/library/captcha.php

<?php

/**
 * Basic captcha library
 */
// TODO: wrap in a class too?
/**
 * Retrieve/set unique identifier
 *
 * @param     mixed  Code length|File
 * @param     string Unique key
 * @staticvar string Charset
 * @return    string
 */
function captcha_id($test = 6, $key = 0) {
  static $chars = 'jklmn-JKLMN#rstuvwx@RSTUVWX+56789=ABCDEFG';


  if ( ! is_num($test)) {
    if ( ! is_file($test)) {
      return FALSE;
    }

    $test = preg_split('/\b|[\s\t]+/', read($test));
    $test = array_filter(array_unique($test));
    $hash = $test[array_rand($test, 1)];
  } else {
    $hash = '';
    $max  = strlen($chars) - 1;

    if ($test > 10) {
      $test = 10;
    }

    while(strlen($hash) < $test) {
      $old = substr($chars, mt_rand(0, $max), 1);

      if ( ! is_false(strpos($hash, $old))) {
        continue;
      }

      $hash .= $old;
    }
  }


  session("--captcha-id$$key", $hash);

  return $hash;
}


/**
 * Generate the captcha image
 *
 * @param     string  Hash
 * @param     integer Width
 * @param     integer Height
 * @param     string  Fontfile
 * @param     boolean Invert color?
 * @staticvar mixed   Function callback
 * @return    string
 */
function captcha_src($hash, $width = 120, $height = 24, $font = '', $invert = FALSE) {
  static $negative = NULL;


  if (is_null($negative)) {
    $negative = function ($num) {
      return $num * -1;
    };
  }


  $length   = strlen($hash);
  $resource = imagecreatetruecolor($width, $height);

  imagesavealpha($resource, TRUE);
  imagealphablending($resource, TRUE);


  $dark  = array(mt_rand(0, 96), mt_rand(0, 96), mt_rand(0, 96));
  $light = array(mt_rand(127, 240), mt_rand(127, 240), mt_rand(127, 240));

  if (is_true($invert)) {
    $bgcolor = imagecolorallocatealpha($resource, 0, 0, 0, 0);
    $light   = array_map($negative, $light);
    $dark    = array_map($negative, $dark);
  } else {
    $bgcolor = imagecolorallocatealpha($resource, 255, 255, 255, 127);
  }

  imagefill($resource, 0, 0, $bgcolor);


  $bg = imagecolorallocatealpha($resource, $light[0], $light[1], $light[2], mt_rand(45, 85));
  $fg = imagecolorallocatealpha($resource, $dark[0], $dark[1], $dark[2], mt_rand(33, 52));


  $left   = substr($hash, 0, ceil($length / 2));
  $right  = substr($hash, strlen($left));
  $factor = floor($width / $length);
  $font   = realpath($font);

  if ( ! is_file($font)) {
    $top = ($width * $height) / 3.3;

    for ($i = 0; $i < $top; $i += 1) {
      imagefilledellipse($resource, mt_rand(0, $width), mt_rand(0, $height), 1, mt_rand(1, 3), $bg);
    }

    for ($i = 0; $i < $length; $i += 1) {
      imagestring($resource, 5, ($factor / 3) + $i * $factor, mt_rand(0, $height - mt_rand(13, 20)), substr($hash, $i, 1), $fg);

      if (mt_rand(0, 75) % 9) {
        $img = imagerotate($resource, is_odd($i) ? - .8 : .7, $bgcolor);
      }
    }
  } else {
    $box = imageftbbox($factor, 0, $font, 'Q');

    $w   = max(abs($box[2]) - abs($box[0]), 1);
    $h   = max(abs($box[7]) - abs($box[6]), 1);

    imagettftext($resource, $factor, mt_rand(-4, 5), $x = mt_rand($w / strlen($left), $w * 1.3), mt_rand($h, $h * 1.33), $fg, $font, $left);

    for ($i = 2; $i < $factor; $i += 1) {
      imagettftext($resource, 16, mt_rand(20, 33), ($i - 1.5) * $factor, $i * 15, $bg, $font, str_shuffle($hash));
    }


    $a = $x + ($w * strlen($left));
    $b = $width - ($w * strlen($right)) - $w;

    imagettftext($resource, $factor, mt_rand(-3, 4), mt_rand(min($a, $b), max($a, $b)), $h * 1.20, ($fg * 1.3) / 96, $font, $right);
  }

  header('Content-Type: image/png');

  imagepng($resource);
  imagedestroy($resource);

  exit;
}


/**
 * Captcha code validation
 *
 * @param  string  Received code
 * @param  string  Unique key
 * @param  boolean Strict?
 * @return boolean
 */
function captcha_valid($test, $key = 0, $strict = FALSE) {
  if ( ! empty($test)) {
    $old = session("--captcha-id$$key");

    if (is_true($strict)) {
      return ! strcmp($old, $test);
    }
    return strtolower($old) === strtolower($test);
  }
  return FALSE;
}

/* EOF: ./library/captcha.php */