/*
 * 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.internal;

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.config.event.ConfigEventType.*;
import static org.apache.juneau.internal.CollectionUtils.*;
import static org.apache.juneau.internal.CollectionUtils.map;

import java.io.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.stream.*;

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.store.*;
import org.apache.juneau.internal.*;

/**
 * Represents the parsed contents of a configuration.
 */
public class ConfigMap implements ConfigStoreListener {

   private final ConfigStore store;         // The store that created this object.
   private volatile String contents;        // The original contents of this object.
   final String name;                       // The name  of this object.

   // Changes that have been applied since the last load.
   private final List<ConfigEvent> changes = synced(new ConfigEvents());

   // Registered listeners listening for changes during saves or reloads.
   private final Set<ConfigEventListener> listeners = synced(Utils.set());

   // The parsed entries of this map with all changes applied.
   final Map<String,ConfigSection> entries = synced(map());

   // The original entries of this map before any changes were applied.
   final Map<String,ConfigSection> oentries = synced(map());

   // Import statements in this config.
   final List<Import> imports = new CopyOnWriteArrayList<>();

   private final SimpleReadWriteLock lock = new SimpleReadWriteLock();

   /**
    * Constructor.
    *
    * @param store The config store.
    * @param name The config name.
    * @throws IOException Thrown by underlying stream.
    */
   public ConfigMap(ConfigStore store, String name) throws IOException {
      this.store = store;
      this.name = name;
      load(store.read(name));
   }

   ConfigMap(ConfigStore store, String name, String contents) throws IOException {
      this.store = store;
      this.name = name;
      load(contents);
   }

   private ConfigMap load(String contents) throws IOException {
      if (contents == null)
         contents = "";
      this.contents = contents;

      entries.clear();
      oentries.clear();
      imports.forEach(Import::unregisterAll);
      imports.clear();

      var imports2 = mapOf(String.class, ConfigMap.class);

      List<String> lines = new LinkedList<>();
      try (var scanner = new Scanner(contents)) {
         while (scanner.hasNextLine()) {
            var line = scanner.nextLine();
            var c = firstChar(line);
            var c2 = StringUtils.lastNonWhitespaceChar(line);
            if (c == '[') {
               var l = line.trim();
               if (c2 != ']' || ! isValidNewSectionName(l.substring(1, l.length()-1)))
                  throw new ConfigException("Invalid section name found in configuration:  {0}", line);
            } else if (c == '<') {
               var l = line.trim();
               var i = l.indexOf('>');
               if (i != -1) {
                  var l2 = l.substring(1, i);
                  if (! isValidConfigName(l2))
                     throw new ConfigException("Invalid import config name found in configuration:  {0}", line);
                  var l3 = l.substring(i+1);
                  if (! (Utils.isEmpty(l3) || firstChar(l3) == '#'))
                     throw new ConfigException("Invalid import config name found in configuration:  {0}", line);
                  var importName = l2.trim();
                  try {
                     if (! imports2.containsKey(importName))
                        imports2.put(importName, store.getMap(importName));
                  } catch (StackOverflowError e) {
                     throw new IOException("Import loop detected in configuration '"+name+"'->'"+importName+"'");
                  }
               }
            }
            lines.add(line);
         }
      }

      List<Import> irl = Utils.listOfSize(imports2.size());
      forEachReverse(listFrom(imports2.values()), x -> irl.add(new Import(x).register(listeners)));
      this.imports.addAll(irl);

      // Add [blank] section.
      var inserted = false;
      var foundComment = false;
      for (var li = lines.listIterator(); li.hasNext();) {
         var l = li.next();
         var c = firstNonWhitespaceChar(l);
         if (c != '#') {
            if (c == 0 && foundComment) {
               li.set("[]");
               inserted = true;
            }
            break;
         }
         foundComment = true;
      }
      if (! inserted)
         lines.add(0, "[]");

      // Collapse any multi-lines.
      var li = lines.listIterator(lines.size());
      String accumulator = null;
      while (li.hasPrevious()) {
         var l = li.previous();
         var c = firstChar(l);
         if (c == '\t') {
            c = firstNonWhitespaceChar(l);
            if (c != '#') {
               if (accumulator == null)
                  accumulator = l.substring(1);
               else
                  accumulator = l.substring(1) + "\n" + accumulator;  // NOSONAR - Intentionally not using StringBuilder.
               li.remove();
            }
         } else if (accumulator != null) {
            li.set(l + "\n" + accumulator);
            accumulator = null;
         }
      }

      lines = copyOf(lines);
      var last = lines.size()-1;

      final int
         S1 = 1, // Looking for section.
         S2 = 2; // Found section, looking for start.

