/*
 * 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.config;

import static org.apache.juneau.common.utils.IOUtils.*;
import static org.apache.juneau.common.utils.StringUtils.*;
import static org.apache.juneau.common.utils.ThrowableUtils.*;
import static org.apache.juneau.common.utils.Utils.*;
import static org.apache.juneau.internal.CollectionUtils.*;
import static org.apache.juneau.internal.CollectionUtils.map;

import java.io.*;
import java.lang.annotation.*;
import java.lang.reflect.*;
import java.util.*;
import java.util.concurrent.atomic.*;

import org.apache.juneau.*;
import org.apache.juneau.collections.*;
import org.apache.juneau.common.utils.*;
import org.apache.juneau.config.event.*;
import org.apache.juneau.config.internal.*;
import org.apache.juneau.config.mod.*;
import org.apache.juneau.config.store.*;
import org.apache.juneau.config.vars.*;
import org.apache.juneau.internal.*;
import org.apache.juneau.json.*;
import org.apache.juneau.parser.*;
import org.apache.juneau.serializer.*;
import org.apache.juneau.svl.*;
import org.apache.juneau.utils.*;

/**
 * Main configuration API class.
 *
 * <h5 class='section'>Notes:</h5><ul>
 *    <li class='note'>This class is thread safe and reusable.
 * </ul>
 *
 * <h5 class='section'>See Also:</h5><ul>
 *    <li class='link'><a class="doclink" href="https://juneau.apache.org/docs/topics/JuneauConfigBasics">juneau-config Basics</a>
 * </ul>
 */
public class Config extends Context implements ConfigEventListener {

   //-----------------------------------------------------------------------------------------------------------------
   // Static
   //-----------------------------------------------------------------------------------------------------------------

   private static final boolean DISABLE_AUTO_SYSTEM_PROPS = Boolean.getBoolean("juneau.disableAutoSystemProps");
   private static final AtomicReference<Config> SYSTEM_DEFAULT = new AtomicReference<>(findSystemDefault());

   /**
    * Sets a system default configuration.
    *
    * @param systemDefault The new system default configuration.
    */
   public static synchronized void setSystemDefault(Config systemDefault) {
      SYSTEM_DEFAULT.set(systemDefault);
   }

   /**
    * Returns the system default configuration.
    *
    * @return The system default configuration, or <jk>null</jk> if it doesn't exist.
    */
   public static synchronized Config getSystemDefault() {
      return SYSTEM_DEFAULT.get();
   }

   private static synchronized Config findSystemDefault() {

      for (var n : getCandidateSystemDefaultConfigNames()) {
         var config = find(n);
         if (config != null) {
            if (! DISABLE_AUTO_SYSTEM_PROPS)
               config.setSystemProperties();
            return config;
         }
      }

      return null;
   }

   /**
    * Returns the list of candidate system default configuration file names.
    *
    * <p>
    * If the <js>"juneau.configFile"</js> system property is set, returns a singleton of that value.
    * <br>Otherwise, returns a list consisting of the following values:
    * <ol>
    *    <li>File with same name as jar file but with <js>".cfg"</js> extension.  (e.g. <js>"myjar.cfg"</js>)
    *    <li>Any file ending in <js>".cfg"</js> in the home directory (names ordered alphabetically).
    *    <li><js>"juneau.cfg"</js>
    *    <li><js>"default.cfg"</js>
    *    <li><js>"application.cfg"</js>
    *    <li><js>"app.cfg"</js>
    *    <li><js>"settings.cfg"</js>
    *    <li><js>"application.properties"</js>
    * </ol>
    * <p>
    *
    * @return
    *    A list of candidate file names.
    *    <br>The returned list is modifiable.
    *    <br>Each call constructs a new list.
    */
   public static synchronized List<String> getCandidateSystemDefaultConfigNames() {
      var l = listOf(String.class);

      var s = System.getProperty("juneau.configFile");
      if (s != null) {
         l.add(s);
         return l;
      }

      var cmd = System.getProperty("sun.java.command", "not_found").split("\\s+")[0];
      if (cmd.endsWith(".jar") && ! cmd.contains("surefirebooter")) {
         cmd = cmd.replaceAll(".*?([^\\\\\\/]+)\\.jar$", "$1");
         l.add(cmd + ".cfg");
         cmd = cmd.replaceAll("[\\.\\_].*$", "");  // Try also without version in jar name.
         l.add(cmd + ".cfg");
      }

