Support removing a reviewer via REST API

curl -X DELETE \
  http://localhost/changes/test~master~I2933f24c.../reviewers/1000000

Change-Id: I98057ceb7590642a3e5bbcd3c4b17ebef6364eab

gerrit-server/src/main/java/com/google/gerrit/server/change/DeleteReviewer.java

@@ -0,0 +1,88 @@
+// Copyright (C) 2012 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.common.base.Predicate;
+import com.google.common.collect.Iterables;
+import com.google.common.collect.Lists;
+import com.google.gerrit.extensions.restapi.AuthException;
+import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
+import com.google.gerrit.extensions.restapi.RestModifyView;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.reviewdb.client.PatchSetApproval;
+import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.change.DeleteReviewer.Input;
+import com.google.gerrit.server.project.ChangeControl;
+import com.google.gwtorm.server.OrmException;
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+
+import java.util.List;
+
+class DeleteReviewer implements RestModifyView<ReviewerResource, Input> {
+  static class Input {
+  }
+
+  private final Provider<ReviewDb> dbProvider;
+
+  @Inject
+  DeleteReviewer(Provider<ReviewDb> dbProvider) {
+    this.dbProvider = dbProvider;
+  }
+
+  @Override
+  public Class<Input> inputType() {
+    return Input.class;
+  }
+
+  @Override
+  public Object apply(ReviewerResource rsrc, Input input)
+      throws AuthException, ResourceNotFoundException, OrmException {
+    ChangeControl control = rsrc.getControl();
+    Change.Id changeId = rsrc.getChange().getId();
+    ReviewDb db = dbProvider.get();
+    db.changes().beginTransaction(changeId);
+    try {
+      List<PatchSetApproval> del = Lists.newArrayList();
+      for (PatchSetApproval a : approvals(db, rsrc)) {
+        if (control.canRemoveReviewer(a)) {
+          del.add(a);
+        } else {
+          throw new AuthException("delete not permitted");
+        }
+      }
+      if (del.isEmpty()) {
+        throw new ResourceNotFoundException();
+      }
+      db.patchSetApprovals().delete(del);
+      db.commit();
+    } finally {
+      db.rollback();
+    }
+    return new Object();
+  }
+
+  private Iterable<PatchSetApproval> approvals(ReviewDb db,
+      final ReviewerResource rsrc) throws OrmException {
+    return Iterables.filter(
+        db.patchSetApprovals().byChange(rsrc.getChange().getId()),
+        new Predicate<PatchSetApproval>() {
+          @Override
+          public boolean apply(PatchSetApproval input) {
+            return input.getAccountId().equals(rsrc.getAccount().getId());
+          }
+        });
+  }
+}