Add dark mode

5 files changed, 455 insertions, 2 deletions

diff --git a/README.md b/README.md
index 88cfd4e..db58bc0 100644
--- a/README.md
+++ b/README.md
@@ -9,8 +9,7 @@ Simple, text-focussed and minimal personal portfolio theme based on https://gith
 * Markdown supported
 * Easy to personalize
 * RSS feed
- - TODO
-   - Dark mode
+* Dark mode (taken from https://www.gwern.net/ as it is.)
 
 
 ## Installation
@@ -79,5 +78,6 @@ Too much to rant :(
 ## Credits
 
 * Thanks to [Vegard's](https://github.com/vegarsti) personal site from which the theme was heavily inspired.
+* Also to https://www.gwern.net/ for the dark mode.
 
 Feel free to contribute and open issues.
diff --git a/images/screenshot.png b/images/screenshot.png
index 7437b49..0ce8fde 100644
--- a/images/screenshot.png
+++ b/images/screenshot.png
diff --git a/images/tn.png b/images/tn.png
index e0d8d78..7fbfe7a 100644
--- a/images/tn.png
+++ b/images/tn.png
diff --git a/layouts/partials/head.html b/layouts/partials/head.html
index 8df8052..7cc35fb 100644
--- a/layouts/partials/head.html
+++ b/layouts/partials/head.html
@@ -10,4 +10,6 @@
     <link rel="icon" type="image/png" href="/assets/img/favicon.ico" />
     <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.8.2/css/all.css"
         integrity="sha384-oS3vJWv+0UjzBfQzYUhtDYW+Pj2yciDJxpsK1OYPAYjqT085Qq/1cq5FLXAZQ7Ay" crossorigin="anonymous">
+    <script src="/js/dark.js" defer=""></script>
+
 </head>
\ No newline at end of file
diff --git a/static/js/dark.js b/static/js/dark.js
new file mode 100644
index 0000000..cacb561
--- /dev/null
+++ b/static/js/dark.js
@@ -0,0 +1,451 @@
+// darkmode.js: Javascript library for controlling page appearance, toggling between regular white and 'dark mode'
+// Author: Said Achmiz
+// Date: 2020-03-20
+// When:  Time-stamp: "2020-03-23 09:36:20 gwern"
+// license: PD
+
+/* Experimental 'dark mode': Mac OS (Safari) lets users specify via an OS widget 'dark'/'light' to make everything appear */
+/* bright-white or darker (eg for darker at evening to avoid straining eyes & disrupting circadian rhyhms); this then is */
+/* exposed by Safari as a CSS variable which can be selected on. This is also currently supported by Firefox weakly as an */
+/* about:config variable. Hypothetically, iOS in the future might use its camera or the clock to set 'dark mode' */
+/* automatically. https://drafts.csswg.org/mediaqueries-5/#prefers-color-scheme */
+/* https://webkit.org/blog/8718/new-webkit-features-in-safari-12-1/ */
+/* https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-color-scheme
+
+/* Because many users do not have access to a browser/OS which explicitly supports dark mode, cannot modify the browser/OS setting without undesired side-effects, wish to opt in only for specific websites, or simply forget that they turned on dark mode & dislike it, we make dark mode controllable by providing a widget at the top of the page. */
+
+/* For gwern.net, the default white-black */
+/* scheme is 'light', and it can be flipped to a 'dark' scheme fairly easily by inverting it; the main visual problem is */
+/* that blockquotes appear to become much harder to see & image-focus.js doesn't work well without additional tweaks. */
+/* Known bugs: images get inverted on zoom or hover; invert filters are slow, leading to 'janky' slow rendering on scrolling. */
+
+/****************/
+/* MISC HELPERS */
+/****************/
+
+/*      Given an HTML string, creates an element from that HTML, adds it to
+        #ui-elements-container (creating the latter if it does not exist), and
+        returns the created element.