      var files = sortedSet(new File(".").listFiles());
      for (var f : files)
         if (f.getName().endsWith(".cfg"))
            l.add(f.getName());

      l.add("juneau.cfg");
      l.add("default.cfg");
      l.add("application.cfg");
      l.add("app.cfg");
      l.add("settings.cfg");
      l.add("application.properties");

      return l;
   }

   private static synchronized Config find(String name) {
      if (name == null)
         return null;
      if (FileStore.DEFAULT.exists(name))
         return Config.create(name).store(FileStore.DEFAULT).build();
      if (ClasspathStore.DEFAULT.exists(name))
         return Config.create(name).store(ClasspathStore.DEFAULT).build();
      return null;
   }

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

   /**
    * Same as {@link #create()} but initializes the builder with the specified config name.
    *
    * @param name The configuration name.
    * @return A new builder.
    */
   public static Builder create(String name) {
      return new Builder().name(name);
   }

   //-------------------------------------------------------------------------------------------------------------------
   // Builder
   //-------------------------------------------------------------------------------------------------------------------

   /**
    * Builder class.
    */
   public static class Builder extends Context.Builder {

      String name;
      ConfigStore store;
      WriterSerializer serializer;
      ReaderParser parser;
      Map<Character,Mod> mods;
      VarResolver varResolver;
      int binaryLineLength;
      BinaryFormat binaryFormat;
      boolean multiLineValuesOnSeparateLines, readOnly;

      /**
       * Constructor, default settings.
       */
      protected Builder() {
         name = env("Config.name", "Configuration.cfg");
         store = FileStore.DEFAULT;
         serializer = Json5Serializer.DEFAULT;
         parser = JsonParser.DEFAULT;
         mods = map();
         mods(XorEncodeMod.INSTANCE);
         varResolver = VarResolver.DEFAULT;
         binaryLineLength = env("Config.binaryLineLength", -1);
         binaryFormat = env("Config.binaryFormat", BinaryFormat.BASE64);
         multiLineValuesOnSeparateLines = env("Config.multiLineValuesOnSeparateLines", false);
         readOnly = env("Config.readOnly", false);
      }

      /**
       * Copy constructor.
       *
       * @param copyFrom The bean to copy from.
       */
      protected Builder(Config copyFrom) {
         super(copyFrom);
         name = copyFrom.name;
         store = copyFrom.store;
         serializer = copyFrom.serializer;
         parser = copyFrom.parser;
         mods = copyOf(copyFrom.mods);
         varResolver = copyFrom.varResolver;
         binaryLineLength = copyFrom.binaryLineLength;
         binaryFormat = copyFrom.binaryFormat;
         multiLineValuesOnSeparateLines = copyFrom.multiLineValuesOnSeparateLines;
         readOnly = copyFrom.readOnly;
      }

      /**
       * Copy constructor.
       *
       * @param copyFrom The builder to copy from.
       */
      protected Builder(Builder copyFrom) {
         super(copyFrom);
         name = copyFrom.name;
         store = copyFrom.store;
         serializer = copyFrom.serializer;
         parser = copyFrom.parser;
         mods = copyOf(copyFrom.mods);
         varResolver = copyFrom.varResolver;
         binaryLineLength = copyFrom.binaryLineLength;
         binaryFormat = copyFrom.binaryFormat;
         multiLineValuesOnSeparateLines = copyFrom.multiLineValuesOnSeparateLines;
         readOnly = copyFrom.readOnly;
      }

      @Override /* Context.Builder */
      public Builder copy() {
         return new Builder(this);
      }

      @Override /* Context.Builder */
      public Config build() {
         return build(Config.class);
      }

      //-----------------------------------------------------------------------------------------------------------------
      // Properties
      //-----------------------------------------------------------------------------------------------------------------

      /**
       * Configuration name.
       *
       * <p>
       * Specifies the configuration name.
       * <br>This is typically the configuration file name, although
       * the name can be anything identifiable by the {@link ConfigStore} used for retrieving and storing the configuration.
       *
       * @param value
       *    The new value for this property.
       *    <br>The default is the first value found:
       *    <ul>
       *       <li>System property <js>"Config.name"
       *       <li>Environment variable <js>"CONFIG_NAME"
       *       <li><js>"Configuration.cfg"</js>
       *    </ul>
       * @return This object.
       */
      public Builder name(String value) {
         name = value;
         return this;
      }

