[ggj][codegen] feat: add per-type default value composer (#345)

* fix!: refactor field into MethodArgument, add enum/msg flags

* feat: partial isAssignableFrom VaporRef support, enable full-name type usage

* feat: support negative numeric literals

* fix: separate resname tokenizing from class composer

* feat: add per-type default value composer

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

@@ -0,0 +1,189 @@
+// Copyright 2020 Google LLC
+//
+// 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.api.generator.gapic.composer;
+
+import com.google.api.generator.engine.ast.ConcreteReference;
+import com.google.api.generator.engine.ast.Expr;
+import com.google.api.generator.engine.ast.MethodInvocationExpr;
+import com.google.api.generator.engine.ast.NewObjectExpr;
+import com.google.api.generator.engine.ast.PrimitiveValue;
+import com.google.api.generator.engine.ast.StringObjectValue;
+import com.google.api.generator.engine.ast.TypeNode;
+import com.google.api.generator.engine.ast.ValueExpr;
+import com.google.api.generator.gapic.model.Field;
+import com.google.api.generator.gapic.model.MethodArgument;
+import com.google.api.generator.gapic.model.ResourceName;
+import com.google.api.generator.gapic.utils.JavaStyle;
+import com.google.api.generator.gapic.utils.ResourceNameConstants;
+import com.google.common.base.Preconditions;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+public class DefaultValueComposer {
+  static Expr createDefaultValue(
+      MethodArgument methodArg, Map<String, ResourceName> resourceNames) {
+    if (methodArg.isResourceNameHelper()) {
+      Preconditions.checkState(
+          methodArg.field().hasResourceReference(),
+          String.format(
+              "No corresponding resource reference for argument %s found on field %s %s",
+              methodArg.name(), methodArg.field().type(), methodArg.field().name()));
+      ResourceName resourceName =
+          resourceNames.get(methodArg.field().resourceReference().resourceTypeString());
+      Preconditions.checkNotNull(
+          resourceName,
+          String.format(
+              "No resource name found for reference %s",
+              methodArg.field().resourceReference().resourceTypeString()));
+      return createDefaultValue(
+          resourceName, resourceNames.values().stream().collect(Collectors.toList()));
+    }
+
+    if (methodArg.type().equals(methodArg.field().type())) {
+      return createDefaultValue(methodArg.field());
+    }
+
+    return createDefaultValue(
+        Field.builder().setName(methodArg.name()).setType(methodArg.type()).build());
+  }
+
+  static Expr createDefaultValue(Field f) {
+    if (f.isRepeated()) {
+      TypeNode newType =
+          TypeNode.withReference(
+              ConcreteReference.withClazz(f.isMap() ? HashMap.class : ArrayList.class));
+      return NewObjectExpr.builder().setType(newType).setIsGeneric(true).build();
+    }
+
+    if (f.isEnum()) {
+      return MethodInvocationExpr.builder()
+          .setStaticReferenceType(f.type())
+          .setMethodName("forNumber")
+          .setArguments(
+              ValueExpr.withValue(
+                  PrimitiveValue.builder().setType(TypeNode.INT).setValue("0").build()))
+          .setReturnType(f.type())
+          .build();
+    }
+
+    if (f.isMessage()) {
+      MethodInvocationExpr newBuilderExpr =
+          MethodInvocationExpr.builder()
+              .setStaticReferenceType(f.type())
+              .setMethodName("newBuilder")
+              .build();
+      return MethodInvocationExpr.builder()
+          .setExprReferenceExpr(newBuilderExpr)
+          .setMethodName("build")
+          .setReturnType(f.type())
+          .build();
+    }
+
+    if (f.type().equals(TypeNode.STRING)) {
+      return ValueExpr.withValue(
+          StringObjectValue.withValue(String.format("%s%s", f.name(), f.name().hashCode())));
+    }
+
+    if (TypeNode.isNumericType(f.type())) {
+      return ValueExpr.withValue(
+          PrimitiveValue.builder()
+              .setType(f.type())
+              .setValue(String.format("%s", f.name().hashCode()))
+              .build());
+    }
+
+    if (f.type().equals(TypeNode.BOOLEAN)) {
+      return ValueExpr.withValue(
+          PrimitiveValue.builder().setType(f.type()).setValue("true").build());
+    }
+
+    throw new UnsupportedOperationException(
+        String.format(
+            "Default value for field %s with type %s not implemented yet.", f.name(), f.type()));
+  }
+
+  static Expr createDefaultValue(ResourceName resourceName, List<ResourceName> resnames) {
+    boolean hasOnePattern = resourceName.patterns().size() == 1;
+    if (resourceName.isOnlyWildcard()) {
+      List<ResourceName> unexaminedResnames = new ArrayList<>(resnames);
+      for (ResourceName resname : resnames) {
+        if (resname.isOnlyWildcard()) {
+          unexaminedResnames.remove(resname);
+          continue;
+        }
+        unexaminedResnames.remove(resname);
+        return createDefaultValue(resname, unexaminedResnames);
+      }
+      // Should not get here.
+      Preconditions.checkState(
+          !unexaminedResnames.isEmpty(),
+          String.format(
+              "No default resource name found for wildcard %s", resourceName.resourceTypeString()));
+    }
+
+    // The cost tradeoffs of new ctors versus distinct() don't really matter here, since this list
+    // will usually have a very small number of elements.
+    List<String> patterns = new ArrayList<>(new HashSet<>(resourceName.patterns()));
+    boolean containsOnlyDeletedTopic =
+        patterns.size() == 1 && patterns.get(0).equals(ResourceNameConstants.DELETED_TOPIC_LITERAL);
+    String ofMethodName = "of";
+    List<String> patternPlaceholderTokens = new ArrayList<>();
+
+    if (containsOnlyDeletedTopic) {
+      ofMethodName = "ofDeletedTopic";
+    } else {
+      for (String pattern : resourceName.patterns()) {
+        if (pattern.equals(ResourceNameConstants.WILDCARD_PATTERN)
+            || pattern.equals(ResourceNameConstants.DELETED_TOPIC_LITERAL)) {
+          continue;
+        }
+        patternPlaceholderTokens.addAll(
+            ResourceNameTokenizer.parseTokenHierarchy(Arrays.asList(pattern)).get(0));
+        break;
+      }
+    }
+
+    if (!hasOnePattern) {
+      ofMethodName =
+          String.format(
+              "of%sName",
+              String.join(
+                  "",
+                  patternPlaceholderTokens.stream()
+                      .map(s -> JavaStyle.toUpperCamelCase(s))
+                      .collect(Collectors.toList())));
+    }
+
+    TypeNode resourceNameJavaType = resourceName.type();
+    List<Expr> argExprs =
+        patternPlaceholderTokens.stream()
+            .map(
+                s ->
+                    ValueExpr.withValue(
+                        StringObjectValue.withValue(String.format("[%s]", s.toUpperCase()))))
+            .collect(Collectors.toList());
+    return MethodInvocationExpr.builder()
+        .setStaticReferenceType(resourceNameJavaType)
+        .setMethodName(ofMethodName)
+        .setArguments(argExprs)
+        .setReturnType(resourceNameJavaType)
+        .build();
+  }
+}