add transcript view ('r') for text-to-speech read-aloud extensions

Read-aloud browser extensions cannot walk a reveal.js deck: slides
outside the current one are display:none and the visible page text is
indexed only once at page load, so such extensions stop after the title
slide. Pressing 'r' now toggles a transcript view -- a single scrollable
page containing every slide's content and speaker notes (overview TOC
lists excluded, fragments shown, rebuilt on every open) -- which
extensions can read from start to finish. Styled in the ids theme;
closes on click or Escape.

Change-Id: Ia3df9dfa68b9699d318d747831ac8a0e270c8271
diff --git a/inst/reveal.js-5.2.1/dist/theme/ids.css b/inst/reveal.js-5.2.1/dist/theme/ids.css
index 16c8f5e..d1b8467 100644
--- a/inst/reveal.js-5.2.1/dist/theme/ids.css
+++ b/inst/reveal.js-5.2.1/dist/theme/ids.css
@@ -1091,4 +1091,51 @@
   color: var(--r-heading-color);
 }
 
+/*********************************************
+ * TRANSCRIPT / READ-ALOUD VIEW ('r')
+ *********************************************/
+#ids-transcript {
+  position: fixed;
+  inset: 0;
+  z-index: 90;
+  background: #fff;
+  color: #444444;
+  font-family: "Fira Sans", "Fira Sans Condensed", sans-serif;
+  font-size: 18px;
+  line-height: 1.5;
+  overflow-y: auto;
+  -webkit-overflow-scrolling: touch;
+  padding: max(32px, env(safe-area-inset-top)) max(40px, env(safe-area-inset-right))
+           max(32px, env(safe-area-inset-bottom)) max(40px, env(safe-area-inset-left));
+}
+#ids-transcript[hidden] {
+  display: none;
+}
+#ids-transcript .ids-transcript-slide {
+  max-width: 900px;
+  margin: 0 auto 2.5em auto;
+}
+#ids-transcript h1, #ids-transcript h2 {
+  color: var(--r-heading-color);
+  margin: 0 0 0.4em 0;
+}
+#ids-transcript h1 { font-size: 1.4em; }
+#ids-transcript h2 { font-size: 1.2em; }
+#ids-transcript .fragment {
+  opacity: 1;
+  visibility: visible;
+}
+#ids-transcript .ids-transcript-notes {
+  border-left: 3px solid #f6a800;
+  padding: 0.2em 0 0.2em 0.8em;
+  margin-top: 0.8em;
+  color: #666;
+}
+#ids-transcript .ids-transcript-notes:empty {
+  display: none;
+}
+#ids-transcript img, #ids-transcript video, #ids-transcript iframe {
+  max-width: 100%;
+}
+
 /*# sourceMappingURL=ids.css.map */
diff --git a/inst/rmarkdown/templates/revealjs_presentation/resources/default.html b/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
index 062ffa7..003336b 100644
--- a/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
+++ b/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
@@ -1045,5 +1045,74 @@
     }
   })();
 </script>
+<script>
+  // Practice/read-aloud view: pressing 'r' toggles a single scrollable page
+  // containing every slide's content and speaker notes. Text-to-speech
+  // browser extensions cannot walk a reveal.js deck (hidden slides are
+  // display:none and indexed only once at page load), but they can read
+  // this flat transcript from start to finish. Styling in the ids theme.
+  (function () {
+    var overlay = null;
+
+    function build() {
+      overlay = document.createElement('div');
+      overlay.id = 'ids-transcript';
+      overlay.hidden = true;
+      overlay.setAttribute('aria-label', 'Transcript of all slides and notes');
+      Reveal.getSlides().forEach(function (slide) {
+        var section = document.createElement('section');
+        section.className = 'ids-transcript-slide';
+        var heading = slide.querySelector('h1,h2');
+        if (heading) section.appendChild(heading.cloneNode(true));
+        Array.prototype.forEach.call(slide.childNodes, function (node) {
+          if (node.nodeType !== Node.ELEMENT_NODE) return;
+          if (node.tagName === 'ASIDE' || node.tagName === 'H1' ||
+              node.tagName === 'H2' || node.tagName === 'SECTION' ||
+              (node.classList && node.classList.contains('ids-overview-toc'))) return;
+          section.appendChild(node.cloneNode(true));
+        });
+        var notes = Array.prototype.map.call(
+          slide.querySelectorAll('aside.notes'),
+          function (n) { return n.innerHTML; }
+        ).join('');
+        if (notes) {
+          var block = document.createElement('div');
+          block.className = 'ids-transcript-notes';
+          block.innerHTML = notes;
+          section.appendChild(block);
+        }
+        overlay.appendChild(section);
+      });
+      overlay.addEventListener('click', function () { overlay.hidden = true; });
+      document.body.appendChild(overlay);
+    }
+
+    function toggle() {
+      if (typeof Reveal === 'undefined' || !Reveal.isReady()) return;
+      if (!overlay) build();
+      overlay.hidden = !overlay.hidden;
+      if (!overlay.hidden) {
+        overlay.scrollTop = 0;
+        // rebuild on every open so the transcript reflects the current deck
+        overlay.remove();
+        overlay = null;
+        build();
+        overlay.hidden = false;
+      }
+    }
+
+    document.addEventListener('keydown', function (e) {
+      if (e.key !== 'r' && e.key !== 'R') return;
+      if (e.ctrlKey || e.altKey || e.metaKey) return;
+      var tag = e.target && e.target.tagName;
+      if (tag === 'INPUT' || tag === 'TEXTAREA' || (e.target && e.target.isContentEditable)) return;
+      e.preventDefault();
+      toggle();
+    });
+    document.addEventListener('keydown', function (e) {
+      if (e.key === 'Escape' && overlay && !overlay.hidden) overlay.hidden = true;
+    });
+  })();
+</script>
   </body>
 </html>