      /**
       * Configuration store.
       *
       * <p>
       * The configuration store used for retrieving and storing configurations.
       *
       * @param value
       *    The new value for this property.
       *    <br>The default is {@link FileStore#DEFAULT}.
       * @return This object.
       */
      public Builder store(ConfigStore value) {
         store = value;
         return this;
      }

      /**
       * Configuration store.
       *
       * <p>
       * Convenience method for calling <code>store(ConfigMemoryStore.<jsf>DEFAULT</jsf>)</code>.
       *
       * @return This object.
       */
      public Builder memStore() {
         store = MemoryStore.DEFAULT;
         return this;
      }

      /**
       * POJO serializer.
       *
       * <p>
       * The serializer to use for serializing POJO values.
       *
       * @param value
       *    The new value for this property.
       *    <br>The default is {@link Json5Serializer#DEFAULT}
       * @return This object.
       */
      public Builder serializer(WriterSerializer value) {
         serializer = value;
         return this;
      }

      /**
       * POJO parser.
       *
       * <p>
       * The parser to use for parsing values to POJOs.
       *
       * @param value
       *    The new value for this property.
       *    <br>The default is {@link JsonParser#DEFAULT}.
       * @return This object.
       */
      public Builder parser(ReaderParser value) {
         parser = value;
         return this;
      }

      /**
       * Adds a value modifier.
       *
       * <p>
       * Modifiers are used to modify entry value before being persisted.
       *
       * @param values
       *    The mods to apply to this config.
       * @return This object.
       */
      public Builder mods(Mod...values) {
         for (var value : values)
            mods.put(value.getId(), value);
         return this;
      }

      /**
       * SVL variable resolver.
       *
       * <p>
       * The resolver to use for resolving SVL variables.
       *
       * @param value
       *    The new value for this property.
       *    <br>The default is {@link VarResolver#DEFAULT}.
       * @return This object.
       */
      public Builder varResolver(VarResolver value) {
         varResolver = value;
         return this;
      }

      /**
       * Binary value line length.
       *
       * <p>
       * When serializing binary values, lines will be split after this many characters.
       * <br>Use <c>-1</c> to represent no line splitting.
       *
       * @param value
       *    The new value for this property.
       *    <br>The default is the first value found:
       *    <ul>
       *       <li>System property <js>"Config.binaryLineLength"
       *       <li>Environment variable <js>"CONFIG_BINARYLINELENGTH"
       *       <li><c>-1</c>
       *    </ul>
       * @return This object.
       */
      public Builder binaryLineLength(int value) {
         binaryLineLength = value;
         return this;
      }

      /**
       * Binary value format.
       *
       * <p>
       * The format to use when persisting byte arrays.
       *
       * <ul class='values'>
       *    <li>{@link BinaryFormat#BASE64} - BASE64-encoded string.
       *    <li>{@link BinaryFormat#HEX} - Hexadecimal.
       *    <li>{@link BinaryFormat#SPACED_HEX} - Hexadecimal with spaces between bytes.
       * </ul>
       *
       * @param value
       *    The new value for this property.
       *    <br>The default is the first value found:
       *    <ul>
       *       <li>System property <js>"Config.binaryFormat"
       *       <li>Environment variable <js>"CONFIG_BINARYFORMAT"
       *       <li>{@link BinaryFormat#BASE64}
       *    </ul>
       * @return This object.
       */
      public Builder binaryFormat(BinaryFormat value) {
         binaryFormat = value;
         return this;
      }

      /**
       * Multi-line values on separate lines.
       *
       * <p>
       * When enabled, multi-line values will always be placed on a separate line from the key.
       *
       * <p>
       * The default is the first value found:
       *    <ul>
       *       <li>System property <js>"Config.multiLineValuesOnSeparateLine"
       *       <li>Environment variable <js>"CONFIG_MULTILINEVALUESONSEPARATELINE"
       *       <li><jk>false</jk>
       *    </ul>
       *
       * @return This object.
       */
      public Builder multiLineValuesOnSeparateLines() {
         multiLineValuesOnSeparateLines = true;
         return this;
      }

