From e1be63b1ca9982e86502f8454229462a0f2f59c1 Mon Sep 17 00:00:00 2001
From: Felix Schlusche <fschlusche@liva-pms.com>
Date: Thu, 23 Oct 2025 17:53:03 +0200
Subject: [PATCH] Add utility functions for date formatting, time rounding, and
 notifications

- Implemented functions to format dates between YYYY-MM-DD and DD.MM.YYYY
- Added functions to get today's date in ISO format
- Created functions to round time to the nearest 15 minutes
- Developed a function to format time as HH:MM
- Added a function to format duration in HH:MM:SS
- Implemented a toast notification system with auto-remove functionality
- Added functions to get day of the week and month names in German
---
 public/index.html             | 144 ++++++++++++++++++---------
 public/js/api.js              | 180 ++++++++++++++++++++++++++++++++++
 public/js/holidays.js         | 154 +++++++++++++++++++++++++++++
 public/{app.js => js/main.js} |   0
 public/js/utils.js            | 126 ++++++++++++++++++++++++
 5 files changed, 556 insertions(+), 48 deletions(-)
 create mode 100644 public/js/api.js
 create mode 100644 public/js/holidays.js
 rename public/{app.js => js/main.js} (100%)
 create mode 100644 public/js/utils.js

diff --git a/public/index.html b/public/index.html
index 280c5ba..e9d4435 100644
--- a/public/index.html
+++ b/public/index.html
@@ -258,6 +258,19 @@
       flex-shrink: 0;
     }
     
+    /* Details/Summary chevron rotation */
+    details[open] .details-chevron {
+      transform: rotate(180deg);
+    }
+    
+    details summary {
+      list-style: none;
+    }
+    
+    details summary::-webkit-details-marker {
+      display: none;
+    }
+    
     /* Blink animation for running timer icon */
     @keyframes blink {
       0%, 100% { opacity: 1; }
@@ -402,49 +415,57 @@
         </div>
       </div>
       
-      <!-- Date Range Filter -->
-      <div class="flex flex-wrap gap-4 items-end">
-        <div class="flex-1 min-w-[200px]">
-          <label for="filterFrom" class="block text-sm font-medium text-gray-300 mb-1">Von</label>
-          <input type="text" id="filterFrom" 
-            class="w-full px-4 py-2 border border-gray-600 bg-gray-700 text-gray-100 rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-transparent"
-            placeholder="DD.MM.YYYY">
-        </div>
-        
-        <div class="flex-1 min-w-[200px]">
-          <label for="filterTo" class="block text-sm font-medium text-gray-300 mb-1">Bis</label>
-          <input type="text" id="filterTo" 
-            class="w-full px-4 py-2 border border-gray-600 bg-gray-700 text-gray-100 rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-transparent"
-            placeholder="DD.MM.YYYY">
-        </div>
-        
-        <div class="flex gap-2">
-          <button id="btnFilter" 
-            class="inline-flex items-center justify-center w-10 h-10 bg-blue-600 text-white rounded-lg hover:bg-blue-700 transition-all duration-200 shadow-sm" title="Filtern">
-            <i data-lucide="search" class="w-5 h-5"></i>
-          </button>
+      <!-- CSV Filter & Export Section (Collapsible) -->
+      <details class="mt-4 pt-4 border-t border-gray-700">
+        <summary class="cursor-pointer text-gray-300 hover:text-gray-100 font-medium flex items-center gap-2 select-none">
+          <i data-lucide="chevron-down" class="w-5 h-5 transition-transform details-chevron"></i>
+          <i data-lucide="filter" class="w-5 h-5 text-blue-400"></i>
+          <span>CSV Filter & Export</span>
+        </summary>
+        <div class="mt-4 flex flex-wrap gap-4 items-end">
+          <div class="flex-1 min-w-[200px]">
+            <label for="filterFrom" class="block text-sm font-medium text-gray-300 mb-1">Von</label>
+            <input type="text" id="filterFrom" 
+              class="w-full px-4 py-2 border border-gray-600 bg-gray-700 text-gray-100 rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-transparent"
+              placeholder="DD.MM.YYYY">
+          </div>
           
