Add dark modeHEADmaster

Add dark mode

See #65 

12 files changed, 179 insertions, 48 deletions

diff --git a/assets/scss/tale/_base.scss b/assets/scss/tale/_base.scss
index 6c2471b..c096ebb 100644
--- a/assets/scss/tale/_base.scss
+++ b/assets/scss/tale/_base.scss
@@ -5,8 +5,8 @@
 
 html,
 body {
-  color: $default-color;
-  background-color: #fff;
+  color: var(--default-color);
+  background-color: var(--background-color);
   margin: 0;
   padding: 0;
 }
@@ -31,19 +31,19 @@ h3,
 h4,
 h5,
 h6 {
-  color: $default-shade;
+  color: var(--default-shade);
   font-family: $sans-serif;
   line-height: normal;
 }
 
 a {
-  color: $blue;
+  color: var(--blue);
   text-decoration: none;
 }
 
 blockquote {
-  border-left: .25rem solid $grey-2;
-  color: $grey-1;
+  border-left: .25rem solid var(--grey-2);
+  color: var(--grey-1);
   margin: .8rem 0;
   padding: .5rem 1rem;
 
diff --git a/assets/scss/tale/_catalogue.scss b/assets/scss/tale/_catalogue.scss
index 0587bc5..ec065a1 100644
--- a/assets/scss/tale/_catalogue.scss
+++ b/assets/scss/tale/_catalogue.scss
@@ -1,7 +1,7 @@
 .catalogue {
   &-item {
-    border-bottom: 1px solid $grey-2;
-    color: $default-color;
+    border-bottom: 1px solid var(--grey-2);
+    color: var(--default-color);
     display: block;
     padding: 2rem 0;
 
@@ -16,13 +16,13 @@
   }
 
   &-time {
-    color: $default-tint;
+    color: var(--default-tint);
     font-family: $serif-secondary;
     letter-spacing: .5px;
   }
 
   &-title {
-    color: $default-shade;
+    color: var(--default-shade);
     display: block;
     font-family: $sans-serif;
     font-size: 2rem;
@@ -31,8 +31,8 @@
   }
 
   &-line {
-    @include transition(all .3s ease-out);
-    border-top: .2rem solid $default-shade;
+    @include transition($color-transition, width .3s ease-out);
+    border-top: .2rem solid var(--default-shade);
     display: block;
     width: 2rem;
   }
diff --git a/assets/scss/tale/_code.scss b/assets/scss/tale/_code.scss
index 11f1c53..6d97161 100644
--- a/assets/scss/tale/_code.scss
+++ b/assets/scss/tale/_code.scss
@@ -4,9 +4,9 @@ code {
 }
 
 code {
-  background-color: $grey-4;
+  background-color: var(--grey-4);
   border-radius: 3px;
-  color: $code-color;
+  color: var(--code-color);
   font-size: 85%;
   padding: .25em .5em;
   white-space: pre-wrap;
@@ -23,8 +23,14 @@ pre code {
   padding: 0;
 }
 
+pre code > span {
+    // This isn't very pretty, but the precise RGB values are generated
+    // server-side, the usual trick of putting the colors in CSS variables does
+    // not quite work and this is the best I could come up with.
+    filter: var(--code-filter);
+}
 .highlight {
-  background-color: $grey-4;
+  background-color: var(--grey-4);
   border-radius: 3px;
   line-height: 1.4;
   margin: 0 0 1rem;
@@ -36,7 +42,7 @@ pre code {
   }
 
   .lineno {
-    color: $default-tint;
+    color: var(--default-tint);
     display: inline-block; // Ensures the null space also isn't selectable
     padding: 0 .75rem 0 .25rem;
     // Make sure numbers aren't selectable
diff --git a/assets/scss/tale/_layout.scss b/assets/scss/tale/_layout.scss
index 8d56834..c459510 100644
--- a/assets/scss/tale/_layout.scss
+++ b/assets/scss/tale/_layout.scss
@@ -1,3 +1,7 @@
+* {
+    @include transition($color-transition);
+}
+
 .container {
   margin: 0 auto;
   max-width: 800px;
@@ -17,8 +21,19 @@ footer,
   width: 80%;
 }
 
