From fb33ea8144442b6fc4ad29e77a69fec29b169c4e Mon Sep 17 00:00:00 2001
From: Felix Schlusche <fschlusche@liva-pms.com>
Date: Fri, 24 Oct 2025 19:12:47 +0200
Subject: [PATCH] feat: add bridge days recommendations feature with display
 and calculation logic

---
 public/index.html        |  21 +++
 public/js/bridge-days.js | 219 +++++++++++++++++++++++++++++++
 public/js/main.js        | 269 +++++++++++++++++++++++++++++++--------
 3 files changed, 453 insertions(+), 56 deletions(-)
 create mode 100644 public/js/bridge-days.js

diff --git a/public/index.html b/public/index.html
index d80aa0d..f1f9ff5 100644
--- a/public/index.html
+++ b/public/index.html
@@ -263,6 +263,10 @@
       transform: rotate(180deg);
     }
     
+    .details-chevron {
+      transition: transform 0.2s ease;
+    }
+    
     details summary {
       list-style: none;
     }
@@ -677,6 +681,22 @@
       </div>
     </div>
 
+    <!-- Bridge Days Recommendations -->
+    <details id="bridgeDaysContainer" class="mb-6 glass-card rounded-xl border border-cyan-600/30 hidden">
+      <summary class="cursor-pointer p-4 hover:bg-gray-700/30 rounded-t-xl transition-colors select-none">
+        <div class="flex items-center gap-2">
+          <i data-lucide="lightbulb" class="w-5 h-5 text-cyan-400"></i>
+          <h3 class="text-sm font-semibold text-cyan-400 uppercase tracking-wide">Brückentags-Empfehlungen</h3>
+          <i data-lucide="chevron-down" class="w-4 h-4 text-gray-400 ml-auto details-chevron"></i>
+        </div>
+      </summary>
+      <div class="p-4 pt-2">
+        <div id="bridgeDaysList" class="space-y-2">
+          <!-- Will be populated by JavaScript -->
+        </div>
+      </div>
+    </details>
+
     <!-- Bulk Edit Actions Bar -->
     <div id="bulkEditBar" class="hidden mb-6 bg-gray-800 rounded-lg shadow p-4 border border-gray-700">
       <div class="flex items-center justify-between flex-wrap gap-3">
@@ -878,6 +898,7 @@
   <script src="js/state.js"></script>
   <script src="js/utils.js"></script>
   <script src="js/holidays.js"></script>
+  <script src="js/bridge-days.js"></script>
   <script src="js/api.js"></script>
   <script src="js/main.js"></script>
   
