      if (!sentinel || !grid) return;
      if (sentinel.getAttribute("data-has-next") !== "true") return;
      var nextPage = sentinel.getAttribute("data-next-page");
      if (!nextPage) return;

      scrollLoading = true;
      if (loadingEl) loadingEl.style.display = "block";
      var params = new URLSearchParams(window.location.search);
      params.set("page", nextPage);
      fetch(apiPath + "?" + params.toString(), {
        credentials: "same-origin",
        headers: { Accept: "application/json" },
      })
        .then(function (r) {
          if (!r.ok) throw new Error("HTTP " + r.status);
          return r.json();
        })
        .then(function (data) {
          if (data.html) {
            grid.insertAdjacentHTML("beforeend", data.html);
          }
          if (data.hasNext) {
            sentinel.setAttribute("data-next-page", String(data.nextPage || parseInt(nextPage, 10) + 1));
            sentinel.setAttribute("data-has-next", "true");
          } else {
            disconnectInfiniteScroll();
            var foot = document.getElementById("lecture-infinite-footer");
            if (foot && foot.parentNode) foot.remove();
          }
        })
        .catch(function (e) {
          var msg = "";
          if (e) {
            if (e.message) msg = e.message;
            else msg = String(e);
          }
          console.warn("[learning] 다음 페이지 로드 실패(재시도 가능):", msg);
        })
        .finally(function () {
          scrollLoading = false;
          if (loadingEl) loadingEl.style.display = "none";
          setTimeout(function () {
            if (shouldLoadMore()) loadNextPage();
          }, 0);
        });
    }

    function loadMoreIfNeeded() {
      if (!shouldLoadMore()) return;
      loadNextPage();
    }

    var sentinelEl = document.getElementById("infinite-scroll-sentinel");
    var gridEl = document.getElementById("lecture-grid");
    if (!sentinelEl || !gridEl) return;

    var rafScheduled = false;
    scrollListener = function () {
      if (scrollLoading || rafScheduled) return;
      rafScheduled = true;
      requestAnimationFrame(function () {
        rafScheduled = false;
        loadMoreIfNeeded();
      });
    };

    function addScrollRoot(r) {
      if (r && scrollRootsBound.indexOf(r) === -1) scrollRootsBound.push(r);
    }
    addScrollRoot(window);
    addScrollRoot(document.scrollingElement || document.documentElement);
    scrollRootsBound.forEach(function (t) {
      t.addEventListener("scroll", scrollListener, { passive: true });
    });
    window.addEventListener("resize", scrollListener, { passive: true });

    wheelHandler = function () {
      if (scrollLoading) return;
      requestAnimationFrame(loadMoreIfNeeded);
    };
    document.addEventListener("wheel", wheelHandler, { passive: true, capture: true });

    pollTimer = setInterval(function () {
      if (scrollLoading) return;
      loadMoreIfNeeded();
    }, 400);

    scrollObserver = new IntersectionObserver(
      function (entries) {
        if (!entries.some(function (e) {
          return e.isIntersecting;
        }))
          return;
        loadNextPage();
      },
      { root: null, rootMargin: "0px 0px 1600px 0px", threshold: 0 }
    );
    scrollObserver.observe(sentinelEl);

    setTimeout(loadMoreIfNeeded, 0);
    setTimeout(loadMoreIfNeeded, 400);

    var loadMoreBtn = document.getElementById("lecture-load-more-btn");
    if (loadMoreBtn) {
      loadMoreBtn.addEventListener("click", function () {
        loadNextPage();
      });
    }
  }

  function applyLiveSearch() {
    if (!form || !resultsRoot) return;
    var params = new URLSearchParams(new FormData(form));
    params.set("page", "1");
    fetch(apiPath + "?" + params.toString())
      .then(function (r) {
        return r.json();
      })
      .then(function (data) {
        if (data.error) return;
        var total = typeof data.totalCount === "number" ? data.totalCount : 0;
        if (countEl) countEl.textContent = total;
        var html = (data.html || "").trim();
        if (total === 0 || !html) {
          disconnectInfiniteScroll();
          resultsRoot.innerHTML = '<p class="empty" id="lecture-empty-msg">등록된 항목이 없습니다.</p>';
        } else {
          var nextP = data.nextPage != null ? data.nextPage : 2;
          var sentinelBlock = data.hasNext
            ? '<div id="lecture-infinite-footer"><div id="infinite-scroll-sentinel" class="infinite-scroll-sentinel" data-next-page="' +
              String(nextP) +
              '" data-has-next="true"></div><p class="infinite-scroll-loading" id="infinite-scroll-loading" style="display:none;text-align:center;padding:16px;color:#666;">불러오는 중...</p><div class="lecture-load-more-wrap" id="lecture-load-more-wrap"><button type="button" class="lecture-load-more-btn" id="lecture-load-more-btn">더 불러오기</button></div></div>'
            : "";
          resultsRoot.innerHTML = '<div class="lecture-grid" id="lecture-grid">' + data.html + "</div>" + sentinelBlock;
          setupInfiniteScroll();
        }
        if (window.history && window.history.replaceState) {
          var forUrl = new URLSearchParams(params);
          forUrl.delete("page");
          var u = new URL(viewerBasePath, window.location.origin);
          u.search = forUrl.toString() ? "?" + forUrl.toString() : "";
          window.history.replaceState({}, "", u.pathname + u.search);
        }
      })
      .catch(function () {});
  }

  var searchDebounce;
  if (qInput) {
    qInput.addEventListener("input", function () {
      clearTimeout(searchDebounce);
      searchDebounce = setTimeout(applyLiveSearch, 280);
    });
  }

  setupInfiniteScroll();
})();