+#darkModeToggle {
+    float: right;
+    position: sticky;
+    top: 2rem;
+    margin-right: 2rem;
+    margin-top: 2rem;
+    font-size: 2rem;
+
+    cursor: pointer;
+}
+
 .nav {
-  box-shadow: 0 2px 2px -2px $shadow-color;
+  box-shadow: 0 2px 2px -2px var(--shadow-color);
   overflow: auto;
 
   &-container {
@@ -28,8 +43,8 @@ footer,
   }
 
   &-title {
-    @include transition(all .2s ease-out);
-    color: $default-color;
+    @include transition($color-transition, opacity .2s ease-out);
+    color: var(--default-color);
     display: inline-block;
     margin: 0;
     padding-right: .2rem;
@@ -48,8 +63,8 @@ footer,
   }
 
   li {
-    @include transition(all .2s ease-out);
-    color: $default-color;
+    @include transition($color-transition, opacity .2s ease-out);
+    color: var(--default-color);
     display: inline-block;
     opacity: .6;
     padding: 0 2rem 0 0;
@@ -65,7 +80,7 @@ footer,
   }
 
   a {
-    color: $default-color;
+    color: var(--default-color);
     font-family: $sans-serif;
   }
 }
@@ -90,7 +105,7 @@ footer {
   text-align: center;
 
   span {
-    color: $default-color;
+    color: var(--default-color);
     font-size: .8rem;
   }
 }
diff --git a/assets/scss/tale/_pagination.scss b/assets/scss/tale/_pagination.scss
index 3700e15..8b391b5 100644
--- a/assets/scss/tale/_pagination.scss
+++ b/assets/scss/tale/_pagination.scss
@@ -1,18 +1,18 @@
 .pagination {
-  border-top: .5px solid $grey-2;
+  border-top: .5px solid var(--grey-2);
   font-family: $serif-secondary;
   padding-top: 2rem;
   position: relative;
   text-align: center;
 
   span {
-    color: $default-shade;
+    color: var(--default-shade);
     font-size: 1.1rem;
   }
 
   .top {
-    @include transition(all .3s ease-out);
-    color: $default-color;
+    @include transition($color-transition, opacity .3s ease-out);
+    color: var(--default-color);
     font-family: $sans-serif;
     font-size: 1.1rem;
     opacity: .6;
@@ -23,8 +23,8 @@
   }
 
   .arrow {
-    @include transition(all .3s ease-out);
-    color: $default-color;
+    @include transition($color-transition, opacity .3s ease-out);
+    color: var(--default-color);
     position: absolute;
 
     &:hover,
diff --git a/assets/scss/tale/_post.scss b/assets/scss/tale/_post.scss
index 3680d80..61cff18 100644
--- a/assets/scss/tale/_post.scss
+++ b/assets/scss/tale/_post.scss
@@ -2,7 +2,7 @@
   padding: 3rem 0;
 
   &-info {
-    color: $default-tint;
+    color: var(--default-tint);
     font-family: $serif-secondary;
     letter-spacing: 0.5px;
     text-align: center;
@@ -13,7 +13,7 @@
   }
 
   &-title {
-    color: $default-shade;
+    color: var(--default-shade);
     font-family: $sans-serif;
     font-size: 4rem;
     margin: 1rem 0;
@@ -21,7 +21,7 @@
   }
 
