(function () {
  "use strict";

  var slides = Array.prototype.slice.call(document.querySelectorAll("section.slide"));
  var total = slides.length;
  var progressEl = document.querySelector(".progress");
  var baseTitle = document.title;
  var renderedMermaid = {};
  var fragmentsCache = {};
  var current = 1;
  var fragmentIndex = 0;
  var gridMode = false;

  function clamp(n) {
    if (n < 1) return 1;
    if (n > total) return total;
    return n;
  }

  // fragmentsFor returns the "fragment" elements of the given 1-based slide
  // index, in document order, computed and cached once per slide. A slide
  // marked with data-incremental="true" gets its top-level list items
  // auto-tagged as fragments in addition to any explicitly marked via raw
  // HTML (class="fragment").
  function fragmentsFor(index) {
    if (fragmentsCache[index]) return fragmentsCache[index];
    var slide = slides[index - 1];
    if (!slide) return [];

    if (slide.dataset.incremental === "true") {
      var autoItems = slide.querySelectorAll(":scope > ul > li, :scope > ol > li");
      Array.prototype.forEach.call(autoItems, function (li) {
        li.classList.add("fragment");
      });
    }

    var frags = Array.prototype.slice.call(slide.querySelectorAll(".fragment"));
    frags.forEach(function (el, i) {
      el.setAttribute("data-fragment-index", String(i + 1));
    });
    fragmentsCache[index] = frags;
    return frags;
  }

  function applyFragments(index, count) {
    fragmentsFor(index).forEach(function (el, i) {
      el.classList.toggle("fragment-visible", i < count);
    });
  }

  function parseHash() {
    var raw = location.hash.replace("#", "");
    var parts = raw.split(".");
    var slide = parseInt(parts[0], 10);
    var fragment = parseInt(parts[1], 10);
    return {
      slide: isNaN(slide) ? 1 : clamp(slide),
      fragment: isNaN(fragment) ? 0 : Math.max(0, fragment)
    };
  }

  function renderMermaid(index) {
    if (renderedMermaid[index]) return;
    var slide = slides[index - 1];
    if (!slide) return;
    var nodes = slide.querySelectorAll("pre.mermaid");
    if (nodes.length === 0) return;
    renderedMermaid[index] = true;
    mermaid.run({ nodes: Array.prototype.slice.call(nodes) });
  }

  function show(index, fragment, updateHash) {
    current = clamp(index);
    var frags = fragmentsFor(current);
    fragmentIndex = typeof fragment === "number" ? Math.min(Math.max(fragment, 0), frags.length) : 0;

    slides.forEach(function (slide, i) {
      slide.classList.toggle("active", i === current - 1);
    });
    applyFragments(current, fragmentIndex);

    if (progressEl) {
      progressEl.textContent = current + " / " + total;
    }
    var slideTitle = slides[current - 1].dataset.title;
    document.title = slideTitle ? slideTitle + " · " + baseTitle : baseTitle;
    if (updateHash !== false) {
      location.hash = fragmentIndex > 0 ? current + "." + fragmentIndex : String(current);
    }
    renderMermaid(current);
  }

  function next() {
    var frags = fragmentsFor(current);
    if (fragmentIndex < frags.length) {
      show(current, fragmentIndex + 1);
      return;
    }
    show(current + 1, 0);
  }

  function prev() {
    if (fragmentIndex > 0) {
      show(current, fragmentIndex - 1);
      return;
    }
    var target = current - 1;
    if (target < 1) return;
    show(target, fragmentsFor(target).length);
  }

  function toggleGrid() {
    gridMode = !gridMode;
    document.body.classList.toggle("grid-mode", gridMode);
  }

  function exitGrid() {
    if (!gridMode) return;
    gridMode = false;
    document.body.classList.remove("grid-mode");
  }

  window.addEventListener("hashchange", function () {
    var h = parseHash();
    show(h.slide, h.fragment, false);
  });

  document.addEventListener("keydown", function (e) {
    if (e.key === "o" || e.key === "O") {
      e.preventDefault();
      toggleGrid();
      return;
    }
    if (gridMode) {
      if (e.key === "Escape") {
        e.preventDefault();
        exitGrid();
      }
      return;
    }
    switch (e.key) {
      case "ArrowRight":
      case " ":
      case "PageDown":
        e.preventDefault();
        next();
        break;
      case "ArrowLeft":
      case "PageUp":
        e.preventDefault();
        prev();
        break;
      case "Home":
        e.preventDefault();
        show(1, 0);
        break;
      case "End":
        e.preventDefault();
        show(total, 0);
        break;
    }
  });

  document.querySelectorAll(".nav-zone.prev, .nav-button.prev").forEach(function (el) {
    el.addEventListener("click", prev);
  });
  document.querySelectorAll(".nav-zone.next, .nav-button.next").forEach(function (el) {
    el.addEventListener("click", next);
  });

  slides.forEach(function (slide, i) {
    slide.addEventListener("click", function () {
      if (!gridMode) return;
      exitGrid();
      show(i + 1, 0);
    });
  });

  var initial = parseHash();
  show(initial.slide, initial.fragment, true);
})();