      /**
       * Read-only mode.
       *
       * <p>
       * When enabled, attempts to call any setters on this object will throw an {@link UnsupportedOperationException}.
       *
       * <p>
       *    The default is the first value found:
       *    <ul>
       *       <li>System property <js>"Config.readOnly"
       *       <li>Environment variable <js>"CONFIG_READONLY"
       *       <li><jk>false</jk>
       *    </ul>
       *
       * @return This object.
       */
      public Builder readOnly() {
         readOnly = true;
         return this;
      }
      @Override /* Overridden from Builder */
      public Builder annotations(Annotation...values) {
         super.annotations(values);
         return this;
      }

      @Override /* Overridden from Builder */
      public Builder annotations(List<Annotation> values) {
         super.annotations(values);
         return this;
      }

      @Override /* Overridden from Builder */
      public Builder apply(AnnotationWorkList work) {
         super.apply(work);
         return this;
      }

      @Override /* Overridden from Builder */
      public Builder applyAnnotations(Object...from) {
         super.applyAnnotations(from);
         return this;
      }

      @Override /* Overridden from Builder */
      public Builder applyAnnotations(Class<?>...from) {
         super.applyAnnotations(from);
         return this;
      }

      @Override /* Overridden from Builder */
      public Builder cache(Cache<HashKey,? extends org.apache.juneau.Context> value) {
         super.cache(value);
         return this;
      }

      @Override /* Overridden from Builder */
      public Builder debug() {
         super.debug();
         return this;
      }

      @Override /* Overridden from Builder */
      public Builder debug(boolean value) {
         super.debug(value);
         return this;
      }

      @Override /* Overridden from Builder */
      public Builder impl(Context value) {
         super.impl(value);
         return this;
      }

      @Override /* Overridden from Builder */
      public Builder type(Class<? extends org.apache.juneau.Context> value) {
         super.type(value);
         return this;
      }
   }

   //-------------------------------------------------------------------------------------------------------------------
   // Instance
   //-------------------------------------------------------------------------------------------------------------------

   final String name;
   final ConfigStore store;
   final WriterSerializer serializer;
   final ReaderParser parser;
   final Map<Character,Mod> mods;
   final VarResolver varResolver;
   final int binaryLineLength;
   final BinaryFormat binaryFormat;
   final boolean multiLineValuesOnSeparateLines, readOnly;
   final BeanSession beanSession;
   final VarResolverSession varSession;

   private final ConfigMap configMap;
   private final List<ConfigEventListener> listeners = synced(new LinkedList<>());


   @Override /* Context */
   public Builder copy() {
      return new Builder(this);
   }

   /**
    * Constructor.
    *
    * @param builder The builder for this object.
    * @throws IOException Thrown by underlying stream.
    */
   public Config(Builder builder) throws IOException {
      super(builder);

      name = builder.name;
      store = builder.store;
      configMap = store.getMap(name);
      configMap.register(this);
      serializer = builder.serializer;
      parser = builder.parser;
      beanSession = parser.getBeanContext().getSession();
      mods = u(copyOf(builder.mods));
      varResolver = builder.varResolver;
      varSession = varResolver
         .copy()
         .vars(ConfigVar.class)
         .bean(Config.class, this)
         .build()
         .createSession();
      binaryLineLength = builder.binaryLineLength;
      binaryFormat = builder.binaryFormat;
      multiLineValuesOnSeparateLines = builder.multiLineValuesOnSeparateLines;
      readOnly = builder.readOnly;
   }

   Config(Config copyFrom, VarResolverSession varSession) {
      super(copyFrom);
      name = copyFrom.name;
      store = copyFrom.store;
      configMap = copyFrom.configMap;
      configMap.register(this);
      serializer = copyFrom.serializer;
      parser = copyFrom.parser;
      mods = copyFrom.mods;
      varResolver = copyFrom.varResolver;
      this.varSession = varSession;
      binaryLineLength = copyFrom.binaryLineLength;
      binaryFormat = copyFrom.binaryFormat;
      multiLineValuesOnSeparateLines = copyFrom.multiLineValuesOnSeparateLines;
      readOnly = copyFrom.readOnly;
      beanSession = copyFrom.beanSession;
   }

   /**
    * Creates a copy of this config using the specified var session for resolving variables.
    *
    * <p>
    * This creates a shallow copy of the config but replacing the variable resolver.
    *
    * @param varSession The var session used for resolving string variables.
    * @return A new config object.
    */
   public Config resolving(VarResolverSession varSession) {
      return new Config(this, varSession);
   }

