[TASK] add color switch option btn

frontend/main.ts

@@ -8,6 +8,8 @@ export interface choiceMap {
 let choiceObjects: choiceMap = {};
 
 document.addEventListener('DOMContentLoaded', function() {
+  changeTheme();
+  initcolorTheme();
   initSearch();
   initSidebar();
   initToggle();
@@ -20,6 +22,75 @@ document.addEventListener('DOMContentLoaded', function() {
   setCurrentdate(<HTMLInputElement>document.querySelector('#departure'));
 });
 
+function changeTheme() {
+  let toggleBtn = <HTMLElement>document.querySelector('#theme-toggle-js');
+
+  if(toggleBtn) {
+    toggleBtn.addEventListener('click', function() {
+      if(toggleBtn.dataset.theme === 'light') {
+        setTheme('dark', true);
+      } else {
+        setTheme('light', true);
+      }
+    });
+  } 
+}
+
+/***
+* init javascript
+* 1) detect native color scheme or use set theme in local storage
+* 2) detect view (desktop or responsive) if on mobile device with touch screen
+* 3) set base font size to 112.5% -> 18px
+*/
+function initcolorTheme() {
+  colorThemeWatcher();
+  let theme = localStorage.getItem('theme');
+  if (theme == null || theme === 'auto') {
+      if (window.matchMedia && window.matchMedia('(prefers-color-scheme: dark)').matches) {
+          setTheme('dark', false);
+      } else {
+          setTheme('light', false);
+      }
+  } else {
+      setTheme(theme)
+  }
+}
+
+/***
+* Listener operating system native color configuration
+*/
+function colorThemeWatcher() {
+  try {
+      window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', e => {
+          setTheme(e.matches ? 'dark' : 'light');
+      });
+  } catch {
+      console.warn('color theme watcher not supported');
+  }
+}
+
+/**
+* Define color scheme, colors without losing the base font size configuration
+* and add data-theme to html tag
+* @param theme
+*/
+function setTheme(theme: string, setLocalStorage = true) {
+  let toggleBtn = document.querySelector('#theme-toggle-js');
+
+  if(toggleBtn) {
+    if (setLocalStorage) {
+      localStorage.setItem('theme', theme);
+    }
+    toggleBtn.setAttribute('data-theme', theme);
+
+    if (document.documentElement.classList.contains('dark') && theme === 'light') {
+        document.documentElement.classList.remove('dark');
+    } else if(theme === 'dark'){
+        document.documentElement.classList.add('dark');
+    }
+  }
+}
+
 function setCurrentdate(input: HTMLInputElement) {
   if(input) {
           const now = new Date();

frontend/tailwind.config.cjs

@@ -41,5 +41,6 @@ export default {
   },
   plugins: [],
   important: true,
+  darkMode: 'class',
 }