/*
 * FindBugs - Find Bugs in Java programs
 * Copyright (C) 2003-2007 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.jsr305;

import javax.annotation.meta.When;

/**
 * Flow value type for type qualifier dataflow analysis.
 * 
 * @author David Hovemeyer
 */
public enum FlowValue {

    TOP(0), ALWAYS(Bits.YES), NEVER(Bits.NO), UNKNOWN(Bits.YES | Bits.NO | Bits.UNCERTAIN);

    private interface Bits {
        public static final int YES = 1;

        public static final int UNCERTAIN = 2;

        public static final int NO = 4;
    }

    private final int bits;

    private FlowValue(int bits) {
        this.bits = bits;
    }

    public boolean isYes() {
        return (bits & Bits.YES) != 0;
    }

    public boolean isUncertain() {
        return (bits & Bits.UNCERTAIN) != 0;
    }

    public boolean isNo() {
        return (bits & Bits.NO) != 0;
    }

    // Dataflow lattice:
    //
    // Top
    // / \
    // Always Never
    // \ /
    // Unknown
    //
    private static final FlowValue[][] mergeMatrix = {
            // TOP ALWAYS NEVER UNKNOWN
            /* TOP */{ TOP, },
            /* ALWAYS */{ ALWAYS, ALWAYS, },
            /* NEVER */{ NEVER, UNKNOWN, NEVER, },
            /* UNKNOWN */{ UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN }, };

    public static final FlowValue meet(FlowValue a, FlowValue b) {
        int aIndex = a.ordinal();
        int bIndex = b.ordinal();

        if (aIndex < bIndex) {
            int tmp = aIndex;
            aIndex = bIndex;
            bIndex = tmp;
        }

        return mergeMatrix[aIndex][bIndex];
    }

    /**
     * Determine whether given flow values conflict.
     * 
     * @param forward
     *            a forwards flow value
     * @param backward
     *            a backwards flow value
     * @return true if values conflict, false otherwise
     */
    public static boolean valuesConflict(FlowValue forward, FlowValue backward) {
        if (forward == TOP || backward == TOP) {
            return false;
        }
        return (forward == ALWAYS && backward == NEVER) || (forward == NEVER && backward == ALWAYS);
    }

    /**
     * Convert a When value to a FlowValue value.
     * 
     * @param when
     *            a When value
     * @return the corresponding FlowValue
     */
    public static FlowValue flowValueFromWhen(When when) {
        switch (when) {
        case ALWAYS:
            return FlowValue.ALWAYS;
        case MAYBE:
            return FlowValue.UNKNOWN;
        case NEVER:
            return FlowValue.NEVER;
        case UNKNOWN:
            return FlowValue.UNKNOWN;
        default:
            throw new IllegalStateException();
        }
    }

    /**
     * Determine whether given backwards FlowValue conflicts with given source.
     * 
     * @param backwardsFlowValue
     *            a backwards FlowValue
     * @param source
     *            SourceSinkInfo object representing a source reached by the
     *            backwards flow value
     * @param typeQualifierValue
     *            TypeQualifierValue being checked
     * @return true if backwards value conflicts with source, false if not
     */
    public static boolean backwardsValueConflictsWithSource(FlowValue backwardsFlowValue, SourceSinkInfo source,
            TypeQualifierValue typeQualifierValue) {

        When sourceWhen = source.getWhen();

        if (typeQualifierValue.isStrictQualifier()) {
            // strict checking
            return (backwardsFlowValue == ALWAYS && sourceWhen != When.ALWAYS)
                    || (backwardsFlowValue == NEVER && sourceWhen != When.NEVER);
        } else {
            // NOT strict checking
            return (backwardsFlowValue == ALWAYS && (sourceWhen == When.NEVER || sourceWhen == When.MAYBE))
                    || (backwardsFlowValue == NEVER && (sourceWhen == When.ALWAYS || sourceWhen == When.MAYBE));
        }
    }

}