SimpleTerminalConsole.java

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2017 Minecrell <https://github.com/Minecrell>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

package net.minecrell.terminalconsole;

import org.apache.logging.log4j.LogManager;
import org.checkerframework.checker.nullness.qual.Nullable;
import org.jline.reader.Completer;
import org.jline.reader.EndOfFileException;
import org.jline.reader.LineReader;
import org.jline.reader.LineReaderBuilder;
import org.jline.reader.UserInterruptException;
import org.jline.terminal.Terminal;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

/**
 * A simple, optional base implementation of a basic console input command
 * reader using {@link TerminalConsoleAppender}. Once started, it displays
 * a command prompt ("{@code > }") and reads input commands from the console.
 *
 * <p><strong>Usage:</strong> Extend this class and implement the abstract
 * methods for your application. Consider overriding
 * {@link #buildReader(LineReaderBuilder)} to add further features to the
 * console (e.g. call {@link LineReaderBuilder#completer(Completer)} with
 * a custom completer to provide command completion).</p>
 */
public abstract class SimpleTerminalConsole {

    /**
     * Determines if the application is still running and accepting input.
     *
     * @return {@code true} to continue reading input
     */
    protected abstract boolean isRunning();

    /**
     * Run a command entered in the console.
     *
     * @param command The command line to run
     */
    protected abstract void runCommand(String command);

    /**
     * Shutdown the application and perform a clean exit.
     *
     * <p>This is called if the application receives SIGINT while reading input,
     * e.g. when pressing CTRL+C on most terminal implementations.</p>
     */
    protected abstract void shutdown();

    /**
     * Process an input line entered through the console.
     *
     * <p>The default implementation trims leading and trailing whitespace
     * from the input and skips execution if the command is empty.</p>
     *
     * @param input The input line
     */
    protected void processInput(String input) {
        String command = input.trim();
        if (!command.isEmpty()) {
            runCommand(command);
        }
    }

    /**
     * Configures the {@link LineReaderBuilder} and {@link LineReader} with
     * additional options.
     *
     * <p>Override this method to make further changes, (e.g. call
     * {@link LineReaderBuilder#appName(String)} or
     * {@link LineReaderBuilder#completer(Completer)}).</p>
     *
     * <p>The default implementation sets some opinionated default options,
     * which are considered to be appropriate for most applications:</p>
     *
     * <ul>
     *     <li>{@link LineReader.Option#DISABLE_EVENT_EXPANSION}: JLine implements
     *     <a href="http://www.gnu.org/software/bash/manual/html_node/Event-Designators.html">
     *     Bash's Event Designators</a> by default. These usually do not
     *     behave as expected in a simple command environment, so it's
     *     recommended to disable it.</li>
     *     <li>{@link LineReader.Option#INSERT_TAB}: By default, JLine inserts
     *     a tab character when attempting to tab-complete on empty input.
     *     It is more intuitive to show a list of commands instead.</li>
     * </ul>
     *
     * @param builder The builder to configure
     * @return The built line reader
     */
    protected LineReader buildReader(LineReaderBuilder builder) {
        LineReader reader = builder.build();
        reader.setOpt(LineReader.Option.DISABLE_EVENT_EXPANSION);
        reader.unsetOpt(LineReader.Option.INSERT_TAB);
        return reader;
    }

    /**
     * Start reading commands from the console.
     *
     * <p>Note that this method won't return until one of the following
     * conditions are met:</p>
     *
     * <ul>
     *     <li>{@link #isRunning()} returns {@code false}, indicating that the
     *     application is shutting down.</li>
     *     <li>{@link #shutdown()} is triggered by the user (e.g. due to
     *     pressing CTRL+C)</li>
     *     <li>The input stream is closed.</li>
     * </ul>
     */
    public void start() {
        try {
            final @Nullable Terminal terminal = TerminalConsoleAppender.getTerminal();
            if (terminal != null) {
                readCommands(terminal);
            } else {
                readCommands(System.in);
            }
        } catch (IOException e) {
            LogManager.getLogger("TerminalConsole").error("Failed to read console input", e);
        }
    }

    private void readCommands(Terminal terminal) {
        LineReader reader = buildReader(LineReaderBuilder.builder().terminal(terminal));
        TerminalConsoleAppender.setReader(reader);

        try {
            String line;
            while (isRunning()) {
                try {
                    line = reader.readLine("> ");
                } catch (EndOfFileException ignored) {
                    // Continue reading after EOT
                    continue;
                }

                if (line == null) {
                    break;
                }

                processInput(line);
            }
        } catch (UserInterruptException e) {
            shutdown();
        } finally {
            TerminalConsoleAppender.setReader(null);
        }
    }

    private void readCommands(InputStream in) throws IOException {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(in))) {
            String line;
            while (isRunning() && (line = reader.readLine()) != null) {
                processInput(line);
            }
        }
    }

}