Add table of contents

Add table of contents

See #64

8 files changed, 178 insertions, 5 deletions

diff --git a/assets/scss/tale.scss b/assets/scss/tale.scss
index 9d1c12f..53f9dec 100644
--- a/assets/scss/tale.scss
+++ b/assets/scss/tale.scss
@@ -4,6 +4,7 @@
 @import 'tale/post';
 @import 'tale/syntax';
 @import 'tale/layout';
+@import 'tale/toc';
 @import 'tale/pagination';
 @import 'tale/catalogue';
 @import 'tale/disqus';
diff --git a/assets/scss/tale/_code.scss b/assets/scss/tale/_code.scss
index 8d3db57..11f1c53 100644
--- a/assets/scss/tale/_code.scss
+++ b/assets/scss/tale/_code.scss
@@ -4,7 +4,7 @@ code {
 }
 
 code {
-  background-color: $grey-3;
+  background-color: $grey-4;
   border-radius: 3px;
   color: $code-color;
   font-size: 85%;
@@ -24,7 +24,7 @@ pre code {
 }
 
 .highlight {
-  background-color: $grey-3;
+  background-color: $grey-4;
   border-radius: 3px;
   line-height: 1.4;
   margin: 0 0 1rem;
diff --git a/assets/scss/tale/_layout.scss b/assets/scss/tale/_layout.scss
index ba4a7b0..8d56834 100644
--- a/assets/scss/tale/_layout.scss
+++ b/assets/scss/tale/_layout.scss
@@ -4,7 +4,11 @@
   width: 80%;
 }
 
-main,
+// Carve out an exception from the 80% narrowing of the viewport for the table
+// of contents. This is ugly, but there isn't a better way, since the table of
+// contents must be a child of the "main" element so that it its scrolling
+// behavior is intuitive.
+main > *,
 footer,
 .nav-container {
   display: block;
diff --git a/assets/scss/tale/_toc.scss b/assets/scss/tale/_toc.scss
new file mode 100644
index 0000000..6492ba7
--- /dev/null
+++ b/assets/scss/tale/_toc.scss
@@ -0,0 +1,89 @@
+aside.toc {
+    position: sticky;
+    top: 0;
+    max-width: 30%;
+
+    // We want the table of contents to be on the left (horizontally), to be
+    // positioned at a specific point (vertically), stick to the top on scroll
+    // and it should not affect the layout of other elements.
+    // "float: left" accomplishes the horizontal positioning, position in the
+    // element tree the vertical positioning and "position: sticky" does the
+    // stickiness. "height: 0" makes sure that the flow of other elements is not
+    // affected.
+    //
+    // There does not seem to be a better way to do this unless one is willing
+    // to implement scrolling in JS: "position" must be set to sticky so neither
+    // fixed, nor absolute, nor relative positioning can be used.
+    float: left;
+    height: 0;
+    overflow: display;
+}
+
+#tocTitle {
+    // This is so that we can measure it in JS
+    width: fit-content;
+}
+
+#tocContainer:hover {
+    width: calc(2rem + var(--measured-expanded-width));
+}
+
+#tocContainer:hover div#tocCollapsible {
+    height: var(--measured-height);
+    width: var(--measured-expanded-width);
+}
+
+#tocContainer {
+    background: $grey-3;
+    border-radius: 1rem;
+    margin: 2rem;
+    padding: 1rem;
+
+    // This makes the gap between the two contained divs vanish. Why that gap
+    // exists, no clue.
+    display: flex;
+    flex-direction: column;
+
+    // We want to hide the table of contents before revealing it on hover
+    overflow: hidden;
+
+    // In addition to the measured width of the title, we need to add the two
+    // rems for the border (we are using box-sizing: border-box). Also add a
+    // reasonable default value to minimize visual changes while the page is
+    // loading.
+    width: calc(2rem + var(--measured-title-width));
+    --measured-title-width: 2.4rem;
+
+    @include transition(all .1s ease-out);
+}
+
+#tocContainer > div {
+    border-left: 0.4rem solid black;
+    padding-left: 1rem;
+}
+
+#tocContainer div#tocCollapsible {
+    // Collapsed by default
+    height: 0;
+
+    // If we did not force this element to a given width, it would keep
+    // re-wrapping during the opening/closing transition.
+    width: var(--measured-expanded-width);
+
+    // No transition on width so that there is no re-wrapping during the
+    // opening/closing transition
+    @include transition(height .1s ease-out);
+}
+
+nav#TableOfContents ul {
+    list-style-type: none;
+    padding-inline-start: 1rem;
+}
+
+nav#TableOfContents > ul {
+    padding-inline-start: 0;
+}
+
+nav#TableOfContents li {
+    margin-top: 0.4rem;
+}
diff --git a/assets/scss/tale/_variables.scss b/assets/scss/tale/_variables.scss
index 8a064f3..92d1114 100644
--- a/assets/scss/tale/_variables.scss
+++ b/assets/scss/tale/_variables.scss
@@ -4,7 +4,8 @@ $default-shade: #353535;
 $default-tint: #aaa;
 $grey-1: #979797;
 $grey-2: #e5e5e5;
-$grey-3: #f9f9f9;
+$grey-3: #f0f0f0;
+$grey-4: #f9f9f9;
 $white: #fff;
 $blue: #4a9ae1;
 $shadow-color: rgba(0, 0, 0, .2);
diff --git a/layouts/_default/single.html b/layouts/_default/single.html
index dba8344..f5f6f6e 100644
--- a/layouts/_default/single.html
+++ b/layouts/_default/single.html
@@ -1,7 +1,9 @@
 {{ define "main" }}
 