diff --git a/public/js/bridge-days.js b/public/js/bridge-days.js
new file mode 100644
index 0000000..d0a7d80
--- /dev/null
+++ b/public/js/bridge-days.js
@@ -0,0 +1,219 @@
+/**
+ * Bridge Days Calculator
+ * Calculates optimal vacation days based on public holidays
+ */
+
+/**
+ * Calculate bridge days and optimal vacation periods for a month
+ * @param {number} year - The year to calculate for
+ * @param {number} month - The month (0-11)
+ * @param {string} bundesland - The German state code
+ * @returns {Array} Array of bridge day recommendations
+ */
+function calculateBridgeDays(year, month, bundesland) {
+  const recommendations = [];
+  
+  // Get all holidays for the year
+  const holidays = getPublicHolidays(year, bundesland);
+  
+  // Create a calendar map for the entire year
+  const calendar = createYearCalendar(year, holidays);
+  
+  // Find all work day blocks (consecutive work days between weekends/holidays)
+  const workBlocks = findWorkDayBlocks(calendar);
+  
+  // Evaluate each block and calculate benefit
+  workBlocks.forEach(block => {
+    const benefit = evaluateBlock(block, calendar);
+    if (benefit.ratio >= 2.0) { // Only show if at least 2x benefit
+      recommendations.push(benefit);
+    }
+  });
+  
+  // Sort by benefit ratio (best deals first)
+  recommendations.sort((a, b) => b.ratio - a.ratio);
+  
+  // Filter for the specific month
+  const monthRecommendations = recommendations.filter(rec => {
+    const startDate = new Date(rec.startDate);
+    return startDate.getMonth() === month && startDate.getFullYear() === year;
+  });
+  
+  return monthRecommendations;
+}
+
+/**
+ * Create a calendar map for the entire year
+ * @param {number} year - The year
+ * @param {Array} holidays - Array of holiday objects
+ * @returns {Map} Map of date strings to day types
+ */
+function createYearCalendar(year, holidays) {
+  const calendar = new Map();
+  
+  // Create holiday map for fast lookup
+  const holidayMap = new Map();
+  holidays.forEach(h => {
+    const dateStr = formatDateKey(h.date);
+    holidayMap.set(dateStr, h.name);
+  });
+  
+  // Process each day of the year
+  for (let month = 0; month < 12; month++) {
+    const daysInMonth = new Date(year, month + 1, 0).getDate();
+    
+    for (let day = 1; day <= daysInMonth; day++) {
+      const date = new Date(year, month, day);
+      const dateStr = formatDateKey(date);
+      const dayOfWeek = date.getDay();
+      
+      let type;
+      if (holidayMap.has(dateStr)) {
+        type = { status: 'HOLIDAY', name: holidayMap.get(dateStr) };
+      } else if (dayOfWeek === 0 || dayOfWeek === 6) {
+        type = { status: 'WEEKEND' };
+      } else {
+        type = { status: 'WORKDAY' };
+      }
+      
+      calendar.set(dateStr, type);
+    }
+  }
+  
+  return calendar;
+}
+
+/**
+ * Format date as YYYY-MM-DD
+ */
+function formatDateKey(date) {
+  const year = date.getFullYear();
+  const month = String(date.getMonth() + 1).padStart(2, '0');
+  const day = String(date.getDate()).padStart(2, '0');
+  return `${year}-${month}-${day}`;
+}
+
+/**
+ * Find all work day blocks in the calendar
+ * @param {Map} calendar - The calendar map
+ * @returns {Array} Array of work day blocks
+ */
+function findWorkDayBlocks(calendar) {
+  const blocks = [];
+  let currentBlock = null;
+  
+  // Sort dates for sequential processing
+  const sortedDates = Array.from(calendar.keys()).sort();
+  
+  sortedDates.forEach(dateStr => {
+    const dayType = calendar.get(dateStr);
+    
+    if (dayType.status === 'WORKDAY') {
+      if (!currentBlock) {
