/**
   * Classes are processed in 3 phases:
   *
   * <ol>
   *   <li>The class name is extracted.
   *   <li>Class members are processed and rewritten.
   *   <li>The constructor is built.
   * </ol>
   */
  private void visitClass(Node classNode, Node parent) {
    checkClassReassignment(classNode);
    // Collect Metadata
    ClassDeclarationMetadata metadata = ClassDeclarationMetadata.create(classNode, parent);

    if (metadata == null || metadata.fullClassName == null) {
      cannotConvert(
          parent,
          "Can only convert classes that are declarations or the right hand"
              + " side of a simple assignment.");
      return;
    }
    if (metadata.hasSuperClass() && !metadata.superClassNameNode.isQualifiedName()) {
      compiler.report(JSError.make(metadata.superClassNameNode, DYNAMIC_EXTENDS_TYPE));
      return;
    }

    boolean useUnique = NodeUtil.isStatement(classNode) && !NodeUtil.isInFunction(classNode);
    String uniqueFullClassName =
        useUnique ? getUniqueClassName(metadata.fullClassName) : metadata.fullClassName;
    Node classNameAccess = NodeUtil.newQName(compiler, uniqueFullClassName);
    Node prototypeAccess = NodeUtil.newPropertyAccess(compiler, classNameAccess, "prototype");

    Preconditions.checkState(
        NodeUtil.isStatement(metadata.insertionPoint),
        "insertion point must be a statement: %s",
        metadata.insertionPoint);

    Node constructor = null;
    JSDocInfo ctorJSDocInfo = null;
    // Process all members of the class
    Node classMembers = classNode.getLastChild();
    Map<String, JSDocInfo> prototypeMembersToDeclare = new LinkedHashMap<>();
    Map<String, JSDocInfo> classMembersToDeclare = new LinkedHashMap<>();
    for (Node member : classMembers.children()) {
      if (member.isEmpty()) {
        continue;
      }
      Preconditions.checkState(
          member.isMemberFunctionDef()
              || member.isGetterDef()
              || member.isSetterDef()
              || (member.isComputedProp() && !member.getBooleanProp(Node.COMPUTED_PROP_VARIABLE)),
          "Member variables should have been transpiled earlier: ",
          member);

      if (member.isGetterDef() || member.isSetterDef()) {
        JSTypeExpression typeExpr = getTypeFromGetterOrSetter(member).clone();
        addToDefinePropertiesObject(metadata, member);

        Map<String, JSDocInfo> membersToDeclare =
            member.isStaticMember() ? classMembersToDeclare : prototypeMembersToDeclare;
        JSDocInfo existingJSDoc = membersToDeclare.get(member.getString());
        JSTypeExpression existingType = existingJSDoc == null ? null : existingJSDoc.getType();
        if (existingType != null && !existingType.equals(typeExpr)) {
          compiler.report(JSError.make(member, CONFLICTING_GETTER_SETTER_TYPE, member.getString()));
        } else {
          JSDocInfoBuilder jsDoc = new JSDocInfoBuilder(false);
          jsDoc.recordType(typeExpr);
          if (member.getJSDocInfo() != null && member.getJSDocInfo().isExport()) {
            jsDoc.recordExport();
          }
          if (member.isStaticMember()) {
            jsDoc.recordNoCollapse();
          }
          membersToDeclare.put(member.getString(), jsDoc.build());
        }
      } else if (member.isMemberFunctionDef() && member.getString().equals("constructor")) {
        ctorJSDocInfo = member.getJSDocInfo();
        constructor = member.getFirstChild().detachFromParent();
        if (!metadata.anonymous) {
          // Turns class Foo { constructor: function() {} } into function Foo() {},
          // i.e. attaches the name the ctor function.
          constructor.replaceChild(constructor.getFirstChild(), metadata.classNameNode.cloneNode());
        }
      } else {
        Node qualifiedMemberAccess =
            getQualifiedMemberAccess(compiler, member, classNameAccess, prototypeAccess);
        Node method = member.getLastChild().detachFromParent();

        Node assign = IR.assign(qualifiedMemberAccess, method);
        assign.useSourceInfoIfMissingFromForTree(member);

        JSDocInfo info = member.getJSDocInfo();
        if (member.isStaticMember() && NodeUtil.referencesThis(assign.getLastChild())) {
          JSDocInfoBuilder memberDoc = JSDocInfoBuilder.maybeCopyFrom(info);
          memberDoc.recordThisType(
              new JSTypeExpression(
                  new Node(Token.BANG, new Node(Token.QMARK)), member.getSourceFileName()));
          info = memberDoc.build();
        }
        if (info != null) {
          assign.setJSDocInfo(info);
        }

