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 {
        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. */
    @Override
    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. */
    @Override
    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 */
    @Override
    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;
        }
    }

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

}