+        currentBlock = {
+          startDate: dateStr,
+          endDate: dateStr,
+          days: [dateStr]
+        };
+      } else {
+        currentBlock.endDate = dateStr;
+        currentBlock.days.push(dateStr);
+      }
+    } else {
+      if (currentBlock) {
+        blocks.push(currentBlock);
+        currentBlock = null;
+      }
+    }
+  });
+  
+  // Don't forget the last block
+  if (currentBlock) {
+    blocks.push(currentBlock);
+  }
+  
+  return blocks;
+}
+
+/**
+ * Evaluate a work day block and calculate benefit
+ * @param {Object} block - The work day block
+ * @param {Map} calendar - The calendar map
+ * @returns {Object} Benefit information
+ */
+function evaluateBlock(block, calendar) {
+  const vacationDaysNeeded = block.days.length;
+  
+  // Find the extended free period (including surrounding weekends/holidays)
+  let startDate = new Date(block.startDate);
+  let endDate = new Date(block.endDate);
+  
+  // Extend backwards to include preceding weekends/holidays
+  let currentDate = new Date(startDate);
+  currentDate.setDate(currentDate.getDate() - 1);
+  while (true) {
+    const dateStr = formatDateKey(currentDate);
+    const dayType = calendar.get(dateStr);
+    if (!dayType || dayType.status === 'WORKDAY') break;
+    startDate = new Date(currentDate);
+    currentDate.setDate(currentDate.getDate() - 1);
+  }
+  
+  // Extend forwards to include following weekends/holidays
+  currentDate = new Date(endDate);
+  currentDate.setDate(currentDate.getDate() + 1);
+  while (true) {
+    const dateStr = formatDateKey(currentDate);
+    const dayType = calendar.get(dateStr);
+    if (!dayType || dayType.status === 'WORKDAY') break;
+    endDate = new Date(currentDate);
+    currentDate.setDate(currentDate.getDate() + 1);
+  }
+  
+  // Calculate total free days
+  const totalFreeDays = Math.floor((endDate - startDate) / (1000 * 60 * 60 * 24)) + 1;
+  
+  // Calculate benefit ratio
+  const ratio = totalFreeDays / vacationDaysNeeded;
+  
+  // Find holidays in the period for description
+  const holidaysInPeriod = [];
+  currentDate = new Date(startDate);
+  while (currentDate <= endDate) {
+    const dateStr = formatDateKey(currentDate);
+    const dayType = calendar.get(dateStr);
+    if (dayType && dayType.status === 'HOLIDAY') {
+      holidaysInPeriod.push(dayType.name);
+    }
+    currentDate.setDate(currentDate.getDate() + 1);
+  }
+  
+  return {
+    startDate: formatDateKey(startDate),
+    endDate: formatDateKey(endDate),
+    vacationDays: block.days,
+    vacationDaysNeeded: vacationDaysNeeded,
+    totalFreeDays: totalFreeDays,
+    ratio: ratio,
+    holidays: holidaysInPeriod
+  };
+}
+
+/**
+ * Get a human-readable description for a bridge day recommendation
+ * @param {Object} recommendation - The recommendation object
+ * @returns {string} Description text
+ */
+function getBridgeDayDescription(recommendation) {
+  const { vacationDaysNeeded, totalFreeDays, ratio, holidays } = recommendation;
+  
+  let description = `${vacationDaysNeeded} Urlaubstag${vacationDaysNeeded > 1 ? 'e' : ''} für ${totalFreeDays} freie Tage`;
+  
+  if (holidays.length > 0) {
+    description += ` (inkl. ${holidays.join(', ')})`;
+  }
+  
+  description += ` - ${ratio.toFixed(1)}x Ertrag`;
+  
+  return description;
+}
diff --git a/public/js/main.js b/public/js/main.js
index 5ea91a9..6a4badd 100644
--- a/public/js/main.js
+++ b/public/js/main.js
@@ -1282,6 +1282,7 @@ async function loadMonthlyView() {
   renderMonthlyView(entries);
   updateMonthDisplay();
   updateStatistics(entries);
+  updateBridgeDaysDisplay();
   