-          <button id="btnClearFilter" 
-            class="inline-flex items-center justify-center w-10 h-10 bg-gray-700 text-gray-100 rounded-lg hover:bg-gray-600 transition-all duration-200 shadow-sm" title="Filter zurücksetzen">
-            <i data-lucide="x-circle" class="w-5 h-5"></i>
-          </button>
+          <div class="flex-1 min-w-[200px]">
+            <label for="filterTo" class="block text-sm font-medium text-gray-300 mb-1">Bis</label>
+            <input type="text" id="filterTo" 
+              class="w-full px-4 py-2 border border-gray-600 bg-gray-700 text-gray-100 rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-transparent"
+              placeholder="DD.MM.YYYY">
+          </div>
           
-          <button id="btnExport" 
-            class="inline-flex items-center justify-center w-10 h-10 bg-green-600 text-white rounded-lg hover:bg-green-700 transition-all duration-200 shadow-sm" title="Export (alle)">
-            <i data-lucide="download" class="w-5 h-5"></i>
-          </button>
-          
-          <button id="btnExportDeviations" 
-            class="inline-flex items-center justify-center w-10 h-10 bg-amber-600 text-white rounded-lg hover:bg-amber-700 transition-all duration-200 shadow-sm" title="Export (nur Abweichungen)">
-            <i data-lucide="alert-circle" class="w-5 h-5"></i>
-          </button>
+          <div class="flex gap-2">
+            <button id="btnFilter" 
+              class="inline-flex items-center justify-center w-10 h-10 bg-blue-600 text-white rounded-lg hover:bg-blue-700 transition-all duration-200 shadow-sm" title="Filtern">
+              <i data-lucide="search" class="w-5 h-5"></i>
+            </button>
+            
+            <button id="btnClearFilter" 
+              class="inline-flex items-center justify-center w-10 h-10 bg-gray-700 text-gray-100 rounded-lg hover:bg-gray-600 transition-all duration-200 shadow-sm" title="Filter zurücksetzen">
+              <i data-lucide="x-circle" class="w-5 h-5"></i>
+            </button>
+            
+            <button id="btnExport" 
+              class="inline-flex items-center justify-center w-10 h-10 bg-green-600 text-white rounded-lg hover:bg-green-700 transition-all duration-200 shadow-sm" title="Export (alle)">
+              <i data-lucide="download" class="w-5 h-5"></i>
+            </button>
+            
+            <button id="btnExportDeviations" 
+              class="inline-flex items-center justify-center w-10 h-10 bg-amber-600 text-white rounded-lg hover:bg-amber-700 transition-all duration-200 shadow-sm" title="Export (nur Abweichungen)">
+              <i data-lucide="alert-circle" class="w-5 h-5"></i>
+            </button>
+          </div>
         </div>
-      </div>
+      </details>
       
       <!-- Settings Section (Collapsible) -->
       <details class="mt-4 pt-4 border-t border-gray-700">
-        <summary class="cursor-pointer text-gray-300 hover:text-gray-100 font-medium text-sm flex items-center gap-2">
-          <span class="text-lg">⚙️</span>
+        <summary class="cursor-pointer text-gray-300 hover:text-gray-100 font-medium flex items-center gap-2 select-none">
+          <i data-lucide="chevron-down" class="w-5 h-5 transition-transform details-chevron"></i>
+          <i data-lucide="settings" class="w-5 h-5 text-purple-400"></i>
           <span>Einstellungen</span>
         </summary>
         <div class="mt-4 flex flex-wrap gap-4 items-center">
@@ -560,8 +581,9 @@
 
