feat(ng-dev): create a spinner utility (#183)

PR Close #183

ng-dev/utils/spinner.ts

@@ -0,0 +1,55 @@
+/**
+ * @license
+ * Copyright Google LLC 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 {cursorTo, clearLine} from 'readline';
+
+/** ANSI escape code to hide cursor in terminal. */
+const hideCursor = '\x1b[?25l';
+/** ANSI escape code to show cursor in terminal. */
+const showCursor = '\x1b[?25h';
+
+export class Spinner {
+  /** The id of the interval being used to trigger frame printing. */
+  private intervalId = setInterval(() => this.printFrame(), 125);
+  /** The characters to iterate through to create the appearance of spinning in the spinner. */
+  private spinnerCharacters = ['⠋', '⠙', '⠹', '⠸', '⠼', '⠴', '⠦', '⠧', '⠇', '⠏'];
+  /** The index of the spinner character used in the frame. */
+  private currentSpinnerCharacterIndex = 0;
+
+  constructor(private text: string) {
+    process.stdout.write(hideCursor);
+  }
+
+  /** Get the next spinner character. */
+  private getNextSpinnerCharacter() {
+    this.currentSpinnerCharacterIndex =
+      (this.currentSpinnerCharacterIndex % this.spinnerCharacters.length) + 1;
+    return this.spinnerCharacters[this.currentSpinnerCharacterIndex - 1];
+  }
+
+  /** Print the current text for the spinner to the  */
+  private printFrame(prefix = this.getNextSpinnerCharacter(), text = this.text) {
+    cursorTo(process.stdout, 0);
+    process.stdout.write(` ${prefix} ${text}`);
+    // Clear to the right of the cursor location in case the new frame is shorter than the previous.
+    clearLine(process.stdout, 1);
+    cursorTo(process.stdout, 0);
+  }
+
+  /** Updates the spinner text with the provided text. */
+  update(text: string) {
+    this.text = text;
+  }
+
+  /** Completes the spinner. */
+  complete() {
+    clearInterval(this.intervalId);
+    process.stdout.write('\n');
+    process.stdout.write(showCursor);
+  }
+}