   // Show/hide PDF export button based on whether month is complete
   const today = new Date();
@@ -1531,6 +1532,116 @@ async function updateVacationStatistics() {
   document.getElementById('statVacationRemaining').textContent = `${vacationRemaining} / ${totalVacationDays}`;
 }
 
+/**
+ * Update bridge days display for current month
+ */
+function updateBridgeDaysDisplay() {
+  const container = document.getElementById('bridgeDaysContainer');
+  const list = document.getElementById('bridgeDaysList');
+  
+  // Calculate bridge days for current month
+  const recommendations = calculateBridgeDays(displayYear, displayMonth, currentBundesland);
+  
+  if (recommendations.length === 0) {
+    container.classList.add('hidden');
+    return;
+  }
+  
+  // Show container and populate list
+  container.classList.remove('hidden');
+  list.innerHTML = '';
+  
+  recommendations.forEach((rec, index) => {
+    const startDate = new Date(rec.startDate);
+    const endDate = new Date(rec.endDate);
+    
+    const item = document.createElement('div');
+    item.className = 'flex items-start gap-3 p-3 bg-gray-800/50 rounded-lg border border-cyan-600/20 hover:border-cyan-600/40 transition-colors';
+    
+    // Format date range
+    const startStr = formatDateDisplay(rec.startDate);
+    const endStr = formatDateDisplay(rec.endDate);
+    
+    // Create vacation days list
+    const vacDaysList = rec.vacationDays.map(d => {
+      const date = new Date(d);
+      return `${date.getDate()}.${String(date.getMonth() + 1).padStart(2, '0')}.`;
+    }).join(', ');
+    
+    item.innerHTML = `
+      <div class="flex-shrink-0 w-8 h-8 rounded-full bg-cyan-600/20 flex items-center justify-center text-cyan-400 font-bold text-sm">
+        ${Math.round(rec.ratio)}x
+      </div>
+      <div class="flex-1 min-w-0">
+        <div class="text-sm font-medium text-gray-200">
+          ${startStr} - ${endStr}
+        </div>
+        <div class="text-xs text-gray-400 mt-1">
+          ${rec.vacationDaysNeeded} Urlaubstag${rec.vacationDaysNeeded > 1 ? 'e' : ''} (${vacDaysList}) für ${rec.totalFreeDays} freie Tage
+        </div>
+        ${rec.holidays.length > 0 ? `
+          <div class="text-xs text-cyan-400 mt-1">
+            ${rec.holidays.join(', ')}
+          </div>
+        ` : ''}
+      </div>
+      <button class="btn-add-bridge-days flex-shrink-0 px-3 py-1 bg-cyan-600 hover:bg-cyan-700 text-white text-xs rounded transition-colors" 
+              data-days='${JSON.stringify(rec.vacationDays)}' 
+              title="Als Urlaub eintragen">
+        <i data-lucide="calendar-plus" class="w-3 h-3"></i>
+      </button>
+    `;
+    
+    list.appendChild(item);
+  });
+  
+  // Re-initialize icons
+  if (typeof lucide !== 'undefined' && lucide.createIcons) {
+    lucide.createIcons();
+  }
+  
+  // Add event listeners for quick add buttons
+  document.querySelectorAll('.btn-add-bridge-days').forEach(btn => {
+    btn.addEventListener('click', async () => {
+      const days = JSON.parse(btn.dataset.days);
+      await addBridgeDaysAsVacation(days);
+    });
+  });
+}
+
+/**
+ * Add bridge days as vacation entries
+ */
+async function addBridgeDaysAsVacation(days) {
+  let created = 0;
+  let skipped = 0;
+  
+  for (const dateStr of days) {
+    try {
+      const response = await fetch('/api/entries', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({
+          date: dateStr,
+          entryType: 'vacation'
+        })
+      });
+      
+      if (response.ok) {
+        created++;
+      } else {
+        skipped++;
+      }
+    } catch (error) {
+      console.error('Error creating vacation entry:', error);
+      skipped++;
+    }
+  }
+  
+  await reloadView();
+  showNotification(`✓ ${created} Urlaubstag${created > 1 ? 'e' : ''} eingetragen${skipped > 0 ? `, ${skipped} übersprungen` : ''}`, 'success');
+}
+
 /**
  * Calculate balance from all previous months (starting from first month with entries)
  */
@@ -2696,7 +2807,65 @@ async function handleBundeslandChange(event) {
   const newBundesland = event.target.value;
   const oldBundesland = currentBundesland;
   
