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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/**
 * 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;
    }
}