Refactor field selection and helpers

- Add FieldSelector.SelectorHelper with static methods to create selectors
- Add SelectorHelperTest
- Rename dns.AbstractOption to Option, make other Option classes abstract
- Add OptionTest class to resource manager and refactor other OptionTest classes

gcloud-java-bigquery/src/main/java/com/google/gcloud/bigquery/BigQuery.java

@@ -22,6 +22,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Lists;
 import com.google.gcloud.FieldSelector;
+import com.google.gcloud.FieldSelector.SelectorHelper;
 import com.google.gcloud.Page;
 import com.google.gcloud.Service;
 import com.google.gcloud.bigquery.spi.BigQueryRpc;
@@ -192,7 +193,7 @@ private DatasetOption(BigQueryRpc.Option option, Object value) {
      */
     public static DatasetOption fields(DatasetField... fields) {
       return new DatasetOption(BigQueryRpc.Option.FIELDS,
-          selector(DatasetField.REQUIRED_FIELDS, fields));
+          SelectorHelper.selector(DatasetField.REQUIRED_FIELDS, fields));
     }
   }
 
@@ -262,7 +263,7 @@ private TableOption(BigQueryRpc.Option option, Object value) {
      */
     public static TableOption fields(TableField... fields) {
       return new TableOption(BigQueryRpc.Option.FIELDS,
-          selector(TableField.REQUIRED_FIELDS, fields));
+          SelectorHelper.selector(TableField.REQUIRED_FIELDS, fields));
     }
   }
 
@@ -359,10 +360,9 @@ public static JobListOption pageToken(String pageToken) {
      * listing jobs.
      */
     public static JobListOption fields(JobField... fields) {
-      StringBuilder builder =
-          selector(new StringBuilder().append("etag,jobs("), JobField.REQUIRED_FIELDS, fields)
-              .append(",state,errorResult),nextPageToken");
-      return new JobListOption(BigQueryRpc.Option.FIELDS, builder.toString());
+      return new JobListOption(BigQueryRpc.Option.FIELDS,
+          SelectorHelper.selector("jobs", JobField.REQUIRED_FIELDS, fields, "state",
+              "errorResult"));
     }
   }
 
@@ -386,7 +386,7 @@ private JobOption(BigQueryRpc.Option option, Object value) {
      */
     public static JobOption fields(JobField... fields) {
       return new JobOption(BigQueryRpc.Option.FIELDS,
-          Option.selector(JobField.REQUIRED_FIELDS, fields));
+          SelectorHelper.selector(JobField.REQUIRED_FIELDS, fields));
     }
   }
 

gcloud-java-bigquery/src/main/java/com/google/gcloud/bigquery/Option.java

@@ -18,21 +18,16 @@
 
 import static com.google.common.base.Preconditions.checkNotNull;
 
-import com.google.common.base.Joiner;
 import com.google.common.base.MoreObjects;
-import com.google.common.collect.Sets;
-import com.google.gcloud.FieldSelector;
 import com.google.gcloud.bigquery.spi.BigQueryRpc;
 
 import java.io.Serializable;
-import java.util.List;
 import java.util.Objects;
-import java.util.Set;
 
 /**
  * Base class for BigQuery operation option.
  */
-class Option implements Serializable {
+abstract class Option implements Serializable {
 
   private static final long serialVersionUID = -6647817677804099207L;
 
@@ -73,20 +68,4 @@ public String toString() {
         .add("value", value)
         .toString();
   }
-
-  static String selector(List<FieldSelector> required, FieldSelector... others) {
-    Set<String> fieldStrings = Sets.newHashSetWithExpectedSize(required.size() + others.length);
-    for (FieldSelector field : required) {
-      fieldStrings.add(field.selector());
-    }
-    for (FieldSelector field : others) {
-      fieldStrings.add(field.selector());
-    }
-    return Joiner.on(',').join(fieldStrings);
-  }
-
-  static StringBuilder selector(StringBuilder partialSelector, List<FieldSelector> required,
-      FieldSelector... others) {
-    return partialSelector.append(selector(required, others));
-  }
 }

gcloud-java-bigquery/src/test/java/com/google/gcloud/bigquery/BigQueryImplTest.java

