/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package java.text;

import libcore.icu.CollationElementIteratorICU;

/**
 * Created by a {@code RuleBasedCollator} to iterate through a string. The
 * result of each iteration is a 32-bit collation element that defines the
 * ordering priority of the next character or sequence of characters in the
 * source string.
 * <p>
 * For illustration, consider the following in Spanish:
 * <p>
 * "ca": the first collation element is collation_element('c') and second
 * collation element is collation_element('a').
 * <p>
 * Since "ch" in Spanish sorts as one entity, the example below returns one
 * collation element for the two characters 'c' and 'h':
 * <p>
 * "cha": the first collation element is collation_element('ch') and the second
 * one is collation_element('a').
 * <p>
 * In German, since the character '&#92;u0086' is a composed character of 'a'
 * and 'e', the iterator returns two collation elements for the single character
 * '&#92;u0086':
 * <p>
 * "&#92;u0086b": the first collation element is collation_element('a'), the
 * second one is collation_element('e'), and the third collation element is
 * collation_element('b').
 *
 * <p>Note that calls to {@code next} and {@code previous} can not be mixed.
 * To change iteration direction, {@code reset}, {@code setOffset} or {@code setText}
 * must be called to reset the iterator. If a change of direction is done without one
 * of these calls, the result is undefined.
 */
public final class CollationElementIterator {

    /**
     * This constant is returned by the iterator in the methods
     * {@code next()} and {@code previous()} when the end or the
     * beginning of the source string has been reached, and there are no more
     * valid collation elements to return.
     */
    public static final int NULLORDER = -1;

    private CollationElementIteratorICU icuIterator;

    CollationElementIterator(CollationElementIteratorICU iterator) {
        this.icuIterator = iterator;
    }

    /**
     * Returns the maximum length of any expansion sequence that ends with the
     * specified collation element. Returns {@code 1} if there is no expansion
     * with this collation element as the last element.
     *
     * @param order
     *            a collation element that has been previously obtained from a
     *            call to either the {@link #next()} or {@link #previous()}
     *            method.
     */
    public int getMaxExpansion(int order) {
        return this.icuIterator.getMaxExpansion(order);
    }

    /**
     * Returns the character offset in the source string corresponding to the
     * next collation element. This value could be any of:
     * <ul>
     * <li>The index of the first character in the source string that matches
     * the value of the next collation element. This means that if
     * {@code setOffset(offset)} sets the index in the middle of a contraction,
     * {@code getOffset()} returns the index of the first character in the
     * contraction, which may not be equal to the original offset that was set.
     * Hence calling {@code getOffset()} immediately after
     * {@code setOffset(offset)} does not guarantee that the original offset set
     * will be returned.</li>
     * <li>If normalization is on, the index of the immediate subsequent
     * character, or composite character with the first character, having a
     * combining class of 0.</li>
     * <li>The length of the source string, if iteration has reached the end.
     * </li>
     * </ul>
     */
    public int getOffset() {
        return this.icuIterator.getOffset();
    }

    /**
     * Returns the next collation element in the source string or {@code NULLORDER} if
     * the end of the iteration has been reached.
     */
    public int next() {
        return this.icuIterator.next();
    }

    /**
     * Returns the previous collation element in the source string or {@code NULLORDER} if
     * the start of the iteration has been reached.
     */
    public int previous() {
        return this.icuIterator.previous();
    }

    /**
     * Returns the primary order of the specified collation element, i.e. the
     * first 16 bits. This value is unsigned.
     *
     * @param order
     *            the element of the collation.
     */
    public static final int primaryOrder(int order) {
        return CollationElementIteratorICU.primaryOrder(order);
    }

    /**
     * Repositions the cursor to point at the first element of the current
     * string. The next call to {@link #next()} or {@link #previous()} will
     * return the first and last collation element in the string, respectively.
     * <p>
     * If the {@code RuleBasedCollator} used by this iterator has had its
     * attributes changed, calling {@code reset()} reinitializes the iterator to
     * use the new attributes.
     */
    public void reset() {
        this.icuIterator.reset();
    }

    /**
     * Returns the secondary order of the specified collation element, i.e. the
     * 16th to 23th bits, inclusive. This value is unsigned.
     *
     * @param order
     *            the element of the collator.
     */
    public static final short secondaryOrder(int order) {
        return (short) CollationElementIteratorICU.secondaryOrder(order);
    }

    /**
     * Points the iterator at the collation element associated with the
     * character in the source string which is found at the supplied offset.
     * After this call completes, an invocation of the {@link #next()} method
     * will return this collation element.
     * <p>
     * If {@code newOffset} corresponds to a character which is part of a
     * sequence that maps to a single collation element then the iterator is
     * adjusted to the start of that sequence. As a result of this, any
     * subsequent call made to {@code getOffset()} may not return the same value
     * set by this method.
     * <p>
     * If the decomposition mode is on, and offset is in the middle of a
     * decomposable range of source text, the iterator may not return a correct
     * result for the next forwards or backwards iteration. The user must ensure
     * that the offset is not in the middle of a decomposable range.
     *
     * @param newOffset
     *            the character offset into the original source string to set.
     *            Note that this is not an offset into the corresponding
     *            sequence of collation elements.
     */
    public void setOffset(int newOffset) {
        this.icuIterator.setOffset(newOffset);
    }

    /**
     * Sets a new source string iterator for iteration, and resets the offset to
     * the beginning of the text.
     *
     * @param source
     *            the new source string iterator for iteration.
     */
    public void setText(CharacterIterator source) {
        this.icuIterator.setText(source);
    }

    /**
     * Sets a new source string for iteration, and resets the offset to the
     * beginning of the text.
     *
     * @param source
     *            the new source string for iteration.
     */
    public void setText(String source) {
        this.icuIterator.setText(source);
    }

    /**
     * Returns the tertiary order of the specified collation element, i.e. the
     * last 8 bits. This value is unsigned.
     *
     * @param order
     *            the element of the collation.
     */
    public static final short tertiaryOrder(int order) {
        return (short) CollationElementIteratorICU.tertiaryOrder(order);
    }
}