package java_cup;

/** The "core" of an LR item.  This includes a production and the position
 *  of a marker (the "dot") within the production.  Typically item cores 
 *  are written using a production with an embedded "dot" to indicate their 
 *  position.  For example: <pre>
 *     A ::= B * C d E
 *  </pre>
 *  This represents a point in a parse where the parser is trying to match
 *  the given production, and has succeeded in matching everything before the 
 *  "dot" (and hence is expecting to see the symbols after the dot next).  See 
 *  lalr_item, lalr_item_set, and lalr_start for full details on the meaning 
 *  and use of items.
 *
 * @see     java_cup.lalr_item
 * @see     java_cup.lalr_item_set
 * @see     java_cup.lalr_state
 * @version last updated: 11/25/95
 * @author  Scott Hudson
*/

public class lr_item_core {

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

	/** Full constructor.
	 * @param prod production this item uses.
	 * @param pos  position of the "dot" within the item.
	 */
	public lr_item_core(production prod, int pos) throws internal_error
	{
		symbol after_dot = null;
		production_part part;

		if (prod == null)
			throw new internal_error(
					"Attempt to create an lr_item_core with a null production");

		_the_production = prod;

		if (pos < 0 || pos > _the_production.rhs_length())
			throw new internal_error(
					"Attempt to create an lr_item_core with a bad dot position");

		_dot_pos = pos;

		/* compute and cache hash code now */
		_core_hash_cache = 13 * _the_production.hashCode() + pos;

		/* cache the symbol after the dot */
		if (_dot_pos < _the_production.rhs_length())
		{
			part = _the_production.rhs(_dot_pos);
			if (!part.is_action())
				_symbol_after_dot = ((symbol_part) part).the_symbol();
		}
	}

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

	/** Constructor for dot at start of right hand side. 
	 * @param prod production this item uses.
	 */
	public lr_item_core(production prod) throws internal_error
	{
		this(prod, 0);
	}

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

	/** The production for the item. */
	protected production _the_production;

	/** The production for the item. */
	public production the_production() {
		return _the_production;
	}

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

	/** The position of the "dot" -- this indicates the part of the production 
	 *  that the marker is before, so 0 indicates a dot at the beginning of 
	 *  the RHS.
	 */
	protected int _dot_pos;

	/** The position of the "dot" -- this indicates the part of the production 
	 *  that the marker is before, so 0 indicates a dot at the beginning of 
	 *  the RHS.
	 */
	public int dot_pos() {
		return _dot_pos;
	}

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

	/** Cache of the hash code. */
	protected int _core_hash_cache;

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

	/** Cache of symbol after the dot. */
	protected symbol _symbol_after_dot = null;

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

	/** Is the dot at the end of the production? */
	public boolean dot_at_end()
	{
		return _dot_pos >= _the_production.rhs_length();
	}

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

	/** Return the symbol after the dot.  If there is no symbol after the dot
	 *  we return null. */
	public symbol symbol_after_dot()
	{
		/* use the cached symbol */
		return _symbol_after_dot;
	}

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

	/** Determine if we have a dot before a non terminal, and if so which one 
	 *  (return null or the non terminal). 
	 */
	public non_terminal dot_before_nt()
	{
		symbol sym;

		/* get the symbol after the dot */
		sym = symbol_after_dot();

		/* if it exists and is a non terminal, return it */
		if (sym != null && sym.is_non_term())
			return (non_terminal) sym;
		else
			return null;
	}

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

	/** Produce a new lr_item_core that results from shifting the dot one 
	 *  position to the right. 
	 */
	public lr_item_core shift_core() throws internal_error
	{
		if (dot_at_end())
			throw new internal_error(
					"Attempt to shift past end of an lr_item_core");

		return new lr_item_core(_the_production, _dot_pos + 1);
	}

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

	/** Equality comparison for the core only.  This is separate out because we 
	 *  need separate access in a super class. 
	 */
	public boolean core_equals(lr_item_core other)
	{
		return other != null &&
				_the_production.equals(other._the_production) &&
				_dot_pos == other._dot_pos;
	}

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

	/** Equality comparison. */
	public boolean equals(lr_item_core other) {
		return core_equals(other);
	}

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

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

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

	/** Hash code for the core (separated so we keep non overridden version). */
	public int core_hashCode()
	{
		return _core_hash_cache;
	}

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

	/** Hash code for the item. */
	public int hashCode()
	{
		return _core_hash_cache;
	}

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

	/** Return the hash code that object would have provided for us so we have 
	 *  a (nearly) unique id for debugging.
	 */
	protected int obj_hash()
	{
		return super.hashCode();
	}

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

	/** Convert to a string (separated out from toString() so we can call it
	 *  from subclass that overrides toString()).
	 */
	public String to_simple_string() throws internal_error
	{
		String result;
		production_part part;

		if (_the_production.lhs() != null &&
				_the_production.lhs().the_symbol() != null &&
				_the_production.lhs().the_symbol().name() != null)
			result = _the_production.lhs().the_symbol().name();
		else
			result = "$$NULL$$";

		result += " ::= ";

		for (int i = 0; i < _the_production.rhs_length(); i++)
		{
			/* do we need the dot before this one? */
			if (i == _dot_pos)
				result += "(*) ";

			/* print the name of the part */
			if (_the_production.rhs(i) == null)
			{
				result += "$$NULL$$ ";
			}
			else
			{
				part = _the_production.rhs(i);
				if (part == null)
					result += "$$NULL$$ ";
				else if (part.is_action())
					result += "{ACTION} ";
				else if (((symbol_part) part).the_symbol() != null &&
						((symbol_part) part).the_symbol().name() != null)
					result += ((symbol_part) part).the_symbol().name() + " ";
				else
					result += "$$NULL$$ ";
			}
		}

		/* put the dot after if needed */
		if (_dot_pos == _the_production.rhs_length())
			result += "(*) ";

		return result;
	}

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

	/** Convert to a string */
	public String toString()
	{
		/* can't throw here since super class doesn't, so we crash instead */
		try {
			return to_simple_string();
		} catch (internal_error e) {
			e.crash();
			return null;
		}
	}

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

}
