/*
 * 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;

import static org.apache.juneau.commons.utils.CollectionUtils.*;
import static org.apache.juneau.commons.utils.FileUtils.*;
import static org.apache.juneau.commons.utils.IoUtils.*;
import static org.apache.juneau.commons.utils.ThrowableUtils.*;
import static org.apache.juneau.commons.utils.Utils.*;

import java.io.*;
import java.nio.file.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.jar.*;
import java.util.logging.*;

import org.apache.juneau.collections.*;
import org.apache.juneau.commons.reflect.*;
import org.apache.juneau.config.*;
import org.apache.juneau.config.event.*;
import org.apache.juneau.config.store.*;
import org.apache.juneau.config.store.FileStore;
import org.apache.juneau.config.vars.*;
import org.apache.juneau.cp.*;
import org.apache.juneau.microservice.console.*;
import org.apache.juneau.microservice.resources.*;
import org.apache.juneau.parser.ParseException;
import org.apache.juneau.svl.*;
import org.apache.juneau.svl.vars.*;
import org.apache.juneau.utils.*;

/**
 * Parent class for all microservices.
 *
 * <p>
 * A microservice defines a simple API for starting and stopping simple Java services contained in executable jars.
 *
 * <p>
 * The general command for creating and starting a microservice from a main method is as follows:
 * <p class='bjava'>
 *    <jk>public static void</jk> main(String[] <jv>args</jv>) {
 *       Microservice.<jsm>create</jsm>().args(<jv>args</jv>).build().start().join();
 *  }
 * </p>
 *
 * <p>
 * Your microservice class must be specified as the <jk>Main-Class</jk> entry in the manifest file of your microservice
 * jar file if it's an executable jar.
 *
 * <h5 class='topic'>Microservice Configuration</h5>
 *
 * This class defines the following method for accessing configuration for your microservice:
 * <ul class='spaced-list'>
 *    <li>
 *       {@link #getArgs()} - The command-line arguments passed to the jar file.
 *    <li>
 *       {@link #getConfig()} - An external INI-style configuration file.
 *    <li>
 *       {@link #getManifest()} - The manifest file for the main jar file.
 * </ul>
 *
 * <h5 class='topic'>Lifecycle Methods</h5>
 *
 * Subclasses must implement the following lifecycle methods:
 * <ul class='spaced-list'>
 *    <li>
 *       {@link #init()} - Gets executed immediately following construction.
 *    <li>
 *       {@link #start()} - Gets executed during startup.
 *    <li>
 *       {@link #stop()} - Gets executed when 'exit' is typed in the console or an external shutdown signal is received.
 *    <li>
 *       {@link #kill()} - Can be used to forcibly shut down the service.  Doesn't get called during normal operation.
 * </ul>
 *
 * <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 class Microservice implements ConfigEventListener {
   /**
    * Builder class.
    */
   public static class Builder {

      Args args;
      ManifestFile manifest;
      Logger logger;
      LogConfig logConfig;
      Config config;
      String configName;
      ConfigStore configStore;
      Config.Builder configBuilder = Config.create();
      Boolean consoleEnabled;
      List<ConsoleCommand> consoleCommands = list();
      VarResolver.Builder varResolver = VarResolver.create().defaultVars().vars(ConfigVar.class);
      Scanner consoleReader;
      PrintWriter consoleWriter;
      MicroserviceListener listener;
      File workingDir = System.getProperty("juneau.workingDir") == null ? null : new File(System.getProperty("juneau.workingDir"));

      /**
       * Constructor.
       */
      protected Builder() {}

      /**
       * Copy constructor.
       *
       * @param copyFrom The builder to copy.
       */
      protected Builder(Builder copyFrom) {
         this.args = copyFrom.args;
         this.manifest = copyFrom.manifest;
         this.logger = copyFrom.logger;
         this.configName = copyFrom.configName;
         this.logConfig = copyFrom.logConfig == null ? null : copyFrom.logConfig.copy();
         this.consoleEnabled = copyFrom.consoleEnabled;
         this.configBuilder = copyFrom.configBuilder;
         this.varResolver = copyFrom.varResolver;
         this.consoleReader = copyFrom.consoleReader;
         this.consoleWriter = copyFrom.consoleWriter;
         this.workingDir = copyFrom.workingDir;
      }

      /**
       * Specifies the command-line arguments passed into the Java command.
       *
       * <p>
       * This is required if you use {@link Microservice#getArgs()} or <c>$A</c> string variables.
       *
       * @param args
       *    The command-line arguments passed into the Java command as a pre-parsed {@link Args} object.
       * @return This object.
       */
      public Builder args(Args args) {
         this.args = args;
         return this;
      }

      /**
       * Specifies the command-line arguments passed into the Java command.
       *
       * <p>
       * This is required if you use {@link Microservice#getArgs()} or <c>$A</c> string variables.
       *
       * @param args
       *    The command-line arguments passed into the Java command as the raw command-line arguments.
       * @return This object.
       */
      public Builder args(String...args) {
         this.args = new Args(args);
         return this;
      }