+        */
+function addUIElement(element_html) {
+        var ui_elements_container = document.querySelector("#ui-elements-container");
+        if (!ui_elements_container) {
+                ui_elements_container = document.createElement("div");
+                ui_elements_container.id = "ui-elements-container";
+                document.querySelector("body").appendChild(ui_elements_container);
+        }
+
+        ui_elements_container.insertAdjacentHTML("beforeend", element_html);
+        return ui_elements_container.lastElementChild;
+}
+
+if (typeof window.GW == "undefined")
+        window.GW = { };
+GW.temp = { };
+
+if (GW.mediaQueries == null)
+    GW.mediaQueries = { };
+GW.mediaQueries.mobileNarrow = matchMedia("(max-width: 520px)");
+GW.mediaQueries.mobileWide = matchMedia("(max-width: 900px)");
+GW.mediaQueries.mobileMax = matchMedia("(max-width: 960px)");
+GW.mediaQueries.hover = matchMedia("only screen and (hover: hover) and (pointer: fine)");
+GW.mediaQueries.systemDarkModeActive = matchMedia("(prefers-color-scheme: dark)");
+
+GW.modeOptions = [
+    [ 'auto', 'Auto', 'Set light or dark mode automatically, according to system-wide setting' ],
+    [ 'light', 'Light', 'Light mode at all times' ],
+    [ 'dark', 'Dark', 'Dark mode at all times' ]
+];
+GW.modeStyles = `
+    :root {
+        --GW-blockquote-background-color: #ddd
+    }
+    body::before,
+    body > * {
+        filter: invert(90%)
+    }
+    body::before {
+        content: '';
+        width: 100vw;
+        height: 100%;
+        position: fixed;
+        left: 0;
+        top: 0;
+        background-color: #fff;
+        z-index: -1
+    }
+    img,
+    video {
+        filter: invert(100%);
+    }
+    #markdownBody, #mode-selector button {
+        text-shadow: 0 0 0 #000
+    }
+    article > :not(#TOC) a:link {
+        text-shadow:
+                 0      0 #777,
+             .03em      0 #fff,
+            -.03em      0 #fff,
+                 0  .03em #fff,
+                 0 -.03em #fff,
+             .06em      0 #fff,
+            -.06em      0 #fff,
+             .09em      0 #fff,
+            -.09em      0 #fff,
+             .12em      0 #fff,
+            -.12em      0 #fff,
+             .15em      0 #fff,
+            -.15em      0 #fff
+    }
+    article > :not(#TOC) blockquote a:link {
+        text-shadow:
+                 0      0 #777,
+             .03em      0 var(--GW-blockquote-background-color),
+            -.03em      0 var(--GW-blockquote-background-color),
+                 0  .03em var(--GW-blockquote-background-color),
+                 0 -.03em var(--GW-blockquote-background-color),
+             .06em      0 var(--GW-blockquote-background-color),
+            -.06em      0 var(--GW-blockquote-background-color),
+             .09em      0 var(--GW-blockquote-background-color),
+            -.09em      0 var(--GW-blockquote-background-color),
+             .12em      0 var(--GW-blockquote-background-color),
+            -.12em      0 var(--GW-blockquote-background-color),
+             .15em      0 var(--GW-blockquote-background-color),
+            -.15em      0 var(--GW-blockquote-background-color)
+    }
+    #logo img {
+        filter: none;
+    }
+    #mode-selector {
+        opacity: 0.6;
+    }
+    #mode-selector:hover {
+        background-color: #fff;
+    }
+`;
+
+/****************/
+/* DEBUG OUTPUT */
+/****************/
+
+function GWLog (string) {
+    if (GW.loggingEnabled || localStorage.getItem("logging-enabled") == "true")
+        console.log(string);
+}
+
+/***********/
+/* HELPERS */
+/***********/
+
+/*  Run the given function immediately if the page is already loaded, or add
+    a listener to run it as soon as the page loads.
