feat: implement DonationRepository with sorting and filtering methods

src/main/java/edu/group5/app/model/donation/DonationRepository.java

@@ -1,4 +1,110 @@
 package edu.group5.app.model.donation;
 
-public class DonationRepository {
+import edu.group5.app.model.DBRepository;
+
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/**
+ * Repository class for Donation.
+ *
+ * <p>
+ *   Extends {@link DBRepository} and manages Donation entities.
+ * </p>
+ */
+public class DonationRepository extends DBRepository<Integer, Donation> {
+  private final HashMap<Integer, Donation> content;
+
+  /**
+   * Constructs DonationRepository using Hashmap,
+   * and extends the content from DBRepository.
+   * @param content the underlying map used to store donations,
+   *                where the key represents the donation ID
+   */
+  public DonationRepository(HashMap<Integer, Donation> content){
+    super(content);
+    this.content = content;
+  }
+
+  /**
+   * Adds a new donation to the repository
+   * <p>
+   *   The donation is stored using its {@code donationId} as the key.
+   *   If a donation with the same ID already exists, the donation
+   *   will not be added.
+   * </p>
+   *
+   * @param donation the donation to add
+   * @return {@code true} if the donation was successfully added, and
+   * {@code false} if a donation with the same ID already exists
+   */
+  public boolean addDonation(Donation donation) {
+    if(content.containsKey(donation.donationId())){
+      return false;
+    }
+    content.put(donation.donationId(), donation);
+    return true;
+  }
+
+  /**
+   * Returns all donations sorted by date (ascending).
+   *
+   * <p>
+   *   The returned map preserves the sorted order.
+   * </p>
+   *
+   * @return a new {@link HashMap} containing the donations sorted by date
+   */
+  public HashMap<Integer, Donation> sortByDate(){
+    return content.entrySet().stream()
+        .sorted(Map.Entry.comparingByValue(
+            Comparator.comparing(Donation::date)))
+        .collect(Collectors.toMap(
+            Map.Entry::getKey,
+            Map.Entry::getValue,
+            (e1, e2) -> e1,
+            LinkedHashMap::new));
+  }
+
+  /**
+   * Returns all donations sorted by amount (ascending).
+   *
+   * <p>
+   *   The returned map preserves the sorted order from lowest to highest amount.
+   * </p>
+   *
+   * @return a new {@link HashMap} containing the donations sorted by amount.
+   */
+  public HashMap<Integer, Donation> sortByAmount() {
+    return content.entrySet().stream()
+        .sorted(Map.Entry.comparingByValue(
+            Comparator.comparing(Donation::amount)))
+        .collect(Collectors.toMap(
+            Map.Entry::getKey,
+            Map.Entry::getValue,
+            (e1, e2) -> e1,
+            LinkedHashMap::new
+        ));
+  }
+
+  /**
+   * Returns all donations associated with a specific organization.
+   *
+   * @param orgNumber the organization ID to filter by
+   * @return a map containing all donations that belong to the given organization
+   */
+  public HashMap<Integer, Donation> filterByOrganization(int orgNumber) {
+    return content.entrySet()
+        .stream()
+        .filter(entry -> entry.getValue().organizationId()  == orgNumber)
+        .collect(Collectors.toMap(
+            Map.Entry::getKey,
+            Map.Entry::getValue,
+            (e1, e2) -> e1,
+            LinkedHashMap::new
+        ));
+  }
 }