@@ -886,12 +886,14 @@ public com.google.api.services.bigquery.model.Job apply(Job job) {
     assertEquals(cursor, page.nextPageCursor());
     assertArrayEquals(jobList.toArray(), Iterables.toArray(page.values(), Job.class));
     String selector = (String) capturedOptions.getValue().get(JOB_OPTION_FIELDS.rpcOption());
-    assertTrue(selector.contains("etag,jobs("));
+    assertTrue(selector.contains("nextPageToken,jobs("));
     assertTrue(selector.contains("configuration"));
     assertTrue(selector.contains("jobReference"));
     assertTrue(selector.contains("statistics"));
-    assertTrue(selector.contains("state,errorResult),nextPageToken"));
-    assertEquals(80, selector.length());
+    assertTrue(selector.contains("state"));
+    assertTrue(selector.contains("errorResult"));
+    assertTrue(selector.contains(")"));
+    assertEquals(75, selector.length());
   }
 
   @Test

gcloud-java-bigquery/src/test/java/com/google/gcloud/bigquery/OptionTest.java

@@ -17,22 +17,49 @@
 package com.google.gcloud.bigquery;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNull;
 
 import com.google.gcloud.bigquery.spi.BigQueryRpc;
 
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.ExpectedException;
 
 public class OptionTest {
 
+  private static final BigQueryRpc.Option RPC_OPTION = BigQueryRpc.Option.PAGE_TOKEN;
+  private static final BigQueryRpc.Option ANOTHER_RPC_OPTION = BigQueryRpc.Option.FIELDS;
+  private static final String VALUE = "some value";
+  private static final String OTHER_VALUE = "another value";
+  private static final Option OPTION = new Option(RPC_OPTION, VALUE) {};
+  private static final Option OPTION_EQUALS = new Option(RPC_OPTION, VALUE) {};
+  private static final Option OPTION_NOT_EQUALS1 = new Option(RPC_OPTION, OTHER_VALUE) {};
+  private static final Option OPTION_NOT_EQUALS2 = new Option(ANOTHER_RPC_OPTION, VALUE) {};
+
+  @Rule
+  public ExpectedException thrown = ExpectedException.none();
+
+  @Test
+  public void testEquals() {
+    assertEquals(OPTION, OPTION_EQUALS);
+    assertNotEquals(OPTION, OPTION_NOT_EQUALS1);
+    assertNotEquals(OPTION, OPTION_NOT_EQUALS2);
+  }
+
   @Test
-  public void testOption() {
-    Option option = new Option(BigQueryRpc.Option.PAGE_TOKEN, "token");
-    assertEquals(BigQueryRpc.Option.PAGE_TOKEN, option.rpcOption());
-    assertEquals("token", option.value());
+  public void testHashCode() {
+    assertEquals(OPTION.hashCode(), OPTION_EQUALS.hashCode());
   }
 
-  @Test(expected = NullPointerException.class)
-  public void testNullRpcOption() {
-    new Option(null, "token");
+  @Test
+  public void testConstructor() {
+    assertEquals(RPC_OPTION, OPTION.rpcOption());
+    assertEquals(VALUE, OPTION.value());
+    Option option = new Option(RPC_OPTION, null) {};
+    assertEquals(RPC_OPTION, option.rpcOption());
+    assertNull(option.value());
+    thrown.expect(NullPointerException.class);
+    new Option(null, VALUE) {};
   }
 }

gcloud-java-core/src/main/java/com/google/gcloud/FieldSelector.java

@@ -16,9 +16,18 @@
 
 package com.google.gcloud;
 
+import com.google.common.base.Function;
+import com.google.common.base.Joiner;
+import com.google.common.collect.Lists;
+import com.google.common.collect.Sets;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Set;
+
 /**
  * Interface for Google Cloud resource's fields. Implementations of this interface can be used to
- * select only desired fields when getting or listing Google Cloud resources.
+ * select only desired fields from a returned Google Cloud resource.
  */
 public interface FieldSelector {
 
