////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2013 Saxonica Limited.
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package net.sf.saxon.functions;

import net.sf.saxon.expr.Container;
import net.sf.saxon.expr.Expression;
import net.sf.saxon.expr.StaticContext;
import net.sf.saxon.om.FunctionItem;
import net.sf.saxon.om.StructuredQName;
import net.sf.saxon.trans.XPathException;

import java.io.Serializable;

/**
 * A FunctionLibrary handles the binding of function calls in XPath (or XQuery) expressions.
 * There are a number of implementations of this
 * class to handle different kinds of function: system functions, constructor functions, vendor-defined
 * functions, Java extension functions, stylesheet functions, and so on. There is also an implementation
 * {@link net.sf.saxon.functions.FunctionLibraryList} that allows a FunctionLibrary
 * to be constructed by combining other FunctionLibrary objects.
 */

public interface FunctionLibrary extends Serializable {

    /**
     * Test whether a function with a given name and arity is available
     * <p>This supports the function-available() function in XSLT.</p>
     * @param functionName  the qualified name of the function being called
     * @param arity         The number of arguments.
     * @return true if a function of this name and arity is available for calling
     */

    /*@Nullable*/
    public boolean isAvailable(StructuredQName functionName, int arity);


    /**
     * Bind a function, given the URI and local parts of the function name,
     * and the list of expressions supplied as arguments. This method is called at compile
     * time.
     *
     *
     * @param functionName the QName of the function being called
     * @param arity The number of arguments supplied in the function call
     * @param staticArgs May be null; if present, the length of the array must match the
     * value of arity. Contains the expressions supplied statically in arguments to the function call.
     * The intention is
     * that the static type of the arguments (obtainable via getItemType() and getCardinality()) may
     * be used as part of the binding algorithm. In some cases it may be possible for the function
     * to be pre-evaluated at compile time, for example if these expressions are all constant values.
     * <p>
     * The conventions of the XPath language demand that the results of a function depend only on the
     * values of the expressions supplied as arguments, and not on the form of those expressions. For
     * example, the result of f(4) is expected to be the same as f(2+2). The actual expression is supplied
     * here to enable the binding mechanism to select the most efficient possible implementation (including
     * compile-time pre-evaluation where appropriate).
     * @param env The static context of the function call
     * @param container The container for the newly created Expression
     * @return An expression equivalent to a call on the specified function, if one is found;
     * null if no function was found matching the required name and arity.
     * @throws net.sf.saxon.trans.XPathException if a function is found with the required name and arity, but
     * the implementation of the function cannot be loaded or used; or if an error occurs
     * while searching for the function.
     */

    /*@Nullable*/ public Expression bind(StructuredQName functionName, int arity, Expression[] staticArgs, StaticContext env, Container container)
            throws XPathException;

    /**
     * This method creates a copy of a FunctionLibrary: if the original FunctionLibrary allows
     * new functions to be added, then additions to this copy will not affect the original, or
     * vice versa.
     * @return a copy of this function library. This must be an instance of the original class.
     */

    public FunctionLibrary copy();



}