     <!-- Month Navigation -->
     <div class="mb-8 glass-card rounded-xl p-5 border border-gray-700/50">
-      <div class="flex items-center justify-between flex-wrap gap-4">
-        <div class="flex gap-3 flex-wrap">
+      <div class="grid grid-cols-1 lg:grid-cols-3 items-center gap-4">
+        <!-- Left: Action Buttons (hidden on mobile, shown on desktop at start) -->
+        <div class="hidden lg:flex gap-3 flex-wrap justify-start order-2 lg:order-1">
           <button id="btnToggleBulkEdit" 
             class="btn-elevated inline-flex items-center gap-2 px-5 py-3 bg-gradient-to-r from-gray-700 to-gray-600 text-gray-100 rounded-xl font-semibold" title="Mehrfachauswahl aktivieren">
             <i data-lucide="check-square" class="w-5 h-5"></i>
@@ -572,14 +594,10 @@
             <i data-lucide="calendar-check" class="w-5 h-5"></i>
             <span>Ausfüllen</span>
           </button>
-          <button id="btnExportPDF" 
-            class="btn-elevated inline-flex items-center gap-2 px-5 py-3 bg-gradient-to-r from-red-600 to-red-500 text-white rounded-xl font-semibold" title="Monat als PDF exportieren">
-            <i data-lucide="file-text" class="w-5 h-5"></i>
-            <span>PDF Export</span>
-          </button>
         </div>
         
-        <div id="monthNavigation" class="flex items-center gap-4">
+        <!-- Center: Month Navigation (always visible and centered) -->
+        <div id="monthNavigation" class="flex items-center justify-center gap-4 order-1 lg:order-2">
           <button id="btnPrevMonth" 
             class="btn-elevated inline-flex items-center justify-center w-12 h-12 bg-gradient-to-br from-gray-700 to-gray-600 text-gray-100 rounded-xl">
             <i data-lucide="chevron-left" class="w-6 h-6"></i>
@@ -593,7 +611,33 @@
           </button>
         </div>
         
-        <div class="w-48"></div> <!-- Spacer for alignment -->
+        <!-- Right: Export Button (hidden on mobile, shown on desktop at end) -->
+        <div class="hidden lg:flex justify-end order-3">
+          <button id="btnExportPDF" 
+            class="btn-elevated inline-flex items-center gap-2 px-5 py-3 bg-gradient-to-r from-red-600 to-red-500 text-white rounded-xl font-semibold" title="Monat als PDF exportieren">
+            <i data-lucide="file-text" class="w-5 h-5"></i>
+            <span>PDF Export</span>
+          </button>
+        </div>
+
+        <!-- Mobile Action Buttons (shown only on mobile, below navigation) -->
+        <div class="flex lg:hidden gap-3 flex-wrap justify-center order-3">
+          <button onclick="document.getElementById('btnToggleBulkEdit').click()"
+            class="btn-elevated inline-flex items-center gap-2 px-5 py-3 bg-gradient-to-r from-gray-700 to-gray-600 text-gray-100 rounded-xl font-semibold" title="Mehrfachauswahl aktivieren">
+            <i data-lucide="check-square" class="w-5 h-5"></i>
+            <span>Auswahl</span>
+          </button>
+          <button onclick="document.getElementById('btnAutoFill').click()"
+            class="btn-elevated inline-flex items-center gap-2 px-5 py-3 bg-gradient-to-r from-indigo-600 to-indigo-500 text-white rounded-xl font-semibold" title="Monat ausfüllen (8h)">
+            <i data-lucide="calendar-check" class="w-5 h-5"></i>
+            <span>Ausfüllen</span>
+          </button>
+          <button onclick="document.getElementById('btnExportPDF').click()"
+            class="btn-elevated inline-flex items-center gap-2 px-5 py-3 bg-gradient-to-r from-red-600 to-red-500 text-white rounded-xl font-semibold" title="Monat als PDF exportieren">
+            <i data-lucide="file-text" class="w-5 h-5"></i>
+            <span>PDF Export</span>
+          </button>
+        </div>
       </div>
     </div>
 
@@ -789,8 +833,12 @@
   <script src="https://cdnjs.cloudflare.com/ajax/libs/jspdf/2.5.1/jspdf.umd.min.js"></script>
   <script src="https://cdnjs.cloudflare.com/ajax/libs/jspdf-autotable/3.8.2/jspdf.plugin.autotable.min.js"></script>
   
