EnvAppConfigurationKeyHelper

/*
 * Copyright 2012-2013 smartics, Kronseder & Reiner GmbH
 *
 * Licensed 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 de.smartics.properties.impl.config.domain.key.envapp;

import java.net.InetAddress;

import de.smartics.properties.api.config.domain.key.ApplicationId;
import de.smartics.properties.api.config.domain.key.ApplicationIdLoader;
import de.smartics.properties.api.config.domain.key.ConfigurationKeyHelper;
import de.smartics.properties.api.config.domain.key.EnvironmentId;

/**
 * Helper to construct configuration keys by analyzing the runtime environment.
 */
public final class EnvAppConfigurationKeyHelper implements ConfigurationKeyHelper
{
  // ********************************* Fields *********************************

  // --- constants ------------------------------------------------------------

  /**
   * The class version identifier.
   */
  private static final long serialVersionUID = 1L;

  /**
   * The name of the system property that stores the name of the environment.
   * <p>
   * The value of this constant is {@value}.
   * </p>
   */
  public static final String SYSTEM_PROPERTY_ENVIRONMENT_NAME =
      "properties.environment.name";

  /**
   * The name of the system property that stores the node name of the
   * environment.
   * <p>
   * The value of this constant is {@value}.
   * </p>
   */
  public static final String SYSTEM_PROPERTY_ENVIRONMENT_NODE =
      "properties.environment.node";

  // --- members --------------------------------------------------------------

  /**
   * The flag to signal that the manifest of a EAR file (with the extension
   * <code>ear</code>) is preferred if present.
   *
   * @serial
   */
  private final boolean preferEarManifest;

  // ****************************** Initializer *******************************

  // ****************************** Constructors ******************************

  /**
   * Convenience constructor preferring manifest information from EARs.
   */
  public EnvAppConfigurationKeyHelper()
  {
    this(true);
  }

  /**
   * Default constructor.
   *
   * @param preferEarManifest the flag to signal that the manifest of a EAR file
   *          (with the extension <code>ear</code>) is preferred if present.
   */
  public EnvAppConfigurationKeyHelper(final boolean preferEarManifest)
  {
    this.preferEarManifest = preferEarManifest;
  }

  // ****************************** Inner Classes *****************************

  // ********************************* Methods ********************************

  // --- init -----------------------------------------------------------------

  // --- get&set --------------------------------------------------------------

  // --- business -------------------------------------------------------------

  /**
   * Loads the application identifier from the manifest file pointed at by the
   * given {@code locator} class.
   *
   * @param locator the class to locate the manifest file to load. It is the
   *          manifest file of the archive this class is part of.
   * @return the application identifier.
   * @throws IllegalStateException if the application identifier cannot be read
   *           from the manifest.
   * @see #load(EnvironmentId, Class)
   */
  public EnvAppConfigurationKey load(final Class<?> locator)
    throws IllegalStateException
  {
    return load((String) null, locator);
  }

  /**
   * Loads the application identifier from the manifest file pointed at by the
   * given {@code locator} class.
   *
   * @param environmentName the name of the environment of use. May be
   *          <code>null</code> if the value of the system property
   *          {@link #SYSTEM_PROPERTY_ENVIRONMENT_NAME} should be used (along
   *          with the node name defined by
   *          {@link #SYSTEM_PROPERTY_ENVIRONMENT_NODE}). If not specified, the
   *          name of the host of this runtime is determined.
   * @param locator the class to locate the manifest file to load. It is the
   *          manifest file of the archive this class is part of.
   * @return the application identifier.
   * @throws IllegalStateException if the application identifier cannot be read
   *           from the manifest.
   * @see #load(EnvironmentId, Class)
   */
  public EnvAppConfigurationKey load(final String environmentName,
      final Class<?> locator) throws IllegalStateException
  {
    final EnvironmentId environmentId = loadEnvironmentId(environmentName);
    final ApplicationIdLoader loader = createLoader();
    final ApplicationId applicationId = loader.load(locator);

    final EnvAppConfigurationKey configurationId =
        new EnvAppConfigurationKey(environmentId, applicationId);
    return configurationId;
  }

  private static EnvironmentId loadEnvironmentId(final String environmentName)
  {
    final String name =
        environmentName != null ? environmentName : System.getProperty(
            SYSTEM_PROPERTY_ENVIRONMENT_NAME, "development");
    final String node = calcEnvironmentNode();

    final EnvironmentId environmentId = new EnvironmentId(name, node);
    return environmentId;
  }

  private static String calcEnvironmentNode()
  {
    final String node = System.getProperty(SYSTEM_PROPERTY_ENVIRONMENT_NODE);

    if (node == null)
    {
      try
      {
        final InetAddress address = InetAddress.getLocalHost();
        final String hostName = address.getCanonicalHostName();
        return hostName;
      }
      catch (final Exception e)
      {
        return null;
      }
    }
    return node;
  }

  /**
   * Loads the application identifier from the manifest file pointed at by the
   * given {@code locator} class.
   *
   * @param environmentId the environment part of the configuration key to
   *          construct.
   * @param locator the class to locate the manifest file to load. It is the
   *          manifest file of the archive this class is part of.
   * @return the application identifier.
   * @throws IllegalStateException if the application identifier cannot be read
   *           from the manifest.
   * @see #load(Class)
   * @see #load(String, Class)
   */
  public EnvAppConfigurationKey load(final EnvironmentId environmentId,
      final Class<?> locator) throws IllegalStateException
  {
    final ApplicationIdLoader loader = createLoader();
    final ApplicationId applicationId = loader.load(locator);

    final EnvAppConfigurationKey configurationId =
        new EnvAppConfigurationKey(environmentId, applicationId);
    return configurationId;
  }

  /**
   * Loads the configuration key using the given applicationId and determines
   * the environmentId through system properties or defaults (null for the
   * environment and hostname for the node).
   *
   * @param applicationId the application part of the configuration key to
   *          construct.
   * @return the configuration key.
   */
  public EnvAppConfigurationKey load(final ApplicationId applicationId)
  {
    final EnvironmentId environmentId = loadEnvironmentId(null);

    final EnvAppConfigurationKey configurationId =
        new EnvAppConfigurationKey(environmentId, applicationId);

    return configurationId;
  }

  private ApplicationIdLoader createLoader()
  {
    return new ApplicationIdLoader(preferEarManifest);
  }

  // --- object basics --------------------------------------------------------

}