ProgressSpinner: Simple busy wait entertainment

Keep a user amused while the server does work by spinning a
little ASCII-art object on a single line.

Change-Id: Ie8f181d1aa606d4ae69e5d3ca4db387cea739f38

org.eclipse.jgit/src/org/eclipse/jgit/transport/ProgressSpinner.java

@@ -0,0 +1,149 @@
+/*
+ * Copyright (C) 2015, Google Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.transport;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * A simple spinner connected to an {@code OutputStream}.
+ * <p>
+ * This is class is not thread-safe. The update method may only be used from a
+ * single thread. Updates are sent only as frequently as {@link #update()} is
+ * invoked by the caller, and are capped at no more than 2 times per second by
+ * requiring at least 500 milliseconds between updates.
+ *
+ * @since 4.2
+ */
+public class ProgressSpinner {
+	private static final long MIN_REFRESH_MILLIS = 500;
+	private static final char[] STATES = new char[] { '-', '\\', '|', '/' };
+
+	private final OutputStream out;
+	private String msg;
+	private int state;
+	private boolean write;
+	private boolean shown;
+	private long nextUpdateMillis;
+
+	/**
+	 * Initialize a new spinner.
+	 *
+	 * @param out
+	 *            where to send output to.
+	 */
+	public ProgressSpinner(OutputStream out) {
+		this.out = out;
+		this.write = true;
+	}
+
+	/**
+	 * Begin a time consuming task.
+	 *
+	 * @param title
+	 *            description of the task, suitable for human viewing.
+	 * @param delay
+	 *            delay to wait before displaying anything at all.
+	 * @param delayUnits
+	 *            unit for {@code delay}.
+	 */
+	public void beginTask(String title, long delay, TimeUnit delayUnits) {
+		msg = title;
+		state = 0;
+		shown = false;
+
+		long now = System.currentTimeMillis();
+		if (delay > 0) {
+			nextUpdateMillis = now + delayUnits.toMillis(delay);
+		} else {
+			send(now);
+		}
+	}
+
+	/** Update the spinner if it is showing. */
+	public void update() {
+		long now = System.currentTimeMillis();
+		if (now >= nextUpdateMillis) {
+			send(now);
+			state = (state + 1) % STATES.length;
+		}
+	}
+
+	private void send(long now) {
+		StringBuilder buf = new StringBuilder(msg.length() + 16);
+		buf.append('\r').append(msg).append("... ("); //$NON-NLS-1$
+		buf.append(STATES[state]);
+		buf.append(")  "); //$NON-NLS-1$
+		shown = true;
+		write(buf.toString());
+		nextUpdateMillis = now + MIN_REFRESH_MILLIS;
+	}
+
+	/**
+	 * Denote the current task completed.
+	 *
+	 * @param result
+	 *            text to print after the task's title
+	 *            {@code "$title ... $result"}.
+	 */
+	public void endTask(String result) {
+		if (shown) {
+			write('\r' + msg + "... " + result + "\n"); //$NON-NLS-1$ //$NON-NLS-2$
+		}
+	}
+
+	private void write(String s) {
+		if (write) {
+			try {
+				out.write(s.getBytes(UTF_8));
+				out.flush();
+			} catch (IOException e) {
+				write = false;
+			}
+		}
+	}
+}