        Node newNode = NodeUtil.newExpr(assign);
        metadata.insertNodeAndAdvance(newNode);
      }
    }

    // Add declarations for properties that were defined with a getter and/or setter,
    // so that the typechecker knows those properties exist on the class.
    // This is a temporary solution. Eventually, the type checker should understand
    // Object.defineProperties calls directly.
    for (Map.Entry<String, JSDocInfo> entry : prototypeMembersToDeclare.entrySet()) {
      String declaredMember = entry.getKey();
      Node declaration = IR.getprop(prototypeAccess.cloneTree(), IR.string(declaredMember));
      declaration.setJSDocInfo(entry.getValue());
      metadata.insertNodeAndAdvance(
          IR.exprResult(declaration).useSourceInfoIfMissingFromForTree(classNode));
    }
    for (Map.Entry<String, JSDocInfo> entry : classMembersToDeclare.entrySet()) {
      String declaredMember = entry.getKey();
      Node declaration = IR.getprop(classNameAccess.cloneTree(), IR.string(declaredMember));
      declaration.setJSDocInfo(entry.getValue());
      metadata.insertNodeAndAdvance(
          IR.exprResult(declaration).useSourceInfoIfMissingFromForTree(classNode));
    }

    if (metadata.definePropertiesObjForPrototype.hasChildren()) {
      Node definePropsCall =
          IR.exprResult(
              IR.call(
                  NodeUtil.newQName(compiler, "Object.defineProperties"),
                  prototypeAccess.cloneTree(),
                  metadata.definePropertiesObjForPrototype));
      definePropsCall.useSourceInfoIfMissingFromForTree(classNode);
      metadata.insertNodeAndAdvance(definePropsCall);
    }

    if (metadata.definePropertiesObjForClass.hasChildren()) {
      Node definePropsCall =
          IR.exprResult(
              IR.call(
                  NodeUtil.newQName(compiler, "Object.defineProperties"),
                  classNameAccess.cloneTree(),
                  metadata.definePropertiesObjForClass));
      definePropsCall.useSourceInfoIfMissingFromForTree(classNode);
      metadata.insertNodeAndAdvance(definePropsCall);
    }

    Preconditions.checkNotNull(constructor);

    JSDocInfo classJSDoc = NodeUtil.getBestJSDocInfo(classNode);
    JSDocInfoBuilder newInfo = JSDocInfoBuilder.maybeCopyFrom(classJSDoc);

    newInfo.recordConstructor();

    if (metadata.hasSuperClass()) {
      String superClassString = metadata.superClassNameNode.getQualifiedName();
      if (newInfo.isInterfaceRecorded()) {
        newInfo.recordExtendedInterface(
            new JSTypeExpression(
                new Node(Token.BANG, IR.string(superClassString)),
                metadata.superClassNameNode.getSourceFileName()));
      } else {
        Node inherits =
            IR.call(
                NodeUtil.newQName(compiler, INHERITS),
                NodeUtil.newQName(compiler, metadata.fullClassName),
                NodeUtil.newQName(compiler, superClassString));
        Node inheritsCall = IR.exprResult(inherits);
        compiler.needsEs6Runtime = true;

        inheritsCall.useSourceInfoIfMissingFromForTree(classNode);
        Node enclosingStatement = NodeUtil.getEnclosingStatement(classNode);
        enclosingStatement.getParent().addChildAfter(inheritsCall, enclosingStatement);
        newInfo.recordBaseType(
            new JSTypeExpression(
                new Node(Token.BANG, IR.string(superClassString)),
                metadata.superClassNameNode.getSourceFileName()));
      }
    }

    // Classes are @struct by default.
    if (!newInfo.isUnrestrictedRecorded()
        && !newInfo.isDictRecorded()
        && !newInfo.isStructRecorded()) {
      newInfo.recordStruct();
    }

    if (ctorJSDocInfo != null) {
      newInfo.recordSuppressions(ctorJSDocInfo.getSuppressions());
      for (String param : ctorJSDocInfo.getParameterNames()) {
        newInfo.recordParameter(param, ctorJSDocInfo.getParameterType(param));
      }
      newInfo.mergePropertyBitfieldFrom(ctorJSDocInfo);
    }

    if (NodeUtil.isStatement(classNode)) {
      constructor.getFirstChild().setString("");
      Node ctorVar = IR.let(metadata.classNameNode.cloneNode(), constructor);
      ctorVar.useSourceInfoIfMissingFromForTree(classNode);
      parent.replaceChild(classNode, ctorVar);
    } else {
      parent.replaceChild(classNode, constructor);
    }

