feat(): support ng add (#15323)

* feat(angular): support ng add

* feat(): add build aditions

* chore(): update schematics

* chore(): bad style import

angular/src/schematics/utils/devkit-utils/change.ts

@@ -0,0 +1,127 @@
+/**
+ * @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
+ */
+export interface Host {
+  write(path: string, content: string): Promise<void>;
+  read(path: string): Promise<string>;
+}
+
+
+export interface Change {
+  apply(host: Host): Promise<void>;
+
+  // The file this change should be applied to. Some changes might not apply to
+  // a file (maybe the config).
+  readonly path: string | null;
+
+  // The order this change should be applied. Normally the position inside the file.
+  // Changes are applied from the bottom of a file to the top.
+  readonly order: number;
+
+  // The description of this change. This will be outputted in a dry or verbose run.
+  readonly description: string;
+}
+
+
+/**
+ * An operation that does nothing.
+ */
+export class NoopChange implements Change {
+  description = 'No operation.';
+  order = Infinity;
+  path = null;
+  apply() { return Promise.resolve(); }
+}
+
+
+/**
+ * Will add text to the source code.
+ */
+export class InsertChange implements Change {
+
+  order: number;
+  description: string;
+
+  constructor(public path: string, public pos: number, public toAdd: string) {
+    if (pos < 0) {
+      throw new Error('Negative positions are invalid');
+    }
+    this.description = `Inserted ${toAdd} into position ${pos} of ${path}`;
+    this.order = pos;
+  }
+
+  /**
+   * This method does not insert spaces if there is none in the original string.
+   */
+  apply(host: Host) {
+    return host.read(this.path).then(content => {
+      const prefix = content.substring(0, this.pos);
+      const suffix = content.substring(this.pos);
+
+      return host.write(this.path, `${prefix}${this.toAdd}${suffix}`);
+    });
+  }
+}
+
+/**
+ * Will remove text from the source code.
+ */
+export class RemoveChange implements Change {
+
+  order: number;
+  description: string;
+
+  constructor(public path: string, private pos: number, private toRemove: string) {
+    if (pos < 0) {
+      throw new Error('Negative positions are invalid');
+    }
+    this.description = `Removed ${toRemove} into position ${pos} of ${path}`;
+    this.order = pos;
+  }
+
+  apply(host: Host): Promise<void> {
+    return host.read(this.path).then(content => {
+      const prefix = content.substring(0, this.pos);
+      const suffix = content.substring(this.pos + this.toRemove.length);
+
+      // TODO: throw error if toRemove doesn't match removed string.
+      return host.write(this.path, `${prefix}${suffix}`);
+    });
+  }
+}
+
+/**
+ * Will replace text from the source code.
+ */
+export class ReplaceChange implements Change {
+  order: number;
+  description: string;
+
+  constructor(public path: string, private pos: number, private oldText: string,
+              private newText: string) {
+    if (pos < 0) {
+      throw new Error('Negative positions are invalid');
+    }
+    this.description = `Replaced ${oldText} into position ${pos} of ${path} with ${newText}`;
+    this.order = pos;
+  }
+
+  apply(host: Host): Promise<void> {
+    return host.read(this.path).then(content => {
+      const prefix = content.substring(0, this.pos);
+      const suffix = content.substring(this.pos + this.oldText.length);
+      const text = content.substring(this.pos, this.pos + this.oldText.length);
+
+      if (text !== this.oldText) {
+        return Promise.reject(new Error(`Invalid replace: "${text}" != "${this.oldText}".`));
+      }
+
+      // TODO: throw error if oldText doesn't match removed string.
+      return host.write(this.path, `${prefix}${this.newText}${suffix}`);
+    });
+  }
+}