-  // Show warning with backup recommendation
+  // Check for conflicts with existing entries first
+  const entries = await fetchEntries();
+  const conflicts = [];
+  
+  // Get old and new holidays for comparison
+  const currentYear = new Date().getFullYear();
+  const years = [currentYear - 1, currentYear, currentYear + 1];
+  
+  const oldHolidays = new Set();
+  const newHolidays = new Set();
+  
+  years.forEach(year => {
+    getPublicHolidays(year, oldBundesland).forEach(h => {
+      // Convert to YYYY-MM-DD format for comparison
+      const year = h.date.getFullYear();
+      const month = String(h.date.getMonth() + 1).padStart(2, '0');
+      const day = String(h.date.getDate()).padStart(2, '0');
+      oldHolidays.add(`${year}-${month}-${day}`);
+    });
+    getPublicHolidays(year, newBundesland).forEach(h => {
+      // Convert to YYYY-MM-DD format for comparison
+      const year = h.date.getFullYear();
+      const month = String(h.date.getMonth() + 1).padStart(2, '0');
+      const day = String(h.date.getDate()).padStart(2, '0');
+      const dateKey = `${year}-${month}-${day}`;
+      newHolidays.add(dateKey);
+    });
+  });
+  
+  // Create a map of new holidays with their names
+  const newHolidayMap = new Map();
+  years.forEach(year => {
+    getPublicHolidays(year, newBundesland).forEach(h => {
+      const year = h.date.getFullYear();
+      const month = String(h.date.getMonth() + 1).padStart(2, '0');
+      const day = String(h.date.getDate()).padStart(2, '0');
+      const dateKey = `${year}-${month}-${day}`;
+      newHolidayMap.set(dateKey, h.name);
+    });
+  });
+  
+  // Find dates that are holidays in new state but not in old state, and have entries
+  entries.forEach(entry => {
+    if (newHolidays.has(entry.date) && !oldHolidays.has(entry.date)) {
+      conflicts.push({
+        date: entry.date,
+        displayDate: formatDateDisplay(entry.date),
+        holidayName: newHolidayMap.get(entry.date)
+      });
+    }
+  });
+  
+  // If no conflicts, change directly without warning
+  if (conflicts.length === 0) {
+    await performBundeslandChange(newBundesland, oldBundesland, event);
+    return;
+  }
+  
+  // Show warning with backup recommendation only if conflicts exist
   const bundeslandNames = {
     'BW': 'Baden-Württemberg',
     'BY': 'Bayern',
@@ -2716,17 +2885,23 @@ async function handleBundeslandChange(event) {
     'TH': 'Thüringen'
   };
   
+  const conflictList = conflicts.map(c => `<li class="text-sm">• ${c.displayDate} (<span class="text-yellow-300">${c.holidayName}</span>)</li>`).join('');
+  
   // Create custom modal for bundesland change confirmation
   const modalHTML = `
     <div id="bundeslandWarningModal" class="fixed inset-0 bg-black bg-opacity-50 flex items-center justify-center z-50" style="display: flex;">
       <div class="bg-gray-800 rounded-xl shadow-2xl p-6 max-w-md w-full mx-4 border border-yellow-600">
         <div class="flex items-center gap-3 mb-4">
           <i data-lucide="alert-triangle" class="w-8 h-8 text-yellow-500"></i>
-          <h3 class="text-xl font-bold text-yellow-500">Achtung: Bundesland ändern</h3>
+          <h3 class="text-xl font-bold text-yellow-500">Achtung: Konflikte gefunden</h3>
         </div>
         <div class="text-gray-300 mb-6 space-y-3">
           <p>Sie möchten das Bundesland von <strong>${bundeslandNames[oldBundesland]}</strong> auf <strong>${bundeslandNames[newBundesland]}</strong> ändern.</p>
-          <p class="text-yellow-400"><strong>Warnung:</strong> Durch die Änderung der Feiertage können bestehende Einträge betroffen sein. An Tagen, die zu Feiertagen werden, bleiben Arbeitseinträge erhalten.</p>
+          <p class="text-yellow-400"><strong>Warnung:</strong> Die folgenden Tage werden zu Feiertagen und haben bereits Einträge:</p>
+          <ul class="bg-gray-900 rounded-lg p-3 max-h-40 overflow-y-auto">
+            ${conflictList}
+          </ul>
+          <p class="text-sm text-gray-400">Die Einträge bleiben erhalten, aber die Tage werden als Feiertage markiert.</p>
           <div class="bg-gray-900 border border-blue-600 rounded-lg p-3 mt-4">
             <p class="text-blue-400 text-sm mb-2"><i data-lucide="info" class="w-4 h-4 inline mr-1"></i> Wir empfehlen ein Backup vor der Änderung:</p>
             <button id="quickBackupBtn" class="w-full flex items-center justify-center gap-2 px-4 py-2 bg-blue-600 hover:bg-blue-700 text-white rounded-lg transition-colors text-sm">
@@ -2780,59 +2955,6 @@ async function handleBundeslandChange(event) {
  * Perform the actual bundesland change after confirmation
  */
 async function performBundeslandChange(newBundesland, oldBundesland, event) {
-  // Check for conflicts with existing entries
-  const entries = await fetchEntries();
-  const conflicts = [];
-  
-  // Get old and new holidays for comparison
-  const currentYear = new Date().getFullYear();
-  const years = [currentYear - 1, currentYear, currentYear + 1];
-  
-  const oldHolidays = new Set();
-  const newHolidays = new Set();
-  
-  years.forEach(year => {
-    getPublicHolidays(year, oldBundesland).forEach(h => {
-      oldHolidays.add(h.date.toISOString().split('T')[0]);
-    });
-    getPublicHolidays(year, newBundesland).forEach(h => {
-      newHolidays.add(h.date.toISOString().split('T')[0]);
-    });
-  });
-  
-  // Find dates that are holidays in new state but not in old state, and have entries
-  entries.forEach(entry => {
-    if (newHolidays.has(entry.date) && !oldHolidays.has(entry.date)) {
-      const dateObj = new Date(entry.date);
-      // Temporarily set to new bundesland to get holiday name
-      const tempBundesland = currentBundesland;
-      currentBundesland = newBundesland;
-      const holidayName = getHolidayName(dateObj);
-      currentBundesland = tempBundesland;
-      
-      conflicts.push({
-        date: entry.date,
-        displayDate: formatDateDisplay(entry.date),
-        holidayName: holidayName
-      });
-    }
-  });
-  
-  // Show conflict info if exists
-  if (conflicts.length > 0) {
-    const conflictList = conflicts.map(c => `  • ${c.displayDate} (${c.holidayName})`).join('\n');
-    const message = `Folgende Tage werden zu Feiertagen und haben bereits Einträge:\n\n${conflictList}\n\nDie Einträge bleiben erhalten.`;
-    showNotification(`⚠️ ${conflicts.length} Konflikt(e) gefunden`, 'warning');
-    console.info(message);
-  }
-  
-  // Update state and save
-  currentBundesland = newBundesland;
-  await setSetting('bundesland', newBundesland);
-  
-  // Reload view to show updated holidays
-  await reloadView();
-  
   const bundeslandNames = {
     'BW': 'Baden-Württemberg',
     'BY': 'Bayern',
@@ -2852,6 +2974,13 @@ async function performBundeslandChange(newBundesland, oldBundesland, event) {
     'TH': 'Thüringen'
   };
   