      var state = S1;

      var sections = listOf(ConfigSection.class);

      for (var i = last; i >= 0; i--) {
         var l = lines.get(i);
         var c = firstChar(l);

         if (state == S1) {
            if (c == '[') {
               state = S2;
            }
         } else {
            if (c != '#' && (c == '[' || l.indexOf('=') != -1)) {
               sections.add(new ConfigSection(lines.subList(i+1, last+1)));
               last = i + 1;
               state = (c == '[' ? S2 : S1);
            }
         }
      }

      sections.add(new ConfigSection(lines.subList(0, last+1)));

      for (var i = sections.size() - 1; i >= 0; i--) {
         var cs = sections.get(i);
         if (entries.containsKey(cs.name))
            throw new ConfigException("Duplicate section found in configuration:  [{0}]", cs.name);
         entries.put(cs.name, cs);
       }

      oentries.putAll(entries);
      return this;
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Getters
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Reads an entry from this map.
    *
    * @param section
    *    The section name.
    *    <br>Must not be <jk>null</jk>.
    *    <br>Use blank to refer to the default section.
    * @param key
    *    The entry key.
    *    <br>Must not be <jk>null</jk>.
    * @return The entry, or <jk>null</jk> if the entry doesn't exist.
    */
   public ConfigMapEntry getEntry(String section, String key) {
      checkSectionName(section);
      checkKeyName(key);
      try (var x = lock.read()) {
         var cs = entries.get(section);
         var ce = cs == null ? null : cs.entries.get(key);

         if (ce == null)
            ce = imports.stream().map(y -> y.getConfigMap().getEntry(section, key)).filter(y -> y != null).findFirst().orElse(null);

         return ce;
      }
   }

   /**
    * Returns the pre-lines on the specified section.
    *
    * <p>
    * The pre-lines are all lines such as blank lines and comments that preceed a section.
    *
    * @param section
    *    The section name.
    *    <br>Must not be <jk>null</jk>.
    *    <br>Use blank to refer to the default section.
    * @return
    *    An unmodifiable list of lines, or <jk>null</jk> if the section doesn't exist.
    */
   public List<String> getPreLines(String section) {
      checkSectionName(section);
      try (var x = lock.read()) {
         var cs = entries.get(section);
         return cs == null ? null : cs.preLines;
      }
   }

   /**
    * Returns the keys of the entries in the specified section.
    *
    * @return
    *    An unmodifiable set of keys.
    */
   public Set<String> getSections() {
      var s = imports.isEmpty() ? entries.keySet() : setOf(String.class);
      if (! imports.isEmpty()) {
         imports.forEach(x -> s.addAll(x.getConfigMap().getSections()));
         s.addAll(entries.keySet());
      }
      return u(s);
   }

   /**
    * Returns the keys of the entries in the specified section.
    *
    * @param section
    *    The section name.
    *    <br>Must not be <jk>null</jk>.
    *    <br>Use blank to refer to the default section.
    * @return
    *    An unmodifiable set of keys, or an empty set if the section doesn't exist.
    */
   public Set<String> getKeys(String section) {
      checkSectionName(section);
      var cs = entries.get(section);
      var s = imports.isEmpty() && cs != null ? cs.entries.keySet() : Utils.<String>set();
      if (! imports.isEmpty()) {
         imports.forEach(x -> s.addAll(x.getConfigMap().getKeys(section)));
         if (cs != null)
            s.addAll(cs.entries.keySet());
      }
      return u(s);
   }