   /**
    * Returns the name associated with this config (usually a file name).
    *
    * @return The name associated with this config, or <jk>null</jk> if it has no name.
    */
   public String getName() {
      return name;
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Workhorse getters
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Returns the specified value as a string from the config file.
    *
    * <p>
    * Unlike {@link #getString(String)}, this method doesn't replace SVL variables.
    *
    * @param key The key.
    * @return The value, or <jk>null</jk> if the section or value doesn't exist.
    */
   private String getRaw(String key) {

      var sname = sname(key);
      var skey = skey(key);

      var ce = configMap.getEntry(sname, skey);

      if (ce == null)
         return null;

      return removeMods(ce.getModifiers(), ce.getValue());
   }

   String applyMods(String mods, String x) {
      if (mods != null && x != null)
         for (var i = 0; i < mods.length(); i++)
            x = getMod(mods.charAt(i)).doApply(x);
      return x;
   }

   String removeMods(String mods, String x) {
      if (mods != null && x != null)
         for (int i = mods.length()-1; i > -1; i--)
            x = getMod(mods.charAt(i)).doRemove(x);
      return x;
   }

   Mod getMod(char id) {
      var x = mods.get(id);
      return x == null ? Mod.NO_OP : x;
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Utility methods
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Takes the settings defined in this configuration and sets them as system properties.
    *
    * @return This object.
    */
   public Config setSystemProperties() {
      for (var section : getSectionNames()) {
         for (var key : getKeys(section)) {
            var k = (section.isEmpty() ? key : section + '/' + key);
            System.setProperty(k, getRaw(k));
         }
      }
      return this;
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Workhorse setters
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Sets a value in this config.
    *
    * @param key The key.
    * @param value The value.
    * @return This object.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config set(String key, String value) {
      checkWrite();
      Utils.assertArgNotNull("key", key);
      var sname = sname(key);
      var skey = skey(key);

      var ce = configMap.getEntry(sname, skey);
      if (ce == null && value == null)
         return this;

      var s = applyMods(ce == null ? null : ce.getModifiers(), s(value));

      configMap.setEntry(sname, skey, s, null, null, null);
      return this;
   }

   /**
    * Adds or replaces an entry with the specified key with a POJO serialized to a string using the registered
    * serializer.
    *
    * <p>
    * Equivalent to calling <c>put(key, value, isEncoded(key))</c>.
    *
    * @param key The key.
    * @param value The new value POJO.
    * @return The previous value, or <jk>null</jk> if the section or key did not previously exist.
    * @throws SerializeException
    *    If serializer could not serialize the value or if a serializer is not registered with this config file.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config set(String key, Object value) throws SerializeException {
      return set(key, value, null);
   }

   /**
    * Same as {@link #set(String, Object)} but allows you to specify the serializer to use to serialize the
    * value.
    *
    * @param key The key.
    * @param value The new value.
    * @param serializer
    *    The serializer to use for serializing the object.
    *    If <jk>null</jk>, then uses the predefined serializer on the config file.
    * @return The previous value, or <jk>null</jk> if the section or key did not previously exist.
    * @throws SerializeException
    *    If serializer could not serialize the value or if a serializer is not registered with this config file.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config set(String key, Object value, Serializer serializer) throws SerializeException {
      return set(key, serialize(value, serializer));
   }

   /**
    * Same as {@link #set(String, Object)} but allows you to specify all aspects of a value.
    *
    * @param key The key.
    * @param value The new value.
    * @param serializer
    *    The serializer to use for serializing the object.
    *    If <jk>null</jk>, then uses the predefined serializer on the config file.
    * @param modifiers
    *    Optional modifiers to apply to the value.
    *    <br>If <jk>null</jk>, then previous value will not be replaced.
    * @param comment
    *    Optional same-line comment to add to this value.
    *    <br>If <jk>null</jk>, then previous value will not be replaced.
    * @param preLines
    *    Optional comment or blank lines to add before this entry.
    *    <br>If <jk>null</jk>, then previous value will not be replaced.
    * @return The previous value, or <jk>null</jk> if the section or key did not previously exist.
    * @throws SerializeException
    *    If serializer could not serialize the value or if a serializer is not registered with this config file.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config set(String key, Object value, Serializer serializer, String modifiers, String comment, List<String> preLines) throws SerializeException {
      checkWrite();
      Utils.assertArgNotNull("key", key);
      var sname = sname(key);
      var skey = skey(key);
      modifiers = Utils.nullIfEmpty(modifiers);

      var s = applyMods(modifiers, serialize(value, serializer));

      configMap.setEntry(sname, skey, s, modifiers, comment, preLines);
      return this;
   }

