
/*
 * @(#)Function.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:
 *
 *   1. Redistribution of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 * 
 *   2. Redistribution in binary form must reproduce the above copyright
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 *      documentation and/or other materials provided with the distribution.
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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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 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
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package com.sun.xacml.cond;

import com.sun.xacml.EvaluationCtx;

import com.sun.xacml.attr.AttributeValue;

import java.net.URI;

import java.util.List;


/**
 * Interface that all functions in the system must implement.
 *
 * @since 1.0
 * @author Seth Proctor
 */
public interface Function
{

    /**
     * Evaluates the <code>Function</code> using the given inputs.
     * The <code>List</code> contains <code>Evaluatable<code>s which are all
     * of the correct type if the <code>Function</code> has been created as
     * part of an <code>Apply</code> or <code>TargetMatch</code>, but which
     * may otherwise be invalid. Each parameter should be evaluated by the
     * <code>Function</code>, unless this is a higher-order function (in
     * which case the <code>Apply</code> has already evaluated the inputs
     * to check for any INDETERMINATE conditions), or the <code>Function</code>
     * doesn't need to evaluate all inputs to determine a result (as in the
     * case of the or function). The order of the <code>List</code> is
     * significant, so a <code>Function</code> should have a very good reason
     * if it wants to evaluate the inputs in a different order.
     * <p>
     * Note that if this is a higher-order function, like any-of, then
     * the first argument in the <code>List</code> will actually be a Function
     * object representing the function to apply to some bag. In this case,
     * the second and any subsequent entries in the list are
     * <code>AttributeValue</code> objects (no INDETERMINATE values are
     * allowed, so the function is not given the option of dealing with
     * attributes that cannot be resolved). A function needs to know if it's
     * a higher-order function, and therefore whether or not to look for
     * this case. Also, a higher-order function is responsible for checking
     * that the inputs that it will pass to the <code>Function</code>
     * provided as the first parameter are valid, ie. it must do a
     * <code>checkInputs</code> on its sub-function when
     * <code>checkInputs</code> is called on the higher-order function.
     *
     * @param inputs the <code>List</code> of inputs for the function
     * @param context the representation of the request
     *
     * @return a result containing the <code>AttributeValue</code> computed
     *         when evaluating the function, or <code>Status</code>
     *         specifying some error condition
     */
    public EvaluationResult evaluate(List inputs, EvaluationCtx context);

    /**
     * Returns the identifier of this function as known by the factories.
     * In the case of the standard XACML functions, this will be one of the
     * URIs defined in the standard namespace. This function must always
     * return the complete namespace and identifier of this function.
     *
     * @return the function's identifier
     */
    public URI getIdentifier();

    /**
     * Provides the type of <code>AttributeValue</code> that this function
     * returns from <code>evaluate</code> in a successful evaluation.
     *
     * @return the type returned by this function
     */
    public URI getReturnType();

    /**
     * Tells whether this function will return a bag of values or just a
     * single value.
     *
     * @return true if evaluation will return a bag, false otherwise
     */
    public boolean returnsBag();

    /**
     * Checks that the given inputs are of the right types, in the right
     * order, and are the right number for this function to evaluate. If
     * the function cannot accept the inputs for evaluation, an
     * <code>IllegalArgumentException</code> is thrown.
     *
     * @param inputs a <code>List</code> of <code>Evaluatable</code>s, with
     *               the first argument being a <code>Function</code> if
     *               this is a higher-order function
     *
     * @throws IllegalArgumentException if the inputs do match what the
     *                                  function accepts for evaluation
     */
    public void checkInputs(List inputs) throws IllegalArgumentException;

    /**
     * Checks that the given inputs are of the right types, in the right
     * order, and are the right number for this function to evaluate. If
     * the function cannot accept the inputs for evaluation, an
     * <code>IllegalArgumentException</code> is thrown. Unlike the other
     * <code>checkInput</code> method in this interface, this assumes that
     * the parameters will never provide bags of values. This is useful if
     * you're considering a target function which has a designator or
     * selector in its input list, but which passes the values from the
     * derived bags one at a time to the function, so the function doesn't
     * have to deal with the bags that the selector or designator
     * generates.
     *
     * @param inputs a <code>List</code> of <code>Evaluatable</code>s, with
     *               the first argument being a <code>Function</code> if
     *               this is a higher-order function
     *
     * @throws IllegalArgumentException if the inputs do match what the
     *                                  function accepts for evaluation
     */
    public void checkInputsNoBag(List inputs) throws IllegalArgumentException;
    
}