 <main>
-	<div class="post">
+	{{ partial "toc.html" . }}
+
+        <div class="post">
 		{{ partial "single/post-info.html" . }}
 		{{ partial "single/title.html" . }}
 
diff --git a/layouts/partials/toc.html b/layouts/partials/toc.html
new file mode 100644
index 0000000..81d524a
--- /dev/null
+++ b/layouts/partials/toc.html
@@ -0,0 +1,13 @@
+{{ if .Params.toc }}
+<aside class="toc">
+  <script src="{{ "js/toc.js" | relURL }}"></script>
+  <div id="tocContainer">
+    <div id="tocTitle">
+      &#9776; <!-- Trigram for heaven, aka. hamburger menu -->
+    </div>
+    <div id="tocCollapsible">
+      {{ .TableOfContents }}
+    </div>
+  </div>
+</aside>
+{{ end }}
diff --git a/static/js/toc.js b/static/js/toc.js
new file mode 100644
index 0000000..7229c04
--- /dev/null
+++ b/static/js/toc.js
@@ -0,0 +1,63 @@
+"use strict";
+
+let oldWidth = -1, oldHeight = -1;
+
+function measureToc() {
+    if (window.innerWidth === oldWidth && window.innerHeight === oldHeight) {
+	// In addition to being a bit of optimization, this clause somehow prevents triggering a
+	// bug in Firefox 98.2.0 on Android that makes the stickiness of the table of contents
+	// wonky after scrolling to the bottom, then scrolling up.
+	return;
+    }
+
+    oldWidth = window.innerWidth;
+    oldHeight = window.innerHeight;
+
+    let tocContainer = document.getElementById("tocContainer");
+    let tocTitle = document.getElementById("tocTitle");
+    let tocCollapsible = document.getElementById("tocCollapsible");
+
+    // Set relevant elements to automatic sizing.
+    tocContainer.style.width = "fit-content";
+    tocCollapsible.style.width = "fit-content";
+    tocCollapsible.style.height = "fit-content";
+
+    // Apparently, this call is necessary so that the CSS properties set above take effect.
+    requestAnimationFrame(() => {
+	// These properties apparently round to the nearest integer but rounding down would make
+	// them wrap text differently than when autosizing. Add a pixel because it's better to wrap
+	// too little than to wrap too much,
+	let titleWidth = tocTitle.offsetWidth + 1;
+	let collapsibleWidth = tocCollapsible.offsetWidth + 1;
+	let collapsibleHeight = tocCollapsible.offsetHeight + 1;
+
+	// Make sure the TOC width cannot shrink under that of the title. Sadly,
+	// calc() does not have min() / max() operators.
+	let clampedCollapsibleWidth = Math.max(collapsibleWidth, titleWidth);
+
+	tocContainer.style.setProperty("--measured-title-width", titleWidth + "px");
+	tocContainer.style.setProperty("--measured-expanded-width", clampedCollapsibleWidth + "px");
+	tocCollapsible.style.setProperty("--measured-expanded-width", clampedCollapsibleWidth + "px");
+	tocCollapsible.style.setProperty("--measured-height", collapsibleHeight + "px");
+
+	tocContainer.style.removeProperty("width");
+	tocCollapsible.style.removeProperty("width");
+	tocCollapsible.style.removeProperty("height");
+    });
+}
+
+let resizeTimeout = null;
+
+function measureTocAfterResize() {
+    // Chrome sometimes does not finish layout when the resize event handler is called, so wait a
+    // bit before recalculating sizes. This does not usually result in weird visual effects because
+    // it's really hard to resize a window while hovering over the table of contents so we can
+    // assume that it's closed when the measurement is running.
+    if (resizeTimeout != null) {
+	clearTimeout(resizeTimeout);
+    }
+    resizeTimeout = setTimeout(measureToc, 200);
+}
+
+window.addEventListener("load", measureToc);
+window.addEventListener("resize", measureTocAfterResize);