   &-line {
-    border-top: 0.4rem solid $default-shade;
+    border-top: 0.4rem solid var(--default-shade);
     display: block;
     margin: 0 auto 3rem;
     width: 4rem;
@@ -41,7 +41,7 @@
   }
 
   img + em {
-    color: $default-tint;
+    color: var(--default-tint);
     display: block;
     font-family: $sans-serif;
     font-size: 0.9rem;
diff --git a/assets/scss/tale/_toc.scss b/assets/scss/tale/_toc.scss
index 6492ba7..08ccd47 100644
--- a/assets/scss/tale/_toc.scss
+++ b/assets/scss/tale/_toc.scss
@@ -17,6 +17,10 @@ aside.toc {
     float: left;
     height: 0;
     overflow: display;
+
+    // This is apparenty necessary so that the table of contents covers elements
+    // with the "filter:" property set.
+    z-index: 1;
 }
 
 #tocTitle {
@@ -34,7 +38,7 @@ aside.toc {
 }
 
 #tocContainer {
-    background: $grey-3;
+    background-color: var(--grey-3);
     border-radius: 1rem;
     margin: 2rem;
     padding: 1rem;
@@ -54,11 +58,14 @@ aside.toc {
     width: calc(2rem + var(--measured-title-width));
     --measured-title-width: 2.4rem;
 
-    @include transition(all .1s ease-out);
+@include transition(
+	$color-transition,
+	width .1s ease-out,
+	height .1s ease-out);
 }
 
 #tocContainer > div {
-    border-left: 0.4rem solid black;
+    border-left: 0.4rem solid var(--default-shade);
     padding-left: 1rem;
 }
 
@@ -72,7 +79,7 @@ aside.toc {
 
     // No transition on width so that there is no re-wrapping during the
     // opening/closing transition
-    @include transition(height .1s ease-out);
+    @include transition($color-transition, height .1s ease-out);
 }
 
 nav#TableOfContents ul {
diff --git a/assets/scss/tale/_variables.scss b/assets/scss/tale/_variables.scss
index 92d1114..43914ba 100644
--- a/assets/scss/tale/_variables.scss
+++ b/assets/scss/tale/_variables.scss
@@ -1,15 +1,47 @@
 // Colors
-$default-color: #555;
-$default-shade: #353535;
-$default-tint: #aaa;
-$grey-1: #979797;
-$grey-2: #e5e5e5;
-$grey-3: #f0f0f0;
-$grey-4: #f9f9f9;
-$white: #fff;
-$blue: #4a9ae1;
-$shadow-color: rgba(0, 0, 0, .2);
-$code-color: #bf616a;
+// This is necessary because some elements want to set transitions themselves,
+// which would result in deleting the color transitions specified in less
+// specific selectors.
+$color-transition:
+    background-color .4s ease-out,
+    color .4s ease-out,
+    border-color .4s ease-out,
+    box-shadow .4s ease-out;
+
+
+// Make the default be dark mode. That way, the more complicated case is the
+// default and thus bugs are discovered earlier.
+:root.light {
+    --default-color: #555;
+    --background-color: #fff;
+    --default-shade: #353535;
+    --default-tint: #aaa;
+    --grey-1: #979797;
+    --grey-2: #e5e5e5;
+    --grey-3: #f0f0f0;
+    --grey-4: #f9f9f9;
+    --white: #fff;
+    --blue: #4a9ae1;
+    --shadow-color: rgba(0, 0, 0, .2);
+    --code-color: #bf616a;
+    --code-filter: ;
+}
+
+:root:not(.light) {
+    --default-color: #888;
+    --background-color: #000;
+    --default-shade: #989898;
+    --default-tint: #555;
+    --grey-1: #606060;
+    --grey-2: #404040;
+    --grey-3: #202020;
+    --grey-4: #181818;
+    --white: #fff;
+    --blue: #1d6baf;
+    --shadow-color: rgba(0, 0, 0, .2);
+    --code-color: #a3434c;
+    --code-filter: contrast(0.4) brightness(0.9);
+}
 
