/*
 * FindBugs - Find Bugs in Java programs
 * Copyright (C) 2006, 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.npe2;

/**
 * Symbolic values representing the nullness of a runtime value.
 * 
 * @author David Hovemeyer
 */
public class NullnessValue {
    static final int DEFINITELY_NULL = 0;

    static final int DEFINITELY_NOT_NULL = 1;

    static final int CHECKED = 2;

    static final int NO_KABOOM = 3;

    static final int FLAGS_MAX = 4;

    private static final NullnessValue[] instanceList = new NullnessValue[1 << FLAGS_MAX];
    static {
        for (int i = 0; i < instanceList.length; i++) {
            instanceList[i] = new NullnessValue(i);
        }
    }

    private final int flags;

    private NullnessValue(int flags) {
        this.flags = flags;
    }

    int getFlags() {
        return flags;
    }

    public boolean isDefinitelyNull() {
        return isFlagSet(DEFINITELY_NULL);
    }

    public boolean isDefinitelyNotNull() {
        return isFlagSet(DEFINITELY_NOT_NULL);
    }

    public boolean isChecked() {
        return isFlagSet(CHECKED);
    }

    public boolean isNoKaboom() {
        return isFlagSet(NO_KABOOM);
    }

    public NullnessValue toCheckedValue() {
        return instanceList[flags | (1 << CHECKED)];
    }

    public NullnessValue toNoKaboomValue() {
        return instanceList[flags | (1 << NO_KABOOM)];
    }

    // public NullnessValue toCheckedNullValue() {
    // if (isDefinitelyNull() || isDefinitelyNotNull()) {
    // throw new IllegalStateException();
    // }
    //
    // return fromFlags(flags | DEFINITELY_NULL | CHECKED);
    // }
    //
    // public NullnessValue toCheckedNotNullValue() {
    // if (isDefinitelyNull() || isDefinitelyNotNull()) {
    // throw new IllegalStateException();
    // }
    //
    // return fromFlags(flags | DEFINITELY_NOT_NULL | CHECKED);
    // }

    private boolean isFlagSet(int flag) {
        return (flags & (1 << flag)) != 0;
    }

    static NullnessValue fromFlags(int flags) {
        return instanceList[flags];
    }

    public static NullnessValue definitelyNullValue() {
        return fromFlags(1 << DEFINITELY_NULL);
    }

    public static NullnessValue definitelyNotNullValue() {
        return fromFlags(1 << DEFINITELY_NOT_NULL);
    }

    public static NullnessValue unknownValue() {
        return fromFlags(0);
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString() {
        String pfx = "";

        if (isChecked()) {
            pfx += "c";
        }

        if (isNoKaboom()) {
            pfx += "k";
        }

        String val;

        if (isDefinitelyNull()) {
            val = "n";
        } else if (isDefinitelyNotNull()) {
            val = "N";
        } else {
            val = "-";
        }

        return pfx + val;
    }
}