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 * Copyright (c) 2004, 2010, 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 sun.jvmstat.monitor.*;

/**

 * A class implementing the ExpressionEvaluator to resolve unresolved

 * symbols in an Expression in the context of the available monitoring data.

 * This class also performs some minimal optimizations of the expressions,

 * such as simplification of constant subexpressions.

 *

 * @author Brian Doherty

 * @since 1.5

 */

public class ExpressionResolver implements ExpressionEvaluator {

    private static boolean debug = Boolean.getBoolean("ExpressionResolver.debug");

    private MonitoredVm vm;

    ExpressionResolver(MonitoredVm vm) {

        this.vm = vm;

    }

    /*

     * evaluate the given expression. evaluation in this case means

     * to resolve the counter names in the expression

     */

    public Object evaluate(Expression e) throws MonitorException {

        if (e == null) {

            return null;

        }

        if (debug) {

            System.out.println("Resolving Expression:" + e);

        }

        if (e instanceof Identifier) {

            Identifier id = (Identifier)e;

            // check if it's already resolved

            if (id.isResolved()) {

                return id;

            }

            // look it up

            Monitor m = vm.findByName(id.getName());

            if (m == null) {

                System.err.println("Warning: Unresolved Symbol: "

                                   + id.getName() + " substituted NaN");

                return new Literal(new Double(Double.NaN));

            }

            if (m.getVariability() == Variability.CONSTANT) {

                if (debug) {

                    System.out.println("Converting constant " + id.getName()

                                       + " to literal with value "

                                       + m.getValue());

                }

                return new Literal(m.getValue());

            }

            id.setValue(m);

            return id;

        }

        if (e instanceof Literal) {

            return e;

        }

        Expression l = null;

        Expression r = null;

        if (e.getLeft() != null) {

            l = (Expression)evaluate(e.getLeft());

        }

        if (e.getRight() != null) {

            r = (Expression)evaluate(e.getRight());

        }

        if (l != null && r != null) {

            if ((l instanceof Literal) && (r instanceof Literal)) {

                Literal ll = (Literal)l;

                Literal rl = (Literal)r;

                boolean warn = false;

                Double nan = new Double(Double.NaN);

                if (ll.getValue() instanceof String) {

                    warn = true; ll.setValue(nan);

                }

                if (rl.getValue() instanceof String) {

                    warn = true; rl.setValue(nan);

                }

                if (debug && warn) {

                     System.out.println("Warning: String literal in "

                                        + "numerical expression: "

                                        + "substitutied NaN");

                }

                // perform the operation

                Number ln = (Number)ll.getValue();

                Number rn = (Number)rl.getValue();

                double result = e.getOperator().eval(ln.doubleValue(),

                                                     rn.doubleValue());

                if (debug) {

                    System.out.println("Converting expression " + e

                                       + " (left = " + ln.doubleValue() + ")"

                                       + " (right = " + rn.doubleValue() + ")"

                                       + " to literal value " + result);

                }

                return new Literal(new Double(result));

            }

        }

        if (l != null && r == null) {

            return l;

        }

        e.setLeft(l);

        e.setRight(r);

        return e;

    }

}