+    */
+function doWhenPageLoaded(f) {
+    if (document.readyState == "complete")
+        f();
+    else
+        window.addEventListener("load", f);
+}
+
+/*  Adds an event listener to a button (or other clickable element), attaching
+    it to both "click" and "keyup" events (for use with keyboard navigation).
+    Optionally also attaches the listener to the 'mousedown' event, making the
+    element activate on mouse down instead of mouse up.
+    */
+Element.prototype.addActivateEvent = function(func, includeMouseDown) {
+    let ael = this.activateEventListener = (event) => { if (event.button === 0 || event.key === ' ') func(event) };
+    if (includeMouseDown) this.addEventListener("mousedown", ael);
+    this.addEventListener("click", ael);
+    this.addEventListener("keyup", ael);
+}
+
+/*  Adds a scroll event listener to the page.
+    */
+function addScrollListener(fn, name) {
+    let wrapper = (event) => {
+        requestAnimationFrame(() => {
+            fn(event);
+            document.addEventListener("scroll", wrapper, { once: true, passive: true });
+        });
+    }
+    document.addEventListener("scroll", wrapper, { once: true, passive: true });
+
+    // Retain a reference to the scroll listener, if a name is provided.
+    if (typeof name != "undefined")
+        GW[name] = wrapper;
+}
+
+/************************/
+/* ACTIVE MEDIA QUERIES */
+/************************/
+
+/*  This function provides two slightly different versions of its functionality,
+    depending on how many arguments it gets.
+
+    If one function is given (in addition to the media query and its name), it
+    is called whenever the media query changes (in either direction).
+
+    If two functions are given (in addition to the media query and its name),
+    then the first function is called whenever the media query starts matching,
+    and the second function is called whenever the media query stops matching.
+
+    If you want to call a function for a change in one direction only, pass an
+    empty closure (NOT null!) as one of the function arguments.
+
+    There is also an optional fifth argument. This should be a function to be
+    called when the active media query is canceled.
+    */
+function doWhenMatchMedia(mediaQuery, name, ifMatchesOrAlwaysDo, otherwiseDo = null, whenCanceledDo = null) {
+    if (typeof GW.mediaQueryResponders == "undefined")
+        GW.mediaQueryResponders = { };
+
+    let mediaQueryResponder = (event, canceling = false) => {
+        if (canceling) {
+            GWLog(`Canceling media query “${name}”`);
+
+            if (whenCanceledDo != null)
+                whenCanceledDo(mediaQuery);
+        } else {
+            let matches = (typeof event == "undefined") ? mediaQuery.matches : event.matches;
+
+            GWLog(`Media query “${name}” triggered (matches: ${matches ? "YES" : "NO"})`);
+
+            if (otherwiseDo == null || matches) ifMatchesOrAlwaysDo(mediaQuery);
+            else otherwiseDo(mediaQuery);
+        }
+    };
+    mediaQueryResponder();
+    mediaQuery.addListener(mediaQueryResponder);
+
+    GW.mediaQueryResponders[name] = mediaQueryResponder;
+}
+
+/*  Deactivates and discards an active media query, after calling the function
+    that was passed as the whenCanceledDo parameter when the media query was
+    added.
+    */
+function cancelDoWhenMatchMedia(name) {
+    GW.mediaQueryResponders[name](null, true);
+
+    for ([ key, mediaQuery ] of Object.entries(GW.mediaQueries))
+        mediaQuery.removeListener(GW.mediaQueryResponders[name]);
+
+    GW.mediaQueryResponders[name] = null;
+}
+
+/******************/
+/* MODE SELECTION */
+/******************/
+
+function injectModeSelector() {
+    GWLog("injectModeSelector");
+
+    // Get saved mode setting (or default).
+    let currentMode = localStorage.getItem("selected-mode") || 'auto';
+
+    // Inject the mode selector widget and activate buttons.
