86czcfdm1-implement-optimal-account-balancing-settlement-service-in-splitora feature added

src/main/java/com/satwik/splitora/controller/GroupController.java

@@ -1,6 +1,7 @@
 package com.satwik.splitora.controller;
 
 import com.satwik.splitora.persistence.dto.ResponseModel;
+import com.satwik.splitora.persistence.dto.group.BalanceTransaction;
 import com.satwik.splitora.persistence.dto.group.GroupDTO;
 import com.satwik.splitora.persistence.dto.group.GroupListDTO;
 import com.satwik.splitora.persistence.dto.group.GroupUpdateRequest;
@@ -179,4 +180,22 @@ public ResponseEntity<ResponseModel<String>> deleteMembers(@PathVariable UUID gr
         log.info("Delete Endpoint: delete a member with response: {}", responseModel);
         return ResponseEntity.status(HttpStatus.OK).body(responseModel);
     }
+
+    /**
+     * Retrieves balance transactions for a group.
+     *
+     * This endpoint processes the request to get balance transactions for a group identified by the given group ID.
+     * It logs the incoming request and the resulting response.
+     *
+     * @param groupId the UUID of the group for which balance transactions are to be retrieved.
+     * @return a ResponseEntity containing a BalanceTransaction object with the group's balance transactions.
+     */
+    @GetMapping("/getBalanceTransactions/{groupId}")
+    public ResponseEntity<ResponseModel<BalanceTransaction>> getBalanceTransactions(@PathVariable UUID groupId) {
+        log.info("Get Endpoint: get balance transactions for group with id: {}", groupId);
+        BalanceTransaction transactions = groupService.getBalanceTransactions(groupId);
+        ResponseModel<BalanceTransaction> responseModel = ResponseUtil.success(transactions, HttpStatus.OK, "Balance transactions retrieved successfully");
+        log.info("Get Endpoint: get balance transactions response: {}", responseModel);
+        return ResponseEntity.status(HttpStatus.OK).body(responseModel);
+    }
 }

src/main/java/com/satwik/splitora/persistence/dto/group/BalanceTransaction.java

@@ -0,0 +1,19 @@
+package com.satwik.splitora.persistence.dto.group;
+
+import com.satwik.splitora.settlement.model.Transaction;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+import java.util.List;
+import java.util.UUID;
+
+@Data
+@AllArgsConstructor
+@NoArgsConstructor
+public class BalanceTransaction {
+
+    private UUID groupId;
+    private String groupName;
+    private List<Transaction<UUID>> transactions;
+}

src/main/java/com/satwik/splitora/persistence/entities/BaseEntity.java

@@ -1,5 +1,6 @@
 package com.satwik.splitora.persistence.entities;
 
+import jakarta.persistence.Column;
 import jakarta.persistence.GeneratedValue;
 import jakarta.persistence.Id;
 import jakarta.persistence.MappedSuperclass;
@@ -18,8 +19,9 @@
 public class BaseEntity {
 
     @Id
-    @GenericGenerator(name = "uuid")
+    @GenericGenerator(name = "uuid2", strategy = "uuid2")
     @GeneratedValue(generator = "uuid")
+    @Column(columnDefinition = "BINARY(16)")
     private UUID id;
 
     private UUID createdBy;

src/main/java/com/satwik/splitora/persistence/entities/Expense.java

@@ -17,7 +17,7 @@ public class Expense extends BaseEntity {
     @JoinColumn(name = "group_id")
     private Group group;
 
-    @ManyToOne(fetch = FetchType.LAZY)
+    @ManyToOne(fetch = FetchType.EAGER)
     @JoinColumn(name = "payer_id")
     private User payer;
 

src/main/java/com/satwik/splitora/persistence/entities/Group.java

@@ -20,7 +20,7 @@ public class Group extends BaseEntity {
     @Column(name = "default_group")
     private boolean defaultGroup;
 
-    @ManyToOne(fetch = FetchType.LAZY)
+    @ManyToOne(fetch = FetchType.EAGER)
     @JoinColumn(name = "user_id")
     private User user;
 

src/main/java/com/satwik/splitora/repository/ExpenseRepository.java

@@ -1,7 +1,9 @@
 package com.satwik.splitora.repository;
 
 import com.satwik.splitora.persistence.entities.Expense;
+import com.satwik.splitora.settlement.model.Transaction;
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
 import org.springframework.stereotype.Repository;
 
 import java.util.List;
@@ -11,4 +13,13 @@
 public interface ExpenseRepository extends JpaRepository<Expense, UUID> {
     List<Expense> findByGroupId(UUID groupId);
 
+    @Query("SELECT NEW com.satwik.splitora.settlement.model.Transaction("+
+            "es.user.id, " +
+            "e.payer.id, " +
+            "es.sharedAmount) " +
+            "FROM Expense e " +
+            "JOIN ExpenseShare es " +
+            "ON e.id = es.expense.id " +
+            "WHERE e.group.id = ?1 ")
+    List<Transaction<UUID>> findTransactionsByGroupId(UUID id);
 }

src/main/java/com/satwik/splitora/service/implementations/ExpenseServiceImpl.java

