org.eclipse.userstorage/src/org/eclipse/userstorage/StorageFactory.java

/*
 * Copyright (c) 2015 Eike Stepper (Berlin, Germany) and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Eike Stepper - initial API and implementation
 */
package org.eclipse.userstorage;

import org.eclipse.userstorage.IStorageService.Registry;
import org.eclipse.userstorage.internal.Activator;
import org.eclipse.userstorage.internal.Storage;
import org.eclipse.userstorage.internal.util.StringUtil;
import org.eclipse.userstorage.spi.ISettings;
import org.eclipse.userstorage.spi.StorageCache;
import org.eclipse.userstorage.util.BadApplicationTokenException;
import org.eclipse.userstorage.util.Settings;
import org.eclipse.userstorage.util.Settings.MemorySettings;

import java.util.NoSuchElementException;

/**
 * Creates {@link IStorage storages} and maintains their preferred {@link IStorage#getService() services}
 * in the supplied {@link #getSettings() settings}.
 *
 * @author Eike Stepper
 */
public final class StorageFactory
{
  public static final StorageFactory DEFAULT = new StorageFactory(Settings.DEFAULT);

  private final ISettings settings;

  /**
   * Constructs this storage factory with the given settings.
   *
   * @param settings the settings to use with this storage factory, or <code>null</code> for {@link Settings#NONE no settings}.
   */
  public StorageFactory(ISettings settings)
  {
    this.settings = settings != null ? settings : Settings.NONE;
  }

  /**
   * Constructs this storage factory with {@link MemorySettings in-memory settings}.
   */
  public StorageFactory()
  {
    this(new Settings.MemorySettings());
  }

  /**
   * Returns the settings of this factory.
   *
   * @return the settings of this factory, never <code>null</code>.
   */
  public ISettings getSettings()
  {
    return settings;
  }

  /**
   * Creates a storage for the application identified by the given application token.
   * <p>
   * Calling this method is identical to calling <code>create(applicationToken, null)</code>.
   * <p>
   *
   * @param applicationToken the application token that identifies the application of the storage to be created.
   *        Minimal {@link BadApplicationTokenException#validate(String) lexical validation} is performed on the passed application token.<p>
   * @return the newly created storage, never <code>null</code>.<p>
   * @throws NoSuchElementException if the {@link Registry storage registry} is empty and, hence, there is no default storage available.<p>
   * @throws BadApplicationTokenException if {@link BadApplicationTokenException#validate(String) lexical validation} of the passed application token fails.<p>
   *
   * @see #create(String, StorageCache)
   */
  public IStorage create(String applicationToken) throws NoSuchElementException, BadApplicationTokenException
  {
    return create(applicationToken, null);
  }

  /**
   * Creates a storage for the application identified by the given application token and associates it with a given {@link StorageCache storage cache}.
   * <p>
   * @param applicationToken the application token that identifies the application of the storage to be created.
   *        Minimal {@link BadApplicationTokenException#validate(String) lexical validation} is performed on the passed application token.<p>
   * @param cache a local storage cache to be used as a locally persistent optimization, or <code>null</code> if local caching is not wanted.<p>
   * @return the newly created storage, never <code>null</code>.<p>
   * @throws NoSuchElementException if the {@link Registry storage registry} is empty and, hence, there is no default storage available.<p>
   * @throws BadApplicationTokenException if {@link BadApplicationTokenException#validate(String) lexical validation} of the passed application token fails.<p>
   *
   * @see #create(String)
   * @see StorageCache
   */
  public IStorage create(String applicationToken, StorageCache cache) throws NoSuchElementException, BadApplicationTokenException
  {
    IStorageService service = getService(applicationToken);

    Storage storage = new Storage(this, applicationToken, cache);
    storage.setService(service);
    return storage;
  }

  private IStorageService getService(String applicationToken) throws NoSuchElementException
  {
    if (!StringUtil.isEmpty(applicationToken))
    {
      IStorageService service = getPreferredService(applicationToken);
      if (service != null)
      {
        return service;
      }
    }

    IStorageService service = getPreferredService(null);
    if (service != null)
    {
      return service;
    }

    IStorageService[] storages = IStorageService.Registry.INSTANCE.getServices();
    if (storages.length != 0)
    {
      return storages[0];
    }

    throw new NoSuchElementException("No service registered");
  }

  private IStorageService getPreferredService(String applicationToken) throws NoSuchElementException
  {
    if (StringUtil.isEmpty(applicationToken))
    {
      applicationToken = "<default>";
    }

    try
    {
      String serviceURI = getPreferredServiceURI(applicationToken);
      if (serviceURI != null)
      {
        return IStorageService.Registry.INSTANCE.getService(StringUtil.newURI(serviceURI));
      }
    }
    catch (Exception ex)
    {
      //$FALL-THROUGH$
    }

    return null;
  }

  private String getPreferredServiceURI(String applicationToken)
  {
    try
    {
      return settings.getValue(applicationToken);
    }
    catch (Exception ex)
    {
      Activator.log(ex);
    }

    return null;
  }
}