[ggj][codegen] feat: add header comments to ServiceClient

src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java

@@ -101,6 +101,8 @@ public GapicClass generate(Service service, Map<String, Message> messageTypes) {
 
     ClassDefinition classDef =
         ClassDefinition.builder()
+            .setHeaderCommentStatements(
+                ServiceClientCommentComposer.createClassHeaderComments(service))
             .setPackageString(pakkage)
             .setAnnotations(createClassAnnotations(types))
             .setImplementsTypes(createClassImplements(types))

src/main/java/com/google/api/generator/gapic/composer/ServiceClientCommentComposer.java

@@ -17,14 +17,62 @@
 import com.google.api.generator.engine.ast.CommentStatement;
 import com.google.api.generator.engine.ast.JavaDocComment;
 import com.google.api.generator.engine.ast.TypeNode;
+import com.google.api.generator.gapic.model.Service;
+import com.google.api.generator.gapic.utils.JavaStyle;
+import java.util.Arrays;
+import java.util.List;
 
 class ServiceClientCommentComposer {
+  // Tokens.
   private static final String COLON = ":";
 
+  // Constants.
+  private static final String SERVICE_DESCRIPTION_INTRO_STRING =
+      "This class provides the ability to make remote calls to the backing service through method "
+          + "calls that map to API methods. Sample code to get started:";
+  private static final String SERVICE_DESCRIPTION_CLOSE_STRING =
+      "Note: close() needs to be called on the echoClient object to clean up resources such as "
+          + "threads. In the example above, try-with-resources is used, which automatically calls "
+          + "close().";
+  private static final String SERVICE_DESCRIPTION_SURFACE_SUMMARY_STRING =
+      "The surface of this class includes several types of Java methods for each of the API's "
+          + "methods:";
+  private static final String SERVICE_DESCRIPTION_SURFACE_CODA_STRING =
+      "See the individual methods for example code.";
+  private static final String SERVICE_DESCRIPTION_RESOURCE_NAMES_FORMATTING_STRING =
+      "Many parameters require resource names to be formatted in a particular way. To assist with"
+          + " these names, this class includes a format method for each type of name, and"
+          + " additionally a parse  method to extract the individual identifiers contained within"
+          + " names that are returned.";
+  private static final String SERVICE_DESCRIPTION_CREDENTIALS_SUMMARY_STRING =
+      "To customize credentials:";
+  private static final String SERVICE_DESCRIPTION_ENDPOINT_SUMMARY_STRING =
+      "To customize the endpoint:";
+
+  private static final List<String> SERVICE_DESCRIPTION_SURFACE_DESCRIPTION =
+      Arrays.asList(
+          "A \"flattened\" method. With this type of method, the fields of the request type have"
+              + " been converted into function parameters. It may be the case that not all fields"
+              + " are available as parameters, and not every API method will have a flattened"
+              + " method entry point.",
+          "A \"request object\" method. This type of method only takes one parameter, a request"
+              + " object, which must be constructed before the call. Not every API method will"
+              + " have a request object method.",
+          "A \"callable\" method. This type of method takes no parameters and returns an immutable "
+              + "API callable object, which can be used to initiate calls to the service.");
+
+  // Patterns.
   private static final String CREATE_METHOD_STUB_ARG_PATTERN =
       "Constructs an instance of EchoClient, using the given stub for making calls. This is for"
           + " advanced usage - prefer using create(%s).";
 
+  private static final String SERVICE_DESCRIPTION_CUSTOMIZE_SUMMARY_PATTERN =
+      "This class can be customized by passing in a custom instance of %s to create(). For"
+          + " example:";
+
+  private static final String SERVICE_DESCRIPTION_SUMMARY_PATTERN = "Service Description: %s";
+
+  // Comments.
   static final CommentStatement CREATE_METHOD_NO_ARG_COMMENT =
       toSimpleComment("Constructs an instance of EchoClient with default settings.");
 
@@ -45,6 +93,41 @@ class ServiceClientCommentComposer {
           "Returns the OperationsClient that can be used to query the status of a long-running"
               + " operation returned by another API method call.");
 
+  static List<CommentStatement> createClassHeaderComments(Service service) {
+    JavaDocComment.Builder classHeaderJavadocBuilder = JavaDocComment.builder();
+    if (service.hasDescription()) {
+      classHeaderJavadocBuilder.addComment(
+          String.format(SERVICE_DESCRIPTION_SUMMARY_PATTERN, service.description()));
+    }
+
+    // Service introduction.
+    classHeaderJavadocBuilder.addParagraph(SERVICE_DESCRIPTION_INTRO_STRING);
+    // TODO(summerji): Add sample code here.
+
+    // API surface description.
+    classHeaderJavadocBuilder.addParagraph(SERVICE_DESCRIPTION_CLOSE_STRING);
+    classHeaderJavadocBuilder.addParagraph(SERVICE_DESCRIPTION_SURFACE_SUMMARY_STRING);
+    classHeaderJavadocBuilder.addOrderedList(SERVICE_DESCRIPTION_SURFACE_DESCRIPTION);
+    classHeaderJavadocBuilder.addParagraph(SERVICE_DESCRIPTION_SURFACE_CODA_STRING);
+
+    // Formatting resource names.
+    classHeaderJavadocBuilder.addParagraph(SERVICE_DESCRIPTION_RESOURCE_NAMES_FORMATTING_STRING);
+
+    // Customization examples.
+    classHeaderJavadocBuilder.addParagraph(
+        String.format(
+            SERVICE_DESCRIPTION_CUSTOMIZE_SUMMARY_PATTERN,
+            String.format("%sSettings", JavaStyle.toUpperCamelCase(service.name()))));
+    classHeaderJavadocBuilder.addParagraph(SERVICE_DESCRIPTION_CREDENTIALS_SUMMARY_STRING);
+    // TODO(summerji): Add credentials' customization sample code here.
+    classHeaderJavadocBuilder.addParagraph(SERVICE_DESCRIPTION_ENDPOINT_SUMMARY_STRING);
+    // TODO(summerji): Add endpoint customization sample code here.
+
+    return Arrays.asList(
+        CommentComposer.AUTO_GENERATED_CLASS_COMMENT,
+        CommentStatement.withComment(classHeaderJavadocBuilder.build()));
+  }
+
   static CommentStatement createCreateMethodStubArgComment(TypeNode settingsType) {
     return toSimpleComment(
         String.format(CREATE_METHOD_STUB_ARG_PATTERN, settingsType.reference().name()));

src/main/java/com/google/api/generator/gapic/model/Service.java

@@ -15,8 +15,10 @@
 package com.google.api.generator.gapic.model;
 
 import com.google.auto.value.AutoValue;
+import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
 import java.util.List;
+import javax.annotation.Nullable;
 
 @AutoValue
 public abstract class Service {
@@ -32,7 +34,12 @@ public abstract class Service {
 
   public abstract ImmutableList<Method> methods();
 
-  // TODO(miraleung): Get comments.
+  @Nullable
+  public abstract String description();
+
+  public boolean hasDescription() {
+    return !Strings.isNullOrEmpty(description());
+  }
 
   public static Builder builder() {
     return new AutoValue_Service.Builder().setMethods(ImmutableList.of());
@@ -52,6 +59,8 @@ public abstract static class Builder {
 
     public abstract Builder setMethods(List<Method> methods);
 
+    public abstract Builder setDescription(String description);
+
     public abstract Service build();
   }
 }