feat: idempotent startup backfill for lastModified and history

src/main/java/de/zendric/app/xpensely_server/preparation/HistoryBackfillRunner.java

@@ -0,0 +1,61 @@
+package de.zendric.app.xpensely_server.preparation;
+
+import java.time.LocalDateTime;
+import java.util.HashSet;
+import java.util.Set;
+
+import org.springframework.boot.CommandLineRunner;
+import org.springframework.stereotype.Component;
+import org.springframework.transaction.annotation.Transactional;
+
+import de.zendric.app.xpensely_server.model.Expense;
+import de.zendric.app.xpensely_server.model.ExpenseHistoryEntry;
+import de.zendric.app.xpensely_server.model.HistoryEntryType;
+import de.zendric.app.xpensely_server.repo.ExpenseHistoryRepository;
+import de.zendric.app.xpensely_server.repo.ExpenseRepository;
+
+/**
+ * One-time (idempotent) backfill for the history feature: fills
+ * Expense.lastModified from the expense date and creates a synthetic CREATED
+ * history entry for every expense that predates change logging. Both steps
+ * are no-ops on every startup after the first.
+ */
+@Component
+public class HistoryBackfillRunner implements CommandLineRunner {
+
+    private final ExpenseRepository expenseRepository;
+    private final ExpenseHistoryRepository historyRepository;
+
+    public HistoryBackfillRunner(ExpenseRepository expenseRepository,
+            ExpenseHistoryRepository historyRepository) {
+        this.expenseRepository = expenseRepository;
+        this.historyRepository = historyRepository;
+    }
+
+    @Override
+    @Transactional
+    public void run(String... args) {
+        for (Expense expense : expenseRepository.findByLastModifiedIsNull()) {
+            expense.setLastModified(startOfDayOrNow(expense));
+            expenseRepository.save(expense);
+        }
+
+        Set<Long> loggedExpenseIds = new HashSet<>(historyRepository.findAllExpenseIds());
+        for (Expense expense : expenseRepository.findAll()) {
+            if (loggedExpenseIds.contains(expense.getId()))
+                continue;
+            ExpenseHistoryEntry entry = new ExpenseHistoryEntry();
+            entry.setExpenseList(expense.getExpenseList());
+            entry.setExpenseId(expense.getId());
+            entry.setExpenseTitle(expense.getTitle());
+            entry.setActor(expense.getOwner());
+            entry.setType(HistoryEntryType.CREATED);
+            entry.setTimestamp(startOfDayOrNow(expense));
+            historyRepository.save(entry);
+        }
+    }
+
+    private LocalDateTime startOfDayOrNow(Expense expense) {
+        return expense.getDate() == null ? LocalDateTime.now() : expense.getDate().atStartOfDay();
+    }
+}

src/test/java/de/zendric/app/xpensely_Server/preparation/HistoryBackfillRunnerTest.java

@@ -0,0 +1,92 @@
+package de.zendric.app.xpensely_Server.preparation;
+
+import java.time.LocalDate;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.ArgumentCaptor;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.model.Expense;
+import de.zendric.app.xpensely_server.model.ExpenseHistoryEntry;
+import de.zendric.app.xpensely_server.model.ExpenseList;
+import de.zendric.app.xpensely_server.model.HistoryEntryType;
+import de.zendric.app.xpensely_server.preparation.HistoryBackfillRunner;
+import de.zendric.app.xpensely_server.repo.ExpenseHistoryRepository;
+import de.zendric.app.xpensely_server.repo.ExpenseRepository;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+@ExtendWith(MockitoExtension.class)
+class HistoryBackfillRunnerTest {
+
+    @Mock ExpenseRepository expenseRepository;
+    @Mock ExpenseHistoryRepository historyRepository;
+
+    @InjectMocks
+    HistoryBackfillRunner runner;
+
+    private Expense expense(long id, LocalDate date) {
+        AppUser owner = new AppUser(); owner.setId(1L); owner.setUsername("alice");
+        ExpenseList list = new ExpenseList(); list.setId(10L);
+        Expense e = new Expense();
+        e.setId(id);
+        e.setTitle("Groceries");
+        e.setDate(date);
+        e.setOwner(owner);
+        e.setExpenseList(list);
+        return e;
+    }
+
+    @Test
+    void fillsLastModifiedFromDate_forExpensesMissingIt() throws Exception {
+        Expense e = expense(42L, LocalDate.of(2026, 6, 1));
+        when(expenseRepository.findByLastModifiedIsNull()).thenReturn(List.of(e));
+        when(expenseRepository.findAll()).thenReturn(List.of(e));
+        when(historyRepository.findAllExpenseIds()).thenReturn(List.of(42L));
+
+        runner.run();
+
+        assertThat(e.getLastModified()).isEqualTo(LocalDate.of(2026, 6, 1).atStartOfDay());
+        verify(expenseRepository).save(e);
+    }
+
+    @Test
+    void createsSyntheticCreatedEntry_forExpensesWithoutHistory() throws Exception {
+        Expense e = expense(42L, LocalDate.of(2026, 6, 1));
+        when(expenseRepository.findByLastModifiedIsNull()).thenReturn(List.of());
+        when(expenseRepository.findAll()).thenReturn(List.of(e));
+        when(historyRepository.findAllExpenseIds()).thenReturn(List.of());
+
+        runner.run();
+
+        ArgumentCaptor<ExpenseHistoryEntry> captor = ArgumentCaptor.forClass(ExpenseHistoryEntry.class);
+        verify(historyRepository).save(captor.capture());
+        ExpenseHistoryEntry entry = captor.getValue();
+        assertThat(entry.getType()).isEqualTo(HistoryEntryType.CREATED);
+        assertThat(entry.getExpenseId()).isEqualTo(42L);
+        assertThat(entry.getExpenseTitle()).isEqualTo("Groceries");
+        assertThat(entry.getActor().getUsername()).isEqualTo("alice");
+        assertThat(entry.getTimestamp()).isEqualTo(LocalDate.of(2026, 6, 1).atStartOfDay());
+    }
+
+    @Test
+    void isIdempotent_skipsExpensesThatAlreadyHaveHistory() throws Exception {
+        Expense e = expense(42L, LocalDate.of(2026, 6, 1));
+        when(expenseRepository.findByLastModifiedIsNull()).thenReturn(List.of());
+        when(expenseRepository.findAll()).thenReturn(List.of(e));
+        when(historyRepository.findAllExpenseIds()).thenReturn(List.of(42L));
+
+        runner.run();
+
+        verify(historyRepository, never()).save(any());
+    }
+}