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A Java library to store password securely
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/*
 * Copyright © 2019, Java Keyring
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the  nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL  BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package com.github.javakeyring.internal;

import java.lang.reflect.InvocationTargetException;

import com.github.javakeyring.BackendNotSupportedException;
import com.github.javakeyring.KeyringStorageType;

/**
 * Factory of KeyringBackend.
 */
public class KeyringBackendFactory {

  /**
   * Creates an instance of KeyringBackend.
   * @return the KeyringBackend.
   * @throws BackendNotSupportedException 
   *     if no {@link KeyringBackend} supports this system.
   *     
   */
  public static KeyringBackend create() throws BackendNotSupportedException {
    for (KeyringStorageType keyRing : KeyringStorageType.values()) {
      KeyringBackend backend = tryToCreateBackend(keyRing, false);
      if (backend != null) {
        return backend;
      }
    }
    throw new BackendNotSupportedException("No available keyring backend found");
  }

  /**
   * Creates an instance of KeyringBackend.
   *
   * @param preferred
   *          Preferred backend name
   * @return Creates an instance of KeyringBackend.
   * @throws BackendNotSupportedException 
   *          should the preferred {@link KeyringStorageType} not support this system.
   */
  public static KeyringBackend create(KeyringStorageType preferred) throws BackendNotSupportedException {
    Exception cause;
    KeyringBackend backend;
    try {
      backend = tryToCreateBackend(preferred, true);
      cause = null;
    } catch (Exception ex)  {
      cause = ex;
      backend = null;
    }
    if (backend == null || cause != null) {
      throw new BackendNotSupportedException(String.format("The backend '%s' is not supported", preferred), cause);
    }
    return backend;
  }

  /**
   * Try to create keyring backend instance from Class.
   *
   * @param backendClass
   *          Target backend class
   */
  private static KeyringBackend tryToCreateBackend(KeyringStorageType keyring, boolean throwing)
      throws BackendNotSupportedException {
    KeyringBackend backend;
    try {
      backend = (KeyringBackend) keyring
              .getSupportingClass()
              .getConstructor(new Class[] {})
              .newInstance(new Object[]{});
    } catch (InvocationTargetException | IllegalAccessException | NoSuchMethodException | InstantiationException ex) {
      if (throwing) {
        throw new BackendNotSupportedException("Could not instantiate backend", ex);
      }
      return null;
    }
    return backend;
  }
}