   /**
    * Returns <jk>true</jk> if this config has the specified section.
    *
    * @param section
    *    The section name.
    *    <br>Must not be <jk>null</jk>.
    *    <br>Use blank to refer to the default section.
    * @return <jk>true</jk> if this config has the specified section.
    */
   public boolean hasSection(String section) {
      checkSectionName(section);
      return entries.get(section) != null || imports.stream().anyMatch(x -> x.getConfigMap().hasSection(section));
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Setters
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Adds a new section or replaces the pre-lines on an existing section.
    *
    * @param section
    *    The section name.
    *    <br>Must not be <jk>null</jk>.
    *    <br>Use blank to refer to the default section.
    * @param preLines
    *    The pre-lines on the section.
    *    <br>If <jk>null</jk>, the previous value will not be overwritten.
    * @return This object.
    */
   public ConfigMap setSection(String section, List<String> preLines) {
      checkSectionName(section);
      return applyChange(true, ConfigEvent.setSection(name, section, preLines));
   }

   /**
    * Adds or overwrites an existing entry.
    *
    * @param section
    *    The section name.
    *    <br>Must not be <jk>null</jk>.
    *    <br>Use blank to refer to the default section.
    * @param key
    *    The entry key.
    *    <br>Must not be <jk>null</jk>.
    * @param value
    *    The entry value.
    *    <br>If <jk>null</jk>, the previous value will not be overwritten.
    * @param modifiers
    *    Optional modifiers.
    *    <br>If <jk>null</jk>, the previous value will not be overwritten.
    * @param comment
    *    Optional comment.
    *    <br>If <jk>null</jk>, the previous value will not be overwritten.
    * @param preLines
    *    Optional pre-lines.
    *    <br>If <jk>null</jk>, the previous value will not be overwritten.
    * @return This object.
    */
   public ConfigMap setEntry(String section, String key, String value, String modifiers, String comment, List<String> preLines) {
      checkSectionName(section);
      checkKeyName(key);
      return applyChange(true, ConfigEvent.setEntry(name, section, key, value, modifiers, comment, preLines));
   }


   /**
    * Not implemented.
    *
    * @param section
    *    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 This object.
    */
   public ConfigMap setImport(String section, String importName, List<String> preLines) {
      throw new UnsupportedOperationException("Not implemented.");
   }

   /**
    * Removes a section.
    *
    * <p>
    * This eliminates all entries in the section as well.
    *
    * @param section
    *    The section name.
    *    <br>Must not be <jk>null</jk>.
    *    <br>Use blank to refer to the default section.
    * @return This object.
    */
   public ConfigMap removeSection(String section) {
      checkSectionName(section);
      return applyChange(true, ConfigEvent.removeSection(name, section));
   }

   /**
    * Removes an entry.
    *
    * @param section
    *    The section name.
    *    <br>Must not be <jk>null</jk>.
    *    <br>Use blank to refer to the default section.
    * @param key
    *    The entry key.
    *    <br>Must not be <jk>null</jk>.
    * @return This object.
    */
   public ConfigMap removeEntry(String section, String key) {
      checkSectionName(section);
      checkKeyName(key);
      return applyChange(true, ConfigEvent.removeEntry(name, section, key));
   }

   /**
    * Not implemented.
    *
    * @param section
    *    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.
    */
   public ConfigMap removeImport(String section, String importName) {
      throw new UnsupportedOperationException("Not implemented.");
   }

   private ConfigMap applyChange(boolean addToChangeList, ConfigEvent ce) {
      if (ce == null)
         return this;
      try (var x = lock.write()) {
         var section = ce.getSection();
         var cs = entries.get(section);
         if (ce.getType() == SET_ENTRY) {
            if (cs == null) {
               cs = new ConfigSection(section);
               entries.put(section, cs);
            }
            var oe = cs.entries.get(ce.getKey());
            if (oe == null)
               oe = ConfigMapEntry.NULL;
            cs.addEntry(
               ce.getKey(),
               ce.getValue() == null ? oe.value : ce.getValue(),
               ce.getModifiers() == null ? oe.modifiers : ce.getModifiers(),
               ce.getComment() == null ? oe.comment : ce.getComment(),
               ce.getPreLines() == null ? oe.preLines : ce.getPreLines()
            );
         } else if (ce.getType() == SET_SECTION) {
            if (cs == null) {
               cs = new ConfigSection(section);
               entries.put(section, cs);
            }
            if (ce.getPreLines() != null)
               cs.setPreLines(ce.getPreLines());
         } else if (ce.getType() == REMOVE_ENTRY) {
            if (cs != null)
               cs.entries.remove(ce.getKey());
         } else if (ce.getType() == REMOVE_SECTION) {
            if (cs != null)  // NOSONAR - Intentional.
               entries.remove(section);
         }
         if (addToChangeList)
            changes.add(ce);
      }
      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.
    */
   public ConfigMap load(String contents, boolean synchronous) throws IOException, InterruptedException {

