feat(cli): command line spinner

cli/mod.ts

@@ -8,3 +8,4 @@
 
 export * from "./parse_args.ts";
 export * from "./prompt_secret.ts";
+export * from "./spinner.ts";

cli/spinner.ts

@@ -0,0 +1,109 @@
+// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
+
+const encoder = new TextEncoder();
+
+const LINE_CLEAR = encoder.encode("\r\u001b[K"); // From cli/prompt_secret.ts
+const COLOR_RESET = "\u001b[0m";
+const DEFAULT_SPEED = 75;
+const DEFAULT_SPINNER = ["⠋", "⠙", "⠹", "⠸", "⠼", "⠴", "⠦", "⠧", "⠇", "⠏"];
+
+/** Options for {@linkcode Spinner}. */
+export interface SpinnerOptions {
+  /**
+   * The sequence of characters to be iterated through for animation.
+   *
+   * @default {["⠋", "⠙", "⠹", "⠸", "⠼", "⠴", "⠦", "⠧", "⠇", "⠏"]}
+   */
+  spinner?: string[];
+  /** The message to display next to the spinner. */
+  message?: string;
+  /** The speed of the spinner.
+   *
+   * @default {75}
+   */
+  speed?: number;
+  /** The color of the spinner. Defaults to the default terminal color. */
+  color?: string;
+}
+
+/**
+ * A spinner that can be used to indicate that something is loading.
+ */
+export class Spinner {
+  #spinner: string[];
+  #message: string;
+  #speed: number;
+  #color?: string;
+  #intervalId: number | undefined;
+  #active = false;
+
+  /**
+   * Creates a new spinner.
+   *
+   * @example
+   * ```ts
+   * import { Spinner } from "https://deno.land/std@$STD_VERSION/cli/spinner.ts";
+   *
+   * const spinner = new Spinner({ message: "Loading..." });
+   * ```
+   */
+  constructor(options?: SpinnerOptions) {
+    this.#spinner = options?.spinner ?? DEFAULT_SPINNER;
+    this.#message = options?.message ?? "";
+    this.#speed = options?.speed ?? DEFAULT_SPEED;
+    this.#color = options?.color;
+  }
+
+  /**
+   * Starts the spinner.
+   *
+   * @example
+   * ```ts
+   * import { Spinner } from "https://deno.land/std@$STD_VERSION/cli/spinner.ts";
+   *
+   * const spinner = new Spinner({ message: "Loading..." });
+   * spinner.start();
+   * ```
+   */
+  start() {
+    if (this.#active || Deno.stdout.writable.locked) return;
+    this.#active = true;
+    let i = 0;
+    const color = this.#color ?? "";
+
+    // Updates the spinner after the given interval.
+    const updateFrame = () => {
+      Deno.stdout.writeSync(LINE_CLEAR);
+      const frame = encoder.encode(
+        color + this.#spinner[i] + COLOR_RESET + " " + this.#message,
+      );
+      Deno.stdout.writeSync(frame);
+      i = (i + 1) % this.#spinner.length;
+    };
+    this.#intervalId = setInterval(updateFrame, this.#speed);
+  }
+  /**
+   * Stops the spinner.
+   *
+   * @example
+   * ```ts
+   * import { Spinner } from "https://deno.land/std@$STD_VERSION/cli/spinner.ts";
+   *
+   * const spinner = new Spinner({ message: "Loading..." });
+   * spinner.start();
+   *
+   * setTimeout(() => {
+   *  spinner.stop();
+   *  console.log("Finished loading!");
+   * }, 3000);
+   * ```
+   */
+  stop() {
+    if (this.#intervalId && this.#active) {
+      clearInterval(this.#intervalId);
+      Deno.stdout.writeSync(LINE_CLEAR); // Clear the current line
+      Deno.removeSignalListener("SIGINT", this.stop.bind(this));
+      this.#active = false;
+    }
+  }
+}