New plugin: Allow switching light and dark mode (fix #926)

plugins/dark-switcher.php

@@ -0,0 +1,41 @@
+<?php
+
+/** Allow switching light and dark mode
+* @link https://www.adminer.org/plugins/#use
+* @author Jakub Vrana, https://www.vrana.cz/
+* @license https://www.apache.org/licenses/LICENSE-2.0 Apache License, Version 2.0
+* @license https://www.gnu.org/licenses/gpl-2.0.html GNU General Public License, version 2 (one or other)
+*/
+class AdminerDarkSwitcher {
+
+	function head($dark = null) {
+		?>
+<script <?php echo Adminer\nonce(); ?>>
+let adminerDark;
+
+function adminerDarkSwitch() {
+	adminerDark = !adminerDark;
+	adminerDarkSet();
+}
+
+function adminerDarkSet() {
+	qsa('link[href$="dark.css"]').forEach(link => link.media = (adminerDark ? '' : 'never'));
+	qs('meta[name="color-scheme"]').content = (adminerDark ? 'dark' : 'light');
+	cookie('adminer_dark=' + (adminerDark ? 1 : 0), 30);
+}
+
+const saved = document.cookie.match(/adminer_dark=(\d)/);
+if (saved) {
+	adminerDark = +saved[1];
+	adminerDarkSet();
+}
+</script>
+<?php
+	}
+
+	function navigation($missing) {
+		echo "<label style='position: fixed; bottom: .5em; right: .5em;'><input type='checkbox'> dark</label>"
+			. Adminer\script("if (adminerDark != null) adminerDarkSet(); mixin(qsl('input'), {onclick: adminerDarkSwitch, checked: adminerDark});") . "\n"
+		;
+	}
+}