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// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
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package org.apache.juneau.config.store;

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

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

/**
 * Represents a storage location for configuration files.
 *
 * <p>
 * Content stores require two methods to be implemented:
 * <ul>
 *    <li class='jm'>{@link #read(String)} - Retrieve a config file.
 *    <li class='jm'>{@link #write(String,String,String)} - ConfigStore a config file.
 * </ul>
 */
public abstract class ConfigStore extends Context implements Closeable {

   private final ConcurrentHashMap<String,Set<ConfigStoreListener>> listeners = new ConcurrentHashMap<>();
   private final ConcurrentHashMap<String,ConfigMap> configMaps = new ConcurrentHashMap<>();

   /**
    * Constructor.
    *
    * @param ps The settings for this content store.
    */
   protected ConfigStore(PropertyStore ps) {
      super(ps);
   }

   /**
    * Returns the contents of the configuration file.
    *
    * @param name The config file name.
    * @return
    *    The contents of the configuration file.
    *    <br>A blank string if the config does not exist.
    *    <br>Never <jk>null</jk>.
    * @throws IOException
    */
   public abstract String read(String name) throws IOException;

   /**
    * Saves the contents of the configuration file if the underlying storage hasn't been modified.
    *
    * @param name The config file name.
    * @param expectedContents The expected contents of the file.
    * @param newContents The new contents.
    * @return
    *    If <jk>null</jk>, then we successfully stored the contents of the file.
    *    <br>Otherwise the contents of the file have changed and we return the new contents of the file.
    * @throws IOException
    */
   public abstract String write(String name, String expectedContents, String newContents) throws IOException;

   /**
    * Registers a new listener on this store.
    *
    * @param name The configuration name to listen for.
    * @param l The new listener.
    * @return This object (for method chaining).
    */
   public synchronized ConfigStore register(String name, ConfigStoreListener l) {
      Set<ConfigStoreListener> s = listeners.get(name);
      if (s == null) {
         s = Collections.synchronizedSet(Collections.newSetFromMap(new IdentityHashMap<ConfigStoreListener,Boolean>()));
         listeners.put(name, s);
      }
      s.add(l);
      return this;
   }

   /**
    * Unregisters a listener from this store.
    *
    * @param name The configuration name to listen for.
    * @param l The listener to unregister.
    * @return This object (for method chaining).
    */
   public synchronized ConfigStore unregister(String name, ConfigStoreListener l) {
      Set<ConfigStoreListener> s = listeners.get(name);
      if (s != null)
         s.remove(l);
      return this;
   }

   /**
    * Returns a map file containing the parsed contents of a configuration.
    *
    * @param name The configuration name.
    * @return
    *    The parsed configuration.
    *    <br>Never <jk>null</jk>.
    * @throws IOException
    */
   public synchronized ConfigMap getMap(String name) throws IOException {
      ConfigMap cm = configMaps.get(name);
      if (cm != null)
         return cm;
      cm = new ConfigMap(this, name);
      ConfigMap cm2 = configMaps.putIfAbsent(name, cm);
      if (cm2 != null)
         return cm2;
      register(name, cm);
      return cm;
   }

   /**
    * Called when the physical contents of a config file have changed.
    *
    * <p>
    * Triggers calls to {@link ConfigStoreListener#onChange(String)} on all registered listeners.
    *
    * @param name The config name (e.g. the filename without the extension).
    * @param contents The new contents.
    * @return This object (for method chaining).
    */
   public synchronized ConfigStore update(String name, String contents) {
      Set<ConfigStoreListener> s = listeners.get(name);
      if (s != null)
         for (ConfigStoreListener l : listeners.get(name))
            l.onChange(contents);
      return this;
   }

   /**
    * Convenience method for updating the contents of a file with lines.
    *
    * @param name The config name (e.g. the filename without the extension).
    * @param contentLines The new contents.
    * @return This object (for method chaining).
    */
   public synchronized ConfigStore update(String name, String...contentLines) {
      StringBuilder sb = new StringBuilder();
      for (String l : contentLines)
         sb.append(l).append('\n');
      return update(name, sb.toString());
   }

   /**
    * Unused.
    */
   @Override /* Context */
   public final Session createSession(SessionArgs args) {
      throw new NoSuchMethodError();
   }

   /**
    * Unused.
    */
   @Override /* Context */
   public final SessionArgs createDefaultSessionArgs() {
      throw new NoSuchMethodError();
   }
}