/*

 * Copyright (c) 2004, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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 General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package sun.tools.jstat;

import java.util.*;

import sun.jvmstat.monitor.*;

/**

 * A class implementing the ExpressionEvaluator to evaluate an expression

 * in the context of the available monitoring data.

 *

 * @author Brian Doherty

 * @since 1.5

 */

public class ExpressionExecuter implements ExpressionEvaluator {

    private static final boolean debug =

            Boolean.getBoolean("ExpressionEvaluator.debug");

    private MonitoredVm vm;

    private HashMap<String, Object> map = new HashMap<String, Object>();

    ExpressionExecuter(MonitoredVm vm) {

        this.vm = vm;

    }

    /*

     * evaluate the given expression.

     */

    public Object evaluate(Expression e) {

        if (e == null) {

            return null;

        }

        if (debug) {

            System.out.println("Evaluating expression: " + e);

        }

        if (e instanceof Literal) {

            return ((Literal)e).getValue();

        }

        if (e instanceof Identifier) {

            Identifier id = (Identifier)e;

            if (map.containsKey(id.getName())) {

                return map.get(id.getName());

            } else {

                // cache the data values for coherency of the values over

                // the life of this expression executer.

                Monitor m = (Monitor)id.getValue();

                Object v = m.getValue();

                map.put(id.getName(), v);

                return v;

            }

        }

        Expression l = e.getLeft();

        Expression r = e.getRight();

        Operator op = e.getOperator();

        if (op == null) {

            return evaluate(l);

        } else {

            double lval = ((Number)evaluate(l)).doubleValue();

            double rval = ((Number)evaluate(r)).doubleValue();

            double result = op.eval(lval, rval);

            if (debug) {

                System.out.println("Performed Operation: " + lval + op + rval

                                   + " = " + result);

            }

            return Double.valueOf(result);

        }

    }

}