      /**
       * Instantiate a new microservice using the settings defined on this builder.
       *
       * @return A new microservice.
       * @throws Exception Error occurred.
       */
      public Microservice build() throws Exception {
         return new Microservice(this);
      }

      /**
       * Specifies the config for initializing this microservice.
       *
       * <p>
       * Calling this method overrides the default configuration controlled by the {@link #configName(String)} and {@link #configStore(ConfigStore)} methods.
       *
       * @param config The configuration.
       * @return This object.
       */
      public Builder config(Config config) {
         this.config = config;
         return this;
      }

      /**
       * Specifies the config name for initializing this microservice.
       *
       * <p>
       * If you do not specify the config file location, we attempt to resolve it through the following methods:
       * <ol class='spaced-list'>
       *    <li>
       *       Resolve file first in working directory, then in classpath, using the following names:
       *       <ul>
       *          <li>
       *             The <js>"configFile"</js> argument in the command line arguments passed in through the constructor.
       *          <li>
       *             The value of the <c>Main-Config</c> entry in the manifest file.
       *          <li>
       *             A config file in the same location and with the same name as the executable jar file.
       *             (e.g. <js>"java -jar myjar.jar"</js> will look for <js>"myjar.cfg"</js>).
       *       </ul>
       *    <li>
       *       Resolve any <js>"*.cfg"</js> file that can be found in the working directory.
       *    <li>
       *       Resolve any of the following files in the classpath:  <js>"juneau.cfg"</js>, <js>"system.cfg"</js>
       * </ol>
       *
       * <p>
       * If no configuration file is found, and empty in-memory configuration is used.
       *
       * @param configName The configuration name.
       * @return This object.
       */
      public Builder configName(String configName) {
         this.configName = configName;
         return this;
      }

      /**
       * Specifies the config store to use for storing and retrieving configurations.
       *
       * <p>
       * By default, we use a {@link FileStore} store for configuration files.
       *
       * @param configStore The configuration name.
       * @return This object.
       */
      public Builder configStore(ConfigStore configStore) {
         this.configStore = configStore;
         return this;
      }

      /**
       * Specifies the console input and output.
       *
       * <p>
       * If not specified, uses the console returned by {@link System#console()}.
       * If that is not available, uses {@link System#in} and {@link System#out}.
       *
       * <p>
       * Note that these are ignored if the console is not enabled via {@link #consoleEnabled(boolean)}.
       *
       * @param consoleReader The console input.
       * @param consoleWriter The console output.
       * @return This object.
       */
      public Builder console(Scanner consoleReader, PrintWriter consoleWriter) {
         this.consoleReader = consoleReader;
         this.consoleWriter = consoleWriter;
         return this;
      }

      /**
       * Specifies console commands to make available on the Java console.
       *
       * <p>
       * Note that these are ignored if the console is not enabled via {@link #consoleEnabled(boolean)}.
       *
       * <p>
       * This list augments the commands defined via the <js>"Console/commands"</js> configuration setting.
       *
       * <p>
       * This method can only be used on console commands with no-arg constructors.
       *
       * @param consoleCommands The list of console commands to append to the list of available commands.
       * @return This object.
       * @throws ExecutableException Exception occurred on invoked constructor/method/field.
       */
      @SuppressWarnings("unchecked")
      public Builder consoleCommands(Class<? extends ConsoleCommand>...consoleCommands) throws ExecutableException {
         try {
            for (var cc : consoleCommands)
               this.consoleCommands.add(cc.getDeclaredConstructor().newInstance());
         } catch (Exception e) {
            throw new ExecutableException(e);
         }
         return this;
      }

      /**
       * Specifies console commands to make available on the Java console.
       *
       * <p>
       * Note that these are ignored if the console is not enabled via {@link #consoleEnabled(boolean)}.
       *
       * <p>
       * This list augments the commands defined via the <js>"Console/commands"</js> configuration setting.
       *
       * @param consoleCommands The list of console commands to append to the list of available commands.
       * @return This object.
       */
      public Builder consoleCommands(ConsoleCommand...consoleCommands) {
         addAll(this.consoleCommands, consoleCommands);
         return this;
      }

      /**
       * Specifies that the Java console is enabled for this microservice.
       *
       * <p>
       * If not specified, this value is taken from the <js>"Console/enabled"</js> configuration setting.
       * If not specified in the configuration, defaults to <jk>false</jk>.
       *
       * @param consoleEnabled <jk>true</jk> if the Java console is enabled for this microservice.
       * @return This object.
       */
      public Builder consoleEnabled(boolean consoleEnabled) {
         this.consoleEnabled = consoleEnabled;
         return this;
      }

