ProgressSpinner.java

/*
 * Copyright (C) 2015, Google Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

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;
            }
        }
    }
}