      if (synchronous) {
         final var latch = new CountDownLatch(1);
         var listener = (ConfigStoreListener) x -> latch.countDown();
         store.register(name, listener);
         store.write(name, null, contents);
         if (latch.await(30, TimeUnit.SECONDS)) {
            store.unregister(name, listener);
         } else {
            throw new ConfigException("Unable to store contents of config to store.");
         }
      } else {
         store.write(name, null, contents);
      }
      return this;
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Lifecycle events
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Persist any changes made to this map and signal all listeners.
    *
    * <p>
    * If the underlying contents of the file have changed, this will reload it and apply the changes
    * on top of the modified file.
    *
    * <p>
    * Subsequent changes made to the underlying file will also be signaled to all listeners.
    *
    * <p>
    * We try saving the file up to 10 times.
    * <br>If the file keeps changing on the file system, we throw an exception.
    *
    * @return This object.
    * @throws IOException Thrown by underlying stream.
    */
   public ConfigMap commit() throws IOException {
      try (var x = lock.write()) {
         var newContents = asString();
         for (var i = 0; i <= 10; i++) {
            if (i == 10)
               throw new ConfigException("Unable to store contents of config to store.");
            var currentContents = store.write(name, contents, newContents);
            if (currentContents == null)
               break;
            onChange(currentContents);
         }
         this.changes.clear();
      }
      return this;
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Listeners
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Registers an event listener on this map.
    *
    * @param listener The new listener.
    * @return This object.
    */
   public ConfigMap register(ConfigEventListener listener) {
      listeners.add(listener);
      imports.forEach(x -> x.register(listener));
      return this;
   }

   boolean hasEntry(String section, String key) {
      var cs = entries.get(section);
      var ce = cs == null ? null : cs.entries.get(key);
      return ce != null;
   }

   /**
    * Unregisters an event listener from this map.
    *
    * @param listener The listener to remove.
    * @return This object.
    */
   public ConfigMap unregister(ConfigEventListener listener) {
      listeners.remove(listener);
      imports.forEach(x -> x.register(listener));
      return this;
   }

   /**
    * Returns the listeners currently associated with this config map.
    *
    * @return The listeners currently associated with this config map.
    */
   public Set<ConfigEventListener> getListeners() {
      return u(listeners);
   }

   @Override /* ConfigStoreListener */
   public void onChange(String newContents) {
      ConfigEvents changes2 = null;
      try (var x = lock.write()) {
         if (Utils.ne(contents, newContents)) {
            changes2 = findDiffs(newContents);
            load(newContents);

            // Reapply our changes on top of the modifications.
            this.changes.forEach(y -> applyChange(false, y));
         }
      } catch (IOException e) {
         throw asRuntimeException(e);
      }
      if (changes2 != null && ! changes2.isEmpty())
         signal(changes2);
   }

   @Override /* Object */
   public String toString() {
      try (var x = lock.read()) {
         return asString();
      }
   }

   /**
    * Returns the values in this config map as a map of maps.
    *
    * <p>
    * This is considered a snapshot copy of the config map.
    *
    * <p>
    * The returned map is modifiable, but modifications to the returned map are not reflected in the config map.
    *
    * @return A copy of this config as a map of maps.
    */
   public JsonMap asMap() {
      var m = new JsonMap();
      try (var x = lock.read()) {
         imports.forEach(y -> m.putAll(y.getConfigMap().asMap()));
         entries.values().forEach(z -> {
            var m2 = mapOf(String.class, String.class);
            z.entries.values().forEach(y -> m2.put(y.key, y.value));
            m.put(z.name, m2);
         });
      }
      return m;
   }

   /**
    * Serializes this map to the specified writer.
    *
    * @param w The writer to serialize to.
    * @return The same writer passed in.
    * @throws IOException Thrown by underlying stream.
    */
   public Writer writeTo(Writer w) throws IOException {
      try (var x = lock.read()) {
         for (var cs : entries.values())
            cs.writeTo(w);
      }
      return w;
   }