-  <!-- App Logic -->
-  <script src="app.js"></script>
+  <!-- App Logic - Load in correct order -->
+  <script src="js/state.js"></script>
+  <script src="js/utils.js"></script>
+  <script src="js/holidays.js"></script>
+  <script src="js/api.js"></script>
+  <script src="js/main.js"></script>
   
   <!-- Initialize Lucide Icons -->
   <script>
diff --git a/public/js/api.js b/public/js/api.js
new file mode 100644
index 0000000..ef14175
--- /dev/null
+++ b/public/js/api.js
@@ -0,0 +1,180 @@
+/**
+ * API Functions
+ * Backend communication layer
+ */
+
+/**
+ * Fetch entries from backend
+ */
+async function fetchEntries(fromDate = null, toDate = null) {
+  try {
+    let url = '/api/entries';
+    const params = new URLSearchParams();
+    
+    if (fromDate) params.append('from', fromDate);
+    if (toDate) params.append('to', toDate);
+    
+    if (params.toString()) {
+      url += '?' + params.toString();
+    }
+    
+    const response = await fetch(url);
+    
+    if (!response.ok) {
+      throw new Error('Failed to fetch entries');
+    }
+    
+    const entries = await response.json();
+    return entries;
+  } catch (error) {
+    console.error('Error fetching entries:', error);
+    showNotification('Fehler beim Laden der Einträge', 'error');
+    return [];
+  }
+}
+
+/**
+ * Create a new entry
+ */
+async function createEntry(date, startTime, endTime, pauseMinutes, location) {
+  try {
+    const body = {
+      date: formatDateISO(date),
+      startTime,
+      endTime,
+      location: location || 'office'
+    };
+    
+    // Only include pauseMinutes if explicitly provided (not empty)
+    if (pauseMinutes !== null && pauseMinutes !== undefined && pauseMinutes !== '') {
+      body.pauseMinutes = parseInt(pauseMinutes);
+    }
+    
+    const response = await fetch('/api/entries', {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json'
+      },
+      body: JSON.stringify(body)
+    });
+    
+    if (!response.ok) {
+      const error = await response.json();
+      throw new Error(error.error || 'Failed to create entry');
+    }
+    
+    const entry = await response.json();
+    return entry;
+  } catch (error) {
+    console.error('Error creating entry:', error);
+    showNotification(error.message || 'Fehler beim Erstellen des Eintrags', 'error');
+    return null;
+  }
+}
+
+/**
+ * Update an existing entry
+ */
+async function updateEntry(id, date, startTime, endTime, pauseMinutes, location) {
+  try {
+    const body = {
+      date: formatDateISO(date),
+      startTime,
+      endTime,
+      location: location || 'office'
+    };
+    
+    // Only include pauseMinutes if explicitly provided (not empty)
+    if (pauseMinutes !== null && pauseMinutes !== undefined && pauseMinutes !== '') {
+      body.pauseMinutes = parseInt(pauseMinutes);
+    }
+    
+    const response = await fetch(`/api/entries/${id}`, {
+      method: 'PUT',
+      headers: {
+        'Content-Type': 'application/json'
+      },
+      body: JSON.stringify(body)
+    });
+    
+    if (!response.ok) {
+      const error = await response.json();
+      throw new Error(error.error || 'Failed to update entry');
+    }
+    
+    const entry = await response.json();
+    return entry;
+  } catch (error) {
+    console.error('Error updating entry:', error);
+    showNotification(error.message || 'Fehler beim Aktualisieren des Eintrags', 'error');
+    return null;
