Add data migration export/import endpoints

Add GET /api/export to the Go backend that dumps all users, allowances,
history, and tasks (including completed) as a single JSON snapshot.

Add POST /api/import to the Spring backend that accepts the same JSON,
wipes existing data, inserts all records with original IDs preserved via
native SQL, and resets PostgreSQL sequences to avoid future collisions.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend-spring/src/main/java/be/seeseepuff/allowanceplanner/controller/ApiController.java

@@ -2,6 +2,7 @@ package be.seeseepuff.allowanceplanner.controller;
 
 import be.seeseepuff.allowanceplanner.dto.*;
 import be.seeseepuff.allowanceplanner.service.AllowanceService;
+import be.seeseepuff.allowanceplanner.service.MigrationService;
 import be.seeseepuff.allowanceplanner.service.TaskService;
 import be.seeseepuff.allowanceplanner.service.TransferService;
 import be.seeseepuff.allowanceplanner.service.UserService;
@@ -21,16 +22,19 @@ public class ApiController
 	private final AllowanceService allowanceService;
 	private final TaskService taskService;
 	private final TransferService transferService;
+	private final MigrationService migrationService;
 
 	public ApiController(UserService userService,
 			AllowanceService allowanceService,
 			TaskService taskService,
-			TransferService transferService)
+			TransferService transferService,
+			MigrationService migrationService)
 	{
 		this.userService = userService;
 		this.allowanceService = allowanceService;
 		this.taskService = taskService;
 		this.transferService = transferService;
+		this.migrationService = migrationService;
 	}
 
 	// ---- Users ----
@@ -503,4 +507,13 @@ public class ApiController
 					ResponseEntity.status(HttpStatus.NOT_FOUND).body(new ErrorResponse(result.message()));
 		};
 	}
+
+	// ---- Migration ----
+
+	@PostMapping("/import")
+	public ResponseEntity<?> importData(@RequestBody MigrationDto data)
+	{
+		migrationService.importData(data);
+		return ResponseEntity.ok(new MessageResponse("Import successful"));
+	}
 }

backend-spring/src/main/java/be/seeseepuff/allowanceplanner/dto/MigrationDto.java

@@ -0,0 +1,21 @@
+package be.seeseepuff.allowanceplanner.dto;
+
+import java.util.List;
+
+public record MigrationDto(
+		List<MigrationUserDto> users,
+		List<MigrationAllowanceDto> allowances,
+		List<MigrationHistoryDto> history,
+		List<MigrationTaskDto> tasks
+)
+{
+	public record MigrationUserDto(int id, String name, long balance, double weight) {}
+
+	public record MigrationAllowanceDto(int id, int userId, String name, long target, long balance, double weight,
+			Integer colour) {}
+
+	public record MigrationHistoryDto(int id, int userId, long timestamp, long amount, String description) {}
+
+	public record MigrationTaskDto(int id, String name, long reward, Integer assigned, String schedule,
+			Long completed, Long nextRun) {}
+}

backend-spring/src/main/java/be/seeseepuff/allowanceplanner/service/MigrationService.java

@@ -0,0 +1,104 @@
+package be.seeseepuff.allowanceplanner.service;
+
+import be.seeseepuff.allowanceplanner.dto.MigrationDto;
+import be.seeseepuff.allowanceplanner.repository.AllowanceRepository;
+import be.seeseepuff.allowanceplanner.repository.HistoryRepository;
+import be.seeseepuff.allowanceplanner.repository.TaskRepository;
+import be.seeseepuff.allowanceplanner.repository.UserRepository;
+import jakarta.persistence.EntityManager;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+public class MigrationService
+{
+	private final UserRepository userRepository;
+	private final AllowanceRepository allowanceRepository;
+	private final HistoryRepository historyRepository;
+	private final TaskRepository taskRepository;
+	private final EntityManager entityManager;
+
+	public MigrationService(UserRepository userRepository,
+			AllowanceRepository allowanceRepository,
+			HistoryRepository historyRepository,
+			TaskRepository taskRepository,
+			EntityManager entityManager)
+	{
+		this.userRepository = userRepository;
+		this.allowanceRepository = allowanceRepository;
+		this.historyRepository = historyRepository;
+		this.taskRepository = taskRepository;
+		this.entityManager = entityManager;
+	}
+
+	@Transactional
+	public void importData(MigrationDto data)
+	{
+		// Delete in dependency order
+		taskRepository.deleteAll();
+		historyRepository.deleteAll();
+		allowanceRepository.deleteAll();
+		userRepository.deleteAll();
+
+		// Insert users with original IDs using native SQL to bypass auto-increment
+		for (MigrationDto.MigrationUserDto u : data.users())
+		{
+			entityManager.createNativeQuery(
+							"INSERT INTO users (id, name, balance, weight) VALUES (:id, :name, :balance, :weight)")
+					.setParameter("id", u.id())
+					.setParameter("name", u.name())
+					.setParameter("balance", u.balance())
+					.setParameter("weight", u.weight())
+					.executeUpdate();
+		}
+
+		// Insert allowances with original IDs
+		for (MigrationDto.MigrationAllowanceDto a : data.allowances())
+		{
+			entityManager.createNativeQuery(
+							"INSERT INTO allowances (id, user_id, name, target, balance, weight, colour) VALUES (:id, :userId, :name, :target, :balance, :weight, :colour)")
+					.setParameter("id", a.id())
+					.setParameter("userId", a.userId())
+					.setParameter("name", a.name())
+					.setParameter("target", a.target())
+					.setParameter("balance", a.balance())
+					.setParameter("weight", a.weight())
+					.setParameter("colour", a.colour())
+					.executeUpdate();
+		}
+
+		// Insert history with original IDs
+		for (MigrationDto.MigrationHistoryDto h : data.history())
+		{
+			entityManager.createNativeQuery(
+							"INSERT INTO history (id, user_id, timestamp, amount, description) VALUES (:id, :userId, :timestamp, :amount, :description)")
+					.setParameter("id", h.id())
+					.setParameter("userId", h.userId())
+					.setParameter("timestamp", h.timestamp())
+					.setParameter("amount", h.amount())
+					.setParameter("description", h.description())
+					.executeUpdate();
+		}
+
+		// Insert tasks with original IDs
+		for (MigrationDto.MigrationTaskDto t : data.tasks())
+		{
+			entityManager.createNativeQuery(
+							"INSERT INTO tasks (id, name, reward, assigned, schedule, completed, next_run) VALUES (:id, :name, :reward, :assigned, :schedule, :completed, :nextRun)")
+					.setParameter("id", t.id())
+					.setParameter("name", t.name())
+					.setParameter("reward", t.reward())
+					.setParameter("assigned", t.assigned())
+					.setParameter("schedule", t.schedule())
+					.setParameter("completed", t.completed())
+					.setParameter("nextRun", t.nextRun())
+					.executeUpdate();
+		}
+
+		// Reset sequences so new inserts don't collide with migrated IDs
+		entityManager.createNativeQuery("SELECT setval('users_id_seq', COALESCE((SELECT MAX(id) FROM users), 0))").getSingleResult();
+		entityManager.createNativeQuery("SELECT setval('allowances_id_seq', COALESCE((SELECT MAX(id) FROM allowances), 0))").getSingleResult();
+		entityManager.createNativeQuery("SELECT setval('history_id_seq', COALESCE((SELECT MAX(id) FROM history), 0))").getSingleResult();
+		entityManager.createNativeQuery("SELECT setval('tasks_id_seq', COALESCE((SELECT MAX(id) FROM tasks), 0))").getSingleResult();
+	}
+}