@@ -53,8 +53,8 @@ public ExpenseDTO createGroupedExpense(UUID groupId, ExpenseDTO expenseDTO) {
         User payer = expenseDTO.getPayerId() != null ? userRepository.findById(expenseDTO.getPayerId()).orElseThrow(() -> new DataNotFoundException("Payer not found!")) : authorizationService.getAuthorizedUser();
         Group group = groupRepository.findById(groupId).orElseThrow(() -> new DataNotFoundException(ErrorMessages.GROUP_NOT_FOUND));
 
-        // checking if payer is a member of the group
-        if(!groupMembersRepository.existsByGroupIdAndMemberId(group.getId(), payer.getId()))
+        // checking if payer is a member of the group or owner of the group
+        if(group.getUser().getId() != payer.getId() && !groupMembersRepository.existsByGroupIdAndMemberId(group.getId(), payer.getId()))
             throw new BadRequestException("Payer is not a member of this group!");
 
         Expense expense = new Expense();
@@ -70,6 +70,7 @@ public ExpenseDTO createGroupedExpense(UUID groupId, ExpenseDTO expenseDTO) {
         response.setPayerId(expense.getPayer().getId());
         response.setDescription(expense.getDescription());
         response.setPayerName(expense.getPayer().getUsername());
+        response.setDate(expense.getCreatedOn());
         return response;
     }
 
@@ -91,9 +92,10 @@ public ExpenseDTO createNonGroupedExpense(ExpenseDTO expenseDTO) {
         ExpenseDTO response = new ExpenseDTO();
         response.setExpenseId(expense.getId());
         response.setAmount(expense.getAmount());
+        response.setPayerId(expense.getPayer().getId());
         response.setDescription(expense.getDescription());
         response.setPayerName(expense.getPayer().getUsername());
-        response.setPayerId(expense.getPayer().getId());
+        response.setDate(expense.getCreatedOn());
 
         return response;
     }

src/main/java/com/satwik/splitora/service/implementations/GroupServiceImpl.java

@@ -1,6 +1,7 @@
 package com.satwik.splitora.service.implementations;
 
 import com.satwik.splitora.constants.ErrorMessages;
+import com.satwik.splitora.exception.BadRequestException;
 import com.satwik.splitora.exception.DataNotFoundException;
 import com.satwik.splitora.persistence.dto.expense.ExpenseListDTO;
 import com.satwik.splitora.persistence.dto.group.*;
@@ -15,6 +16,9 @@
 import com.satwik.splitora.repository.GroupRepository;
 import com.satwik.splitora.repository.UserRepository;
 import com.satwik.splitora.service.interfaces.GroupService;
+import com.satwik.splitora.settlement.model.Transaction;
+import com.satwik.splitora.settlement.strategy.SettlementStrategy;
+import com.satwik.splitora.settlement.strategy.SortSettlementStrategy;
 import jakarta.transaction.Transactional;
 import org.springframework.security.access.AccessDeniedException;
 import org.springframework.security.access.prepost.PreAuthorize;
@@ -83,7 +87,11 @@ public GroupListDTO findAllGroup() {
     public String addGroupMembers(UUID groupId, UUID memberId) {
         Group group = groupRepository.findById(groupId).orElseThrow(() -> new DataNotFoundException(ErrorMessages.GROUP_NOT_FOUND));
         User member = userRepository.findById(memberId).orElseThrow(() -> new DataNotFoundException("User not found to add as member!"));
-        // TODO : add check to avoid add members to default group
+
+        if(group.isDefaultGroup()) {
+            throw new BadRequestException("You can't add members to the default group!");
+        }
+
         GroupMembers groupMembers = new GroupMembers();
         groupMembers.setMember(member);
         groupMembers.setGroup(group);
@@ -131,6 +139,7 @@ public String deleteGroupByGroupId(UUID groupId) {
     }
 
     @Override
+    @Transactional
     @PreAuthorize("@authorizationService.isGroupOwner(#groupId)")
     public GroupDTO findGroupByGroupId(UUID groupId) {
         Group group = groupRepository.findById(groupId).orElseThrow(() -> new DataNotFoundException(ErrorMessages.GROUP_NOT_FOUND));
@@ -186,4 +195,21 @@ public String updateGroup(GroupUpdateRequest groupUpdateRequest, UUID groupId) {
         groupRepository.save(group);
         return "%s - Group update successfully!".formatted(group.getId());
     }
+
+    @Override
+    @Transactional
+    @PreAuthorize("@authorizationService.isGroupOwner(#groupId)")
+    public BalanceTransaction getBalanceTransactions(UUID groupId) {
+        Group group = groupRepository.findById(groupId).orElseThrow(() -> new DataNotFoundException(ErrorMessages.GROUP_NOT_FOUND));
+        // Fetch all the transactions related to the group
+        List<Transaction<UUID>> transactions = expenseRepository.findTransactionsByGroupId(group.getId());
+        SettlementStrategy<UUID> settlementStrategy = new SortSettlementStrategy<>();
+        List<Transaction<UUID>> balancingTransaction = settlementStrategy.settle(transactions);
+        BalanceTransaction balanceTransaction = new BalanceTransaction();
+        balanceTransaction.setGroupId(group.getId());
+        balanceTransaction.setGroupName(group.getGroupName());
+        balanceTransaction.setTransactions(balancingTransaction);
+
+        return balanceTransaction;
+    }
 }

