static class BlockDiff {
  public CopyBlock asCopyBlock() { return null; }
  public NewBlock  asNewBlock () { return null; }
}

static class CopyBlock extends BlockDiff {
  int firstLine, lines;

  CopyBlock(int firstLine, int lines) {
    this.firstLine = firstLine;
    this.lines = lines;
  }

  public CopyBlock asCopyBlock() { return this; }
  public int getFirstLine() { return firstLine; }
  public int getLines() { return lines; }
}

static class NewBlock extends BlockDiff {
  int originalStart;
  List<String> contents;

  NewBlock(int originalStart, List<String> contents) {
    this.originalStart = originalStart;
    this.contents = contents;
  }

  public NewBlock  asNewBlock () { return this; }

  public int getOriginalStart() {
    return originalStart;
  }

  public List<String> getContents() {
    return contents;
  }
}

static class ExplodedLine {
  int type;
  String left, right;
  int leftIndex, rightIndex;

  ExplodedLine(int type, String left, String right, int leftIndex, int rightIndex) {
    this.type = type;
    this.left = left;
    this.right = right;
    this.leftIndex = leftIndex;
    this.rightIndex = rightIndex;
  }
  
  public int getType() {
    return type;
  }

  public String getLeft() {
    return left;
  }

  public String getRight() {
    return right;
  }

  public int getLeftIndex() {
    return leftIndex;
  }

  public int getRightIndex() {
    return rightIndex;
  }
}

static class BlockDiffer {
  public static final int IDENTICAL = 0;
  public static final int DIFFERENT = 1;
  public static final int LEFT_ONLY = 2;
  public static final int RIGHT_ONLY = 3;

  private static void printChange(EGDiff.change change) {
    if (change != null) {
      System.out.println("line0="+change.line0+", line1="+change.line1
        +", inserted="+change.inserted+", deleted="+change.deleted);
      printChange(change.link);
    }
  }


  /** Generates the text content of a Unified-format context diff between 2 files
   *  (NB the 'files-changed' header must be added separately).
   */
  public static List<String> generateUniDiff(List<String> fileA, List<String> fileB, int contextSize) {
    EGDiff diff = new EGDiff(fileA.toArray(), fileB.toArray());
    EGDiff.change change = diff.diff_2(false);

    if (change != null) {
      int inserted, deleted;
      List<String> hunkLines = new ArrayList<String>();
      int cumulExtraLinesBwrtA = 0;

      // Each hunk is generated with a header
      do {
        int line0 = change.line0, line1 = change.line1;
        int changeStart = ((line1 < line0) ? line1 : line0);
        int contextStart = ((changeStart > contextSize) ? changeStart - contextSize : 0);
        int headerPosn = hunkLines.size();

        // Provide the first lines of context
        for (int i = contextStart; i < changeStart; i++)
          //System.out.println(" " + fileA.get(i));
          hunkLines.add(" " + fileA.get(i));

        boolean hunkFinish = false;
        // Step through each change giving the change lines and following context
        do {
          inserted = change.inserted;
          deleted = change.deleted;
          line0 = change.line0;
          line1 = change.line1;

          if (line1 < line0) // An insert comes earlier
            while (inserted-- > 0)
              hunkLines.add("+" + fileB.get(line1++));
          while (deleted-- > 0)
            hunkLines.add("-" + fileA.get(line0++));
          while (inserted-- > 0)
            hunkLines.add("+" + fileB.get(line1++));

          // Lines following are trailing context, identical in fileA and fileB
          // The next change may overlap the context, so check and if so, form one hunk
          EGDiff.change nextChange = change.link;
          int nextChangeStart = fileA.size();
          if (nextChange != null)
            nextChangeStart = ((nextChange.line1 < nextChange.line0) ? nextChange.line1 : nextChange.line0);

          if (nextChangeStart - line0 > contextSize * 2) { // A separate hunk
            nextChangeStart = line0 + contextSize;
            hunkFinish = true;
          }
          if (nextChangeStart > fileA.size())
            nextChangeStart = fileA.size(); // Limit to file size
          while (line0 < nextChangeStart) {
            hunkLines.add(" " + fileA.get(line0++));
            line1++; // Keep in sync with trailing context
          }

          change = change.link;
        } while (!hunkFinish && change != null);

        int hunkStartB = contextStart + cumulExtraLinesBwrtA;
        int hunkTotA = line0 - contextStart;
        int hunkTotB = line1 - hunkStartB;

        hunkLines.add(headerPosn, "@@ -" + (contextStart + 1) + ',' + hunkTotA +
                        " +" + (hunkStartB + 1) + ',' + hunkTotB + " @@");
        cumulExtraLinesBwrtA += hunkTotB - hunkTotA;

      } while (change != null);

      return hunkLines;
    }
    return null;
  }

/* For testing:
  private static void printUniDiff(List<String> fileA, List<String> fileB, int contextSize) {
    List<String> uniDiff = generateUniDiff(fileA, fileB, contextSize);

    if (uniDiff != null)
      for (int j = 0; j < uniDiff.size(); j++)
        System.out.println(uniDiff.get(j));
  }
 */


  public static List<BlockDiff> diffLines(List<String> lines, List<String> reference) {
    List<BlockDiff> diffs = new ArrayList<BlockDiff>();

