/*
 * FindBugs - Find Bugs in Java programs
 * Copyright (C) 2006-2007 University of Maryland
 *
 * This library 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 2.1 of the License, or (at your option) any later version.
 *
 * This library 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 library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package edu.umd.cs.findbugs.ba.npe;

import edu.umd.cs.findbugs.ba.DataflowAnalysisException;

/**
 * A dataflow value that indicates what kind of return path is possible at the
 * current program location. Either:
 * <ul>
 * <li>It is possible to return normally</li>
 * <li>It is not possible to return normally (i.e., an exception is guaranteed
 * to be thrown)</li>
 * </ul>
 * 
 * @author David Hovemeyer
 */
public class ReturnPathType {
    private static final int CAN_RETURN_NORMALLY = 0;

    private static final int CANNOT_RETURN_NORMALLY = 1;

    private static final int TOP = 2;

    private int type;

    /**
     * Constructor. Creates a top dataflow fact.
     */
    public ReturnPathType() {
        type = TOP;
    }

    /**
     * @return true if the method can return normally at this location, false
     *         otherwise
     */
    public boolean canReturnNormally() throws DataflowAnalysisException {
        if (!isValid()) {
            throw new DataflowAnalysisException("Checking invalid ReturnPathType");
        }
        return type == CAN_RETURN_NORMALLY;
    }

    /**
     * Make this dataflow fact an exact copy of the other one.
     * 
     * @param other
     *            another dataflow fact
     */
    public void copyFrom(ReturnPathType other) {
        this.type = other.type;
    }

    /**
     * Set the dataflow fact to top.
     */
    public void setTop() {
        type = TOP;
    }

    /**
     * @return true if the dataflow fact is top, false otherwise
     */
    public boolean isTop() {
        return type == TOP;
    }

    /**
     * Set whether or not it is possible to return normally.
     * 
     * @param canReturnNormally
     *            true if the method can return normally at this location, false
     *            otherwise
     */
    public void setCanReturnNormally(boolean canReturnNormally) {
        type = canReturnNormally ? CAN_RETURN_NORMALLY : CANNOT_RETURN_NORMALLY;
    }

    /**
     * Merge this fact with given fact.
     * 
     * @param fact
     *            another dataflow fact
     */
    public void mergeWith(ReturnPathType fact) {
        if (fact.isTop()) {
            // other fact is top: no change to this one
            return;
        } else if (this.isTop()) {
            // this fact is top: copy other fact
            this.copyFrom(fact);
        } else {
            // neither fact is top: as long as one of the two
            // facts represents a (possible) normal return, then the result
            // is a possible normal return
            if (fact.type == CAN_RETURN_NORMALLY) {
                this.type = CAN_RETURN_NORMALLY;
            }
        }
    }

    /**
     * Determine whether this dataflow fact is identical to another one.
     * 
     * @param other
     *            another dataflow fact
     * @return true if the two dataflow facts are identical, false if they are
     *         different
     */
    boolean sameAs(ReturnPathType other) {
        return this.type == other.type;
    }

    /**
     * @return true if this is a valid dataflow fact (not top or bottom), false
     *         if not a valid dataflow fact
     */
    public boolean isValid() {
        return type != TOP;
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString() {
        switch (type) {
        case TOP:
            return "[TOP]";
        case CAN_RETURN_NORMALLY:
            return "-";
        case CANNOT_RETURN_NORMALLY:
            return "X";
        default:
            throw new IllegalStateException();
        }
    }
}