   /**
    * Removes an entry with the specified key.
    *
    * @param key The key.
    * @return The previous value, or <jk>null</jk> if the section or key did not previously exist.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config remove(String key) {
      checkWrite();
      var sname = sname(key);
      var skey = skey(key);
      configMap.removeEntry(sname, skey);
      return this;
   }

   /**
    * Encodes and unencoded entries in this config.
    *
    * <p>
    * If any entries in the config are marked as encoded but not actually encoded,
    * this will encode them.
    *
    * @return This object.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config applyMods() {
      checkWrite();
      for (var section : configMap.getSections()) {
         for (var key : configMap.getKeys(section)) {
            var ce = configMap.getEntry(section, key);
            if (ce.getModifiers() != null) {
               var mods2 = ce.getModifiers();
               var value = ce.getValue();
               for (var i = 0; i < mods2.length(); i++) {
                  var mod = getMod(mods2.charAt(i));
                  if (! mod.isApplied(value)) {
                     configMap.setEntry(section, key, mod.apply(value), null, null, null);
                  }
               }
            }
         }
      }

      return this;
   }

   //-----------------------------------------------------------------------------------------------------------------
   // API methods
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Gets the entry with the specified key.
    *
    * <p>
    * The key can be in one of the following formats...
    * <ul class='spaced-list'>
    *    <li>
    *       <js>"key"</js> - A value in the default section (i.e. defined above any <c>[section]</c> header).
    *    <li>
    *       <js>"section/key"</js> - A value from the specified section.
    * </ul>
    *
    * <p>
    * If entry does not exist, returns an empty {@link Entry} object.
    *
    * @param key The key.
    * @return The entry bean, never <jk>null</jk>.
    */
   public Entry get(String key) {
      return new Entry(this, configMap, sname(key), skey(key));
   }

   /**
    * Gets the entry with the specified key.
    *
    * <p>
    * The key can be in one of the following formats...
    * <ul class='spaced-list'>
    *    <li>
    *       <js>"key"</js> - A value in the default section (i.e. defined above any <c>[section]</c> header).
    *    <li>
    *       <js>"section/key"</js> - A value from the specified section.
    * </ul>
    *
    * <p>
    * If entry does not exist, returns <jk>null</jk>.
    *
    * <h5 class='section'>Notes:</h5><ul>
    *    <li class='note'>This method is equivalent to calling <c>get(<jv>key</jv>).orElse(<jk>null</jk>);</c>.
    * </ul>
    *
    * @param key The key.
    * @return The entry value, or <jk>null</jk> if it doesn't exist.
    */
   public String getString(String key) {
      return new Entry(this, configMap, sname(key), skey(key)).orElse(null);
   }

   /**
    * Gets the section with the specified name.
    *
    * <p>
    * If section does not exist, returns an empty {@link Section} object.
    *
    * @param name The section name.  <jk>null</jk> and blank refer to the default section.
    * @return The section bean, never <jk>null</jk>.
    */
   public Section getSection(String name) {
      return new Section(this, configMap, Utils.emptyIfNull(name));
   }

   /**
    * Returns the keys of the entries in the specified section.
    *
    * @param section
    *    The section name to write from.
    *    <br>If empty, refers to the default section.
    *    <br>Must not be <jk>null</jk>.
    * @return
    *    An unmodifiable set of keys, or an empty set if the section doesn't exist.
    */
   public Set<String> getKeys(String section) {
      return configMap.getKeys(section(section));
   }

   /**
    * Returns the section names defined in this config.
    *
    * @return The section names defined in this config.
    */
   public Set<String> getSectionNames() {
      return u(configMap.getSections());
   }

   /**
    * Returns <jk>true</jk> if this section contains the specified key and the key has a non-blank value.
    *
    * @param key The key.
    * @return <jk>true</jk> if this section contains the specified key and the key has a non-blank value.
    */
   public boolean exists(String key) {
      return Utils.isNotEmpty(get(key).as(String.class).orElse(null));
   }

