/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.juneau.microservice.console;

import java.io.*;
import java.util.*;

import org.apache.juneau.collections.*;

/**
 * Implements a command that can be invoked from the console of the microservice.
 *
 * <p>
 * Console commands allow you to interact with your microservice through the system console.
 *
 * <p>
 * Console commands are associated with the microservice through the following:
 * <ul>
 *    <li>The <js>"Console/commands"</js> configuration value.
 *       <br>This is a comma-delimited list of fully-qualified names of classes implementing this interface.
 *       <br>When associated this way, the implementation class must have a no-arg constructor.
 *    <li>Specifying commands via the {@link org.apache.juneau.microservice.Microservice.Builder#consoleCommands(Class...)} method.
 *       <br>This allows you to override the default implementation above and augment or replace the list
 *          with your own implementation objects.
 * </ul>
 *
 * <p>
 * For example, the {@link HelpCommand} is used to provide help on other commands.
 *
 * <p class='bconsole'>
 *    Running class 'JettyMicroservice' using config file 'examples.cfg'.
 *    Server started on port 10000
 *
 *    List of available commands:
 *       exit -- Shut down service
 *       restart -- Restarts service
 *       help -- Commands help
 *       echo -- Echo command
 *
 *    &gt; <span style='color:green'>help help</span>
 *    NAME
 *       help -- Commands help
 *
 *    SYNOPSIS
 *       help [command]
 *
 *    DESCRIPTION
 *       When called without arguments, prints the descriptions of all available commands.
 *       Can also be called with one or more arguments to get detailed information on a command.
 *
 *    EXAMPLES
 *       List all commands:
 *          &gt; help
 *
 *       List help on the help command:
 *          &gt; help help
 *
 *    &gt;
 * </p>
 *
 * <p>
 * The arguments are available as an {@link Args} object which allows for easy accessed to parsed command lines.
 * Some simple examples of valid command lines:
 *
 * <p class='bjava'>
 *    <jc>// mycommand</jc>
 *    <jv>args</jv>.get(<js>"0"</js>);  <jc>// "mycommand"</jc>
 *
 *    <jc>// mycommand arg1 arg2</jc>
 *    <jv>args</jv>.get(<js>"0"</js>);  <jc>// "mycommand"</jc>
 *    <jv>args</jv>.get(<js>"1"</js>);  <jc>// "arg1"</jc>
 *    <jv>args</jv>.get(<js>"2"</js>);  <jc>// "arg2"</jc>
 *
 *    <jc>// mycommand -optArg1 foo bar -optArg2 baz qux</jc>
 *    <jv>args</jv>.get(<js>"0"</js>);  <jc>// "mycommand"</jc>
 *    <jv>args</jv>.get(<js>"optArg1"</js>, String[].<jk>class</jk>);  <jc>// ["foo","bar"]</jc>
 *    <jv>args</jv>.get(<js>"optArg2"</js>, String[].<jk>class</jk>);  <jc>// ["baz","qux"]</jc>
 *
 *    <jc>// mycommand -optArg1 "foo bar" -optArg2 'baz qux'</jc>
 *    <jv>args</jv>.get(<js>"0"</js>);  <jc>// "mycommand"</jc>
 *    <jv>args</jv>.get(<js>"optArg1"</js>, String[].<jk>class</jk>);  <jc>// ["foo bar"]</jc>
 *    <jv>args</jv>.get(<js>"optArg2"</js>, String[].<jk>class</jk>);  <jc>// ["baz qux"]</jc>
 * </p>
 *
 * <h5 class='section'>See Also:</h5><ul>
 *    <li class='link'><a class="doclink" href="https://juneau.apache.org/docs/topics/JuneauMicroserviceCoreBasics">juneau-microservice-core Basics</a>
 * </ul>
 */
public abstract class ConsoleCommand {

   /**
    * Returns the name of the command.
    *
    * <p>
    * Example:  <js>"help"</js> for the help command.
    *
    * @return
    *    The name of the command.
    *    <br>Must not be <jk>null</jk> or contain spaces.
    */
   abstract public String getName();

   /**
    * Returns the usage synopsis of the command.
    *
    * <p>
    * Example:  <js>"help [command ...]"
    *
    * <p>
    * The default implementation just returns the name, which implies the command takes no additional arguments.
    *
    * @return The synopsis of the command.
    */
   public String getSynopsis() {
      return getName();
   }

   /**
    * Returns a one-line localized description of the command.
    *
    * <p>
    * The locale should be the system locale.
    *
    * @return
    *    The localized description of the command.
    *    <br>Can be <jk>null</jk> if there is no information.
    */
   public String getInfo() {
      return null;
   }

   /**
    * Returns localized details of the command.
    *
    * <p>
    * The locale should be the system locale.
    *
    * @return
    *    The localized details of the command.
    *    <br>Can be <jk>null</jk> if there is no additional description.
    */
   public String getDescription() {
      return null;
   }

   /**
    * Returns localized examples of the command.
    *
    * <p>
    * The locale should be the system locale.
    *
    * @return
    *    The localized examples of the command.
    *    <br>Can be <jk>null</jk> if there is no examples.
    */
   public String getExamples() {
      return null;
   }

   /**
    * Executes a command.
    * @param in The console reader.
    * @param out The console writer.
    * @param args The command arguments.  The first argument is always the command itself.
    *
    * @return
    *    <jk>true</jk> if the console read thread should exit.
    *    <br>Normally you want to return <jk>true</jk> if your action is causing the microservice to exit or restart.
    * @throws Exception
    *    Any thrown exception will simply be sent to STDERR.
    */
   abstract public boolean execute(Scanner in, PrintWriter out, Args args) throws Exception;
}