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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.value.AtomicValue;

/**
 * An AtomicComparer used for comparing strings, untypedAtomic values, and URIs using a collation.
 * A CollatingAtomicComparer is used when it is known in advance that both operands will be of these
 * types. This enables all conversions and promotions to be bypassed: the string values of both operands
 * are simply extracted and passed to the collator for comparison.
 *
 */

public class CollatingAtomicComparer implements AtomicComparer {

    private final StringCollator collator;

    /**
     * Create an GenericAtomicComparer
     *
     * @param collator the collation to be used. If the method is called at compile time, this should
     *                 be a SimpleCollation so that it can be cloned at run-time.
     */

    public CollatingAtomicComparer(/*@Nullable*/ StringCollator collator) {

        if (collator == null) {
            this.collator = CodepointCollator.getInstance();
        } else {
            this.collator = collator;
        }
    }


    @Override
    public StringCollator getCollator() {
        return collator;
    }

    /**
     * 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
     */

    @Override
    public AtomicComparer provideContext(XPathContext context) {
        return this;
    }


    /**
     * 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
     */

    @Override
    public int compareAtomicValues(AtomicValue a, AtomicValue b) {
        if (a == null) {
            if (b == null) {
                return 0;
            } else {
                return -1;
            }
        } else if (b == null) {
            return +1;
        }

        return collator.compareStrings(a.getUnicodeStringValue(), b.getUnicodeStringValue());
    }

    /**
     * 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. 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 equals() method.
     * @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 true if the values are equal, false if not
     * @throws ClassCastException if the objects are not comparable
     */

    @Override
    public boolean comparesEqual(AtomicValue a, AtomicValue b) {
        return compareAtomicValues(a, b) == 0;
    }

    /**
     * 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
     */
    @Override
    public String save() {
        return "CAC|" + getCollator().getCollationURI();
    }

    @Override
    public int hashCode() {
        return collator.hashCode();
    }

    @Override
    public boolean equals(Object obj) {
        return obj instanceof CollatingAtomicComparer && collator.equals(((CollatingAtomicComparer)obj).collator);
    }
}