@@ -27,4 +36,61 @@ public interface FieldSelector {
    * other field selectors) to specify which resource fields should be returned by an API call.
    */
   String selector();
+
+  /**
+   * A helper class used to build composite selectors given a number of fields. This class is not
+   * supposed to be used directly by users.
+   */
+  class SelectorHelper {
+
+    private SelectorHelper() {}
+
+    private static final Function<FieldSelector, String> FIELD_TO_STRING_FUNCTION =
+        new Function<FieldSelector, String>() {
+          @Override
+          public String apply(FieldSelector fieldSelector) {
+            return fieldSelector.selector();
+          }
+        };
+
+    private static String selector(List<FieldSelector> required, FieldSelector[] others,
+      String... extraResourceFields) {
+      Set<String> fieldStrings = Sets.newHashSetWithExpectedSize(required.size() + others.length);
+      fieldStrings.addAll(Lists.transform(required, FIELD_TO_STRING_FUNCTION));
+      fieldStrings.addAll(Lists.transform(Arrays.asList(others), FIELD_TO_STRING_FUNCTION));
+      fieldStrings.addAll(Arrays.asList(extraResourceFields));
+      return Joiner.on(',').join(fieldStrings);
+    }
+
+    /**
+     * Returns a composite selector given a number of fields. The string selector returned by this
+     * method can be used for field selection in API calls that return a single resource. This
+     * method is not supposed to be used directly by users.
+     */
+    public static String selector(List<FieldSelector> required, FieldSelector... others) {
+      return selector(required, others, new String[]{});
+    }
+
+    /**
+     * Returns a composite selector given a number of fields and a container name. The string
+     * selector returned by this method can be used for field selection in API calls that return a
+     * list of resources. This method is not supposed to be used directly by users.
+     */
+    public static String selector(String containerName, List<FieldSelector> required,
+        FieldSelector... others) {
+      return "nextPageToken," + containerName + '(' + selector(required, others) + ')';
+    }
+
+    /**
+     * Returns a composite selector given a number of fields and a container name. This methods also
+     * takes an {@code extraResourceFields} parameter to specify some extra fields as strings. The
+     * string selector returned by this method can be used for field selection in API calls that
+     * return a list of resources. This method is not supposed to be used directly by users.
+     */
+    public static String selector(String containerName, List<FieldSelector> required,
+        FieldSelector[] others, String... extraResourceFields) {
+      return "nextPageToken," + containerName + '('
+          + selector(required, others, extraResourceFields) + ')';
+    }
+  }
 }

gcloud-java-core/src/test/java/com/google/gcloud/SelectorHelperTest.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2016 Google Inc. All Rights Reserved.
+ *
+ * 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.gcloud;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import com.google.common.collect.ImmutableList;
+import com.google.gcloud.FieldSelector.SelectorHelper;
+
+import org.junit.Test;
+
+import java.util.List;
+
+public class SelectorHelperTest {
+
+  private static final FieldSelector FIELD1 = new FieldSelector() {
+    @Override
+    public String selector() {
+      return "field1";
+    }
+  };
+  private static final FieldSelector FIELD2 = new FieldSelector() {
+    @Override
+    public String selector() {
+      return "field2";
+    }
+  };
+  private static final FieldSelector FIELD3 = new FieldSelector() {
+    @Override
+    public String selector() {
+      return "field3";
+    }
+  };
+  private static final List<FieldSelector> REQUIRED_FIELDS = ImmutableList.of(FIELD1, FIELD2);
+  private static final String CONTAINER = "container";
+
+  @Test
+  public void testSelector() {
+    String selector = SelectorHelper.selector(REQUIRED_FIELDS, FIELD3);
+    assertTrue(selector.contains("field1"));
+    assertTrue(selector.contains("field2"));
+    assertTrue(selector.contains("field3"));
+    assertEquals(20, selector.length());
+  }
+
+  @Test
+  public void testListSelector() {
+    String selector = SelectorHelper.selector(CONTAINER, REQUIRED_FIELDS, FIELD3);
+    assertTrue(selector.startsWith("nextPageToken,container("));
+    assertTrue(selector.contains("field1"));
+    assertTrue(selector.contains("field2"));
+    assertTrue(selector.contains("field3"));
+    assertTrue(selector.endsWith(")"));
+    assertEquals(45, selector.length());
+  }
+}