/*
 * @(#)Function.java
 *
 * Copyright 2003-2005 Sun Microsystems, Inc. All Rights Reserved.
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 * Redistribution and use in source and binary forms, with or without
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 * This software is provided "AS IS," without a warranty of any kind. ALL
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package com.sun.xacml.cond;

import java.io.OutputStream;
import java.net.URI;
import java.util.List;

import com.sun.xacml.EvaluationCtx;
import com.sun.xacml.Indenter;

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

    /**
     * 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 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 some argument (typically the
     * first) in the <code>List</code> will actually be a Function object representing the function
     * to apply to some bag. 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<? extends Expression> 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<? extends Expression> 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<? extends Expression> inputs) throws IllegalArgumentException;

    /**
     * Encodes this <code>Function</code> into its XML representation and writes this encoding to
     * the given <code>OutputStream</code> with no indentation.
     * 
     * @param output
     *            a stream into which the XML-encoded data is written
     */
    public void encode(OutputStream output);

    /**
     * Encodes this <code>Function</code> into its XML representation and writes this encoding to
     * the given <code>OutputStream</code> with indentation.
     * 
     * @param output
     *            a stream into which the XML-encoded data is written
     * @param indenter
     *            an object that creates indentation strings
     */
    public void encode(OutputStream output, Indenter indenter);

}