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Library for generating and applying diff/patch files
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/*
   Copyright 2010 Dmitry Naumenko ([email protected])

   Licensed 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 pw.prok.kdiff;

import pw.prok.kdiff.diff.DiffException;
import pw.prok.kdiff.diff.Equalizer;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * Holds the information about the part of text involved in the diff process
 * 

 * 

 * Text is represented as Object[] because the diff engine is
 * capable of handling more than plain ascci. In fact, arrays or lists of any
 * type that implements {@link java.lang.Object#hashCode hashCode()} and
 * {@link java.lang.Object#equals equals()} correctly can be subject to
 * differencing using this library.
 *
 * @param  The type of the compared elements in the 'lines'.
 */
public class Chunk {
    private final int position;
    private List lines;

    /**
     * Creates a chunk and saves a copy of affected lines
     *
     * @param position the start position
     * @param lines    the affected lines
     */
    public Chunk(int position, List lines) {
        this.position = position;
        this.lines = lines;
    }

    /**
     * Creates a chunk and saves a copy of affected lines
     *
     * @param position the start position
     * @param lines    the affected lines
     */
    public Chunk(int position, T[] lines) {
        this.position = position;
        this.lines = Arrays.asList(lines);
    }

    /**
     * Verifies that this chunk's saved text matches the corresponding text in
     * the given sequence.
     *
     * @param target the sequence to verify against.
     * @throws PatchFailedException if the patch cannot be applied.
     */
    public void verify(List target) throws PatchFailedException {
        try {
            applyHunk(target);
        } catch (DiffException e) {
            throw new PatchFailedException(e);
        }
    }

    public int applyHunk(List target) throws DiffException {
        return applyHunk(target, 0);
    }

    public int applyHunk(List target, int lastOffset) throws DiffException {
        return applyHunk(target, lastOffset, (Equalizer) Equalizer.DEFAULT_EQUALIZER);
    }

    public int applyHunk(List target, int lastOffset, Equalizer equalizer) throws DiffException {
        final int actual = search(target, lines, position + lastOffset, equalizer);
        if (actual < 0) throw new DiffException("Hunk cannot be applied");
        return actual - position;
    }

    private static  int search(List where, List what, int point, Equalizer equalizer) {
        final int start = 0;
        final int end = where.size() - what.size();
        if (end < 0) return -1;
        if (equals(where, what, point, equalizer)) return point;
        for (int i = 1; point - i >= start || point + i <= end; i++) {
            if (point - i >= start && equals(where, what, point - i, equalizer)) return point - i;
            if (point + i <= end && equals(where, what, point + i, equalizer)) return point + i;
        }
        return -1;
    }

    private static  boolean equals(List where, List what, int point, Equalizer equalizer) {
        for (int i = 0; i < what.size(); i++) {
            final T o1 = where.get(point + i);
            final T o2 = what.get(i);
            if (!equalizer.equals(o1, o2)) return false;
        }
        return true;
    }

    /**
     * @return the start position of chunk in the text
     */
    public int getPosition() {
        return position;
    }

    public void setLines(List lines) {
        this.lines = lines;
    }

    /**
     * @return the affected lines
     */
    public List getLines() {
        return lines;
    }

    public int size() {
        return lines.size();
    }

    /**
     * @return the index of the last line of the chunk.
     */
    public int last() {
        return getPosition() + size() - 1;
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.lang.Object#hashCode()
     */
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((lines == null) ? 0 : lines.hashCode());
        result = prime * result + position;
        result = prime * result + size();
        return result;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Chunk other = (Chunk) obj;
        if (lines == null) {
            if (other.lines != null)
                return false;
        } else if (!lines.equals(other.lines))
            return false;
        if (position != other.position)
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "[position: " + position + ", size: " + size() + ", lines: " + lines + "]";
    }

    /**
     * @return full copy of this chunk
     */
    public Chunk copy() {
        return new Chunk(position, new ArrayList(lines));
    }
}