# UuidGenerationMixin.java

    /*
     * Copyright 2008 Niclas Hedhman. All rights Reserved.
     *
     * 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 org.qi4j.library.uid.uuid;

    import java.util.UUID;

    public class UuidGenerationMixin
        implements UuidService
    {
        private String uuid;
        private int count;

        public UuidGenerationMixin()
        {
            uuid = UUID.randomUUID().toString() + "-";
        }

        @Override
        public String generateUuid( int hashLength )
        {
            synchronized( this )
            {
                String uid = this.uuid + Integer.toHexString( count++ );
                if( hashLength > 0 )
                {
                    byte[] result = new byte[hashLength];
                    byte[] bytes = uid.getBytes();
                    for( int i = 0; i < bytes.length; i++ )
                    {
                        int pos = i % hashLength;
                        result[ pos ] = (byte) ( result[ pos ] * 31 + 19 + bytes[ i ] );
                    }
                    StringBuffer buf = new StringBuffer();
                    for( int data : result )
                    {
                        if( data < 0 )
                        {
                            data = 256 + data;
                        }
                        String hex = Integer.toHexString( data );
                        if( hex.length() == 1 )
                        {
                            hex = "0" + hex;
                        }
                        buf = buf.append( hex );
                    }
                    uid = buf.toString();
                }
                return uid.toUpperCase();
            }
        }
    }