+  }
+}
+
+/**
+ * Delete an entry
+ */
+async function deleteEntry(id) {
+  try {
+    const response = await fetch(`/api/entries/${id}`, {
+      method: 'DELETE'
+    });
+    
+    if (!response.ok) {
+      throw new Error('Failed to delete entry');
+    }
+    
+    return true;
+  } catch (error) {
+    console.error('Error deleting entry:', error);
+    showNotification('Fehler beim Löschen des Eintrags', 'error');
+    return false;
+  }
+}
+
+/**
+ * Get a setting by key
+ */
+async function getSetting(key) {
+  try {
+    const response = await fetch(`/api/settings/${key}`);
+    
+    if (!response.ok) {
+      if (response.status === 404) {
+        return null; // Setting doesn't exist yet
+      }
+      throw new Error('Failed to get setting');
+    }
+    
+    const data = await response.json();
+    return data.value;
+  } catch (error) {
+    console.error('Error getting setting:', error);
+    return null;
+  }
+}
+
+/**
+ * Set a setting
+ */
+async function setSetting(key, value) {
+  try {
+    const response = await fetch('/api/settings', {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json'
+      },
+      body: JSON.stringify({ key, value })
+    });
+    
+    if (!response.ok) {
+      throw new Error('Failed to set setting');
+    }
+    
+    return true;
+  } catch (error) {
+    console.error('Error setting setting:', error);
+    showNotification('Fehler beim Speichern der Einstellung', 'error');
+    return false;
+  }
+}
diff --git a/public/js/holidays.js b/public/js/holidays.js
new file mode 100644
index 0000000..6669149
--- /dev/null
+++ b/public/js/holidays.js
@@ -0,0 +1,154 @@
+/**
+ * Holiday Functions
+ * German public holidays calculation and checking
+ */
+
+/**
+ * Check if date is weekend
+ */
+function isWeekend(date) {
+  const day = date.getDay();
+  return day === 0 || day === 6; // Sunday or Saturday
+}
+
+/**
+ * Calculate Easter Sunday for a given year (Gauss algorithm)
+ */
+function getEasterSunday(year) {
+  const a = year % 19;
+  const b = Math.floor(year / 100);
+  const c = year % 100;
+  const d = Math.floor(b / 4);
+  const e = b % 4;
+  const f = Math.floor((b + 8) / 25);
+  const g = Math.floor((b - f + 1) / 3);
+  const h = (19 * a + b - d - g + 15) % 30;
+  const i = Math.floor(c / 4);
+  const k = c % 4;
+  const l = (32 + 2 * e + 2 * i - h - k) % 7;
+  const m = Math.floor((a + 11 * h + 22 * l) / 451);
+  const month = Math.floor((h + l - 7 * m + 114) / 31);
+  const day = ((h + l - 7 * m + 114) % 31) + 1;
+  return new Date(year, month - 1, day);
+}
+
+/**
+ * Get all public holidays for a given year and Bundesland
+ */
+function getPublicHolidays(year, bundesland) {
+  const holidays = [];
+  
+  // Fixed holidays (all states)
+  holidays.push({ date: new Date(year, 0, 1), name: 'Neujahr' });
+  holidays.push({ date: new Date(year, 4, 1), name: 'Tag der Arbeit' });
+  holidays.push({ date: new Date(year, 9, 3), name: 'Tag der Deutschen Einheit' });
+  holidays.push({ date: new Date(year, 11, 25), name: '1. Weihnachtstag' });
+  holidays.push({ date: new Date(year, 11, 26), name: '2. Weihnachtstag' });
+  
+  // Heilige Drei Könige (BW, BY, ST)
+  if (['BW', 'BY', 'ST'].includes(bundesland)) {
+    holidays.push({ date: new Date(year, 0, 6), name: 'Heilige Drei Könige' });
+  }
+  
+  // Internationaler Frauentag (BE, MV since 2023)
+  if (['BE'].includes(bundesland) || (bundesland === 'MV' && year >= 2023)) {
