refactor(compiler): introduce ClassBuilder.

Part of #11683

modules/@angular/compiler/src/output/class_builder.ts

@@ -0,0 +1,60 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import * as o from './output_ast';
+
+/**
+ * Create a new class stmts based on the given data.
+ */
+export function createClassStmt(config: {
+  name: string,
+  parent?: o.Expression,
+  parentArgs?: o.Expression[],
+  ctorParams?: o.FnParam[],
+  builders: ClassBuilderPart | ClassBuilderPart[], modifiers?: o.StmtModifier[]
+}): o.ClassStmt {
+  const parentArgs = config.parentArgs || [];
+  const superCtorStmts = config.parent ? [o.SUPER_EXPR.callFn(parentArgs).toStmt()] : [];
+  const builder =
+      concatClassBuilderParts(Array.isArray(config.builders) ? config.builders : [config.builders]);
+  const ctor =
+      new o.ClassMethod(null, config.ctorParams || [], superCtorStmts.concat(builder.ctorStmts));
+
+  return new o.ClassStmt(
+      config.name, config.parent, builder.fields, builder.getters, ctor, builder.methods,
+      config.modifiers || [])
+}
+
+function concatClassBuilderParts(builders: ClassBuilderPart[]): ClassBuilder {
+  return {
+    fields: [].concat(...builders.map(builder => builder.fields || [])),
+    methods: [].concat(...builders.map(builder => builder.methods || [])),
+    getters: [].concat(...builders.map(builder => builder.getters || [])),
+    ctorStmts: [].concat(...builders.map(builder => builder.ctorStmts || [])),
+  };
+}
+
+/**
+ * Collects data for a generated class.
+ */
+export interface ClassBuilderPart {
+  fields?: o.ClassField[];
+  methods?: o.ClassMethod[];
+  getters?: o.ClassGetter[];
+  ctorStmts?: o.Statement[];
+}
+
+/**
+ * Collects data for a generated class.
+ */
+export interface ClassBuilder extends ClassBuilderPart {
+  fields: o.ClassField[];
+  methods: o.ClassMethod[];
+  getters: o.ClassGetter[];
+  ctorStmts: o.Statement[];
+}