    EGDiff diff = new EGDiff(reference.toArray(), lines.toArray());
    EGDiff.change change = diff.diff_2(false);
    //printChange(change);
    //printUniDiff(reference, lines, 3);

    int l0 = 0, l1 = 0;
    while (change != null) {
      if (change.line0 > l0 && change.line1 > l1)
        diffs.add(new CopyBlock(l0, change.line0-l0));

      if (change.inserted != 0)
        diffs.add(new NewBlock(change.line1, lines.subList(change.line1, change.line1+change.inserted)));

      l0 = change.line0 + change.deleted;
      l1 = change.line1 + change.inserted;
      change = change.link;
    }

    if (l0 < reference.size())
      diffs.add(new CopyBlock(l0, reference.size()-l0));

    return diffs;
  }

  /** fills files with empty lines to align matching blocks
   *
   * @param file1 first file
   * @param file2 second file
   * @return an array with two lists
   */
  public static List<ExplodedLine> explode(List<String> file1, List<String> file2) {
    List<ExplodedLine> lines = new ArrayList<ExplodedLine>();
    List<BlockDiff> diffs = BlockDiffer.diffLines(file2, file1);
    int lastLineCopied = 0, rightOnlyStart = -1, rightPosition = 0;
    for (int i = 0; i < diffs.size(); i++) {
      BlockDiff diff = diffs.get(i);
      if (diff instanceof CopyBlock) {
        CopyBlock copyBlock = (CopyBlock) diff;
        if (lastLineCopied < copyBlock.getFirstLine()) {
          if (rightOnlyStart >= 0) {
            int overlap = Math.min(lines.size()-rightOnlyStart, copyBlock.getFirstLine()-lastLineCopied);
            //lines.subList(rightOnlyStart, rightOnlyStart+overlap).clear();
            convertRightOnlyToDifferent(lines, rightOnlyStart, overlap, file1, lastLineCopied);
            lastLineCopied += overlap;
          }
          addBlock(lines, LEFT_ONLY, file1, lastLineCopied, copyBlock.getFirstLine(), lastLineCopied, -1);
        }
        addBlock(lines, IDENTICAL, file1, copyBlock.getFirstLine(), copyBlock.getFirstLine()+copyBlock.getLines(),
          copyBlock.getFirstLine(), rightPosition);
        rightPosition += copyBlock.getLines();
        lastLineCopied = copyBlock.getFirstLine()+copyBlock.getLines();
        rightOnlyStart = -1;
      } else if (diff instanceof NewBlock) {
        NewBlock newBlock = (NewBlock) diff;
        /*if (nextDiff instanceof BlockDiffer.CopyBlock) {
          BlockDiffer.CopyBlock copyBlock = (BlockDiffer.CopyBlock) nextDiff;
          copyBlock.getFirstLine()-lastLineCopied*/
        rightOnlyStart = lines.size();
        addBlock(lines, RIGHT_ONLY, newBlock.getContents(), 0, newBlock.getContents().size(), -1, rightPosition);
        rightPosition += newBlock.getContents().size();
      }
    }

    if (rightOnlyStart >= 0) {
      int overlap = Math.min(lines.size()-rightOnlyStart, file1.size()-lastLineCopied);
      //lines.subList(rightOnlyStart, rightOnlyStart+overlap).clear();
      convertRightOnlyToDifferent(lines, rightOnlyStart, overlap, file1, lastLineCopied);
      lastLineCopied += overlap;
    }
    addBlock(lines, LEFT_ONLY, file1, lastLineCopied, file1.size(), lastLineCopied, -1);

    return lines;
  }

  private static void convertRightOnlyToDifferent(List<ExplodedLine> lines, int start, int numLines,
                                                  List<String> leftLines, int leftStart) {
    for (int i = 0; i < numLines; i++) {
      ExplodedLine line = lines.get(start+i);
      lines.set(start+i,
        new ExplodedLine(DIFFERENT, leftLines.get(i+leftStart), line.getRight(), i+leftStart, line.getRightIndex()));
    }
  }

  private static void addBlock(List<ExplodedLine> lines, int type, List<String> srcLines, int start, int end,
                               int leftStart, int rightStart) {
    for (int i = start; i < end; i++)
      lines.add(new ExplodedLine(type, type == RIGHT_ONLY ? "" : srcLines.get(i),
                                       type == LEFT_ONLY ? "" : srcLines.get(i),
                                       type == RIGHT_ONLY ? -1 : i - start + leftStart,
                                       type == LEFT_ONLY ? -1 : i - start + rightStart));
  }

  public static List<ExplodedLine> condense(List<ExplodedLine> lines) {
    List<ExplodedLine> result = new ArrayList<ExplodedLine>();
    for (Iterator<ExplodedLine> i = lines.iterator(); i.hasNext();) {
      ExplodedLine line = i.next();
      if (line.getType() == IDENTICAL) {
        if (result.isEmpty() || result.get(result.size()-1).getType() != IDENTICAL)
          result.add(new ExplodedLine(IDENTICAL, "[...]", "[...]", -1, -1));
      } else
        result.add(line);
    }
    return result;
  }
}