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

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

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

/**
 * Example of a {@link ConfigStore} that uses a relational database as a backend.
 *
 * <p>
 * This class provides a basic framework but requires implementing the following methods:
 * <ul class='javatree'>
 *    <li class='jm'>{@link #getDatabaseValue(String)}
 *    <li class='jm'>{@link #exists(String)}
 * </ul>
 *
 * <h5 class='section'>See Also:</h5><ul>
 * </ul>
 */
@SuppressWarnings({"resource","unused","javadoc"})
public class SqlStore extends ConfigStore {

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

   static final String
      SQLSTORE_jdbcUrl = "SqlStore.jdbcUrl",
      SQLSTORE_tableName = "SqlStore.tableName",
      SQLSTORE_nameColumn = "SqlStore.nameColumn",
      SQLSTORE_valueColumn = "SqlStore.valueColumn",
      SQLSTORE_pollInterval = "SqlStore.pollInterval";


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

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

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

      String jdbcUrl, tableName, nameColumn, valueColumn;
      int pollInterval;

      Builder() {
         this.jdbcUrl = env(SQLSTORE_jdbcUrl, "jdbc:derby:mydb");
         this.tableName = env(SQLSTORE_tableName, "config");
         this.nameColumn = env(SQLSTORE_nameColumn, "name");
         this.valueColumn = env(SQLSTORE_valueColumn, "value");
         this.pollInterval = env(SQLSTORE_pollInterval, 600);  // Time in seconds.
      }

      public Builder jdbcUrl(String value) {
         this.jdbcUrl = value;
         return this;
      }

      public Builder tableName(String value) {
         this.tableName = value;
         return this;
      }

      public Builder nameColumn(String value) {
         this.nameColumn = value;
         return this;
      }

      public Builder valueColumn(String value) {
         this.valueColumn = value;
         return this;
      }

      public Builder pollInterval(int value) {
         this.pollInterval = value;
         return this;
      }

      @Override
      public Builder copy() {
         return null;
      }

      @Override
      public SqlStore build() {
         return build(SqlStore.class);
      }
   }

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

   private final String jdbcUrl;
   private final String tableName, nameColumn, valueColumn;
   private final Timer watcher;
   private final ConcurrentHashMap<String,String> cache = new ConcurrentHashMap<>();

   /**
    * Constructor.
    *
    * @param builder The builder for this object.
    */
   protected SqlStore(Builder builder) {
      super(builder);
      this.jdbcUrl = builder.jdbcUrl;
      this.tableName = builder.tableName;
      this.nameColumn = builder.nameColumn;
      this.valueColumn = builder.valueColumn;

      int pollInterval = builder.pollInterval;

      TimerTask timerTask = new TimerTask() {
         @Override
         public void run() {
            SqlStore.this.poll();
         }
      };

      this.watcher = new Timer("MyTimer");
      watcher.scheduleAtFixedRate(timerTask, 0, pollInterval * 1000);
   }

   synchronized void poll() {

      // Loop through all our entries and find the latest values.
      cache.forEach((name,cacheContents) -> {
         String newContents = getDatabaseValue(name);

         // Change detected!
         if (! cacheContents.equals(newContents))
            update(name, newContents);
      });
   }

   // Reads the value from the database.
   protected String getDatabaseValue(String name) {
      // Implement me!
      return null;
   }

   @Override /* ConfigStore */
   public boolean exists(String name) {
      // Implement me!
      return false;
   }

   @Override /* ConfigStore */
   public synchronized String read(String name) {
      String contents = cache.get(name);
      if (contents == null) {
         contents = getDatabaseValue(name);
         update(name, contents);
      }
      return contents;
   }

   @Override /* ConfigStore */
   public synchronized String write(String name, String expectedContents, String newContents) {

      // This is a no-op.
      if (StringUtils.eq(expectedContents, newContents))
         return null;

      String currentContents = read(name);

      if (expectedContents != null && StringUtils.ne(currentContents, expectedContents))
         return currentContents;

      update(name, newContents);

      // Success!
      return null;
   }

   @Override /* ConfigStore */
   public synchronized SqlStore update(String name, String newContents) {
      cache.put(name, newContents);
      super.update(name, newContents);  // Trigger any listeners.
      return this;
   }

   @Override /* Closeable */
   public synchronized void close() {
      if (watcher != null)
         watcher.cancel();
   }
}