+    let modeSelector = addUIElement(
+        "<div id='mode-selector'>" +
+        String.prototype.concat.apply("", GW.modeOptions.map(modeOption => {
+            let [ name, label, desc ] = modeOption;
+            let selected = (name == currentMode ? ' selected' : '');
+            let disabled = (name == currentMode ? ' disabled' : '');
+            return `<button type='button' class='select-mode-${name}${selected}'${disabled} tabindex='-1' data-name='${name}' title='${desc}'>${label}</button>`})) +
+        "</div>");
+
+    modeSelector.querySelectorAll("button").forEach(button => {
+        button.addActivateEvent(GW.modeSelectButtonClicked = (event) => {
+            GWLog("GW.modeSelectButtonClicked");
+
+            // Determine which setting was chosen (i.e., which button was clicked).
+            let selectedMode = event.target.dataset.name;
+
+            // Save the new setting.
+            if (selectedMode == "auto") localStorage.removeItem("selected-mode");
+            else localStorage.setItem("selected-mode", selectedMode);
+
+            // Actually change the mode.
+            setMode(selectedMode);
+        });
+    });
+
+    document.querySelector("head").insertAdjacentHTML("beforeend", `<style id='mode-selector-styles'>
+    #mode-selector {
+        position: absolute;
+        right: 3px;
+        top: 4px;
+        display: flex;
+        background-color: #fff;
+        padding: 0.125em 0.25em;
+        border: 3px solid transparent;
+        opacity: 0.3;
+        transition:
+            opacity 2s ease;
+    }
+    #mode-selector.hidden {
+        opacity: 0;
+    }
+    #mode-selector:hover {
+        transition: none;
+        opacity: 1.0;
+        border: 3px double #aaa;
+    }
+    #mode-selector button {
+        -moz-appearance: none;
+        appearance: none;
+        border: none;
+        background-color: transparent;
+        padding: 0.5em;
+        margin: 0;
+        line-height: 1;
+        font-family: Lucida Sans Unicode, Source Sans Pro, Helvetica, Trebuchet MS, sans-serif;
+        font-size: 0.75rem;
+        text-align: center;
+        color: #777;
+        position: relative;
+    }
+    #mode-selector button:hover,
+    #mode-selector button.selected {
+        box-shadow:
+            0 2px 0 6px #fff inset,
+            0 1px 0 6px currentColor inset;
+    }
+    #mode-selector button:not(:disabled):hover {
+        color: #000;
+        cursor: pointer;
+    }
+    #mode-selector button:not(:disabled):active {
+        transform: translateY(2px);
+        box-shadow:
+            0 0px 0 6px #fff inset,
+            0 -1px 0 6px currentColor inset;
+    }
+    #mode-selector button.active:not(:hover)::after {
+        content: "";
+        position: absolute;
+        bottom: 0.25em;
+        left: 0;
+        right: 0;
+        border-bottom: 1px dotted currentColor;
+        width: calc(100% - 12px);
+        margin: auto;
+    }
+    </style>`);
+
+    document.querySelector("head").insertAdjacentHTML("beforeend", `<style id='mode-styles'></style>`);
+
+    setMode(currentMode);
+
+    // We pre-query the relevant elements, so we don’t have to run queryAll on
+    // every firing of the scroll listener.
+    GW.scrollState = {
+        "lastScrollTop":                    window.pageYOffset || document.documentElement.scrollTop,
+        "unbrokenDownScrollDistance":       0,
+        "unbrokenUpScrollDistance":         0,
+        "modeSelector":                     document.querySelectorAll("#mode-selector"),
+    };
+    addScrollListener(updateModeSelectorVisibility, "updateModeSelectorVisibilityScrollListener");
+    GW.scrollState.modeSelector[0].addEventListener("mouseover", () => { showModeSelector(); });
+    doWhenMatchMedia(GW.mediaQueries.systemDarkModeActive, "updateModeSelectorStateForSystemDarkMode", () => { updateModeSelectorState(); });
+}
+
+/*  Show/hide the mode selector in response to scrolling.
