From 179923826fcf3af16a24e9d72e53e777cfbd8220 Mon Sep 17 00:00:00 2001
From: Dmitry Kolosov <mitrichius@gmail.com>
Date: Fri, 18 Feb 2022 14:40:24 +0300
Subject: [PATCH] Remove flash for dark theme on loading #139

---
 layouts/partials/head.html           |  17 ++++
 layouts/partials/theme-switcher.html | 114 +++++++++++++++------------
 2 files changed, 80 insertions(+), 51 deletions(-)

diff --git a/layouts/partials/head.html b/layouts/partials/head.html
index e62029c..4d5ff18 100644
--- a/layouts/partials/head.html
+++ b/layouts/partials/head.html
@@ -16,6 +16,23 @@
 {{ end -}}
 
 {{ partial "favicons.html" . }}
+
+<style>
+  body {
+    visibility: hidden;
+    opacity: 0;
+  }
+</style>
+
+<noscript>
+  <style>
+    body {
+      visibility: visible;
+      opacity: 1;
+    }
+  </style>
+</noscript>
+
 {{ partial "resource.html" (dict "context" . "type" "css" "filename" "css/main.css") }}
 
 {{ if .Site.Params.copyCodeButton | default true }}
diff --git a/layouts/partials/theme-switcher.html b/layouts/partials/theme-switcher.html
index 6ee5cef..f3eff3c 100644
--- a/layouts/partials/theme-switcher.html
+++ b/layouts/partials/theme-switcher.html
@@ -7,67 +7,79 @@
     <button class="theme-switcher">
         {{ i18n "darkTheme" }}
     </button>
+{{ end }}
 
-    <script>
-    const STORAGE_KEY = 'user-color-scheme'
-    const defaultTheme = {{ $style }}
+<script>
+const STORAGE_KEY = 'user-color-scheme'
+const defaultTheme = {{ $style }}
 
-    let currentTheme
-    let switchButton
-    let autoDefinedScheme = window.matchMedia('(prefers-color-scheme: dark)')
+let currentTheme
+let switchButton
+let autoDefinedScheme = window.matchMedia('(prefers-color-scheme: dark)')
 
-    const autoChangeScheme = e => {
-        currentTheme = e.matches ? 'dark' : 'light'
-        document.documentElement.setAttribute('data-theme', currentTheme)
-        changeButtonText()
+const autoChangeScheme = e => {
+    currentTheme = e.matches ? 'dark' : 'light'
+    document.documentElement.setAttribute('data-theme', currentTheme)
+    changeButtonText()
+}
+
+document.addEventListener('DOMContentLoaded', function() {
+    switchButton = document.querySelector('.theme-switcher')
+    currentTheme = detectCurrentScheme()
+    if (currentTheme == 'dark') {
+        document.documentElement.setAttribute('data-theme', 'dark')
+    }
+    if (currentTheme == 'auto') {
+        autoChangeScheme(autoDefinedScheme);
+        autoDefinedScheme.addListener(autoChangeScheme);
     }
 
-    document.addEventListener('DOMContentLoaded', function() {
-        switchButton = document.querySelector('.theme-switcher')
-        currentTheme = detectCurrentScheme()
-        if (currentTheme == 'dark') {
-            document.documentElement.setAttribute('data-theme', 'dark')
-        }
-        if (currentTheme == 'auto') {
-            autoChangeScheme(autoDefinedScheme);
-            autoDefinedScheme.addListener(autoChangeScheme);
-        }
+    if (switchButton) {
         changeButtonText()
         switchButton.addEventListener('click', switchTheme, false)
-    })
-
-    function detectCurrentScheme() {
-        if (localStorage.getItem(STORAGE_KEY)) {
-            return localStorage.getItem(STORAGE_KEY)
-        } 
-        if (defaultTheme) {
-            return defaultTheme
-        } 
-        if (!window.matchMedia) {
-            return 'light'
-        } 
-        if (window.matchMedia('(prefers-color-scheme: dark)').matches) {
-            return 'dark'
-        }
-        return 'light'
     }
+  
+    showContent()
+})
 
-    function changeButtonText()
-    {   
+function detectCurrentScheme() {
+    if (localStorage.getItem(STORAGE_KEY)) {
+        return localStorage.getItem(STORAGE_KEY)
+    } 
+    if (defaultTheme) {
+        return defaultTheme
+    } 
+    if (!window.matchMedia) {
+        return 'light'
+    } 
+    if (window.matchMedia('(prefers-color-scheme: dark)').matches) {
+        return 'dark'
+    }
+    return 'light'
+}
+
+function changeButtonText(switchButton)
+{   
+    if (switchButton) {
         switchButton.textContent = currentTheme == 'dark' ?  {{ i18n "lightTheme" }} : {{ i18n "darkTheme" }}
     }
+}
 
-    function switchTheme(e) {
-        if (currentTheme == 'dark') {
-            localStorage.setItem(STORAGE_KEY, 'light')
-            document.documentElement.setAttribute('data-theme', 'light')
-            currentTheme = 'light'
-        } else {
-            localStorage.setItem(STORAGE_KEY, 'dark')
-            document.documentElement.setAttribute('data-theme', 'dark')
-            currentTheme = 'dark'
-        }
-        changeButtonText()
+function switchTheme(e) {
+    if (currentTheme == 'dark') {
+        localStorage.setItem(STORAGE_KEY, 'light')
+        document.documentElement.setAttribute('data-theme', 'light')
+        currentTheme = 'light'
+    } else {
+        localStorage.setItem(STORAGE_KEY, 'dark')
+        document.documentElement.setAttribute('data-theme', 'dark')
+        currentTheme = 'dark'
     }
-    </script>
-{{ end }}
\ No newline at end of file
+    changeButtonText()
+}
+
+function showContent() {
+    document.body.style.visibility = 'visible';
+    document.body.style.opacity = 1;
+}
+</script>
\ No newline at end of file