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<?
  // //////////////////////////////////////////////////////////
  // sparkline.php
  // sparkline.php?123456789159843695782554
  //
  // process parameters
  $query = $_SERVER["QUERY_STRING"];
  if (empty($query))
    die;
  // only numbers
  $numValues = strlen($query);
  for ($i = 0; $i < $numValues; $i++)
    $hours[$i] = intval($query[$i]);
  // upper limit
  $maxValue = max($hours);
  if ($maxValue == 0)
    $maxValue = 1;
  // bars' configuration
  $barWidth  =  3;
  $barHeight = 10;
  $padding   =  1;
  $minGray   =  0.3;
  $maxGray   =  1.0;
  $width  = $numValues * ($barWidth+$padding) - 1;
  $height = $barHeight;
  // add borders
  $width  += 2;
  $height += 2;
  // create new image, full color range
  $img = imagecreatetruecolor($width, $height);
  imageantialias    ($img, true);
  imagealphablending($img, false);
  imagesavealpha    ($img, true);
  // transparent background
  $background = imagecolorallocatealpha($img, 0,0,0, 127);
  imagefilledrectangle ($img, 1,1, $width-2,$height-2, $background);
  imagecolortransparent($img, $background);
  // black border
  $black = imagecolorallocatealpha($img, 0,0,0, 0);
  imagerectangle($img, 0,0, $width-1,$height-1, $black);
  // sparklines
  $x = 1;
  foreach ($hours as $hour)
  {
    $intensity = $hour/$maxValue;
    // scale to prevent too bright/dark colors
    if ($intensity > 0)
      $intensity = $minGray + ($maxGray-$minGray)*$intensity;
    // the higher the number, the darker (not brighter)
    $intensity = 1 - $intensity;
    // convert to grayscale (red == green == blue)
    $gray = imagecolorallocatealpha($img, 0xFF*$intensity,  // red
                                          0xFF*$intensity,  // green
                                          0xFF*$intensity,  // blue
                                          0x7F*$intensity); // alpha
    // draw single bar
    imagefilledrectangle($img, $x,1, $x+$barWidth-1,$barHeight, $gray);
    // next one
    $x += $barWidth + $padding;
  }
  // send to client, use some caching
  $secondsCache = 3600*24*7+1;
  header("Content-type: image/png");
  header("Last-Modified: ".gmdate("D, d M Y H:i:s", time())." GMT");
  header("Cache-Control: max-age=$secondsCache");
  header("Expires: ".gmdate("D, d M Y H:i:s", time()+$secondsCache)." GMT");
  imagepng($img);
?>