+    holidays.push({ date: new Date(year, 2, 8), name: 'Internationaler Frauentag' });
+  }
+  
+  // Weltkindertag (TH since 2019)
+  if (bundesland === 'TH' && year >= 2019) {
+    holidays.push({ date: new Date(year, 8, 20), name: 'Weltkindertag' });
+  }
+  
+  // Reformationstag (BB, MV, SN, ST, TH, + HB, HH, NI, SH since 2018)
+  const reformationstagStates = ['BB', 'MV', 'SN', 'ST', 'TH'];
+  if (year >= 2018) {
+    reformationstagStates.push('HB', 'HH', 'NI', 'SH');
+  }
+  if (reformationstagStates.includes(bundesland)) {
+    holidays.push({ date: new Date(year, 9, 31), name: 'Reformationstag' });
+  }
+  
+  // Allerheiligen (BW, BY, NW, RP, SL)
+  if (['BW', 'BY', 'NW', 'RP', 'SL'].includes(bundesland)) {
+    holidays.push({ date: new Date(year, 10, 1), name: 'Allerheiligen' });
+  }
+  
+  // Buß- und Bettag (only SN)
+  if (bundesland === 'SN') {
+    // Buß- und Bettag is the Wednesday before November 23
+    let bussbettag = new Date(year, 10, 23);
+    while (bussbettag.getDay() !== 3) { // 3 = Wednesday
+      bussbettag.setDate(bussbettag.getDate() - 1);
+    }
+    bussbettag.setDate(bussbettag.getDate() - 7); // One week before
+    holidays.push({ date: bussbettag, name: 'Buß- und Bettag' });
+  }
+  
+  // Easter-dependent holidays
+  const easter = getEasterSunday(year);
+  
+  // Karfreitag (Good Friday) - 2 days before Easter (all states)
+  const goodFriday = new Date(easter);
+  goodFriday.setDate(easter.getDate() - 2);
+  holidays.push({ date: goodFriday, name: 'Karfreitag' });
+  
+  // Ostermontag (Easter Monday) - 1 day after Easter (all states)
+  const easterMonday = new Date(easter);
+  easterMonday.setDate(easter.getDate() + 1);
+  holidays.push({ date: easterMonday, name: 'Ostermontag' });
+  
+  // Christi Himmelfahrt (Ascension Day) - 39 days after Easter (all states)
+  const ascension = new Date(easter);
+  ascension.setDate(easter.getDate() + 39);
+  holidays.push({ date: ascension, name: 'Christi Himmelfahrt' });
+  
+  // Pfingstmontag (Whit Monday) - 50 days after Easter (all states)
+  const whitMonday = new Date(easter);
+  whitMonday.setDate(easter.getDate() + 50);
+  holidays.push({ date: whitMonday, name: 'Pfingstmontag' });
+  
+  // Fronleichnam (Corpus Christi) - 60 days after Easter (BW, BY, HE, NW, RP, SL, + some communities in SN, TH)
+  if (['BW', 'BY', 'HE', 'NW', 'RP', 'SL'].includes(bundesland)) {
+    const corpusChristi = new Date(easter);
+    corpusChristi.setDate(easter.getDate() + 60);
+    holidays.push({ date: corpusChristi, name: 'Fronleichnam' });
+  }
+  
+  // Mariä Himmelfahrt (Assumption of Mary) - August 15 (BY in some communities, SL)
+  if (['SL'].includes(bundesland)) {
+    holidays.push({ date: new Date(year, 7, 15), name: 'Mariä Himmelfahrt' });
+  }
+  
+  return holidays;
+}
+
+/**
+ * Check if date is a public holiday
+ * Returns the holiday name or null
+ */
+function getHolidayName(date) {
+  const year = date.getFullYear();
+  const holidays = getPublicHolidays(year, currentBundesland);
+  
+  const dateStr = date.toISOString().split('T')[0];
+  const holiday = holidays.find(h => {
+    return h.date.toISOString().split('T')[0] === dateStr;
+  });
+  
+  return holiday ? holiday.name : null;
+}
+
+/**
+ * Check if date is a public holiday
+ */
+function isPublicHoliday(date) {
+  return getHolidayName(date) !== null;
+}
+
+/**
+ * Check if date is weekend or public holiday
