/*
 * Copyright (C) 1996-2000, International Business Machines Corporation and
 * others. All Rights Reserved.
 *
 * $Source: /xsrl/Nsvn/icu/icu4j/src/com/ibm/text/Attic/TransformTransliterator.java,v $ 
 * $Date: 2001/09/28 20:27:02 $ 
 * $Revision: 1.2 $
 */
package com.ibm.text;
import java.util.*;

/**
 * An abstract class for transliterators based on a transform
 * operation.  To create a transliterator that implements a
 * transformation, create a subclass of this class and implement the
 * abstract <code>transform()</code> and <code>hasTransform()</code>
 * methods.
 * @author Alan Liu
 */
public abstract class TransformTransliterator extends Transliterator {

    /**
     * Constructs a transliterator.  For use by subclasses.
     */
    protected TransformTransliterator(String id, UnicodeFilter f) {
        super(id, f);
    }

    /**
     * Implements {@link Transliterator#handleTransliterate}.
     */
    protected void handleTransliterate(Replaceable text,
                                       Position offsets, boolean incremental) {

        int start;
        for (start = offsets.start; start < offsets.limit; ++start) {
            // Scan for the first character that is != its transform.
            // If there are none, we fall out without doing anything.
            char c = text.charAt(start);
            if (hasTransform(c)) {
                // There is a transforming character at start.  Break
                // up the remaining string, from start to
                // offsets.limit, into segments of unfiltered and
                // filtered characters.  Only transform the unfiltered
                // characters.  As always, minimize the number of
                // calls to Replaceable.replace().

                int len = offsets.limit - start;
                // assert(len >= 1);
                
                char[] buf = new char[len];
                text.getChars(start, offsets.limit, buf, 0);

                int segStart = 0;
                int segLimit;
                UnicodeFilter filt = getFilter();

                // lenDelta is the accumulated length difference for
                // all transformed segments.  It is new length - old
                // length.
                int lenDelta = 0;

                // Set segStart, segLimit to the unfiltered segment
                // starting with start.  If the filter is null, then
                // segStart/Limit will be set to the whole string,
                // that is, 0/len.
                do {
                    // Set segLimit to the first filtered char at or
                    // after segStart.
                    segLimit = len;
                    if (filt != null) {
                        segLimit = segStart;
                        while (segLimit < len && filt.contains(buf[segLimit])) {
                             ++segLimit;
                        }
                    }

                    // Transform the unfiltered chars between segStart
                    // and segLimit.
                    int segLen = segLimit - segStart;
                    if (segLen != 0) {
                        String newStr = transform(
                            new String(buf, segStart, segLen));
                        text.replace(start, start + segLen, newStr);
                        start += newStr.length();
                        lenDelta += newStr.length() - segLen;
                    }

                    // Set segStart to the first unfiltered char at or
                    // after segLimit.
                    segStart = segLimit;
                    if (filt != null) {
                        while (segStart < len && !filt.contains(buf[segStart])) {
                            ++segStart;
                        }
                    }
                    start += segStart - segLimit;

                } while (segStart < len);
                
                offsets.limit += lenDelta;
                offsets.contextLimit += lenDelta;
                offsets.start = offsets.limit;
                return;
            }
        }
        // assert(start == offsets.limit);
        offsets.start = start;
    }

    /**
     * Subclasses must implement this method to determine whether a
     * given character has a transform that is not equal to itself.
     * This is approximately equivalent to <code>c !=
     * transform(String.valueOf(c))</code>, where
     * <code>String.valueOf(c)</code> returns a String containing the
     * single character (not integer) <code>c</code>.  Subclasses that
     * transform all their input can simply return <code>true</code>.
     */
    protected abstract boolean hasTransform(int c);

    /**
     * Subclasses must implement this method to transform a string.
     */
    protected abstract String transform(String s);
}