      /**
       * Creates a copy of this builder.
       *
       * @return A new copy of this builder.
       */
      public Builder copy() {
         return new Builder(this);
      }

      /**
       * Registers an event listener for this microservice.
       *
       * @param listener An event listener for this microservice.
       * @return This object.
       */
      public Builder listener(MicroserviceListener listener) {
         this.listener = listener;
         return this;
      }

      /**
       * Specifies logging instructions for the microservice.
       *
       * <p>
       * If not specified, the values are taken from the <js>"Logging"</js> section of the configuration.
       *
       * <p>
       * This method is ignored if {@link #logger(Logger)} is used to set the microservice logger.
       *
       * @param logConfig The log configuration.
       * @return This object.
       */
      public Builder logConfig(LogConfig logConfig) {
         this.logConfig = logConfig;
         return this;
      }

      /**
       * Specifies the logger used by the microservice and returned by the {@link Microservice#getLogger()} method.
       *
       * <p>
       * Calling this method overrides the default logging mechanism controlled by the {@link #logConfig(LogConfig)} method.
       *
       * @param logger The logger to use for logging microservice messages.
       * @return This object.
       */
      public Builder logger(Logger logger) {
         this.logger = logger;
         return this;
      }

      /**
       * Specifies the manifest file of the jar file this microservice is contained within.
       *
       * <p>
       * This is required if you use {@link Microservice#getManifest()}.
       * It's also used to locate initialization values such as <c>Main-Config</c>.
       *
       * <p>
       * If you do not specify the manifest file, we attempt to resolve it through the following methods:
       * <ol class='spaced-list'>
       *    <li>
       *       Looking on the file system for a file at <js>"META-INF/MANIFEST.MF"</js>.
       *       This is primarily to allow for running microservices from within eclipse workspaces where the manifest file
       *       is located in the project root.
       *    <li>
       *       Using the class loader for this class to find the file at the URL <js>"META-INF/MANIFEST.MF"</js>.
       * </ol>
       *
       * @param value
       *    The manifest file of this microservice.
       *    <br>Can be any of the following types:
       *    <ul>
       *       <li>{@link ManifestFile}
       *       <li>{@link Manifest}
       *       <li>{@link Reader} - Containing the raw contents of the manifest.  Note that the input must end with a newline.
       *       <li>{@link InputStream} - Containing the raw contents of the manifest.  Note that the input must end with a newline.
       *       <li>{@link File} - File containing the raw contents of the manifest.
       *       <li>{@link String} - Path to file containing the raw contents of the manifest.
       *       <li>{@link Class} - Finds and loads the manifest file of the jar file that the specified class is contained within.
       *    </ul>
       * @return This object.
       * @throws IOException Thrown by underlying stream.
       */
      public Builder manifest(Object value) throws IOException {
         if (value == null)
            this.manifest = null;
         else if (value instanceof ManifestFile manifestFile)
            this.manifest = manifestFile;
         else if (value instanceof Manifest manifest)
            this.manifest = new ManifestFile(manifest);
         else if (value instanceof Reader reader)
            this.manifest = new ManifestFile(reader);
         else if (value instanceof InputStream inputStream)
            this.manifest = new ManifestFile(inputStream);
         else if (value instanceof File file)
            this.manifest = new ManifestFile(file);
         else if (value instanceof Path path)
            this.manifest = new ManifestFile(path);
         else if (value instanceof String string)
            this.manifest = new ManifestFile(resolveFile(string));
         else if (value instanceof Class clazz)
            this.manifest = new ManifestFile(clazz);
         else
            throw rex("Invalid type passed to Builder.manifest(Object).  Type=[{0}]", cn(value));

         return this;
      }

      /**
       * Adds a bean for vars defined in the var resolver.
       *
       * <p>
       * This calls {@link org.apache.juneau.svl.VarResolver.Builder#bean(Class,Object)} on the var resolver used to construct the configuration
       * object returned by {@link Microservice#getConfig()} and the var resolver returned by {@link Microservice#getVarResolver()}.
       *
       * @param c The bean type.
       * @param value The bean.
       * @param <T> The bean type.
       * @return This object.
       */
      public <T> Builder varBean(Class<T> c, T value) {
         varResolver.bean(c, value);
         return this;
      }

      /**
       * Augments the set of variables defined in the configuration and var resolver.
       *
       * <p>
       * This calls {@link org.apache.juneau.svl.VarResolver.Builder#vars(Class[])} on the var resolver used to construct the configuration
       * object returned by {@link Microservice#getConfig()} and the var resolver returned by {@link Microservice#getVarResolver()}.
       *
       * @param vars The set of variables to append to the var resolver builder.
       * @return This object.
       */
      @SuppressWarnings("unchecked")
      public Builder vars(Class<? extends Var>...vars) {
         varResolver.vars(vars);
         return this;
      }

