/*
    * Copyright 2006-2011 the original author or authors.
    * 
    * 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
    * 
    * https://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 org.springframework.security.oauth2.client.token;
  
  import java.io.UnsupportedEncodingException;
  import java.math.BigInteger;
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.util.LinkedHashMap;
  import java.util.Map;
  
  import org.springframework.security.core.Authentication;
  import org.springframework.security.oauth2.client.resource.OAuth2ProtectedResourceDetails;
  import org.springframework.security.oauth2.common.util.OAuth2Utils;
  
  /**
   * Basic key generator taking into account the client id, scope and username (principal name) if they exist.
   * 
   * @author Dave Syer
   * 
   */
  public class DefaultClientKeyGenerator implements ClientKeyGenerator {
  
  	private static final String CLIENT_ID = "client_id";
  
  	private static final String SCOPE = "scope";
  
  	private static final String USERNAME = "username";
  
  	public String extractKey(OAuth2ProtectedResourceDetails resource, Authentication authentication) {
  		Map<String, String> values = new LinkedHashMap<String, String>();
  		if (authentication != null) {
  			values.put(USERNAME, authentication.getName());
  		}
  		values.put(CLIENT_ID, resource.getClientId());
  		if (resource.getScope() != null) {
  			values.put(SCOPE, OAuth2Utils.formatParameterList(resource.getScope()));
  		}
  		MessageDigest digest;
  		try {
  			digest = MessageDigest.getInstance("MD5");
  		}
  		catch (NoSuchAlgorithmException e) {
  			throw new IllegalStateException("MD5 algorithm not available.  Fatal (should be in the JDK).");
  		}
  
  		try {
  			byte[] bytes = digest.digest(values.toString().getBytes("UTF-8"));
  			return String.format("%032x", new BigInteger(1, bytes));
  		}
  		catch (UnsupportedEncodingException e) {
  			throw new IllegalStateException("UTF-8 encoding not available.  Fatal (should be in the JDK).");
  		}
  	}
  
  }