
package com.sun.java_cup.internal;

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

/** This class represents a set of symbols and provides a series of 
 *  set operations to manipulate them.
 *
 * @see     com.sun.java_cup.internal.symbol
 * @version last updated: 11/25/95
 * @author  Scott Hudson
 */
public class symbol_set {

  /*-----------------------------------------------------------*/
  /*--- Constructor(s) ----------------------------------------*/
  /*-----------------------------------------------------------*/

  /** Constructor for an empty set. */
  public symbol_set() { }

  /** Constructor for cloning from another set. 
   * @param other the set we are cloning from.
   */
  public symbol_set(symbol_set other) throws internal_error
    {
      not_null(other);
      _all = (Hashtable)other._all.clone();
    }

  /*-----------------------------------------------------------*/
  /*--- (Access to) Instance Variables ------------------------*/
  /*-----------------------------------------------------------*/

  /** A hash table to hold the set. Symbols are keyed using their name string. 
   */
  protected Hashtable _all = new Hashtable(11);

  /** Access to all elements of the set. */
  public Enumeration all() {return _all.elements();}

  /** size of the set */
  public int size() {return _all.size();}

  /*-----------------------------------------------------------*/
  /*--- (Access to) Instance Variables ------------------------*/
  /*-----------------------------------------------------------*/

  /** Helper function to test for a null object and throw an exception
   *  if one is found.
   * @param obj the object we are testing.
   */
  protected void not_null(Object obj) throws internal_error
    {
      if (obj == null) 
	throw new internal_error("Null object used in set operation");
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Determine if the set contains a particular symbol. 
   * @param sym the symbol we are looking for.
   */
  public boolean contains(symbol sym) {return _all.containsKey(sym.name());}

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Determine if this set is an (improper) subset of another. 
   * @param other the set we are testing against.
   */
  public boolean is_subset_of(symbol_set other) throws internal_error
    {
      not_null(other);

      /* walk down our set and make sure every element is in the other */
      for (Enumeration e = all(); e.hasMoreElements(); )
	if (!other.contains((symbol)e.nextElement()))
	  return false;

      /* they were all there */
      return true;
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Determine if this set is an (improper) superset of another. 
   * @param other the set we are are testing against.
   */
  public boolean is_superset_of(symbol_set other) throws internal_error
    {
      not_null(other);
      return other.is_subset_of(this);
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Add a single symbol to the set.  
   * @param sym the symbol we are adding.
   * @return true if this changes the set.
   */
  public boolean add(symbol sym) throws internal_error
    {
      Object previous;

      not_null(sym); 

      /* put the object in */
      previous = _all.put(sym.name(),sym);

      /* if we had a previous, this is no change */
      return previous == null;
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Remove a single symbol if it is in the set. 
   * @param sym the symbol we are removing.
   */
  public void remove(symbol sym) throws internal_error
    {
      not_null(sym); 
      _all.remove(sym.name());
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Add (union) in a complete set.  
   * @param other the set we are adding in.
   * @return true if this changes the set. 
   */
  public boolean add(symbol_set other) throws internal_error
    {
      boolean result = false;

      not_null(other);

      /* walk down the other set and do the adds individually */
      for (Enumeration e = other.all(); e.hasMoreElements(); )
	result = add((symbol)e.nextElement()) || result;

      return result;
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Remove (set subtract) a complete set. 
   * @param other the set we are removing.
   */
  public void remove(symbol_set other) throws internal_error
    {
      not_null(other);

      /* walk down the other set and do the removes individually */
      for (Enumeration e = other.all(); e.hasMoreElements(); )
	remove((symbol)e.nextElement());
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Equality comparison. */
  public boolean equals(symbol_set other) 
    {
      if (other == null || other.size() != size()) return false;

      /* once we know they are the same size, then improper subset does test */
      try {
        return is_subset_of(other);
      } catch (internal_error e) {
	/* can't throw the error (because super class doesn't), so we crash */
	e.crash();
	return false;
      }
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Generic equality comparison. */
  public boolean equals(Object other)
    {
      if (!(other instanceof symbol_set))
	return false;
      else
	return equals((symbol_set)other);
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Compute a hash code. */
  public int hashCode()
    {
      int result = 0;
      int cnt;
      Enumeration e;

      /* hash together codes from at most first 5 elements */
      for (e = all(), cnt=0 ; e.hasMoreElements() && cnt<5; cnt++)
	result ^= ((symbol)e.nextElement()).hashCode();

      return result;
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

  /** Convert to a string. */
  public String toString()
    {
      String result;
      boolean comma_flag;

      result = "{";
      comma_flag = false;
      for (Enumeration e = all(); e.hasMoreElements(); )
	{
	  if (comma_flag)
	    result += ", ";
	  else
	    comma_flag = true;

	  result += ((symbol)e.nextElement()).name();
	}
      result += "}";

      return result;
    }

  /*-----------------------------------------------------------*/

}


