Added default theme (#960)

* feat: Added default theme

* Revert "feat: Added default theme"

This reverts commit a11a99f92a.

* feat: Add basic theme feature

* feat: Add theme settings

* fix: Fix default theme value

* fix: Fix CR and doc-string

* Comment out darkMode on exampleSite/hugo.yaml

Signed-off-by: hossainemruz <hossainemruz@gmail.com>

---------

Signed-off-by: hossainemruz <hossainemruz@gmail.com>
Co-authored-by: Emruz Hossain <hossainemruz@gmail.com>

assets/scripts/features/index.js

@@ -10,6 +10,10 @@ if (process.env.FEATURE_DARKMODE === '1') {
   import('./darkmode')
 }
 
+if (process.env.FEATURE_THEME === '1') {
+  import('./theme')
+}
+
 if (process.env.FEATURE_FLOWCHART === '1') {
   import('./flowchart')
 }

assets/scripts/features/theme/index.js

@@ -0,0 +1,88 @@
+import * as params from '@params';
+const PERSISTENCE_KEY = 'theme-scheme'
+
+const themeOptions = params.theme || {}
+const THEME_DARK = typeof themeOptions.dark === 'undefined' ? true : themeOptions.dark;
+const THEME_LIGHT = typeof themeOptions.light === 'undefined' ? true : themeOptions.light;
+const THEME_DEFAULT = typeof themeOptions.default === 'undefined' ? "system" : themeOptions.default;
+
+window.addEventListener('load', async () => {
+  const menu = document.getElementById('themeMenu')
+  const $icon = document.getElementById('navbar-theme-icon-svg')
+  if (menu == null || $icon == null) return
+
+  const btns = menu.getElementsByTagName('a')
+  const iconMap = Array.from(btns).reduce((map, btn) => {
+    const $img = btn.getElementsByTagName('img')[0]
+    map[btn.dataset.scheme] = $img.src
+    return map
+  }, {})
+
+
+  function checkScheme(scheme) {
+    if (THEME_LIGHT === false) return "dark"
+    if (THEME_DARK === false) return "light"
+    return scheme
+  }
+
+  function loadScheme() {
+    return localStorage.getItem(PERSISTENCE_KEY) || loadDefaultScheme()
+  }
+
+  function loadDefaultScheme() {
+    return THEME_DEFAULT || "system"
+  }
+
+  function saveScheme(scheme) {
+    localStorage.setItem(PERSISTENCE_KEY, scheme)
+  }
+
+  function getPreferredColorScheme() {
+    const isDarkMode = window.matchMedia("(prefers-color-scheme: dark)").matches;
+    return isDarkMode ? "dark" : "light";
+  }
+
+  function setScheme(newScheme) {
+    let theme = newScheme
+    if (newScheme === 'system') {
+      theme = getPreferredColorScheme()
+    }
+    // set data-theme attribute on html tag
+    document.querySelector("html").dataset.theme = theme;
+
+    // update icon
+    $icon.src = iconMap[newScheme]
+
+    // save preference to local storage
+    saveScheme(newScheme)
+  
+    setImages(theme)
+  }
+
+  const checkedScheme = checkScheme(loadScheme())
+  setScheme(checkedScheme)
+
+  Array.from(menu.getElementsByTagName('a')).forEach((btn) => {
+    btn.addEventListener('click', () => {
+      const { scheme } = btn.dataset
+      setScheme(scheme)
+    })
+  })
+})
+
+function setImages(newScheme) {
+  const els = Array.from(document.getElementsByClassName('logo-holder'));
+  for (const el of els) {
+    const light = el.querySelector('.light-logo');
+    const dark = el.querySelector('.dark-logo');
+
+    if (newScheme === "dark" && dark !== null) {
+      if (light !== null) light.style.display = 'none'
+      dark.style.display = 'inline'
+    }
+    else {
+      if (light !== null) light.style.display = 'inline'
+      if (dark !== null) dark.style.display = 'none'
+    }
+  }
+}