+
+    Called by the ‘updateModeSelectorVisibilityScrollListener’ scroll listener.
+    */
+function updateModeSelectorVisibility(event) {
+    GWLog("updateModeSelectorVisibility");
+
+    let newScrollTop = window.pageYOffset || document.documentElement.scrollTop;
+    GW.scrollState.unbrokenDownScrollDistance = (newScrollTop > GW.scrollState.lastScrollTop) ?
+                                                        (GW.scrollState.unbrokenDownScrollDistance + newScrollTop - GW.scrollState.lastScrollTop) :
+                                                        0;
+    GW.scrollState.unbrokenUpScrollDistance = (newScrollTop < GW.scrollState.lastScrollTop) ?
+                                                     (GW.scrollState.unbrokenUpScrollDistance + GW.scrollState.lastScrollTop - newScrollTop) :
+                                                     0;
+    GW.scrollState.lastScrollTop = newScrollTop;
+
+    // Hide mode selector when scrolling a full page down.
+    if (GW.scrollState.unbrokenDownScrollDistance > window.innerHeight) {
+        hideModeSelector();
+    }
+
+    // On desktop, show mode selector when scrolling to top of page,
+    // or a full page up.
+    // On mobile, show mode selector on ANY scroll up.
+    if (GW.mediaQueries.mobileNarrow.matches) {
+        if (GW.scrollState.unbrokenUpScrollDistance > 0 || GW.scrollState.lastScrollTop <= 0)
+            showModeSelector();
+    } else if (   GW.scrollState.unbrokenUpScrollDistance > window.innerHeight
+               || GW.scrollState.lastScrollTop == 0) {
+        showModeSelector();
+    }
+}
+
+function hideModeSelector() {
+    GWLog("hideModeSelector");
+
+    GW.scrollState.modeSelector[0].classList.add("hidden");
+}
+
+function showModeSelector() {
+    GWLog("showModeSelector");
+
+    GW.scrollState.modeSelector[0].classList.remove("hidden");
+}
+
+/*  Update the states of the mode selector buttons.
+    */
+function updateModeSelectorState() {
+    // Get saved mode setting (or default).
+    let currentMode = localStorage.getItem("selected-mode") || 'auto';
+
+    // Clear current buttons state.
+    let modeSelector = document.querySelector("#mode-selector");
+    modeSelector.childNodes.forEach(button => {
+        button.classList.remove("active", "selected");
+        button.disabled = false;
+    });
+
+    // Set the correct button to be selected.
+    modeSelector.querySelectorAll(`.select-mode-${currentMode}`).forEach(button => {
+        button.classList.add("selected");
+        button.disabled = true;
+    });
+
+    // Ensure the right button (light or dark) has the “currently active”
+    // indicator, if the current mode is ‘auto’.
+    if (currentMode == "auto") {
+        if (GW.mediaQueries.systemDarkModeActive.matches)
+            modeSelector.querySelector(".select-mode-dark").classList.add("active");
+        else
+            modeSelector.querySelector(".select-mode-light").classList.add("active");
+    }
+}
+
+/*  Set specified color mode (auto, light, dark).
+    */
+function setMode(modeOption) {
+    GWLog("setMode");
+
+    // Inject the appropriate styles.
+    let modeStyles = document.querySelector("#mode-styles");
+    if (modeOption == 'auto') {
+        modeStyles.innerHTML = `@media (prefers-color-scheme:dark) {${GW.modeStyles}}`;
+    } else if (modeOption == 'dark') {
+        modeStyles.innerHTML = GW.modeStyles;
+    } else {
+        modeStyles.innerHTML = "";
+    }
+
+    // Update selector state.
+    updateModeSelectorState();
+}
+
+/******************/
+/* INITIALIZATION */
+/******************/
+
+doWhenPageLoaded(() => {
+    injectModeSelector();
+});