implement automatic anchor generation for headings

src/blog.rs

@@ -120,7 +120,7 @@ impl Post {
 // library updates. Updaing this value invalidates all
 // existing cache and they will be recompiled when someone
 // visits.
-const CACHE_VERSION: &'static str = "0003";
+const CACHE_VERSION: &'static str = "0007";
 
 // The prefix path used for caching remote images
 pub const IMG_CACHE_PREFIX: &'static str = "/imgcache/";
@@ -203,6 +203,60 @@ impl PostContentCache {
         }
     }
 
+    // Do some HTML-level transformations to the compiled result
+    // Because the Markdown parser doesn't always allow us to do
+    // everything, like adding `id` attributes to tags
+    fn transform_html(html: &mut String) {
+        // Generate IDs for all headings in article
+        // This allows navigation via the hash part of the URL
+        let mut last_idx: usize = 0;
+        loop {
+            let len = html.len();
+            
+            let idx = match (&html[last_idx..len]).find("<h") {
+                Some(i) => i + last_idx,
+                None => break,
+            };
+    
+            if idx >= len - 4 {
+                break;
+            }
+    
+            last_idx = idx + 3;
+    
+            if &html[idx + 3..idx + 4] != ">" {
+                continue;
+            }
+    
+            // Now we have found a <h*> tag
+            let htype = &html[idx + 1..idx + 3];
+    
+            // Find the closing tag for this one
+            // Since it's generated by the Markdown engine,
+            // we can assume it's correct HTML
+            let end_idx = match (&html[idx + 3..len]).find(&format!("</{}>", htype)) {
+                Some(i) => i + idx + 3,
+                None => continue,
+            };
+    
+            if end_idx >= len - 4 {
+                break;
+            }
+    
+            let heading = &html[idx + 4..end_idx];
+            // We also assume there should be no other HTML tags in the heading
+            // This should be fine for me but I don't know about others
+            // However it's really tedious to do anything better...
+            let heading_anchor = filter_non_ascii_alphanumeric(
+                &heading.to_lowercase()).replace(" ", "-");
+            let inserted_id = format!(" id=\"{}\"", heading_anchor);
+    
+            html.insert_str(idx + 3, &inserted_id);
+            
+            last_idx = idx + 3 + inserted_id.len();
+        }
+    }
+
     // Only renders the content and spits out a cache object
     // can be used to display the page or to write to cache
     // Despite the signature, this function BLOCKS
@@ -224,6 +278,7 @@ impl PostContentCache {
         }
         let mut html_output = String::new();
         html::push_html(&mut html_output, parser.into_iter());
+        Self::transform_html(&mut html_output);
         PostContentCache {
             uuid: post.uuid.clone(),
             version: CACHE_VERSION.to_owned(),

theme/default/post.hbs

@@ -9,7 +9,7 @@
         <div class="page-wrapper">
             {{> sidebar.hbs }}
             <article class="content">
-                <h1>{{ title }}</h1>
+                <h1 id="paprika-post-title">{{ title }}</h1>
                 <span class="date">{{ format_date timestamp "%e %b, %Y" }}</span>
                 {{{ content }}}
             </article>

theme/default/static/script.js

@@ -12,3 +12,113 @@ avatar.onanimationend = (ev) => {
 window.onbeforeunload = (ev) => {
   document.getElementsByClassName("loading-progress")[0].className = "loading-progress force-visible";
 };
+
+window.onload = function() {
+  let content = document.getElementsByClassName("content");
+  if (content.length == 0) return;
+
+  let level = 0;
+  let maxLevel = 0;
+  let toc = "";
+  content[0].querySelectorAll("h1, h2, h3, h4, h5").forEach((elem) => {
+    let openLevel = parseInt(elem.tagName.toLowerCase().replace("h", ""));
+    if (openLevel > level) {
+      toc += (new Array(openLevel - level + 1)).join("<ul>");
+    } else if (openLevel < level) {
+      toc += (new Array(level - openLevel + 1)).join("</ul>");
+    }
+
+    level = openLevel;
+    if (level > maxLevel) maxLevel = level;
+
+    let anchor = elem.getAttribute("id");
+    let titleText = elem.innerText;
+    toc += "<li><a href=\"#" + anchor + "\">" + titleText + "</a></li>";
+  });
+
+  if (level) {
+    toc += (new Array(level + 1)).join("</ul>");
+  }
+
+  if (maxLevel > 1) {
+    document.getElementsByClassName("toc")[0].innerHTML = toc;
+    document.getElementsByClassName("toc-wrapper")[0].className = "toc-wrapper"; // remove hidden
+
+    // Get rid of ul layers that have only one ul child
+    removeTrivialUlLayer(document.getElementsByClassName("toc")[0]);
+
+    var curAnchorLink = null;
+    window.onscroll = (ev) => {
+      let anchor = findClosestAnchor(content[0].querySelectorAll("h1, h2, h3, h4, h5"));
+      let name = anchor.getAttribute("id");
+      let tocLink = document.querySelector("a[href=\"#" + name + "\"").parentElement;
+      if (tocLink != curAnchorLink) {
+        tocLink.className = "current";
+        if (curAnchorLink != null) {
+          curAnchorLink.className = "";
+        }
+        curAnchorLink = tocLink;
+      }
+    };
+
+    window.onscroll();
+  }
+};
+
+function removeTrivialUlLayer(elem) {
+  let children = elem.getElementsByTagName("ul");
+  if (elem.childNodes.length == 1 && children.length == 1) {
+    // Every child is a ul
+    elem.innerHTML = children[0].innerHTML;
+    removeTrivialUlLayer(elem);
+  } else {
+    for (const child of children) {
+      removeTrivialUlLayer(child);
+    }
+  }
+}
+
+// <https://stackoverflow.com/questions/10642587/finding-closest-anchor-href-via-scrolloffset>
+// findPos : courtesy of @ppk - see http://www.quirksmode.org/js/findpos.html
+var findPos = function (obj) {
+  var curleft = 0,
+    curtop = 0;
+  if (obj.offsetParent) {
+    curleft = obj.offsetLeft;
+    curtop = obj.offsetTop;
+    while ((obj = obj.offsetParent)) {
+      curleft += obj.offsetLeft;
+      curtop += obj.offsetTop;
+    }
+  }
+  return [curleft, curtop];
+};
+
+var findClosestAnchor = function (anchors) {
+  var sortByDistance = function (element1, element2) {
+    var pos1 = findPos(element1),
+      pos2 = findPos(element2);
+
+    // vect1 & vect2 represent 2d vectors going from the top left extremity of each element to the point positionned at the scrolled offset of the window
+    var vect1 = [
+      window.scrollX - pos1[0],
+      window.scrollY - pos1[1]
+    ],
+      vect2 = [
+        window.scrollX - pos2[0],
+        window.scrollY - pos2[1]
+      ];
+
+    // we compare the length of the vectors using only the sum of their components squared
+    // no need to find the magnitude of each (this was inspired by Mageek’s answer)
+    var sqDist1 = vect1[0] * vect1[0] + vect1[1] * vect1[1],
+      sqDist2 = vect2[0] * vect2[0] + vect2[1] * vect2[1];
+
+    if (sqDist1 < sqDist2) return -1;
+    else if (sqDist1 > sqDist2) return 1;
+    else return 0;
+  };
+
+  // Convert the nodelist to an array, then returns the first item of the elements sorted by distance
+  return Array.prototype.slice.call(anchors).sort(sortByDistance)[0];
+};