path: root/libjava/java/text/RuleBasedCollator.java

/* RuleBasedCollator.java -- Concrete Collator Class
   Copyright (C) 1998, 1999, 2000, 2001, 2003  Free Software Foundation, Inc.

This file is part of GNU Classpath.

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package java.text;

import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Vector;

/* Written using "Java Class Libraries", 2nd edition, plus online
 * API docs for JDK 1.2 from http://www.javasoft.com.
 * Status: Believed complete and correct
 */

/**
 * This class is a concrete subclass of <code>Collator</code> suitable
 * for string collation in a wide variety of languages.  An instance of
 * this class is normally returned by the <code>getInstance</code> method
 * of <code>Collator</code> with rules predefined for the requested
 * locale.  However, an instance of this class can be created manually
 * with any desired rules.
 * <p>
 * Rules take the form of a <code>String</code> with the following syntax
 * <ul>
 * <li> Modifier: '@' 
 * <li> Relation: '&lt;' | ';' | ',' | '=' : <text>
 * <li> Reset: '&amp;' : <text>
 * </ul>
 * The modifier character indicates that accents sort backward as is the
 * case with French.  The modifier applies to all rules <b>after</b>
 * the modifier but before the next primary sequence. If placed at the end
 * of the sequence if applies to all unknown accented character.
 * The relational operators specify how the text 
 * argument relates to the previous term.  The relation characters have
 * the following meanings:
 * <ul>
 * <li>'&lt;' - The text argument is greater than the prior term at the primary
 * difference level.
 * <li>';' - The text argument is greater than the prior term at the secondary
 * difference level.
 * <li>',' - The text argument is greater than the prior term at the tertiary
 * difference level.
 * <li>'=' - The text argument is equal to the prior term
 * </ul>
 * <p>
 * As for the text argument itself, this is any sequence of Unicode
 * characters not in the following ranges: 0x0009-0x000D, 0x0020-0x002F,
 * 0x003A-0x0040, 0x005B-0x0060, and 0x007B-0x007E. If these characters are 
 * desired, they must be enclosed in single quotes.  If any whitespace is 
 * encountered, it is ignored.  (For example, "a b" is equal to "ab").  
 * <p>
 * The reset operation inserts the following rule at the point where the
 * text argument to it exists in the previously declared rule string.  This
 * makes it easy to add new rules to an existing string by simply including
 * them in a reset sequence at the end.  Note that the text argument, or
 * at least the first character of it, must be present somewhere in the
 * previously declared rules in order to be inserted properly.  If this
 * is not satisfied, a <code>ParseException</code> will be thrown. 
 * <p>
 * This system of configuring <code>RuleBasedCollator</code> is needlessly
 * complex and the people at Taligent who developed it (along with the folks
 * at Sun who accepted it into the Java standard library) deserve a slow
 * and agonizing death.
 * <p>
 * Here are a couple of example of rule strings:
 * <p>
 * "&lt; a &lt; b &lt; c" - This string says that a is greater than b which is 
 * greater than c, with all differences being primary differences.
 * <p>
 * "&lt; a,A &lt; b,B &lt; c,C" - This string says that 'A' is greater than 'a' with
 * a tertiary strength comparison.  Both 'b' and 'B' are greater than 'a' and
 * 'A' during a primary strength comparison.  But 'B' is greater than 'b'
 * under a tertiary strength comparison.
 * <p>
 * "&lt; a &lt; c &amp; a &lt; b " - This sequence is identical in function to the 
 * "&lt; a &lt; b &lt; c" rule string above.  The '&amp;' reset symbol indicates that
 * the rule "&lt; b" is to be inserted after the text argument "a" in the
 * previous rule string segment.
 * <p>
 * "&lt; a &lt; b &amp; y &lt; z" - This is an error.  The character 'y' does not appear
 * anywhere in the previous rule string segment so the rule following the
 * reset rule cannot be inserted.
 * <p>
 * "&lt; a &amp; A @ &lt; e &amp; E &lt; f&amp; F" - This sequence is equivalent to the following
 * "&lt; a &amp; A &lt; E &amp; e &lt; f &amp; F".
 * <p>
 * For a description of the various comparison strength types, see the
 * documentation for the <code>Collator</code> class.
 * <p>
 * As an additional complication to this already overly complex rule scheme,
 * if any characters precede the first rule, these characters are considered
 * ignorable.  They will be treated as if they did not exist during 
 * comparisons.  For example, "- &lt; a &lt; b ..." would make '-' an ignorable
 * character such that the strings "high-tech" and "hightech" would
 * be considered identical.
 * <p>
 * A <code>ParseException</code> will be thrown for any of the following
 * conditions:
 * <ul>
 * <li>Unquoted punctuation characters in a text argument.
 * <li>A relational or reset operator not followed by a text argument
 * <li>A reset operator where the text argument is not present in
 * the previous rule string section.
 * </ul>
 *
 * @author Aaron M. Renn <arenn@urbanophile.com>
 * @author Tom Tromey <tromey@cygnus.com>
 * @author Guilhem Lavaux <guilhem@kaffe.org>
 */
public class RuleBasedCollator extends Collator
{
  /**
   * This class describes what rank has a character (or a sequence of characters) 
   * in the lexicographic order. Each element in a rule has a collation element.
   */
  final class CollationElement
  {
    String key;
    char relation;

