/**
    * 
    */
   package edu.virginia.lib.ole.akubra;
   
   import java.io.UnsupportedEncodingException;
   import java.net.URI;
   import java.net.URLDecoder;
   import java.net.URLEncoder;
  import java.util.zip.Adler32;
  
  import org.akubraproject.map.IdMapper;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * @author ajs6f
   * @version 1.0
   * @see org.akubraproject.map.IdMapper
   */
  public class BitStringMapper implements IdMapper {
  
  	private static final Logger log = LoggerFactory
  			.getLogger(BitStringMapper.class);
  
  	/**
  	 * @see org.akubraproject.map.IdMapper#getExternalId(java.net.URI)
  	 */
  	public URI getExternalId(URI internalId) throws NullPointerException {
  		String uriandpath = internalId.toString();
  		String uri = "";
  		try {
  			uri = URLDecoder.decode(
  					uriandpath.substring(uriandpath.lastIndexOf('/') + 1),
  					"UTF-8");
  		} catch (UnsupportedEncodingException e) {
  			// useless catch block since UTF-8 is spec'd above
  		}
  		return URI.create(uri);
  	}
  
  	/**
  	 * @see org.akubraproject.map.IdMapper#getInternalId(java.net.URI)
  	 */
  	public URI getInternalId(URI externalId) throws NullPointerException {
  		log.debug("Entering BitStringMapper.getInternalId()");
  		String characters = "";
  		try {
  			characters = URLEncoder.encode(externalId.toString(), "UTF-8");
  		} catch (UnsupportedEncodingException e) {
  			// useless catch block since UTF-8 is spec'd above
  		}
  		String hashcharacters = Long.toBinaryString(hash(characters));
  		log.debug("Using hashcharacters: " + hashcharacters);
  		StringBuffer path = new StringBuffer();
  		for (int i = 0; i < hashcharacters.length() - Constants.CHUNK; i = i
  				+ Constants.CHUNK) {
  			String section = hashcharacters.substring(i, i + Constants.CHUNK)
  					+ "/";
  			log.debug("Appending: '" + section + "' to path");
  			path.append(section);
  		}
  		String uristring = path.toString() + characters;
  		log.debug("Exiting BitStringMapper.getInternalId() with: " + uristring);
  		return URI.create(String.valueOf(uristring));
  	}
  
  	/**
  	 * @param externalPrefix ignored
  	 * @return always returns empty string, since there is no defined prefix for this mapper
  	 * @see org.akubraproject.map.IdMapper#getInternalPrefix(java.lang.String)
  	 */
  	public String getInternalPrefix(String externalPrefix)
  			throws NullPointerException {
  		return "";
  	}
  	
  	/**
  	 * @param {@link String} characters
  	 * @return {@link Long} Adler32 hash of input
  	 * @see Adler32
  	 */
  	private Long hash(String characters) {
  		Adler32 hasher = new Adler32();
  		hasher.reset();
  		hasher.update(characters.getBytes());
  		return hasher.getValue();
  	}
  
  }