    if (NodeUtil.isStatement(constructor)) {
      constructor.setJSDocInfo(newInfo.build());
    } else if (parent.isName()) {
      // The constructor function is the RHS of a var statement.
      // Add the JSDoc to the VAR node.
      Node var = parent.getParent();
      var.setJSDocInfo(newInfo.build());
    } else if (constructor.getParent().isName()) {
      // Is a newly created VAR node.
      Node var = constructor.getParent().getParent();
      var.setJSDocInfo(newInfo.build());
    } else if (parent.isAssign()) {
      // The constructor function is the RHS of an assignment.
      // Add the JSDoc to the ASSIGN node.
      parent.setJSDocInfo(newInfo.build());
    } else {
      throw new IllegalStateException("Unexpected parent node " + parent);
    }

    compiler.reportCodeChange();
  }
  private void visitScriptNode(NodeTraversal t) {
    if (mode == Mode.SINGLE_FILE && requires.isEmpty()) {
      // Likely a file that isn't using Closure at all.
      return;
    }

    Set<String> namespaces = new HashSet<>();

    // For every usage, check that there is a goog.require, and warn if not.
    for (Map.Entry<String, Node> entry : usages.entrySet()) {
      String namespace = entry.getKey();
      if (namespace.endsWith(".call") || namespace.endsWith(".apply")) {
        namespace = namespace.substring(0, namespace.lastIndexOf('.'));
      }
      if (namespace.startsWith("goog.global.")) {
        continue;
      }

      Node node = entry.getValue();
      JSDocInfo info = NodeUtil.getBestJSDocInfo(NodeUtil.getEnclosingStatement(node));
      if (info != null && info.getSuppressions().contains("missingRequire")) {
        continue;
      }

      String outermostClassName = getOutermostClassName(namespace);
      // The parent namespace is also checked as part of the requires so that classes
      // used by goog.module are still checked properly. This may cause missing requires
      // to be missed but in practice that should happen rarely.
      String nonNullClassName = outermostClassName != null ? outermostClassName : namespace;
      String parentNamespace = null;
      int separatorIndex = nonNullClassName.lastIndexOf('.');
      if (separatorIndex > 0) {
        parentNamespace = nonNullClassName.substring(0, separatorIndex);
      }
      boolean notProvidedByConstructors =
          !providedNames.contains(namespace)
              && !providedNames.contains(outermostClassName)
              && !providedNames.contains(parentNamespace);
      boolean notProvidedByRequires =
          !requires.containsKey(namespace)
              && !requires.containsKey(outermostClassName)
              && !requires.containsKey(parentNamespace);
      if (notProvidedByConstructors
          && notProvidedByRequires
          && !namespaces.contains(namespace)
          && !"goog".equals(parentNamespace)) {
        // TODO(mknichel): If the symbol is not explicitly provided, find the next best
        // symbol from the provides in the same file.
        String rootName = Splitter.on('.').split(namespace).iterator().next();
        if (mode != Mode.SINGLE_FILE || closurizedNamespaces.contains(rootName)) {
          if (node.isCall()) {
            compiler.report(t.makeError(node, MISSING_REQUIRE_CALL_WARNING, namespace));
          } else {
            compiler.report(t.makeError(node, MISSING_REQUIRE_WARNING, namespace));
          }
          namespaces.add(namespace);
        }
      }
    }

    // For every goog.require, check that there is a usage (in either usages or weakUsages)
    // and warn if there is not.
    for (Map.Entry<String, Node> entry : requires.entrySet()) {
      String require = entry.getKey();
      Node call = entry.getValue();
      Node parent = call.getParent();
      if (parent.isAssign()) {
        // var baz = goog.require('foo.bar.baz');
        // Assume that the var 'baz' is used somewhere, and don't warn.
        continue;
      }
      if (!usages.containsKey(require) && !weakUsages.containsKey(require)) {
        reportExtraRequireWarning(call, require);
      }
    }
  }
  /**
   * Classes are processed in 3 phases: 1) The class name is extracted. 2) Class members are
   * processed and rewritten. 3) The constructor is built.
   */
  private void visitClass(Node classNode, Node parent) {
    checkClassReassignment(classNode);
    // Collect Metadata
    Node className = classNode.getFirstChild();
    Node superClassName = className.getNext();
    Node classMembers = classNode.getLastChild();

