/*
 * The Alphanum Algorithm is an improved sorting algorithm for strings
 * containing numbers.  Instead of sorting numbers in ASCII order like
 * a standard sort, this algorithm sorts numbers in numeric order.
 *
 * The Alphanum Algorithm is discussed at http://www.DaveKoelle.com
 *
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */
package org.simantics.utils.strings;

import java.nio.CharBuffer;
import java.util.Comparator;

/**
 * This is an updated version with enhancements made by Daniel Migowski, Andre
 * Bogus, and David Koelle
 * 
 * To convert to use Templates (Java 1.5+): - Change "implements Comparator" to
 * "implements Comparator<String>" - Change "compare(Object o1, Object o2)" to
 * "compare(String s1, String s2)" - Remove the type checking and casting in
 * compare().
 * 
 * To use this class: Use the static "sort" method from the
 * java.util.Collections class: Collections.sort(your list, new
 * AlphanumComparator());
 * 
 * Modified by Tuukka Lehtonen to re-use two CharBuffer instances compared to
 * 2*chunk-count StringBuilders per single comparison for some added efficiency.
 */
public class AlphanumComparator implements Comparator<Object>
{
    private static final CaseInsensitiveComparator CASE_INSENSITIVE_ORDER = new CaseInsensitiveComparator();

    private static class CaseInsensitiveComparator implements Comparator<CharBuffer>, java.io.Serializable {

        private static final long serialVersionUID = 5247677019801470582L;

        @Override
        public int compare(CharBuffer s1, CharBuffer s2) {
            int n1 = s1.limit(), n2 = s2.limit();
            for (int i1 = 0, i2 = 0; i1 < n1 && i2 < n2; i1++, i2++) {
                char c1 = s1.charAt(i1);
                char c2 = s2.charAt(i2);
                if (c1 != c2) {
                    c1 = Character.toUpperCase(c1);
                    c2 = Character.toUpperCase(c2);
                    if (c1 != c2) {
                        c1 = Character.toLowerCase(c1);
                        c2 = Character.toLowerCase(c2);
                        if (c1 != c2) {
                            return c1 - c2;
                        }
                    }
                }
            }
            return n1 - n2;
        }
    }

    public static final AlphanumComparator COMPARATOR  = new AlphanumComparator(null);
    public static final AlphanumComparator CASE_INSENSITIVE_COMPARATOR = new AlphanumComparator(CASE_INSENSITIVE_ORDER);

    private final Comparator<CharBuffer> comparator;

    private static class Buffers {
        CharBuffer b1 = CharBuffer.allocate(0);
        CharBuffer b2 = b1;
    }

    private static final ThreadLocal<Buffers> buffers = new ThreadLocal<Buffers>() {
        protected Buffers initialValue() {
            return new Buffers();
        }
    };

    private AlphanumComparator(Comparator<CharBuffer> comparator) {
        this.comparator = comparator;
    }

    private final boolean isDigit(char ch)
    {
        return ch >= 48 && ch <= 57;
    }

    /** Length of string is passed in for improved efficiency (only need to calculate it once) **/
    private final CharBuffer getChunk(String s, int slength, int marker, CharBuffer chunk)
    {
        if (chunk == null || chunk.capacity() < slength) {
            chunk = CharBuffer.allocate(slength);
        } else {
            chunk.rewind();
            chunk.limit(chunk.capacity());
        }

        char c = s.charAt(marker);
        chunk.append(c);
        marker++;
        if (isDigit(c))
        {
            while (marker < slength)
            {
                c = s.charAt(marker);
                if (!isDigit(c))
                    break;
                chunk.append(c);
                marker++;
            }
        } else
        {
            while (marker < slength)
            {
                c = s.charAt(marker);
                if (isDigit(c))
                    break;
                chunk.append(c);
                marker++;
            }
        }
        chunk.limit(chunk.position());
        chunk.rewind();
        return chunk;
    }

    @Override
    public int compare(Object o1, Object o2)
    {
        if (o1 == o2)
            return 0;

        String s1 = o1.toString();
        String s2 = o2.toString();

        int thisMarker = 0;
        int thatMarker = 0;
        int s1Length = s1.length();
        int s2Length = s2.length();

        Buffers bufs = buffers.get();
        CharBuffer thisChunk = bufs.b1;
        CharBuffer thatChunk = bufs.b2;

        try {
            while (thisMarker < s1Length && thatMarker < s2Length)
            {
                thisChunk = getChunk(s1, s1Length, thisMarker, thisChunk);
                thisMarker += thisChunk.limit();

                thatChunk = getChunk(s2, s2Length, thatMarker, thatChunk);
                thatMarker += thatChunk.limit();

                // If both chunks contain numeric characters, sort them numerically
                int result = 0;
                if (isDigit(thisChunk.charAt(0)) && isDigit(thatChunk.charAt(0)))
                {
                    // Simple chunk comparison by length.
                    int thisChunkLength = thisChunk.limit();
                    result = thisChunkLength - thatChunk.limit();
                    // If equal, the first different number counts
                    if (result == 0)
                    {
                        for (int i = 0; i < thisChunkLength; i++)
                        {
                            result = thisChunk.charAt(i) - thatChunk.charAt(i);
                            if (result != 0)
                            {
                                return result;
                            }
                        }
                    }
                } else
                {
                    result = comparator != null ? comparator.compare(thisChunk, thatChunk) : thisChunk.compareTo(thatChunk);
                }

                if (result != 0)
                    return result;
            }

            return s1Length - s2Length;
        } finally {
            bufs.b1 = reset(thisChunk);
            bufs.b2 = reset(thatChunk);
        }
    }

    private static CharBuffer reset(CharBuffer buffer) {
        buffer.rewind();
        buffer.limit(buffer.capacity());
        return buffer;
    }

}