feat: add file system utilities for 'upgrade' process

'fs-promise.ts' is a utility file for asynchronous read/write operations
'change.ts' implements some change interfaces as specified by the upgrade design doc linked below:
https://github.com/hansl/angular-cli/blob/7ea3e78ff3d899d5277aac5dfeeece4056d0efe3/docs/design/upgrade.md

addon/ng2/utilities/change.ts

@@ -0,0 +1,114 @@
+'use strict';
+
+import * as Promise from 'ember-cli/lib/ext/promise';
+import fs = require('fs');
+
+const readFile = Promise.denodeify(fs.readFile);
+const writeFile = Promise.denodeify(fs.writeFile);
+
+export interface Change {
+
+  apply(): Promise<void>;
+
+  // The file this change should be applied to. Some changes might not apply to
+  // a file (maybe the config).
+  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.
+  order: number;
+
+  // The description of this change. This will be outputted in a dry or verbose run.
+  description: string;
+}
+
+/**
+ * Will add text to the source code.
+ */
+export class InsertChange implements Change {
+
+  const order: number;
+  const description: string;
+
+  constructor(
+      public path: string,
+      private pos: number,
+      private toAdd: string,
+      ) {
+    if (pos < 0) {
+      throw new Error('Negative positions are invalid');
+    }
+    this.description = `Inserted ${toAdd} into position ${pos} of ${path}`;
+    this.order = pos;
+  }
+
+  /**
+   * This method does not insert spaces if there is none in the original string.
+   */
+  apply(): Promise<any> {
+    return readFile(this.path, 'utf8').then(content => {
+      let prefix = content.substring(0, this.pos);
+      let suffix = content.substring(this.pos);
+      return writeFile(this.path, `${prefix}${this.toAdd}${suffix}`);
+    });
+  }
+}
+
+/**
+ * Will remove text from the source code.
+ */
+export class RemoveChange implements Change {
+
+  const order: number;
+  const 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 ${path}`;
+    this.order = pos;
+  }
+
+  apply(): Promise<any> {
+    return readFile(this.path, 'utf8').then(content => {
+      let prefix = content.substring(0, this.pos);
+      let suffix = content.substring(this.pos + this.toRemove.length);
+      // TODO: throw error if toRemove doesn't match removed string.
+      return writeFile(this.path, `${prefix}${suffix}`);
+    });
+  }
+}
+
+/**
+ * Will replace text from the source code.
+ */
+export class ReplaceChange implements Change {
+
+  const order: number;
+  const 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 ${newText}`;
+    this.order = pos;
+  }
+
+  apply(): Promise<any> {
+    return readFile(this.path, 'utf8').then(content => {
+      let prefix = content.substring(0, this.pos);
+      let suffix = content.substring(this.pos + this.oldText.length);
+      // TODO: throw error if oldText doesn't match removed string.
+      return writeFile(this.path, `${prefix}${this.newText}${suffix}`);
+    });
+  }
+}

tests/acceptance/change.spec.ts

@@ -0,0 +1,120 @@
+'use strict';
+
+// This needs to be first so fs module can be mocked correctly.
+let mockFs = require('mock-fs');
+
+import {expect} from 'chai';
+import {InsertChange, RemoveChange, ReplaceChange} from '../../addon/ng2/utilities/change';
+import fs = require('fs');
+
+let path = require('path');
+let Promise = require('ember-cli/lib/ext/promise');
+
+const readFile =  Promise.denodeify(fs.readFile);
+
+describe('Change', () => {
+  let sourcePath = 'src/app/my-component';
+
+  beforeEach(() => {
+    let mockDrive = {
+      'src/app/my-component': {
+        'add-file.txt': 'hello',
+        'remove-replace-file.txt': 'import * as foo from "./bar"',
+        'replace-file.txt': 'import { FooComponent } from "./baz"'
+      }
+    };
+    mockFs(mockDrive);
+  });
+  afterEach(() => {
+    mockFs.restore();
+  });
+
+  describe('InsertChange', () => {
+    let sourceFile = path.join(sourcePath, 'add-file.txt');
+
+    it('adds text to the source code', () => {
+      let changeInstance = new InsertChange(sourceFile, 6, ' world!');
+      return changeInstance
+        .apply()
+        .then(() => readFile(sourceFile, 'utf8'))
+        .then(contents => {
+          expect(contents).to.equal('hello world!');
+        });
+    });
+    it('fails for negative position', () => {
+      expect(() => new InsertChange(sourceFile, -6, ' world!')).to.throw(Error);
+    });
+    it('adds nothing in the source code if empty string is inserted', () => {
+      let changeInstance = new InsertChange(sourceFile, 6, '');
+      return changeInstance
+        .apply()
+        .then(() => readFile(sourceFile, 'utf8'))
+        .then(contents => {
+          expect(contents).to.equal('hello');
+        });
+    });
+  });
+
+  describe('RemoveChange', () => {
+    let sourceFile = path.join(sourcePath, 'remove-replace-file.txt');
+
+    it('removes given text from the source code', () => {
+      let changeInstance = new RemoveChange(sourceFile, 9, 'as foo');
+      return changeInstance
+        .apply()
+        .then(() => readFile(sourceFile, 'utf8'))
+        .then(contents => {
+          expect(contents).to.equal('import *  from "./bar"');
+        });
+    });
+    it('fails for negative position', () => {
+      expect(() => new RemoveChange(sourceFile, -6, ' world!')).to.throw(Error);
+    });
+    it('does not change the file if told to remove empty string', () => {
+      let changeInstance = new RemoveChange(sourceFile, 9, '');
+      return changeInstance
+        .apply()
+        .then(() => readFile(sourceFile, 'utf8'))
+        .then(contents => {
+          expect(contents).to.equal('import * as foo from "./bar"');
+        });
+    });
+  });
+
+  describe('ReplaceChange', () => {
+    it('replaces the given text in the source code', () => {
+      let sourceFile = path.join(sourcePath, 'remove-replace-file.txt');
+      let changeInstance = new ReplaceChange(sourceFile, 7, '* as foo', '{ fooComponent }');
+      return changeInstance
+        .apply()
+        .then(() => readFile(sourceFile, 'utf8'))
+        .then(contents => {
+          expect(contents).to.equal('import { fooComponent } from "./bar"');
+        });
+    });
+    it('fails for negative position', () => {
+      let sourceFile = path.join(sourcePath, 'remove-replace-file.txt');
+      expect(() => new ReplaceChange(sourceFile, -6, 'hello', ' world!')).to.throw(Error);
+    });
+    it('adds string to the position of an empty string', () => {
+      let sourceFile = path.join(sourcePath, 'replace-file.txt');
+      let changeInstance = new ReplaceChange(sourceFile, 9, '', 'BarComponent, ');
+      return changeInstance
+        .apply()
+        .then(() => readFile(sourceFile, 'utf8'))
+        .then(contents => {
+          expect(contents).to.equal('import { BarComponent, FooComponent } from "./baz"');
+        });
+    });
+    it('removes the given string only if an empty string to add is given', () => {
+      let sourceFile = path.join(sourcePath, 'remove-replace-file.txt');
+      let changeInstance = new ReplaceChange(sourceFile, 9, ' as foo', '');
+      return changeInstance
+        .apply()
+        .then(() => readFile(sourceFile, 'utf8'))
+        .then(contents => {
+          expect(contents).to.equal('import * from "./bar"');
+        });
+    });
+  });
+});