    CollationElement(String key, char relation)
    {
      this.key = key;
      this.relation = relation;
    }
  }

  // True if we are using French-style accent ordering.
  private boolean frenchAccents;

  /**
   * This the the original rule string.
   */
  private String rules;

  // This maps strings onto collation values.
  private Hashtable map;
  
  // An entry in this hash means that more lookahead is required for
  // the prefix string.
  private Hashtable prefixes;
  
  /**
   * This method initializes a new instance of <code>RuleBasedCollator</code>
   * with the specified collation rules.  Note that an application normally
   * obtains an instance of <code>RuleBasedCollator</code> by calling the
   * <code>getInstance</code> method of <code>Collator</code>.  That method
   * automatically loads the proper set of rules for the desired locale.
   *
   * @param rules The collation rule string.
   *
   * @exception ParseException If the rule string contains syntax errors.
   */
  public RuleBasedCollator(String rules) throws ParseException
  {
    if (rules.equals(""))
      throw new ParseException("empty rule set", 0);
    
    this.rules = rules;

    // We keep each rule in order in a vector.  At the end we traverse
    // the vector and compute collation values from it.
    int insertion_index = 0;
    Vector vec = new Vector ();

    int index;
    StringBuffer argument = new StringBuffer();
    int len = rules.length();

    for (index = 0; index < len; ++index)
      {
	char c = rules.charAt(index);

	// Just skip whitespace.
	if (Character.isWhitespace(c))
	  continue;

	// Modifier.
	if (c == '@')
	  {
	    frenchAccents = true;
	    continue;
	  }

	// Check for relation or reset operator.
	if (! (c == '<' || c == ';' || c == ',' || c == '=' || c == '&'))
	  throw new ParseException ("invalid character", index);

	++index;
	while (index < len)
	  {
	    if (! Character.isWhitespace(rules.charAt(index)))
	      break;
	    ++index;
	  }
	if (index == len)
	  throw new ParseException ("missing argument", index);

	int save = index;
	index = text_argument (rules, index, argument);
	if (argument.length() == 0)
	  throw new ParseException ("invalid character", save);
	String arg = argument.toString();
	int item_index = -1;
        
        for (int j = 0; j < vec.size(); ++j)
          {
            CollationElement e = (CollationElement) vec.elementAt (j);

            if (arg.equals (e.key))
              {
                item_index = j;
                break;
              }
          }
	
	if (c != '&')
	  {
	    // If the argument already appears in the vector, then we
	    // must remove it in order to re-order.
	    if (item_index != -1)
	      {
		vec.removeElementAt(item_index);
		if (insertion_index >= item_index)
		  --insertion_index;
	      }
	    CollationElement r = new CollationElement (arg, c);
	    vec.insertElementAt(r, insertion_index);
	    ++insertion_index;
	  }
	else
	  {
	    // Reset.
	    if (item_index == -1)
	      throw
		new ParseException ("argument to reset not previously seen",
				    save);
	    insertion_index = item_index + 1;
	  }

	// Ugly: in this case the resulting INDEX comes from
	// text_argument, which returns the index of the next
	// character we should examine.
	--index;
      }