      /**
       * Specifies the directory to use to resolve the config file and other paths defined with the config file.
       *
       * @param workingDir The working directory, or <jk>null</jk> to use the underlying working directory.
       * @return This object.
       */
      public Builder workingDir(File workingDir) {
         this.workingDir = workingDir;
         return this;
      }

      /**
       * Specifies the directory to use to resolve the config file and other paths defined with the config file.
       *
       * @param workingDir The working directory, or <jk>null</jk> to use the underlying working directory.
       * @return This object.
       */
      public Builder workingDir(String workingDir) {
         this.workingDir = new File(workingDir);
         return this;
      }

      /**
       * Resolves the specified path.
       *
       * <p>
       * If the working directory has been explicitly specified, relative paths are resolved relative to that.
       *
       * @param path The path to resolve.
       * @return The resolved file.
       */
      protected File resolveFile(String path) {
         if (Paths.get(path).isAbsolute())
            return new File(path);
         if (nn(workingDir))
            return new File(workingDir, path);
         return new File(path);
      }
   }

   private static volatile Microservice INSTANCE;

   /**
    * Creates a new builder for this object.
    *
    * @return A new microservice builder.
    */
   public static Builder create() {
      return new Builder();
   }

   /**
    * Returns the Microservice instance.
    *
    * <p>
    * This method only works if there's only one Microservice instance in a JVM.
    * Otherwise, it's just overwritten by the last instantiated microservice.
    *
    * @return The Microservice instance, or <jk>null</jk> if there isn't one.
    */
   public static Microservice getInstance() {
      synchronized (Microservice.class) {
         return INSTANCE;
      }
   }

   private static void setInstance(Microservice m) {
      synchronized (Microservice.class) {
         INSTANCE = m;
      }
   }

   final Messages messages = Messages.of(Microservice.class);

   private final Builder builder;
   private final Args args;
   private final Config config;
   private final ManifestFile manifest;
   private final VarResolver varResolver;
   private final MicroserviceListener listener;
   private final Map<String,ConsoleCommand> consoleCommandMap = new ConcurrentHashMap<>();
   private final boolean consoleEnabled;
   private final Scanner consoleReader;
   private final PrintWriter consoleWriter;
   private final Thread consoleThread;
   final File workingDir;
   private final String configName;

   private volatile Logger logger;

   /**
    * Constructor.
    *
    * @param builder The builder containing the settings for this microservice.
    * @throws IOException Problem occurred reading file.
    * @throws ParseException Malformed input encountered.
    */
   @SuppressWarnings("resource")
   protected Microservice(Builder builder) throws IOException, ParseException {
      setInstance(this);
      this.builder = builder.copy();
      this.workingDir = builder.workingDir;
      this.configName = builder.configName;

      this.args = nn(builder.args) ? builder.args : new Args(new String[0]);

      // --------------------------------------------------------------------------------
      // Try to get the manifest file if it wasn't already set.
      // --------------------------------------------------------------------------------
      var manifest = builder.manifest;
      if (manifest == null) {
         var m = new Manifest();

         // If running within an eclipse workspace, need to get it from the file system.
         var f = resolveFile("META-INF/MANIFEST.MF");
         if (f.exists() && f.canRead()) {
            try (var fis = new FileInputStream(f)) {
               m.read(fis);
            } catch (IOException e) {
               throw ioex(e, "Problem detected in MANIFEST.MF.  Contents below:\n{0}", read(f), e);
            }
         } else {
            // Otherwise, read from manifest file in the jar file containing the main class.
            var url = getClass().getResource("META-INF/MANIFEST.MF");
            if (nn(url)) {
               try {
                  m.read(url.openStream());
               } catch (IOException e) {
                  throw ioex(e, "Problem detected in MANIFEST.MF.  Contents below:\n{0}", read(url.openStream()), e);
               }
            }
         }
         manifest = new ManifestFile(m);
      }
      ManifestFileVar.init(manifest);
      this.manifest = manifest;

      // --------------------------------------------------------------------------------
      // Try to resolve the configuration if not specified.
      // --------------------------------------------------------------------------------
      var config = builder.config;
      var configBuilder = builder.configBuilder.varResolver(builder.varResolver.build()).store(MemoryStore.DEFAULT);
      if (config == null) {
         var store = builder.configStore;
         var cfs = workingDir == null ? FileStore.DEFAULT : FileStore.create().directory(workingDir).build();
         for (var name : getCandidateConfigNames()) {
            if (nn(store)) {
               if (store.exists(name)) {
                  configBuilder.store(store).name(name);
                  break;
               }
            } else {
               if (cfs.exists(name)) {
                  configBuilder.store(cfs).name(name);
                  break;
               }
               if (ClasspathStore.DEFAULT.exists(name)) {
                  configBuilder.store(ClasspathStore.DEFAULT).name(name);
                  break;
               }
            }
         }
         config = configBuilder.build();
      }
      this.config = config;
      Config.setSystemDefault(this.config);
      this.config.addListener(this);
      this.varResolver = builder.varResolver.bean(Config.class, config).build();