    // This is a statement node. We insert methods of the
    // transpiled class after this node.
    Node insertionPoint;

    if (!superClassName.isEmpty() && !superClassName.isQualifiedName()) {
      compiler.report(JSError.make(superClassName, DYNAMIC_EXTENDS_TYPE));
      return;
    }

    // The fully qualified name of the class, which will be used in the output.
    // May come from the class itself or the LHS of an assignment.
    String fullClassName = null;

    // Whether the constructor function in the output should be anonymous.
    boolean anonymous;

    // If this is a class statement, or a class expression in a simple
    // assignment or var statement, convert it. In any other case, the
    // code is too dynamic, so just call cannotConvert.
    if (NodeUtil.isStatement(classNode)) {
      fullClassName = className.getString();
      anonymous = false;
      insertionPoint = classNode;
    } else if (parent.isAssign() && parent.getParent().isExprResult()) {
      // Add members after the EXPR_RESULT node:
      // example.C = class {}; example.C.prototype.foo = function() {};
      fullClassName = parent.getFirstChild().getQualifiedName();
      if (fullClassName == null) {
        cannotConvert(
            parent,
            "Can only convert classes that are declarations or the right hand"
                + " side of a simple assignment.");
        return;
      }
      anonymous = true;
      insertionPoint = parent.getParent();
    } else if (parent.isName()) {
      // Add members after the 'var' statement.
      // var C = class {}; C.prototype.foo = function() {};
      fullClassName = parent.getString();
      anonymous = true;
      insertionPoint = parent.getParent();
    } else {
      cannotConvert(
          parent,
          "Can only convert classes that are declarations or the right hand"
              + " side of a simple assignment.");
      return;
    }

    if (!className.isEmpty() && !className.getString().equals(fullClassName)) {
      // cannot bind two class names in the case of: var Foo = class Bar {};
      cannotConvertYet(classNode, "named class in an assignment");
      return;
    }

    boolean useUnique = NodeUtil.isStatement(classNode) && !isInFunction(classNode);
    String uniqueFullClassName = useUnique ? getUniqueClassName(fullClassName) : fullClassName;
    String superClassString = superClassName.getQualifiedName();

    Verify.verify(NodeUtil.isStatement(insertionPoint));

    Node constructor = null;
    JSDocInfo ctorJSDocInfo = null;
    // Process all members of the class
    for (Node member : classMembers.children()) {
      if (member.isEmpty()) {
        continue;
      }

      if (member.isMemberDef() && member.getString().equals("constructor")) {
        ctorJSDocInfo = member.getJSDocInfo();
        constructor = member.getFirstChild().detachFromParent();
        if (!anonymous) {
          constructor.replaceChild(constructor.getFirstChild(), className.cloneNode());
        }
      } else {
        Node qualifiedMemberName;
        Node method;
        if (member.isMemberDef()) {
          if (member.isStaticMember()) {
            qualifiedMemberName =
                NodeUtil.newQualifiedNameNode(
                    compiler.getCodingConvention(),
                    Joiner.on(".").join(uniqueFullClassName, member.getString()));
          } else {
            qualifiedMemberName =
                NodeUtil.newQualifiedNameNode(
                    compiler.getCodingConvention(),
                    Joiner.on(".").join(uniqueFullClassName, "prototype", member.getString()));
          }
          method = member.getFirstChild().detachFromParent();
        } else if (member.isComputedProp()) {
          if (member.isStaticMember()) {
            qualifiedMemberName =
                IR.getelem(
                    NodeUtil.newQualifiedNameNode(
                        compiler.getCodingConvention(), uniqueFullClassName),
                    member.removeFirstChild());
          } else {
            qualifiedMemberName =
                IR.getelem(
                    NodeUtil.newQualifiedNameNode(
                        compiler.getCodingConvention(),
                        Joiner.on('.').join(uniqueFullClassName, "prototype")),
                    member.removeFirstChild());
          }
          method = member.getLastChild().detachFromParent();
        } else {
          throw new IllegalStateException("Unexpected class member: " + member);
        }
        Node assign = IR.assign(qualifiedMemberName, method);
        assign.useSourceInfoIfMissingFromForTree(member);

        JSDocInfo info = member.getJSDocInfo();
        if (member.isStaticMember() && NodeUtil.referencesThis(assign.getLastChild())) {
          JSDocInfoBuilder memberDoc;
          if (info == null) {
            memberDoc = new JSDocInfoBuilder(true);
          } else {
            memberDoc = JSDocInfoBuilder.copyFrom(info);
          }
          memberDoc.recordThisType(
              new JSTypeExpression(
                  new Node(Token.BANG, new Node(Token.QMARK)), member.getSourceFileName()));
          info = memberDoc.build(assign);
        }
        if (info != null) {
          info.setAssociatedNode(assign);
          assign.setJSDocInfo(info);
        }

