/*
 * @(#)RoundFunction.java
 *
 * Copyright 2003-2004 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
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 *      this list of conditions and the following disclaimer.
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 *   2. Redistribution in binary form must reproduce the above copyright
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 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
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package com.sun.xacml.cond;

import com.sun.xacml.EvaluationCtx;

import com.sun.xacml.attr.AttributeValue;
import com.sun.xacml.attr.DoubleAttribute;

import java.util.HashSet;
import java.util.List;
import java.util.Set;


/**
 * A class that implements the round function. It takes one double
 * operand, rounds that value to an integer and returns that integer.
 * If the operand is indeterminate, an indeterminate result is returned.
 *
 * @since 1.0
 * @author Steve Hanna
 * @author Seth Proctor
 */
public class RoundFunction extends FunctionBase
{

    /**
     * Standard identifier for the round function.
     */
    public static final String NAME_ROUND = FUNCTION_NS + "round";

    /**
     * Creates a new <code>RoundFunction</code> object.
     *
     * @param functionName the standard XACML name of the function to be
     *                     handled by this object, including the full namespace
     *
     * @throws IllegalArgumentException if the function is unknown
     */
    public RoundFunction(String functionName) {
        super(NAME_ROUND, 0, DoubleAttribute.identifier, false, 1,
              DoubleAttribute.identifier, false);

        if (! functionName.equals(NAME_ROUND)) {
            throw new IllegalArgumentException("unknown round function: "
                                               + functionName);
        }
    }

    /**
     * Returns a <code>Set</code> containing all the function identifiers
     * supported by this class.
     *
     * @return a <code>Set</code> of <code>String</code>s
     */
    public static Set<String> getSupportedIdentifiers() {
        Set<String> set = new HashSet<String>();

        set.add(NAME_ROUND);

        return set;
    }

    /**
     * Evaluate the function, using the specified parameters.
     *
     * @param inputs a <code>List</code> of <code>Evaluatable</code>
     *               objects representing the arguments passed to the function
     * @param context an <code>EvaluationCtx</code> so that the
     *                <code>Evaluatable</code> objects can be evaluated
     * @return an <code>EvaluationResult</code> representing the
     *         function's result
     */
    public EvaluationResult evaluate(List<Expression> inputs, EvaluationCtx context) {

        // Evaluate the arguments
        AttributeValue [] argValues = new AttributeValue[inputs.size()];
        EvaluationResult result = evalArgs(inputs, context, argValues);
        if (result != null) {
            return result;
        }
        // Now that we have real values, perform the round operation
        double arg = ((DoubleAttribute) argValues[0]).getValue();
        double roundValue = Math.round(arg);
        
        // Make it round half even, not round nearest
        double lower = Math.floor(arg);
        double higher = lower + 1;
        
        //Equality test for floating point numbers that is 
        //resilient against errors.
        if (Math.abs((arg - lower) - (higher - arg)) < .0000001 ) {
            if ((lower % 2) == 0) {
                roundValue = lower;
            } else {
                roundValue = higher;
            }
        }
        
        return new EvaluationResult(new DoubleAttribute(roundValue));
    }
}