src/main/java/com/satwik/splitora/service/interfaces/GroupService.java

@@ -1,5 +1,6 @@
 package com.satwik.splitora.service.interfaces;
 
+import com.satwik.splitora.persistence.dto.group.BalanceTransaction;
 import com.satwik.splitora.persistence.dto.group.GroupDTO;
 import com.satwik.splitora.persistence.dto.group.GroupListDTO;
 import com.satwik.splitora.persistence.dto.group.GroupUpdateRequest;
@@ -24,4 +25,6 @@ public interface GroupService {
     List<UserDTO> findMembers(UUID groupId);
 
     String deleteMembers(UUID groupId, UUID groupMemberId);
+
+    BalanceTransaction getBalanceTransactions(UUID groupId);
 }

src/main/java/com/satwik/splitora/settlement/model/Transaction.java

@@ -0,0 +1,17 @@
+package com.satwik.splitora.settlement.model;
+
+import lombok.Data;
+
+@Data
+public class Transaction<U> {
+
+    U debtor;
+    U creditor;
+    Double amount;
+
+    public Transaction(U debtor, U creditor, Double amount) {
+        this.debtor = debtor;
+        this.creditor = creditor;
+        this.amount = amount;
+    }
+}

src/main/java/com/satwik/splitora/settlement/strategy/SettlementStrategy.java

@@ -0,0 +1,17 @@
+package com.satwik.splitora.settlement.strategy;
+
+import com.satwik.splitora.settlement.model.Transaction;
+
+import java.util.List;
+
+public interface SettlementStrategy <U> {
+
+    /**
+     * Settle a list of transactions and return the settled transactions.
+     *
+     * @param transactions List of transactions to be settled
+     * @return List of settled transactions
+     */
+    List<Transaction<U>> settle(List<Transaction<U>> transactions);
+
+}

src/main/java/com/satwik/splitora/settlement/strategy/SortSettlementStrategy.java

@@ -0,0 +1,83 @@
+package com.satwik.splitora.settlement.strategy;
+
+import com.satwik.splitora.settlement.model.Transaction;
+import lombok.Data;
+
+import java.util.*;
+
+public class SortSettlementStrategy<U> implements SettlementStrategy<U> {
+
+    @Data
+    private class Person {
+        private U id;
+        private Double balance;
+
+        public Person(U id, Double balance) {
+            this.id = id;
+            this.balance = balance;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (o == null || getClass() != o.getClass()) return false;
+            Person person = (Person) o;
+            return Objects.equals(id, person.id);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(id);
+        }
+    }
+
+    @Override
+    public List<Transaction<U>> settle(List<Transaction<U>> transactions) {
+        HashMap<U, Double> balances = new HashMap<>();
+        for (Transaction<U> transaction : transactions) {
+            U creditor = transaction.getCreditor();
+            U debtor = transaction.getDebtor();
+            double amount = transaction.getAmount();
+
+            balances.put(creditor, balances.getOrDefault(creditor, 0.0) + amount);
+            balances.put(debtor, balances.getOrDefault(debtor, 0.0) - amount);
+        }
+
+        // Create lists for creditors and debtors
+        List<Person> creditors = new ArrayList<>();
+        List<Person> debtors = new ArrayList<>();
+
+        for (var entry : balances.entrySet()) {
+            U personId = entry.getKey();
+            Double balance = entry.getValue();
+
+            if (balance < 0) {
+                creditors.add(new Person(personId, balance));
+            } else if (balance > 0) {
+                debtors.add(new Person(personId, balance));
+            }
+        }
+
+        creditors.sort(Comparator.comparingDouble(Person::getBalance));
+        debtors.sort(Comparator.comparingDouble(Person::getBalance));
+
+        List<Transaction<U>> settlingTransactions = new ArrayList<>();
+
+        int i = 0;
+        int j = 0;
+        while (i < creditors.size() && j < debtors.size()) {
+            Person creditor = creditors.get(i);
+            Person debtor = debtors.get(j);
+
+            double minAmount = Math.min(creditor.balance, debtor.balance);
+            settlingTransactions.add(new Transaction<>(debtor.getId(), creditor.getId(), Math.abs(minAmount)));
+
+            creditor.balance -= minAmount;
+            debtor.balance -= minAmount;
+
+            if (creditor.balance == 0) i++;
+            if (debtor.balance == 0) j++;
+        }
+
+        return settlingTransactions;
+    }
+}