      // --------------------------------------------------------------------------------
      // Initialize console commands.
      // --------------------------------------------------------------------------------
      this.consoleEnabled = firstNonNull(builder.consoleEnabled, config.get("Console/enabled").asBoolean().orElse(false));
      if (consoleEnabled) {
         var c = System.console();
         this.consoleReader = firstNonNull(builder.consoleReader, new Scanner(c == null ? new InputStreamReader(System.in) : c.reader()));
         this.consoleWriter = firstNonNull(builder.consoleWriter, c == null ? new PrintWriter(System.out, true) : c.writer());

         for (var cc : builder.consoleCommands) {
            consoleCommandMap.put(cc.getName(), cc);
         }
         for (var s : config.get("Console/commands").asStringArray().orElse(new String[0])) {
            try {
               var cc = (ConsoleCommand)Class.forName(s).getDeclaredConstructor().newInstance();
               consoleCommandMap.put(cc.getName(), cc);
            } catch (Exception e) {
               getConsoleWriter().println("Could not create console command '" + s + "', " + lm(e));
            }
         }
         consoleThread = new Thread("ConsoleThread") {
            @Override /* Overridden from Thread */
            public void run() {
               var in = getConsoleReader();
               var out = getConsoleWriter();

               out.println(messages.getString("ListOfAvailableCommands"));
               for (var cc : new TreeMap<>(getConsoleCommands()).values())
                  out.append("\t").append(cc.getName()).append(" -- ").append(cc.getInfo()).println();
               out.println();

               while (true) {
                  out.append("> ").flush();
                  var line = in.nextLine();
                  var args = new Args(line);
                  if (! args.isEmpty())
                     executeCommand(args, in, out);
               }
            }
         };
         consoleThread.setDaemon(true);
      } else {
         this.consoleReader = null;
         this.consoleWriter = null;
         this.consoleThread = null;
      }
      this.listener = nn(builder.listener) ? builder.listener : new BasicMicroserviceListener();

      init();
   }

   /**
    * Prints a localized message to STDERR.
    *
    * <p>
    * Ignored if <js>"Console/enabled"</js> is <jk>false</jk>.
    *
    * @param mb The message bundle containing the message.
    * @param messageKey The message key.
    * @param args Optional {@link MessageFormat}-style arguments.
    */
   public void err(Messages mb, String messageKey, Object...args) {
      var msg = mb.getString(messageKey, args);
      if (consoleEnabled)
         System.err.println(mb.getString(messageKey, args));  // NOT DEBUG
      log(Level.SEVERE, msg);
   }

   /**
    * Executes a console command.
    *
    * @param args
    *    The command arguments.
    *    <br>The first entry in the arguments is always the command name.
    * @param in Console input.
    * @param out Console output.
    * @return <jk>true</jk> if the command returned <jk>true</jk> meaning the console thread should exit.
    */
   public boolean executeCommand(Args args, Scanner in, PrintWriter out) {
      var cc = consoleCommandMap.get(args.getArg(0));
      if (cc == null) {
         out.println(messages.getString("UnknownCommand"));
      } else {
         try {
            return cc.execute(in, out, args);
         } catch (Exception e) {
            e.printStackTrace(out);
         }
      }
      return false;
   }

   /**
    * Convenience method for executing a console command directly.
    *
    * <p>
    * Allows you to execute a console command outside the console by simulating input and output.
    *
    * @param command The command name to execute.
    * @param input Optional input to the command.  Can be <jk>null</jk>.
    * @param args Optional command arguments to pass to the command.
    * @return The command output.
    */
   public String executeCommand(String command, String input, Object...args) {
      var sw = new StringWriter();
      var l = list();
      l.add(command);
      for (var a : args)
         l.add(s(a));
      var args2 = new Args(l.toArray(new String[l.size()]));
      try (var in = new Scanner(input); var out = new PrintWriter(sw)) {
         executeCommand(args2, in, out);
      }
      return sw.toString();
   }

   /**
    * Stops the console (if it's started) and calls {@link System#exit(int)}.
    *
    * @throws Exception Error occurred
    */
   public void exit() throws Exception {
      try {
         stopConsole();
      } catch (Exception e) {
         e.printStackTrace();
      }
      System.exit(0);
   }

   /**
    * Returns the command-line arguments passed into the application.
    *
    * <p>
    * This method can be called from the class constructor.
    *
    * <p>
    * See {@link Args} for details on using this method.
    *
    * @return The command-line arguments passed into the application.
    */
   public Args getArgs() { return args; }

