We are the wild!

app/src/main/java/itmo/lab5/cli/helpers/FlatComparatorFactory.java

@@ -0,0 +1,68 @@
+package itmo.lab5.cli.helpers;
+
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+
+import itmo.lab5.models.Flat;
+import java.util.ArrayList;
+import java.util.HashMap;
+
+/**
+ * The FlatComparatorFactory class provides functionality to create comparators 
+ * for sorting Flat objects based on various fields such as ID, name, area, 
+ * number of rooms, and creation date.
+ */
+public class FlatComparatorFactory {
+    public enum SortField {
+        ID,
+        NAME,
+        AREA,
+        NUMBER_OF_ROOMS,
+        CREATION_DATE
+    }
+
+    /**
+     * Returns a Comparator for Flat objects based on the specified sort field.
+     *
+     * @param field the field by which to sort the Flat objects
+     * @return a Comparator for Flat objects
+     * @throws IllegalArgumentException if the specified sort field is unknown
+     */
+    public static Comparator<Flat> getComparator(SortField field) {
+        switch (field) {
+            case ID:
+                return Comparator.comparingInt(Flat::getId);
+            case NAME:
+                return Comparator.comparing(Flat::getName);
+            case AREA:
+                return Comparator.comparingDouble(Flat::getArea);
+            case NUMBER_OF_ROOMS:
+                return Comparator.comparingInt(Flat::getNumberOfRooms);
+            case CREATION_DATE:
+                return Comparator.comparing(Flat::getCreationDate);
+            default:
+                throw new IllegalArgumentException("Unknown sort field: " + field);
+        }
+    }
+    
+    /**
+     * Sorts a HashMap of Flat objects based on the specified sort field and 
+     * returns a new sorted HashMap.
+     *
+     * @param flatsMap the HashMap of Flat objects to be sorted
+     * @param field the field by which to sort the Flat objects
+     * @return a new HashMap containing the sorted Flat objects
+     */
+    public static HashMap<Integer, Flat> sortFlats(HashMap<Integer, Flat> flatsMap, SortField field) {
+        List<Flat> flatList = new ArrayList<>(flatsMap.values());
+        Collections.sort(flatList, getComparator(field));
+
+
+        var sortedMap = new HashMap<Integer, Flat>();
+        for (Flat flat : flatList) {
+            sortedMap.put(flat.getId(), flat);
+        }
+        return sortedMap;
+    }
+}

app/src/main/java/itmo/lab5/parser/Reader.java

@@ -10,6 +10,7 @@ import java.util.Scanner;
 import java.util.stream.Collectors;
 
 import itmo.lab5.models.enums.*;
+import itmo.lab5.cli.helpers.FlatComparatorFactory;
 import itmo.lab5.models.*;
 
 public class Reader {
@@ -42,17 +43,13 @@ public class Reader {
       collection.put(parsedFlat.getId(), parsedFlat);
     }
 
-    collection = collection.entrySet()
+    var sortedById = FlatComparatorFactory.sortFlats(
-        .stream()
+            collection, 
-        .sorted(HashMap.Entry.comparingByKey())
+            FlatComparatorFactory.SortField.ID
-        .collect(Collectors.toMap(
+    );
-            Map.Entry::getKey,
-            Map.Entry::getValue,
-            (oldValue, newValue) -> oldValue,
-            HashMap::new));
     
     scanner.close();
-    return collection;
+    return sortedById;
   }
 
   private static Flat parseFlat(String lineToParse) throws IllegalArgumentException, ParseException {

app/src/main/java/itmo/lab5/parser/Writer.java

@@ -1,5 +1,6 @@
 package itmo.lab5.parser;
 
+import itmo.lab5.cli.helpers.FlatComparatorFactory;
 import java.io.*;
 import java.text.SimpleDateFormat;
 import java.util.HashMap;
@@ -14,6 +15,11 @@ public class Writer {
         OutputStreamWriter osw = new OutputStreamWriter(fos);
         BufferedWriter writer = new BufferedWriter(osw)) {
         
+        flats = FlatComparatorFactory.sortFlats(
+                flats, 
+                FlatComparatorFactory.SortField.ID
+        );
+        
         for (Flat flat : flats.values()) {
           String date = "";