   /**
    * Creates the specified section if it doesn't exist.
    *
    * <p>
    * Returns the existing section if it already exists.
    *
    * @param name
    *    The section name.
    *    <br>Must not be <jk>null</jk>.
    *    <br>Use blank for the default section.
    * @param preLines
    *    Optional comment and blank lines to add immediately before the section.
    *    <br>If <jk>null</jk>, previous pre-lines will not be replaced.
    * @return The appended or existing section.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config setSection(String name, List<String> preLines) {
      try {
         return setSection(section(name), preLines, null);
      } catch (SerializeException e) {
         throw asRuntimeException(e);  // Impossible.
      }
   }

   /**
    * Creates the specified section if it doesn't exist.
    *
    * @param name
    *    The section name.
    *    <br>Must not be <jk>null</jk>.
    *    <br>Use blank for the default section.
    * @param preLines
    *    Optional comment and blank lines to add immediately before the section.
    *    <br>If <jk>null</jk>, previous pre-lines will not be replaced.
    * @param contents
    *    Values to set in the new section.
    *    <br>Can be <jk>null</jk>.
    * @return The appended or existing section.
    * @throws SerializeException Contents could not be serialized.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config setSection(String name, List<String> preLines, Map<String,Object> contents) throws SerializeException {
      checkWrite();
      configMap.setSection(section(name), preLines);

      if (contents != null)
         for (var e : contents.entrySet())
            set(section(name) + '/' + e.getKey(), e.getValue());

      return this;
   }

   /**
    * Removes the section with the specified name.
    *
    * @param name The name of the section to remove
    * @return This object.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config removeSection(String name) {
      checkWrite();
      configMap.removeSection(name);
      return this;
   }

   /**
    * Creates the specified import statement if it doesn't exist.
    *
    * @param sectionName
    *    The section name where to place the import statement.
    *    <br>Must not be <jk>null</jk>.
    *    <br>Use blank for the default section.
    * @param importName
    *    The import name.
    *    <br>Must not be <jk>null</jk>.
    * @param preLines
    *    Optional comment and blank lines to add immediately before the import statement.
    *    <br>If <jk>null</jk>, previous pre-lines will not be replaced.
    * @return The appended or existing import statement.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config setImport(String sectionName, String importName, List<String> preLines) {
      checkWrite();
      configMap.setImport(section(name), importName, preLines);
      return this;
   }

   /**
    * Removes the import statement with the specified name from the specified section.
    *
    * @param sectionName
    *    The section name where to place the import statement.
    *    <br>Must not be <jk>null</jk>.
    *    <br>Use blank for the default section.
    * @param importName
    *    The import name.
    *    <br>Must not be <jk>null</jk>.
    * @return This object.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config removeImport(String sectionName, String importName) {
      checkWrite();
      configMap.removeImport(sectionName, importName);
      return this;
   }

   /**
    * Loads the contents of the specified map of maps into this config.
    *
    * @param m The maps to load.
    * @return This object.
    * @throws SerializeException Value could not be serialized.
    */
   public Config load(Map<String,Map<String,Object>> m) throws SerializeException {
      if (m != null)
         for (var e : m.entrySet()) {
            setSection(e.getKey(), null, e.getValue());
         }
      return this;
   }

   /**
    * Commit the changes in this config to the store.
    *
    * @return This object.
    * @throws IOException Thrown by underlying stream.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config commit() throws IOException {
      checkWrite();
      configMap.commit();
      return this;
   }

   /**
    * Saves this config file to the specified writer as an INI file.
    *
    * <p>
    * The writer will automatically be closed.
    *
    * @param w The writer to send the output to.
    * @return This object.
    * @throws IOException If a problem occurred trying to send contents to the writer.
    */
   public Writer writeTo(Writer w) throws IOException {
      return configMap.writeTo(w);
   }

   /**
    * Add a listener to this config to react to modification events.
    *
    * <p>
    * Listeners should be removed using {@link #removeListener(ConfigEventListener)}.
    *
    * @param listener The new listener to add.
    * @return This object.
    */
   public synchronized Config addListener(ConfigEventListener listener) {
      listeners.add(listener);
      return this;
   }

   /**
    * Removes a listener from this config.
    *
    * @param listener The listener to remove.
    * @return This object.
    */
   public synchronized Config removeListener(ConfigEventListener listener) {
      listeners.remove(listener);
      return this;
   }

