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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2022 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.expr.sort;

import net.sf.saxon.expr.XPathContext;
import net.sf.saxon.lib.StringCollator;
import net.sf.saxon.trans.NoDynamicContextException;
import net.sf.saxon.value.AtomicValue;

/**
 * Interface representing an object that can be used to compare two XPath atomic values for equality or
 * for ordering.
 */

public interface AtomicComparer {

    /**
     * Get the collation used by this AtomicComparer if any
     *
     * @return the collation used for comparing strings, or null if not applicable
     */

    StringCollator getCollator();

    /**
     * Supply the dynamic context in case this is needed for the comparison
     *
     * @param context the dynamic evaluation context
     * @return either the original AtomicComparer, or a new AtomicComparer in which the context
     *         is known. The original AtomicComparer is not modified
     */

    AtomicComparer provideContext(XPathContext context);

    /**
     * Compare two AtomicValue objects according to the rules for their data type. UntypedAtomic
     * values are compared as if they were strings; if different semantics are wanted, the conversion
     * must be done by the caller.
     *
     * @param a the first object to be compared. It is intended that this should be an instance
     *          of AtomicValue, though this restriction is not enforced. If it is a StringValue, the
     *          collator is used to compare the values, otherwise the value must implement the java.util.Comparable
     *          interface.
     * @param b the second object to be compared. This must be comparable with the first object: for
     *          example, if one is a string, they must both be strings.
     * @return <0 if a<b, 0 if a=b, >0 if a>b
     * @throws ClassCastException        if the objects are not comparable
     * @throws NoDynamicContextException if this comparer required access to dynamic context information,
     *                                   notably the implicit timezone, and this information is not available. In general this happens if a
     *                                   context-dependent comparison is attempted at compile-time, and it signals the compiler to generate
     *                                   code that tries again at run-time.
     */

    int compareAtomicValues(AtomicValue a, AtomicValue b) throws NoDynamicContextException;

    /**
     * Compare two AtomicValue objects for equality according to the rules for their data type. UntypedAtomic
     * values are compared by converting to the type of the other operand.
     *
     * @param a the first object to be compared.
     * @param b the second object to be compared.
     * @return true if the values are equal, false if not
     * @throws ClassCastException if the objects are not comparable
     * @throws NoDynamicContextException if no dynamic context has been supplied, and a dynamic context is needed
     * (for example, because the comparison uses the implicit timezone)
     */

    boolean comparesEqual(AtomicValue a, AtomicValue b) throws NoDynamicContextException;

    /**
     * Create a string representation of this AtomicComparer that can be saved in a compiled
     * package and used to reconstitute the AtomicComparer when the package is reloaded
     * @return a string representation of the AtomicComparer
     */

    String save();

}