   /**
    * Returns the external INI-style configuration file that can be used to configure your microservice.
    *
    * <p>
    * The config location is determined in the following order:
    * <ol class='spaced-list'>
    *    <li>
    *       The first argument passed to the microservice jar.
    *    <li>
    *       The <c>Main-Config</c> entry in the microservice jar manifest file.
    *    <li>
    *       The name of the microservice jar with a <js>".cfg"</js> suffix (e.g.
    *       <js>"mymicroservice.jar"</js>-&gt;<js>"mymicroservice.cfg"</js>).
    * </ol>
    *
    * <p>
    * If all methods for locating the config fail, then this method returns an empty config.
    *
    * <p>
    * Subclasses can set their own config file by using the following methods:
    * <ul class='javatree'>
    *    <li class='jm'>{@link Builder#configStore(ConfigStore)}
    *    <li class='jm'>{@link Builder#configName(String)}
    * </ul>
    *
    * <p>
    * String variables are automatically resolved using the variable resolver returned by {@link #getVarResolver()}.
    *
    * <p>
    * This method can be called from the class constructor.
    *
    * <h5 class='section'>Example:</h5>
    * <p class='bini'>
    *    <cc>#--------------------------</cc>
    *    <cc># My section</cc>
    *    <cc>#--------------------------</cc>
    *    <cs>[MySection]</cs>
    *
    *    <cc># An integer</cc>
    *    <ck>anInt</ck> = 1
    *
    *    <cc># A boolean</cc>
    *    <ck>aBoolean</ck> = true
    *
    *    <cc># An int array</cc>
    *    <ck>anIntArray</ck> = 1,2,3
    *
    *    <cc># A POJO that can be converted from a String</cc>
    *    <ck>aURL</ck> = http://foo
    *
    *    <cc># A POJO that can be converted from JSON</cc>
    *    <ck>aBean</ck> = {foo:'bar',baz:123}
    *
    *    <cc># A system property</cc>
    *    <ck>locale</ck> = $S{java.locale, en_US}
    *
    *    <cc># An environment variable</cc>
    *    <ck>path</ck> = $E{PATH, unknown}
    *
    *    <cc># A manifest file entry</cc>
    *    <ck>mainClass</ck> = $MF{Main-Class}
    *
    *    <cc># Another value in this config file</cc>
    *    <ck>sameAsAnInt</ck> = $C{MySection/anInt}
    *
    *    <cc># A command-line argument in the form "myarg=foo"</cc>
    *    <ck>myArg</ck> = $A{myarg}
    *
    *    <cc># The first command-line argument</cc>
    *    <ck>firstArg</ck> = $A{0}
    *
    *    <cc># Look for system property, or env var if that doesn't exist, or command-line arg if that doesn't exist.</cc>
    *    <ck>nested</ck> = $S{mySystemProperty,$E{MY_ENV_VAR,$A{0}}}
    *
    *    <cc># A POJO with embedded variables</cc>
    *    <ck>aBean2</ck> = {foo:'$A{0}',baz:$C{MySection/anInt}}
    * </p>
    *
    * <p class='bjava'>
    *    <jc>// Java code for accessing config entries above.</jc>
    *    Config <jv>config</jv> = getConfig();
    *
    *    <jk>int</jk> <jv>anInt</jv> = <jv>config</jv>.get(<js>"MySection/anInt"</js>).asInteger().orElse(-1);
    *    <jk>boolean</jk> <jv>aBoolean</jv> = <jv>config</jv>.get(<js>"MySection/aBoolean"</js>).asBoolean().orElse(<jk>false</jk>);
    *    <jk>int</jk>[] <jv>anIntArray</jv> = <jv>config</jv>.get(<js>"MySection/anIntArray"</js>).as(<jk>int</jk>[].<jk>class</jk>).orElse(<jk>null</jk>);
    *    URL <jv>aURL</jv> = <jv>config</jv>.get(<js>"MySection/aURL"</js>).as(URL.<jk>class</jk>).orElse(<jk>null</jk>);
    *    MyBean <jv>aBean</jv> = <jv>config</jv>.get(<js>"MySection/aBean"</js>).as(MyBean.<jk>class</jk>).orElse(<jk>null</jk>);
    *    Locale <jv>locale</jv> = <jv>config</jv>.get(<js>"MySection/locale"</js>).as(Locale.<jk>class</jk>).orElse(<jk>null</jk>);
    *    String <jv>path</jv> = <jv>config</jv>.get(<js>"MySection/path"</js>).orElse(<jk>null</jk>);
    *    String <jv>mainClass</jv> = <jv>config</jv>.get(<js>"MySection/mainClass"</js>).orElse(<jk>null</jk>);
    *    <jk>int</jk> <jv>sameAsAnInt</jv> = <jv>config</jv>.get(<js>"MySection/sameAsAnInt"</js>).asInteger().orElse(<jk>null</jk>);
    *    String <jv>myArg</jv> = <jv>config</jv>.getString(<js>"MySection/myArg"</js>);
    *    String <jv>firstArg</jv> = <jv>config</jv>.getString(<js>"MySection/firstArg"</js>);
    * </p>
    *
    * @return The config file for this application, or <jk>null</jk> if no config file is configured.
    */
   public Config getConfig() { return config; }