   /**
    * Closes this configuration object by unregistering it from the underlying config map.
    */
   public void close() {
      configMap.unregister(this);
   }

   /**
    * Overwrites the contents of the config file.
    *
    * @param contents The new contents of the config file.
    * @param synchronous Wait until the change has been persisted before returning this map.
    * @return This object.
    * @throws IOException Thrown by underlying stream.
    * @throws InterruptedException Thread was interrupted.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config load(Reader contents, boolean synchronous) throws IOException, InterruptedException {
      checkWrite();
      configMap.load(read(contents), synchronous);
      return this;
   }

   /**
    * Overwrites the contents of the config file.
    *
    * @param contents The new contents of the config file.
    * @param synchronous Wait until the change has been persisted before returning this map.
    * @return This object.
    * @throws IOException Thrown by underlying stream.
    * @throws InterruptedException Thread was interrupted.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config load(String contents, boolean synchronous) throws IOException, InterruptedException {
      checkWrite();
      configMap.load(contents, synchronous);
      return this;
   }

   /**
    * Does a rollback of any changes on this config currently in memory.
    *
    * @return This object.
    * @throws UnsupportedOperationException If configuration is read only.
    */
   public Config rollback() {
      checkWrite();
      configMap.rollback();
      return this;
   }

   /**
    * Returns the contents of this config as a simple map.
    *
    * @return The contents of this config as a simple map.
    */
   public JsonMap toMap() {
      return configMap.asMap();
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Test methods
   //-----------------------------------------------------------------------------------------------------------------

   ConfigMap getConfigMap() {
      return configMap;
   }

   List<ConfigEventListener> getListeners() {
      return u(listeners);
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Interface methods
   //-----------------------------------------------------------------------------------------------------------------

   @Override /* ConfigEventListener */
   public synchronized void onConfigChange(ConfigEvents events) {
      listeners.forEach(x -> x.onConfigChange(events));
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Private methods
   //-----------------------------------------------------------------------------------------------------------------

   private String serialize(Object value, Serializer serializer) throws SerializeException {
      if (value == null)
         return "";
      if (serializer == null)
         serializer = this.serializer;
      var c = value.getClass();
      if (value instanceof CharSequence cs)
         return nlIfMl(cs);
      if (isSimpleType(c))
         return value.toString();

      if (value instanceof byte[] b) {
         String s = null;
         if (binaryFormat == BinaryFormat.HEX)
            s = toHex(b);
         else if (binaryFormat == BinaryFormat.SPACED_HEX)
            s = toSpacedHex(b);
         else
            s = base64Encode(b);
         var l = binaryLineLength;
         if (l <= 0 || s.length() <= l)
            return s;
         var sb = new StringBuilder();
         for (var i = 0; i < s.length(); i += l)
            sb.append(binaryLineLength > 0 ? "\n" : "").append(s.substring(i, Math.min(s.length(), i + l)));
         return sb.toString();
      }

      String r = null;
      if (multiLineValuesOnSeparateLines)
         r = "\n" + (String)serializer.serialize(value);
      else
         r = (String)serializer.serialize(value);

      if (r.startsWith("'"))
         return r.substring(1, r.length()-1);
      return r;
   }

   private String nlIfMl(CharSequence cs) {
      var s = cs.toString();
      if (s.indexOf('\n') != -1 && multiLineValuesOnSeparateLines)
         return "\n" + s;
      return s;
   }

   private boolean isSimpleType(Type t) {
      if (! (t instanceof Class))
         return false;
      var c = (Class<?>)t;
      return (c == String.class || c.isPrimitive() || c.isAssignableFrom(Number.class) || c == Boolean.class || c.isEnum());
   }

   private String sname(String key) {
      Utils.assertArgNotNull("key", key);
      var i = key.indexOf('/');
      if (i == -1)
         return "";
      return key.substring(0, i);
   }

   private String skey(String key) {
      var i = key.indexOf('/');
      if (i == -1)
         return key;
      return key.substring(i+1);
   }

   private String section(String section) {
      Utils.assertArgNotNull("section", section);
      if (Utils.isEmpty(section))
         return "";
      return section;
   }

   void checkWrite() {
      if (readOnly)
         throw new UnsupportedOperationException("Cannot call this method on a read-only configuration.");
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Other methods
   //-----------------------------------------------------------------------------------------------------------------

   @Override /* Object */
   public String toString() {
      return configMap.toString();
   }
}