+ */
+function isWeekendOrHoliday(date) {
+  return isWeekend(date) || isPublicHoliday(date);
+}
diff --git a/public/app.js b/public/js/main.js
similarity index 100%
rename from public/app.js
rename to public/js/main.js
diff --git a/public/js/utils.js b/public/js/utils.js
new file mode 100644
index 0000000..f375718
--- /dev/null
+++ b/public/js/utils.js
@@ -0,0 +1,126 @@
+/**
+ * Utility Functions
+ * Date/Time formatting, rounding, duration formatting
+ */
+
+/**
+ * Format date from YYYY-MM-DD to DD.MM.YYYY
+ */
+function formatDateDisplay(dateStr) {
+  const [year, month, day] = dateStr.split('-');
+  return `${day}.${month}.${year}`;
+}
+
+/**
+ * Format date from DD.MM.YYYY to YYYY-MM-DD
+ */
+function formatDateISO(dateStr) {
+  const [day, month, year] = dateStr.split('.');
+  return `${year}-${month}-${day}`;
+}
+
+/**
+ * Get today's date in YYYY-MM-DD format
+ */
+function getTodayISO() {
+  const today = new Date();
+  const year = today.getFullYear();
+  const month = String(today.getMonth() + 1).padStart(2, '0');
+  const day = String(today.getDate()).padStart(2, '0');
+  return `${year}-${month}-${day}`;
+}
+
+/**
+ * Round time down to nearest 15 minutes
+ */
+function roundDownTo15Min(date) {
+  const minutes = date.getMinutes();
+  const roundedMinutes = Math.floor(minutes / 15) * 15;
+  date.setMinutes(roundedMinutes);
+  date.setSeconds(0);
+  date.setMilliseconds(0);
+  return date;
+}
+
+/**
+ * Round time up to nearest 15 minutes
+ */
+function roundUpTo15Min(date) {
+  const minutes = date.getMinutes();
+  const roundedMinutes = Math.ceil(minutes / 15) * 15;
+  date.setMinutes(roundedMinutes);
+  date.setSeconds(0);
+  date.setMilliseconds(0);
+  return date;
+}
+
+/**
+ * Format time as HH:MM
+ */
+function formatTime(date) {
+  const hours = String(date.getHours()).padStart(2, '0');
+  const minutes = String(date.getMinutes()).padStart(2, '0');
+  return `${hours}:${minutes}`;
+}
+
+/**
+ * Format seconds to HH:MM:SS
+ */
+function formatDuration(seconds) {
+  const hrs = Math.floor(seconds / 3600);
+  const mins = Math.floor((seconds % 3600) / 60);
+  const secs = seconds % 60;
+  return `${String(hrs).padStart(2, '0')}:${String(mins).padStart(2, '0')}:${String(secs).padStart(2, '0')}`;
+}
+
+/**
+ * Show toast notification
+ */
+function showNotification(message, type = 'info') {
+  const container = document.getElementById('toastContainer');
+  
+  // Create toast element
+  const toast = document.createElement('div');
+  toast.className = `toast toast-${type}`;
+  
+  // Icon based on type
+  const icons = {
+    success: '✓',
+    error: '✕',
+    info: 'ℹ'
+  };
+  
+  toast.innerHTML = `
+    <span class="toast-icon">${icons[type] || 'ℹ'}</span>
+    <span>${message}</span>
+  `;
+  
+  container.appendChild(toast);
+  
+  // Auto-remove after 3 seconds
+  setTimeout(() => {
+    toast.classList.add('hiding');
+    setTimeout(() => {
+      container.removeChild(toast);
+    }, 300);
+  }, 3000);
+}
+
+/**
+ * Get day of week abbreviation in German
+ */
+function getDayOfWeek(date) {
+  const days = ['So', 'Mo', 'Di', 'Mi', 'Do', 'Fr', 'Sa'];
+  return days[date.getDay()];
+}
+
+/**
+ * Get month name in German
+ */
+function getMonthName(month) {
+  const months = [
+    'Januar', 'Februar', 'März', 'April', 'Mai', 'Juni',
+    'Juli', 'August', 'September', 'Oktober', 'November', 'Dezember'
+  ];
+  return months[month];
+}