   /**
    * Returns the console commands associated with this microservice.
    *
    * @return The console commands associated with this microservice as an unmodifiable map.
    */
   public final Map<String,ConsoleCommand> getConsoleCommands() { return consoleCommandMap; }

   /**
    * Returns the logger for this microservice.
    *
    * @return The logger for this microservice.
    */
   public Logger getLogger() { return logger; }

   /**
    * Returns the main jar manifest file contents as a simple {@link JsonMap}.
    *
    * <p>
    * This map consists of the contents of {@link Manifest#getMainAttributes()} with the keys and entries converted to
    * simple strings.
    * <p>
    * This method can be called from the class constructor.
    *
    * <h5 class='section'>Example:</h5>
    * <p class='bjava'>
    *    <jc>// Get Main-Class from manifest file.</jc>
    *    String <jv>mainClass</jv> = Microservice.<jsm>getManifest</jsm>().getString(<js>"Main-Class"</js>, <js>"unknown"</js>);
    *
    *    <jc>// Get Rest-Resources from manifest file.</jc>
    *    String[] <jv>restResources</jv> = Microservice.<jsm>getManifest</jsm>().getStringArray(<js>"Rest-Resources"</js>);
    * </p>
    *
    * @return The manifest file from the main jar, or <jk>null</jk> if the manifest file could not be retrieved.
    */
   public ManifestFile getManifest() { return manifest; }

   /**
    * Returns the variable resolver for resolving variables in strings and files.
    *
    * <p>
    * Variables can be controlled by the following methods:
    * <ul class='javatree'>
    *    <li class='jm'>{@link Builder#vars(Class...)}
    *    <li class='jm'>{@link Builder#varBean(Class,Object)}
    * </ul>
    *
    * @return The VarResolver used by this Microservice, or <jk>null</jk> if it was never created.
    */
   public VarResolver getVarResolver() { return varResolver; }

   /**
    * Initializes this microservice.
    *
    * <p>
    * This method can be called whenever the microservice is not started.
    *
    * <p>
    * It will initialize (or reinitialize) the console commands, system properties, and logger.
    *
    * @return This object.
    * @throws ParseException Malformed input encountered.
    * @throws IOException Couldn't read a file.
    */
   public synchronized Microservice init() throws IOException, ParseException {

      // --------------------------------------------------------------------------------
      // Set system properties.
      // --------------------------------------------------------------------------------
      var spKeys = config.getKeys("SystemProperties");
      if (nn(spKeys))
         for (var key : spKeys)
            System.setProperty(key, config.get("SystemProperties/" + key).orElse(null));

      // --------------------------------------------------------------------------------
      // Initialize logging.
      // --------------------------------------------------------------------------------
      this.logger = builder.logger;
      var logConfig = nn(builder.logConfig) ? builder.logConfig : new LogConfig();
      if (this.logger == null) {
         LogManager.getLogManager().reset();
         this.logger = Logger.getLogger("");
         var logFile = firstNonNull(logConfig.logFile, config.get("Logging/logFile").orElse(null));

         if (ne(logFile)) {
            var logDir = firstNonNull(logConfig.logDir, config.get("Logging/logDir").orElse("."));
            var logDirFile = resolveFile(logDir);
            mkdirs(logDirFile, false);
            logDir = logDirFile.getAbsolutePath();
            System.setProperty("juneau.logDir", logDir);

            var append = firstNonNull(logConfig.append, config.get("Logging/append").asBoolean().orElse(false));
            var limit = firstNonNull(logConfig.limit, config.get("Logging/limit").asInteger().orElse(1024 * 1024));
            var count = firstNonNull(logConfig.count, config.get("Logging/count").asInteger().orElse(1));

            var fh = new FileHandler(logDir + '/' + logFile, limit, count, append);

            var f = logConfig.formatter;
            if (f == null) {
               var format = config.get("Logging/format").orElse("[{date} {level}] {msg}%n");
               var dateFormat = config.get("Logging/dateFormat").orElse("yyyy.MM.dd hh:mm:ss");
               var useStackTraceHashes = config.get("Logging/useStackTraceHashes").asBoolean().orElse(false);
               f = new LogEntryFormatter(format, dateFormat, useStackTraceHashes);
            }
            fh.setFormatter(f);
            fh.setLevel(firstNonNull(logConfig.fileLevel, config.get("Logging/fileLevel").as(Level.class).orElse(Level.INFO)));
            logger.addHandler(fh);

            var ch = new ConsoleHandler();
            ch.setLevel(firstNonNull(logConfig.consoleLevel, config.get("Logging/consoleLevel").as(Level.class).orElse(Level.WARNING)));
            ch.setFormatter(f);
            logger.addHandler(ch);
         }
      }

      var loggerLevels = config.get("Logging/levels").as(JsonMap.class).orElseGet(JsonMap::new);
      for (var l : loggerLevels.keySet())
         Logger.getLogger(l).setLevel(loggerLevels.get(l, Level.class));
      for (var l : logConfig.levels.keySet())
         Logger.getLogger(l).setLevel(logConfig.levels.get(l));

      return this;
   }

   /**
    * Joins the application with the current thread.
    *
    * <p>
    * Default implementation is a no-op.
    *
    * @return This object.
    * @throws Exception Error occurred
    */
   public Microservice join() throws Exception {
      return this;
   }