   /**
    * Does a rollback of any changes on this map currently in memory.
    *
    * @return This object.
    */
   public ConfigMap rollback() {
      if (!changes.isEmpty()) {
         try (var x = lock.write()) {
            changes.clear();
            load(contents);
         } catch (IOException e) {
            throw asRuntimeException(e);
         }
      }
      return this;
   }

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

   private void checkSectionName(String s) {
      if (! ("".equals(s) || isValidNewSectionName(s)))
         throw new IllegalArgumentException("Invalid section name: '"+s+"'");
   }

   private void checkKeyName(String s) {
      if (! isValidKeyName(s))
         throw new IllegalArgumentException("Invalid key name: '"+s+"'");
   }

   private boolean isValidKeyName(String s) {
      if (s == null)
         return false;
      s = s.trim();
      if (s.isEmpty())
         return false;
      for (var i = 0; i < s.length(); i++) {
         var c = s.charAt(i);
         if (c == '/' || c == '\\' || c == '[' || c == ']' || c == '=' || c == '#')
            return false;
      }
      return true;
   }

   private boolean isValidNewSectionName(String s) {
      if (s == null)
         return false;
      s = s.trim();
      if (s.isEmpty())
         return false;
      for (var i = 0; i < s.length(); i++) {
         var c = s.charAt(i);
         if (c == '/' || c == '\\' || c == '[' || c == ']')
            return false;
      }
      return true;
   }

   private boolean isValidConfigName(String s) {
      if (s == null)
         return false;
      s = s.trim();
      if (s.isEmpty())
         return false;
      for (var i = 0; i < s.length(); i++) {
         var c = s.charAt(i);
         if (i == 0) {
            if (! Character.isJavaIdentifierStart(c))
               return false;
         } else {
            if (! Character.isJavaIdentifierPart(c))
               return false;
         }
      }
      return true;
   }

   private void signal(ConfigEvents changes) {
      if (Utils.isNotEmpty(changes))
         listeners.forEach(x -> x.onConfigChange(changes));
   }

   private ConfigEvents findDiffs(String updatedContents) throws IOException {
      var changes2 = new ConfigEvents();
      var newMap = new ConfigMap(store, name, updatedContents);

      // Imports added.
      for (var i : newMap.imports) {
         if (! imports.contains(i)) {
            for (var s : i.getConfigMap().entries.values()) {
               for (var e : s.oentries.values()) {
                  if (! newMap.hasEntry(s.name, e.key)) {
                     changes2.add(ConfigEvent.setEntry(name, s.name, e.key, e.value, e.modifiers, e.comment, e.preLines));
                  }
               }
            }
         }
      }

      // Imports removed.
      for (var i : imports) {
         if (! newMap.imports.contains(i)) {
            for (var s : i.getConfigMap().entries.values()) {
               for (var e : s.oentries.values()) {
                  if (! newMap.hasEntry(s.name, e.key)) {
                     changes2.add(ConfigEvent.removeEntry(name, s.name, e.key));
                  }
               }
            }
         }
      }

      for (var ns : newMap.oentries.values()) {
         var s = oentries.get(ns.name);
         if (s == null) {
            for (var ne : ns.entries.values()) {
               changes2.add(ConfigEvent.setEntry(name, ns.name, ne.key, ne.value, ne.modifiers, ne.comment, ne.preLines));
            }
         } else {
            for (var ne : ns.oentries.values()) {
               var e = s.oentries.get(ne.key);
               if (e == null || Utils.ne(e.value, ne.value)) {
                  changes2.add(ConfigEvent.setEntry(name, s.name, ne.key, ne.value, ne.modifiers, ne.comment, ne.preLines));
               }
            }
            for (var e : s.oentries.values()) {
               var ne = ns.oentries.get(e.key);
               if (ne == null) {
                  changes2.add(ConfigEvent.removeEntry(name, s.name, e.key));
               }
            }
         }
      }

      for (var s : oentries.values()) {
         var ns = newMap.oentries.get(s.name);
         if (ns == null) {
            for (var e : s.oentries.values())
               changes2.add(ConfigEvent.removeEntry(name, s.name, e.key));
         }
      }

      return changes2;
   }

   // This method should only be called from behind a lock.
   private String asString() {
      try {
         var sw = new StringWriter();
         for (var cs : entries.values())
            cs.writeTo(sw);
         return sw.toString();
      } catch (IOException e) {
         throw asRuntimeException(e);  // Not possible.
      }
   }

