/*******************************************************************************
 * 
 * Copyright 2010 Alexandru Craciun, and individual contributors as indicated
 * by the @authors tag. 
 * 
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 3 of
 * the License, or (at your option) any later version.
 * 
 * This software is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 ******************************************************************************/
package org.netxilia.api.formula;

import java.io.Serializable;

/**
 * This class contains a Excel-like formula
 * 
 * @author <a href='mailto:ax.craciun@gmail.com'>Alexandru Craciun</a>
 * 
 */
public class Formula implements Serializable {

	private static final long serialVersionUID = -2235033412927337805L;
	private final String formula;

	public Formula(String formula) {
		if (!isFormula(formula)) {
			throw new IllegalArgumentException("The formula has to start with a '='");
		}

		this.formula = formula;
	}

	public String getFormula() {
		return formula;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((formula == null) ? 0 : formula.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Formula other = (Formula) obj;
		if (formula == null) {
			if (other.formula != null)
				return false;
		} else if (!formula.equals(other.formula))
			return false;
		return true;
	}

	@Override
	public String toString() {
		return formula;
	}

	public boolean isEmpty() {
		return formula.isEmpty();
	}

	public static boolean isFormula(String formula) {
		return formula != null && formula.length() > 0 && formula.startsWith("=");
	}

	public static Formula valueOf(String s) {
		if (s == null)
			return null;
		return new Formula(s);
	}
}