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/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;
+  }
+}