   //---------------------------------------------------------------------------------------------
   // ConfigSection
   //---------------------------------------------------------------------------------------------

   class ConfigSection {

      final String name;   // The config section name, or blank if the default section.  Never null.

      final List<String> preLines = synced(Utils.list());
      private final String rawLine;

      final Map<String,ConfigMapEntry> oentries = synced(map());
      final Map<String,ConfigMapEntry> entries = synced(map());

      /**
       * Constructor.
       */
      ConfigSection(String name) {
         this.name = name;
         this.rawLine = "[" + name + "]";
      }

      /**
       * Constructor.
       */
      ConfigSection(List<String> lines) {

         String name2 = null, rawLine2 = null;

         final int
            S1 = 1, // Looking for section.
            S2 = 2; // Found section, looking for end.

         var state = S1;
         var start = 0;

         for (var i = 0; i < lines.size(); i++) {
            var l = lines.get(i);
            var c = StringUtils.firstNonWhitespaceChar(l);
            if (state == S1) {
               if (c == '[') {
                  var i1 = l.indexOf('[');
                  var i2 = l.indexOf(']');
                  name2 = l.substring(i1+1, i2).trim();
                  rawLine2 = l;
                  state = S2;
                  start = i+1;
               } else {
                  preLines.add(l);
               }
            } else {
               if (c != '#' && l.indexOf('=') != -1) {
                  var e = new ConfigMapEntry(l, lines.subList(start, i));
                  if (entries.containsKey(e.key))
                     throw new ConfigException("Duplicate entry found in section [{0}] of configuration:  {1}", name2, e.key);
                  entries.put(e.key, e);
                  start = i+1;
               }
            }
         }

         this.name = name2;
         this.rawLine = rawLine2;
         this.oentries.putAll(entries);
      }

      ConfigSection addEntry(String key, String value, String modifiers, String comment, List<String> preLines) {
         var e = new ConfigMapEntry(key, value, modifiers, comment, preLines);
         this.entries.put(e.key, e);
         return this;
      }

      ConfigSection setPreLines(List<String> preLines) {
         this.preLines.clear();
         this.preLines.addAll(preLines);
         return this;
      }

      Writer writeTo(Writer w) throws IOException {
         for (var s : preLines)
            w.append(s).append('\n');

         if (! name.isEmpty())
            w.append(rawLine).append('\n');
         else {
            // Need separation between default prelines and first-entry prelines.
            if (! preLines.isEmpty())
               w.append('\n');
         }

         for (var e : entries.values())
            e.writeTo(w);

         return w;
      }
   }

   //---------------------------------------------------------------------------------------------
   // Import
   //---------------------------------------------------------------------------------------------

   class Import {

      private final ConfigMap configMap;
      private final Map<ConfigEventListener,ConfigEventListener> listenerMap = synced(map());

      Import(ConfigMap configMap) {
         this.configMap = configMap;
      }

      synchronized Import register(Collection<ConfigEventListener> listeners) {
         listeners.forEach(this::register);
         return this;
      }

      synchronized Import register(final ConfigEventListener listener) {
         var l2 = (ConfigEventListener) events -> {
            var events2 = events.stream().filter(x -> ! hasEntry(x.getSection(), x.getKey())).collect(Collectors.toCollection(ConfigEvents::new));
            if (!events2.isEmpty())
               listener.onConfigChange(events2);
         };
         listenerMap.put(listener, l2);
         configMap.register(l2);
         return this;
      }

      synchronized Import unregister(final ConfigEventListener listener) {
         configMap.unregister(listenerMap.remove(listener));
         return this;
      }

      synchronized Import unregisterAll() {
         listenerMap.values().forEach(configMap::unregister);
         listenerMap.clear();
         return this;
      }

      String getConfigName() {
         return configMap.name;
      }

      ConfigMap getConfigMap() {
         return configMap;
      }

      @Override
      public boolean equals(Object o) {
         return o instanceof Import ir && ir.getConfigName().equals(getConfigName());
      }

      @Override
      public int hashCode() {
         return getConfigName().hashCode();
      }
   }
}