Feature: exporting/importing selected dates.

src/main/java/net/themusicinnoise/vaccalc/PointEngine.java

@@ -3,13 +3,16 @@ package net.themusicinnoise.vaccalc;
 import java.io.BufferedReader;
 import java.io.File;
 import java.io.FileReader;
+import java.io.FileWriter;
 import java.io.IOException;
 import java.time.DayOfWeek;
 import java.time.LocalDate;
 import java.time.Month;
 import java.time.format.DateTimeFormatter;
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -107,4 +110,41 @@ public class PointEngine {
         }
         return defaultPoints;
     }
+
+    public void exportSelectedDates(File exportFile, Set<LocalDate> selectedDates) throws IOException {
+        try (FileWriter writer = new FileWriter(exportFile)) {
+            selectedDates.stream()
+                    .sorted()
+                    .forEach(date -> {
+                        try {
+                            writer.write(String.format("%s%n", date));
+                        } catch (IOException e) {
+                            throw new RuntimeException(e);
+                        }
+                    });
+        }
+    }
+
+    public Set<LocalDate> importSelectedDates(File importFile) throws IOException {
+        Set<LocalDate> dates = new HashSet<>();
+        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
+
+        try (BufferedReader br = new BufferedReader(new FileReader(importFile))) {
+            String line;
+            while ((line = br.readLine()) != null) {
+                line = line.trim();
+                if (line.isEmpty() || line.charAt(0) == '#')
+                    continue;
+
+                try {
+                    LocalDate date = LocalDate.parse(line, formatter);
+                    dates.add(date);
+                } catch (Exception e) {
+                    throw new IllegalArgumentException("Invalid date format in line: '" + line + "'");
+                }
+            }
+        }
+
+        return dates;
+    }
 }

src/main/java/net/themusicinnoise/vaccalc/VacCalc.java

@@ -4,8 +4,10 @@ import javax.swing.*;
 import java.awt.*;
 import java.awt.event.*;
 import java.io.*;
+import java.time.LocalDate;
 import java.time.YearMonth;
 import java.util.Properties;
+import java.util.Set;
 import java.util.stream.Collectors;
 
 public class VacCalc extends JFrame {
@@ -42,6 +44,61 @@ public class VacCalc extends JFrame {
             }
         });
         appMenu.add(importItem);
+        appMenu.addSeparator();
+        JMenuItem exportItem = new JMenuItem("Export selected dates");
+        exportItem.addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent ev) {
+                if (calendarPanel.getSelectedDates().isEmpty()) {
+                    JOptionPane.showMessageDialog(VacCalc.this, "No dates selected.", "Export Error",
+                            JOptionPane.WARNING_MESSAGE);
+                    return;
+                }
+                JFileChooser fileChooser = new JFileChooser();
+                fileChooser.setSelectedFile(new File("vacation_dates.txt"));
+                int ret = fileChooser.showSaveDialog(VacCalc.this);
+                if(ret == JFileChooser.APPROVE_OPTION) {
+                    try {
+                        pointEngine.exportSelectedDates(fileChooser.getSelectedFile(), calendarPanel.getSelectedDates());
+                        JOptionPane.showMessageDialog(VacCalc.this, "Dates exported successfully.", "Export Complete",
+                                JOptionPane.INFORMATION_MESSAGE);
+                    } catch(Exception ex) {
+                        ex.printStackTrace();
+                        JOptionPane.showMessageDialog(VacCalc.this, ex.getMessage(), "Export Error",
+                                JOptionPane.ERROR_MESSAGE);
+                    }
+                }
+            }
+        });
+        appMenu.add(exportItem);
+        JMenuItem importDatesItem = new JMenuItem("Import dates");
+        importDatesItem.addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent ev) {
+                JFileChooser fileChooser = new JFileChooser();
+                int ret = fileChooser.showOpenDialog(VacCalc.this);
+                if(ret == JFileChooser.APPROVE_OPTION) {
+                    try {
+                        calendarPanel.clearSelection();
+                        Set<LocalDate> importedDates = pointEngine.importSelectedDates(fileChooser.getSelectedFile());
+                        if (importedDates.isEmpty()) {
+                            JOptionPane.showMessageDialog(VacCalc.this, "No valid dates found in file.", "Import Warning",
+                                    JOptionPane.WARNING_MESSAGE);
+                            return;
+                        }
+                        calendarPanel.setSelectedDates(importedDates);
+                        JOptionPane.showMessageDialog(VacCalc.this, "Imported " + importedDates.size() + " dates.", "Import Complete",
+                                JOptionPane.INFORMATION_MESSAGE);
+                    } catch(Exception ex) {
+                        ex.printStackTrace();
+                        JOptionPane.showMessageDialog(VacCalc.this, ex.getMessage(), "Import Error",
+                                JOptionPane.ERROR_MESSAGE);
+                    }
+                }
+            }
+        });
+        appMenu.add(importDatesItem);
+        appMenu.addSeparator();
         JMenuItem exitItem = new JMenuItem("Exit");
         exitItem.addActionListener(new ActionListener() {
             @Override