class DiffFormatter

class DiffFormatter {

  /**
   * Should a block header be shown?
   */
  var $show_header = TRUE;

  /**
   * Number of leading context "lines" to preserve.
   *
   * This should be left at zero for this class, but subclasses
   * may want to set this to other values.
   */
  var $leading_context_lines = 0;

  /**
   * Number of trailing context "lines" to preserve.
   *
   * This should be left at zero for this class, but subclasses
   * may want to set this to other values.
   */
  var $trailing_context_lines = 0;

  /**
   * Format a diff.
   *
   * @param $diff object A Diff object.
   * @return string The formatted output.
   */
  function format($diff) {
    $xi = $yi = 1;
    $block = FALSE;
    $context = array();
    $nlead = $this->leading_context_lines;
    $ntrail = $this->trailing_context_lines;
    $this
      ->_start_diff();
    foreach ($diff->edits as $edit) {
      if ($edit->type == 'copy') {
        if (is_array($block)) {
          if (sizeof($edit->orig) <= $nlead + $ntrail) {
            $block[] = $edit;
          }
          else {
            if ($ntrail) {
              $context = array_slice($edit->orig, 0, $ntrail);
              $block[] = new _DiffOp_Copy($context);
            }
            $this
              ->_block($x0, $ntrail + $xi - $x0, $y0, $ntrail + $yi - $y0, $block);
            $block = FALSE;
          }
        }
        $context = $edit->orig;
      }
      else {
        if (!is_array($block)) {
          $context = array_slice($context, sizeof($context) - $nlead);
          $x0 = $xi - sizeof($context);
          $y0 = $yi - sizeof($context);
          $block = array();
          if ($context) {
            $block[] = new _DiffOp_Copy($context);
          }
        }
        $block[] = $edit;
      }
      if ($edit->orig) {
        $xi += sizeof($edit->orig);
      }
      if ($edit->closing) {
        $yi += sizeof($edit->closing);
      }
    }
    if (is_array($block)) {
      $this
        ->_block($x0, $xi - $x0, $y0, $yi - $y0, $block);
    }
    $end = $this
      ->_end_diff();
    if (!empty($xi)) {
      $this->line_stats['counter']['x'] += $xi;
    }
    if (!empty($yi)) {
      $this->line_stats['counter']['y'] += $yi;
    }
    return $end;
  }
  function _block($xbeg, $xlen, $ybeg, $ylen, &$edits) {
    $this
      ->_start_block($this
      ->_block_header($xbeg, $xlen, $ybeg, $ylen));
    foreach ($edits as $edit) {
      if ($edit->type == 'copy') {
        $this
          ->_context($edit->orig);
      }
      elseif ($edit->type == 'add') {
        $this
          ->_added($edit->closing);
      }
      elseif ($edit->type == 'delete') {
        $this
          ->_deleted($edit->orig);
      }
      elseif ($edit->type == 'change') {
        $this
          ->_changed($edit->orig, $edit->closing);
      }
      else {
        trigger_error('Unknown edit type', E_USER_ERROR);
      }
    }
    $this
      ->_end_block();
  }
  function _start_diff() {
    ob_start();
  }
  function _end_diff() {
    $val = ob_get_contents();
    ob_end_clean();
    return $val;
  }
  function _block_header($xbeg, $xlen, $ybeg, $ylen) {
    if ($xlen > 1) {
      $xbeg .= "," . ($xbeg + $xlen - 1);
    }
    if ($ylen > 1) {
      $ybeg .= "," . ($ybeg + $ylen - 1);
    }
    return $xbeg . ($xlen ? $ylen ? 'c' : 'd' : 'a') . $ybeg;
  }
  function _start_block($header) {
    if ($this->show_header) {
      echo $header . "\n";
    }
  }
  function _end_block() {
  }
  function _lines($lines, $prefix = ' ') {
    foreach ($lines as $line) {
      echo "{$prefix} {$line}\n";
    }
  }
  function _context($lines) {
    $this
      ->_lines($lines);
  }
  function _added($lines) {
    $this
      ->_lines($lines, '>');
  }
  function _deleted($lines) {
    $this
      ->_lines($lines, '<');
  }
  function _changed($orig, $closing) {
    $this
      ->_deleted($orig);
    echo "---\n";
    $this
      ->_added($closing);
  }

}