        Node newNode = NodeUtil.newExpr(assign);
        insertionPoint.getParent().addChildAfter(newNode, insertionPoint);
        insertionPoint = newNode;
      }
    }

    // Rewrite constructor
    if (constructor == null) {
      Node body = IR.block();
      if (!superClassName.isEmpty()) {
        Node superCall = baseCall(classNode, "constructor", null);
        body.addChildToBack(IR.exprResult(superCall));
      }
      Node name = anonymous ? IR.name("").srcref(className) : className.detachFromParent();
      constructor =
          IR.function(name, IR.paramList(), body).useSourceInfoIfMissingFromForTree(classNode);
    }
    JSDocInfo classJSDoc = classNode.getJSDocInfo();
    JSDocInfoBuilder newInfo =
        (classJSDoc != null) ? JSDocInfoBuilder.copyFrom(classJSDoc) : new JSDocInfoBuilder(true);

    newInfo.recordConstructor();
    if (!superClassName.isEmpty()) {

      if (newInfo.isInterfaceRecorded()) {
        newInfo.recordExtendedInterface(
            new JSTypeExpression(
                new Node(Token.BANG, IR.string(superClassString)),
                superClassName.getSourceFileName()));
      } else {
        Node inherits =
            IR.call(
                NodeUtil.newQualifiedNameNode(compiler.getCodingConvention(), INHERITS),
                NodeUtil.newQualifiedNameNode(compiler.getCodingConvention(), fullClassName),
                NodeUtil.newQualifiedNameNode(compiler.getCodingConvention(), superClassString));
        Node inheritsCall = IR.exprResult(inherits);
        inheritsCall.useSourceInfoIfMissingFromForTree(classNode);
        Node enclosingStatement = NodeUtil.getEnclosingStatement(classNode);
        enclosingStatement.getParent().addChildAfter(inheritsCall, enclosingStatement);
        newInfo.recordBaseType(
            new JSTypeExpression(
                new Node(Token.BANG, IR.string(superClassString)),
                superClassName.getSourceFileName()));

        Node copyProps =
            IR.call(
                NodeUtil.newQualifiedNameNode(compiler.getCodingConvention(), COPY_PROP),
                NodeUtil.newQualifiedNameNode(compiler.getCodingConvention(), fullClassName),
                NodeUtil.newQualifiedNameNode(compiler.getCodingConvention(), superClassString));
        copyProps.useSourceInfoIfMissingFromForTree(classNode);
        enclosingStatement
            .getParent()
            .addChildAfter(IR.exprResult(copyProps).srcref(classNode), enclosingStatement);
      }
    }

    // Classes are @struct by default.
    if (!newInfo.isUnrestrictedRecorded()
        && !newInfo.isDictRecorded()
        && !newInfo.isStructRecorded()) {
      newInfo.recordStruct();
    }

    if (ctorJSDocInfo != null) {
      newInfo.recordSuppressions(ctorJSDocInfo.getSuppressions());
      for (String param : ctorJSDocInfo.getParameterNames()) {
        newInfo.recordParameter(param, ctorJSDocInfo.getParameterType(param));
      }
    }
    insertionPoint = constructor;

    if (NodeUtil.isStatement(classNode)) {
      constructor.getFirstChild().setString("");
      Node ctorVar = IR.var(IR.name(fullClassName), constructor);
      ctorVar.useSourceInfoIfMissingFromForTree(classNode);
      parent.replaceChild(classNode, ctorVar);
    } else {
      parent.replaceChild(classNode, constructor);
    }

    if (NodeUtil.isStatement(constructor)) {
      insertionPoint.setJSDocInfo(newInfo.build(insertionPoint));
    } else if (parent.isName()) {
      // The constructor function is the RHS of a var statement.
      // Add the JSDoc to the VAR node.
      Node var = parent.getParent();
      var.setJSDocInfo(newInfo.build(var));
    } else if (constructor.getParent().isName()) {
      // Is a newly created VAR node.
      Node var = constructor.getParent().getParent();
      var.setJSDocInfo(newInfo.build(var));
    } else if (parent.isAssign()) {
      // The constructor function is the RHS of an assignment.
      // Add the JSDoc to the ASSIGN node.
      parent.setJSDocInfo(newInfo.build(parent));
    } else {
      throw new IllegalStateException("Unexpected parent node " + parent);
    }

    compiler.reportCodeChange();
  }