package simpledb;

/** Predicate compares tuples to a specified Field value.
 */
public class Predicate {
    
    /** Constants used for return codes in Field.compare */
    public enum Op {
	EQUALS, GREATER_THAN, LESS_THAN, LESS_THAN_OR_EQ, GREATER_THAN_OR_EQ;
	
	/**
	 * Interface to access operations by a string containing an integer
	 * index for command-line convenience.
	 *
	 * @param s a string containing a valid integer Op index
	 */
	public static Op getOp(String s) {
	    return getOp(Integer.parseInt(s));
	}

	/**
	 * Interface to access operations by integer value for command-line
	 * convenience.
	 *
	 * @param i a valid integer Op index
	 */
	public static Op getOp(int i) {
	    switch(i) {
	    case 0: return EQUALS;
	    case 1: return GREATER_THAN;
	    case 2: return LESS_THAN;
	    case 3: return LESS_THAN_OR_EQ;
	    case 4: return GREATER_THAN_OR_EQ;
	    }
	    return null;
	}
    };

    private int field;
    private Op op;
    private Field operand;
    
    /** 
     * Constructor.
     *
     * @param field field number of passed in tuples to compare against.
     * @param op operation to use for comparison
     * @param operand field value to compare passed in tuples to
     */
    public Predicate(int field, Op op, Field operand) {
        this.field = field;
        this.op = op;
        this.operand = operand;
    }
    
    /**
     * Compares the field number of t specified in the constructor to the
     * operand field specified in the constructor using the operator specific
     * in the constructor.
     *
     * @param t The tuple to compare against
     * @return true if the comparison is true, false otherwise.
     */
    public boolean filter(Tuple t) {
        Field f = t.getField(field);
        return f.compare(op, operand);
    }
}