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diff --git a/java/com/google/gerrit/server/change/RebaseUtil.java b/java/com/google/gerrit/server/change/RebaseUtil.java
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+// Copyright (C) 2015 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.change;
+
+import com.google.auto.value.AutoValue;
+import com.google.common.flogger.FluentLogger;
+import com.google.common.primitives.Ints;
+import com.google.gerrit.extensions.restapi.ResourceConflictException;
+import com.google.gerrit.extensions.restapi.RestApiException;
+import com.google.gerrit.extensions.restapi.UnprocessableEntityException;
+import com.google.gerrit.reviewdb.client.Branch;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.reviewdb.client.Change.Status;
+import com.google.gerrit.reviewdb.client.PatchSet;
+import com.google.gerrit.reviewdb.client.RevId;
+import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.PatchSetUtil;
+import com.google.gerrit.server.notedb.ChangeNotes;
+import com.google.gerrit.server.query.change.ChangeData;
+import com.google.gerrit.server.query.change.InternalChangeQuery;
+import com.google.gwtorm.server.OrmException;
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+import java.io.IOException;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevWalk;
+
+/** Utility methods related to rebasing changes. */
+public class RebaseUtil {
+  private static final FluentLogger logger = FluentLogger.forEnclosingClass();
+
+  private final Provider<InternalChangeQuery> queryProvider;
+  private final ChangeNotes.Factory notesFactory;
+  private final Provider<ReviewDb> dbProvider;
+  private final PatchSetUtil psUtil;
+
+  @Inject
+  RebaseUtil(
+      Provider<InternalChangeQuery> queryProvider,
+      ChangeNotes.Factory notesFactory,
+      Provider<ReviewDb> dbProvider,
+      PatchSetUtil psUtil) {
+    this.queryProvider = queryProvider;
+    this.notesFactory = notesFactory;
+    this.dbProvider = dbProvider;
+    this.psUtil = psUtil;
+  }
+
+  public boolean canRebase(PatchSet patchSet, Branch.NameKey dest, Repository git, RevWalk rw) {
+    try {
+      findBaseRevision(patchSet, dest, git, rw);
+      return true;
+    } catch (RestApiException e) {
+      return false;
+    } catch (OrmException | IOException e) {
+      logger.atWarning().withCause(e).log(
+          "Error checking if patch set %s on %s can be rebased", patchSet.getId(), dest);
+      return false;
+    }
+  }
+
+  @AutoValue
+  public abstract static class Base {
+    private static Base create(ChangeNotes notes, PatchSet ps) {
+      if (notes == null) {
+        return null;
+      }
+      return new AutoValue_RebaseUtil_Base(notes, ps);
+    }
+
+    public abstract ChangeNotes notes();
+
+    public abstract PatchSet patchSet();
+  }
+
+  public Base parseBase(RevisionResource rsrc, String base) throws OrmException {
+    ReviewDb db = dbProvider.get();
+
+    // Try parsing the base as a ref string.
+    PatchSet.Id basePatchSetId = PatchSet.Id.fromRef(base);
+    if (basePatchSetId != null) {
+      Change.Id baseChangeId = basePatchSetId.getParentKey();
+      ChangeNotes baseNotes = notesFor(rsrc, baseChangeId);
+      if (baseNotes != null) {
+        return Base.create(
+            notesFor(rsrc, basePatchSetId.getParentKey()),
+            psUtil.get(db, baseNotes, basePatchSetId));
+      }
+    }
+
+    // Try parsing base as a change number (assume current patch set).
+    Integer baseChangeId = Ints.tryParse(base);
+    if (baseChangeId != null) {
+      ChangeNotes baseNotes = notesFor(rsrc, new Change.Id(baseChangeId));
+      if (baseNotes != null) {
+        return Base.create(baseNotes, psUtil.current(db, baseNotes));
+      }
+    }
+
+    // Try parsing as SHA-1.
+    Base ret = null;
+    for (ChangeData cd : queryProvider.get().byProjectCommit(rsrc.getProject(), base)) {
+      for (PatchSet ps : cd.patchSets()) {
+        if (!ps.getRevision().matches(base)) {
+          continue;
+        }
+        if (ret == null || ret.patchSet().getId().get() < ps.getId().get()) {
+          ret = Base.create(cd.notes(), ps);
+        }
+      }
+    }
+    return ret;
+  }
+
+  private ChangeNotes notesFor(RevisionResource rsrc, Change.Id id) throws OrmException {
+    if (rsrc.getChange().getId().equals(id)) {
+      return rsrc.getNotes();
+    }
+    return notesFactory.createChecked(dbProvider.get(), rsrc.getProject(), id);
+  }
+
+  /**
+   * Find the commit onto which a patch set should be rebased.
+   *
+   * <p>This is defined as the latest patch set of the change corresponding to this commit's parent,
+   * or the destination branch tip in the case where the parent's change is merged.
+   *
+   * @param patchSet patch set for which the new base commit should be found.
+   * @param destBranch the destination branch.
+   * @param git the repository.
+   * @param rw the RevWalk.
+   * @return the commit onto which the patch set should be rebased.
+   * @throws RestApiException if rebase is not possible.
+   * @throws IOException if accessing the repository fails.
+   * @throws OrmException if accessing the database fails.
+   */
+  public ObjectId findBaseRevision(
+      PatchSet patchSet, Branch.NameKey destBranch, Repository git, RevWalk rw)
+      throws RestApiException, IOException, OrmException {
+    String baseRev = null;
+    RevCommit commit = rw.parseCommit(ObjectId.fromString(patchSet.getRevision().get()));
+
+    if (commit.getParentCount() > 1) {
+      throw new UnprocessableEntityException("Cannot rebase a change with multiple parents.");
+    } else if (commit.getParentCount() == 0) {
+      throw new UnprocessableEntityException(
+          "Cannot rebase a change without any parents (is this the initial commit?).");
+    }
+
+    RevId parentRev = new RevId(commit.getParent(0).name());
+
+    CHANGES:
+    for (ChangeData cd : queryProvider.get().byBranchCommit(destBranch, parentRev.get())) {
+      for (PatchSet depPatchSet : cd.patchSets()) {
+        if (!depPatchSet.getRevision().equals(parentRev)) {
+          continue;
+        }
+        Change depChange = cd.change();
+        if (depChange.getStatus() == Status.ABANDONED) {
+          throw new ResourceConflictException(
+              "Cannot rebase a change with an abandoned parent: " + depChange.getKey());
+        }
+
+        if (depChange.getStatus().isOpen()) {
+          if (depPatchSet.getId().equals(depChange.currentPatchSetId())) {
+            throw new ResourceConflictException(
+                "Change is already based on the latest patch set of the dependent change.");
+          }
+          baseRev = cd.currentPatchSet().getRevision().get();
+        }
+        break CHANGES;
+      }
+    }
+
+    if (baseRev == null) {
+      // We are dependent on a merged PatchSet or have no PatchSet
+      // dependencies at all.
+      Ref destRef = git.getRefDatabase().exactRef(destBranch.get());
+      if (destRef == null) {
+        throw new UnprocessableEntityException(
+            "The destination branch does not exist: " + destBranch.get());
+      }
+      baseRev = destRef.getObjectId().getName();
+      if (baseRev.equals(parentRev.get())) {
+        throw new ResourceConflictException("Change is already up to date.");
+      }
+    }
+    return ObjectId.fromString(baseRev);
+  }
+}