   /**
    * Kill the JVM by calling <c>System.exit(2);</c>.
    */
   public void kill() {
      // This triggers the shutdown hook.
      System.exit(2);
   }

   @Override /* Overridden from ConfigChangeListener */
   public void onConfigChange(ConfigEvents events) {
      listener.onConfigChange(this, events);
   }

   /**
    * Prints a localized message to the console writer.
    *
    * <p>
    * Ignored if <js>"Console/enabled"</js> is <jk>false</jk>.
    *
    * @param mb The message bundle containing the message.
    * @param messageKey The message key.
    * @param args Optional {@link MessageFormat}-style arguments.
    */
   @SuppressWarnings("resource")
   public void out(Messages mb, String messageKey, Object...args) {
      var msg = mb.getString(messageKey, args);
      if (consoleEnabled)
         getConsoleWriter().println(msg);
      log(Level.INFO, msg);
   }

   /**
    * Start this application.
    *
    * <p>
    * Overridden methods MUST call this method FIRST so that the {@link MicroserviceListener#onStart(Microservice)} method is called.
    *
    * @return This object.
    * @throws Exception Error occurred.
    */
   public synchronized Microservice start() throws Exception {

      if (config.getName() == null)
         err(messages, "RunningClassWithoutConfig", getClass().getSimpleName());
      else
         out(messages, "RunningClassWithConfig", getClass().getSimpleName(), config.getName());

      Runtime.getRuntime().addShutdownHook(new Thread("ShutdownHookThread") {
         @Override /* Overridden from Thread */
         public void run() {
            try {
               Microservice.this.stop();
               Microservice.this.stopConsole();
            } catch (Exception e) {
               e.printStackTrace();
            }
         }
      });

      listener.onStart(this);

      return this;
   }

   /**
    * Starts the console thread for this microservice.
    *
    * @return This object.
    * @throws Exception Error occurred
    */
   public synchronized Microservice startConsole() throws Exception {
      if (nn(consoleThread) && ! consoleThread.isAlive())
         consoleThread.start();
      return this;
   }

   /**
    * Stop this application.
    *
    * <p>
    * Overridden methods MUST call this method LAST so that the {@link MicroserviceListener#onStop(Microservice)} method is called.
    *
    * @return This object.
    * @throws Exception Error occurred
    */
   public Microservice stop() throws Exception {
      listener.onStop(this);
      return this;
   }

   /**
    * Stops the console thread for this microservice.
    *
    * @return This object.
    * @throws Exception Error occurred
    */
   public synchronized Microservice stopConsole() throws Exception {
      if (nn(consoleThread) && consoleThread.isAlive())
         consoleThread.interrupt();
      return this;
   }

   private List<String> getCandidateConfigNames() {
      if (nn(configName))
         return Collections.singletonList(configName);

      var args = getArgs();
      if (getArgs().hasArg("configFile"))
         return Collections.singletonList(args.getArg("configFile"));

      var manifest = getManifest();
      if (manifest.containsKey("Main-Config"))
         return Collections.singletonList(manifest.getString("Main-Config"));

      return Config.getCandidateSystemDefaultConfigNames();
   }

   /**
    * Returns the console reader.
    *
    * <p>
    * Subclasses can override this method to provide their own console input.
    *
    * @return The console reader.  Never <jk>null</jk>.
    */
   protected Scanner getConsoleReader() { return consoleReader; }

   /**
    * Returns the console writer.
    *
    * <p>
    * Subclasses can override this method to provide their own console output.
    *
    * @return The console writer.  Never <jk>null</jk>.
    */
   protected PrintWriter getConsoleWriter() { return consoleWriter; }

   /**
    * Logs a message to the log file.
    *
    * @param level The log level.
    * @param message The message text.
    * @param args Optional {@link MessageFormat}-style arguments.
    */
   protected void log(Level level, String message, Object...args) {
      var msg = args.length == 0 ? message : f(message, args);
      getLogger().log(level, msg);
   }

   /**
    * Resolves the specified path.
    *
    * <p>
    * If the working directory has been explicitly specified, relative paths are resolved relative to that.
    *
    * @param path The path to resolve.
    * @return The resolved path.
    */
   protected File resolveFile(String path) {
      if (Paths.get(path).isAbsolute())
         return new File(path);
      if (nn(workingDir))
         return new File(workingDir, path);
      return new File(path);
   }
}