+  // Update state and save
+  currentBundesland = newBundesland;
+  await setSetting('bundesland', newBundesland);
+  
+  // Reload view to show updated holidays
+  await reloadView();
+  
   showNotification(`✓ Bundesland auf ${bundeslandNames[newBundesland]} gesetzt`, 'success');
 }
 
@@ -2915,6 +3044,34 @@ async function handleVacationDaysChange(event) {
     return;
   }
   
+  // Check for conflicts: More vacation days already taken/planned than new value?
+  const currentYear = new Date().getFullYear();
+  const fromDate = `${currentYear}-01-01`;
+  const toDate = `${currentYear}-12-31`;
+  
+  try {
+    const allEntries = await fetchEntries(fromDate, toDate);
+    const vacationCount = allEntries.filter(e => e.entryType === 'vacation').length;
+    
+    if (vacationCount > newValue) {
+      // Show warning
+      const difference = vacationCount - newValue;
+      const confirmed = confirm(
+        `⚠️ Warnung: Konflikt erkannt!\n\n` +
+        `Sie haben bereits ${vacationCount} Urlaubstage für ${currentYear} eingetragen.\n` +
+        `Der neue Wert von ${newValue} Tag${newValue !== 1 ? 'en' : ''} ist ${difference} Tag${difference > 1 ? 'e' : ''} zu niedrig.\n\n` +
+        `Möchten Sie den Wert trotzdem auf ${newValue} setzen?`
+      );
+      
+      if (!confirmed) {
+        event.target.value = totalVacationDays;
+        return;
+      }
+    }
+  } catch (error) {
+    console.error('Error checking vacation conflicts:', error);
+  }
+  
   totalVacationDays = newValue;
   await setSetting('vacationDays', newValue.toString());
   await updateVacationStatistics();