 // Fonts
 $serif-primary: 'Libre Baskerville', 'Times New Roman', Times, serif;
diff --git a/layouts/_default/baseof.html b/layouts/_default/baseof.html
index 866a593..4bf1dc8 100644
--- a/layouts/_default/baseof.html
+++ b/layouts/_default/baseof.html
@@ -3,6 +3,7 @@
     {{ partial "head.html" . }}
     <body>
         {{ partial "header.html" . }}
+        {{ partial "darkmode.html" . }}
         {{ block "main" . }}{{ end }}
         {{ partial "footer.html" . }}
     </body>
diff --git a/layouts/partials/darkmode.html b/layouts/partials/darkmode.html
new file mode 100644
index 0000000..1016b53
--- /dev/null
+++ b/layouts/partials/darkmode.html
@@ -0,0 +1,3 @@
+<div id="darkModeToggle" onclick="toggleDarkMode()">
+  &#9680; <!-- Circle with left half black -->
+</div>
diff --git a/layouts/partials/head.html b/layouts/partials/head.html
index fe10a91..0d9b512 100644
--- a/layouts/partials/head.html
+++ b/layouts/partials/head.html
@@ -30,4 +30,6 @@
 
 		<!-- RSS -->
 		<link href="{{ with .OutputFormats.Get "RSS" }}{{ .RelPermalink }}{{ end }}" rel="alternate" type="application/rss+xml" title="{{ .Site.Title }}" />
+
+		<script src="{{ "js/darkmode.js" | relURL }}"></script>
 	</head>
diff --git a/static/js/darkmode.js b/static/js/darkmode.js
new file mode 100644
index 0000000..8161f9a
--- /dev/null
+++ b/static/js/darkmode.js
@@ -0,0 +1,65 @@
+"use strict";
+
+const LOCALSTORAGE_KEY = "color-scheme";
+const LIGHT_CLASS = "light";
+let mediaQuery = window.matchMedia("(prefers-color-scheme: dark)");
+
+// true means "dark scheme", false means "light scheme". Ugly, bit simple.
+function storedToBool(s) {
+    if (s === "dark") {
+	return true;
+    } else if (s === "light") {
+	return false;
+    } else {
+	return null;
+    }
+}
+
+function ensureScheme(desiredScheme) {
+    let osScheme = mediaQuery.matches;
+
+    // Only store the preference if it's not the same as the OS one.
+    if (desiredScheme === osScheme) {
+	localStorage.removeItem(LOCALSTORAGE_KEY);
+    } else {
+	localStorage.setItem(LOCALSTORAGE_KEY, desiredScheme ? "dark" : "light");
+    }
+
+    if (desiredScheme) {
+	document.documentElement.classList.remove(LIGHT_CLASS);
+    } else {
+	document.documentElement.classList.add(LIGHT_CLASS);
+    }
+}
+
+function initDarkMode() {
+    let storedScheme = storedToBool(localStorage.getItem(LOCALSTORAGE_KEY));
+    let osScheme = mediaQuery.matches;
+
+    // When the class of the document element is changed from a script running in the <HEAD>
+    // element, no CSS transition defined on the changed properties takes place.
+    ensureScheme(storedScheme === null ? osScheme : storedScheme);
+    mediaQuery.addEventListener("change", osDarkModeChanged);
+}
+
+function osDarkModeChanged(query) {
+    let osScheme = query.matches;
+    let pageScheme = !document.documentElement.classList.contains(LIGHT_CLASS);
+
+    // If the current preference is the same as that of the OS, we assume that the user also wants
+    // to change the color scheme of the web page. If not, we assume that they consciously overrode
+    // the OS and we don't change anything.
+    if (pageScheme != osScheme) {
+	ensureScheme(!pageScheme);
+    }
+}
+
+function toggleDarkMode() {
+    // The easiest is to decide based on the current color scheme.
+    let currentScheme = !document.documentElement.classList.contains(LIGHT_CLASS);
+    ensureScheme(!currentScheme);
+}
+
+// Doing this in an onload handler would let the initial color appear for a
+// split second.
+initDarkMode();