<?php

/**
 * Standalone MSI Plessey-code PHP barcode generator.
 * Use like http;//url/plessy.php?q=12345
 *
 * Tyler Montbriand, 2017, freeware.
 */

/**
 * Calculates Luhn, aka base-10 check digits from a string.
 * Simplified and translated to PHP from 
 * https://wiki.openmrs.org/display/docs/Check+Digit+Algorithm
 */
function luhn($s) {
  if (!$s || strlen($s) < 1) return "";
//  s = s.split("-")[0].toUpperCase();
  $sum = 0;
  for ($i=strlen($s)-1; $i>=0; $i-=2) {
    $ch = substr($s, $i, 1); // s.charAt(i);
//    if (validChars.indexOf(ch) < 0) {
//      return "invalid characters in identifier";
//    }
    $digit = ord(substr($s, $i, 1)) - 48; // s.charCodeAt(i)-48;
    $sum += (2 * $digit) - floor($digit / 5) * 9;
    if ($i>0) {
      $digit = ord(substr($s, $i-1, 1))-48;
      $sum += $digit; // s.charCodeAt(i-1)-48; sum += digit;
    }
  }

  $sum = abs($sum);
  $checkdigit = (10 - ($sum % 10)) % 10;
  return(sprintf("%d", $checkdigit));
}

// Uncomment for example
//$input=array('600168', '234109', '740323');
//foreach($input as $x) {
//	printf("%s:%s\n", $x, luhn($x));
//}

// Pattern of black pixels(1) and spaces(0) for each digit in MSI Plessey
// See https://en.wikipedia.org/wiki/MSI_Barcode
// and https://en.wikipedia.org/wiki/Plessey_Code
$codes=array(
	"s"	=>	"110",			/* Start Code */
	"e"	=>	"1001",			/* End Code */
	"0"	=>	"100100100100",
	"1"	=>	"100100100110",
	"2"	=>	"100100110100",
	"3"	=>	"100100110110",
	"4"	=>	"100110100100",
	"5"	=>	"100110100110",
	"6"	=>	"100110110100",
	"7"	=>	"100110110110",
	"8"	=>	"110100100100",
	"9"	=>	"110100100110",
	);

// Generates a Plessey Code barcode from a string of digits 0-9.
// Also accepted are the special values 's' for start sequence and
// 'e' for end sequence.
//
// Start and end codes are affixed automatically, as well as a 
// base-10 check digit.  Edit the "$c = ..." line if you require
// different behavior.
function plessey($c) {
	global $codes;

	$c = 's' . $c . luhn($c) . 'e';

	$bar = 2;	// Width of narrow bars in pixels
	$h = 40;	// Height of image
	$y = 10;	// Top/bottom margins

	$w = 0;		// Width, to be calculated
	$x = 0;		// X drawing position

	for($m=0; $m < strlen($c); $m++)
		$w += $bar*(strlen($codes[$c[$m]]));

	// Side margins
	$w += 40;
	$x += 40 / 2;

	$im=@imagecreate($w, $h)
		or die("Cannot Initialize new GD image stream");

	$white = imagecolorallocate($im, 255, 255, 255);
	$black = imagecolorallocate($im, 0, 0, 0);
	imagefilledrectangle($im, 0, 0, $w, 50, $white);

	for($m=0; $m < strlen($c); $m++)
	for($n=0; $n < strlen($codes[$c[$m]]); $n++, $x+=2)
	if($codes[$c[$m]][$n] == '1')
		imagefilledrectangle($im, $x, $y, $x+1, $h-$y, $black);

	return($im);
}

if(!array_key_exists("q",$_GET) || preg_match("/[^0-9]/", $_GET['q']))
{
	header("Content-Type: text/html");
	echo("Unknown or invalid query, use q=0123456789");
	exit(0);
}

header("Content-Type: image/png");
imagepng(plessey($_GET['q']));
exit(0);	?>