Execute updates in order

scm-core/src/main/java/sonia/scm/migration/UpdateStep.java

@@ -5,4 +5,6 @@ import sonia.scm.plugin.ExtensionPoint;
 @ExtensionPoint
 public interface UpdateStep {
   void doUpdate();
+
+  String getTargetVersion();
 }

scm-webapp/src/main/java/sonia/scm/UpdateEngine.java

@@ -1,17 +1,29 @@
 package sonia.scm;
 
 import sonia.scm.migration.UpdateStep;
+import sonia.scm.version.Version;
 
 import javax.inject.Inject;
+import java.util.Comparator;
+import java.util.List;
 import java.util.Set;
 
+import static java.util.stream.Collectors.toList;
+
 public class UpdateEngine {
 
-  private final Set<UpdateStep> steps;
+  private final List<UpdateStep> steps;
 
   @Inject
   public UpdateEngine(Set<UpdateStep> steps) {
-    this.steps = steps;
+    this.steps = sortSteps(steps);
+  }
+
+  private List<UpdateStep> sortSteps(Set<UpdateStep> steps) {
+    Comparator<UpdateStep> compareByVersion = Comparator.comparing(step -> Version.parse(step.getTargetVersion()));
+    return steps.stream()
+      .sorted(compareByVersion.reversed())
+      .collect(toList());
   }
 
   public void update() {

scm-webapp/src/test/java/sonia/scm/UpdateEngineTest.java

@@ -0,0 +1,48 @@
+package sonia.scm;
+
+import org.junit.jupiter.api.Test;
+import sonia.scm.migration.UpdateStep;
+
+import java.util.ArrayList;
+import java.util.LinkedHashSet;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class UpdateEngineTest {
+
+  List<String> processedUpdates = new ArrayList<>();
+
+  @Test
+  void shouldProcessStepsInCorrectOrder() {
+    LinkedHashSet<UpdateStep> updateSteps = new LinkedHashSet<>();
+
+    updateSteps.add(new FixedVersionUpdateStep("1.1.1"));
+    updateSteps.add(new FixedVersionUpdateStep("1.2.0"));
+    updateSteps.add(new FixedVersionUpdateStep("1.1.0"));
+
+    UpdateEngine updateEngine = new UpdateEngine(updateSteps);
+    updateEngine.update();
+
+    assertThat(processedUpdates)
+      .containsExactly("1.1.0", "1.1.1", "1.2.0");
+  }
+
+  class FixedVersionUpdateStep implements UpdateStep {
+    private final String version;
+
+    FixedVersionUpdateStep(String version) {
+      this.version = version;
+    }
+
+    @Override
+    public String getTargetVersion() {
+      return version;
+    }
+
+    @Override
+    public void doUpdate() {
+      processedUpdates.add(version);
+    }
+  }
+}