    // Now construct a hash table that maps strings onto their
    // collation values.
    int primary = 0;
    int secondary = 0;
    int tertiary = 0;
    this.map = new Hashtable ();
    this.prefixes = new Hashtable ();
    Enumeration e = vec.elements();
    while (e.hasMoreElements())
      {
	CollationElement r = (CollationElement) e.nextElement();
	switch (r.relation)
	  {
	  case '<':
	    ++primary;
	    secondary = 0;
	    tertiary = 0;
	    break;
	  case ';':
	    ++secondary;
	    tertiary = 0;
	    break;
	  case ',':
	    ++tertiary;
	    break;
	  case '=':
	    break;
	  }
	// This must match CollationElementIterator.
	map.put(r.key, new Integer (primary << 16
				    | secondary << 8 | tertiary));

	// Make a map of all lookaheads we might need.
	for (int i = r.key.length() - 1; i >= 1; --i)
	  prefixes.put(r.key.substring(0, i), Boolean.TRUE);
      }
  }

  /**
   * This method creates a copy of this object.
   *
   * @return A copy of this object.
   */
  public Object clone()
  {
    RuleBasedCollator c = (RuleBasedCollator) super.clone ();
    c.map = (Hashtable) map.clone ();
    c.prefixes = (Hashtable) map.clone ();
    return c;
  }

  // A helper for CollationElementIterator.next().
  int ceiNext (CollationElementIterator cei)
  {
    if (cei.lookahead_set)
      {
	cei.lookahead_set = false;
	return cei.lookahead;
      }

    int save = cei.textIndex;
    int max = cei.text.length();
    String s = null;

    // It is possible to have a case where `abc' has a mapping, but
    // neither `ab' nor `abd' do.  In this case we must treat `abd' as
    // nothing special.
    boolean found = false;

    int i;
    for (i = save + 1; i <= max; ++i)
      {
	s = cei.text.substring(save, i);
	if (prefixes.get(s) == null)
	  break;
	found = true;
      }
    // Assume s != null.

    Object obj = map.get(s);
    // The special case.
    while (found && obj == null && s.length() > 1)
      {
	--i;
	s = cei.text.substring(save, i);
	obj = map.get(s);
      }

    // Update state.
    cei.textIndex = i;

    if (obj == null)
      {
	// This idea, and the values, come from JDK.
	// assert (s.length() == 1)
	cei.lookahead_set = true;
	cei.lookahead = s.charAt(0) << 8;
	return 0x7fff << 16;
      }

    return ((Integer) obj).intValue();
  }

  // A helper for compareTo() that returns the next character that has
  // a nonzero ordering at the indicated strength.  This is also used
  // in CollationKey.
  static final int next (CollationElementIterator iter, int strength)
  {
    while (true)
      {
	int os = iter.next();
	if (os == CollationElementIterator.NULLORDER)
	  return os;
	int c = 0;
	switch (strength)
	  {
	  case PRIMARY:
	    c = os & ~0xffff;
	    break;
	  case SECONDARY:
	    c = os & ~0x00ff;
	    break;
	  case TERTIARY:
	  case IDENTICAL:
	    c = os;
	    break;
	  }
	if (c != 0)
	  return c;
      }
  }

  /**
   * This method returns an integer which indicates whether the first
   * specified <code>String</code> is less than, greater than, or equal to
   * the second.  The value depends not only on the collation rules in
   * effect, but also the strength and decomposition settings of this object.
   *
   * @param source The first <code>String</code> to compare.
   * @param target A second <code>String</code> to compare to the first.
   *
   * @return A negative integer if source &lt; target, a positive integer
   * if source &gt; target, or 0 if source == target.
   */
  public int compare(String source, String target)
  {
    CollationElementIterator cs, ct;

    cs = new CollationElementIterator(this, source);
    ct = new CollationElementIterator(this, target);

    for(;;)
      {
	int os = next (cs, strength);
	int ot = next (ct, strength);

	if (os == CollationElementIterator.NULLORDER
	    && ot == CollationElementIterator.NULLORDER)
	  break;
	else if (os == CollationElementIterator.NULLORDER)
	  {
	    // Source string is shorter, so return "less than".
	    return -1;
	  }
	else if (ot == CollationElementIterator.NULLORDER)
	  {
	    // Target string is shorter, so return "greater than".
	    return 1;
	  }

	if (os != ot)
	  return os - ot;
      }

    return 0;
  }

  /**
   * This method tests this object for equality against the specified 
   * object.  This will be true if and only if the specified object is
   * another reference to this object.
   *
   * @param obj The <code>Object</code> to compare against this object.
   *
   * @return <code>true</code> if the specified object is equal to this object,
   * <code>false</code> otherwise.
   */
  public boolean equals(Object obj)
  {
    if (! (obj instanceof RuleBasedCollator) || ! super.equals(obj))
      return false;
    RuleBasedCollator rbc = (RuleBasedCollator) obj;
    // FIXME: this is probably wrong.  Instead we should compare maps
    // directly.
    return (frenchAccents == rbc.frenchAccents
	    && rules.equals(rbc.rules));
  }

  /**
   * This method returns an instance for <code>CollationElementIterator</code>
   * for the specified <code>String</code> under the collation rules for this
   * object.
   *
   * @param source The <code>String</code> to return the
   * <code>CollationElementIterator</code> instance for.
   *
   * @return A <code>CollationElementIterator</code> for the specified
   * <code>String</code>.
   */
  public CollationElementIterator getCollationElementIterator(String source)
  {
    int len = source.length();
    StringBuffer expand = new StringBuffer(len);
    
    for (int index = 0; index < len; ++index)
      decomposeCharacter(source.charAt(index), expand);
    
    return new CollationElementIterator(this, expand.toString());
  }

  /**
   * This method returns an instance of <code>CollationElementIterator</code>
   * for the <code>String</code> represented by the specified
   * <code>CharacterIterator</code>.
   *
   * @param source The <code>CharacterIterator</code> with the desired <code>String</code>.
   *
   * @return A <code>CollationElementIterator</code> for the specified <code>String</code>.
   */
  public CollationElementIterator getCollationElementIterator(CharacterIterator source)
  {
    StringBuffer expand = new StringBuffer("");
    
    // Right now we assume that we will read from the beginning of the string.
    for (char c = source.first();
	 c != CharacterIterator.DONE;
	 c = source.next())
      decomposeCharacter(c, expand);

    return new CollationElementIterator(this, expand.toString());
  }

  /**
   * This method returns an instance of <code>CollationKey</code> for the
   * specified <code>String</code>.  The object returned will have a
   * more efficient mechanism for its comparison function that could
   * provide speed benefits if multiple comparisons are performed, such
   * as during a sort.
   *
   * @param source The <code>String</code> to create a <code>CollationKey</code> for.
   *
   * @return A <code>CollationKey</code> for the specified <code>String</code>.
   */
  public CollationKey getCollationKey(String source)
  {
    return new CollationKey(this, getCollationElementIterator(source), source,
			    strength);
  }

  /**
   * This method returns a <code>String</code> containing the collation rules
   * for this object.
   *
   * @return The collation rules for this object.
   */
  public String getRules()
  {
    return rules;
  }

  /**
   * This method returns a hash value for this object.
   *
   * @return A hash value for this object.
   */
  public int hashCode()
  {
    return (frenchAccents ? 1231 : 1237
	    ^ rules.hashCode()
	    ^ map.hashCode()
	    ^ prefixes.hashCode());
  }

  private final boolean is_special (char c)
  {
    // Rules from JCL book.
    return ((c >= 0x0021 && c <= 0x002f)
	    || (c >= 0x003a && c <= 0x0040)
	    || (c >= 0x005b && c <= 0x0060)
	    || (c >= 0x007b && c <= 0x007e));
  }

  private final int text_argument (String rules, int index,
				   StringBuffer result)
  {
    result.setLength(0);
    int len = rules.length();
    while (index < len)
      {
	char c = rules.charAt (index);
	if (c == '\''
            && index + 2 < len
	    && rules.charAt (index + 2) == '\'')
          {
            result.append (rules.charAt (index + 1));
            index += 2;
          }
	else if (is_special (c))
	  return index;
        else if (!Character.isWhitespace (c))
          result.append (c);
        
        ++index;
      }
    return index;
  }

}