feat: math captcha added

docs/field-types/captcha.html

@@ -63,6 +63,37 @@ <h2>Google ReCaptcha V3</h2>
 <p>With every user request, reCAPTCHA v3 returns a value between 0 and 1, indicating the probability that the request comes from a bot. If the value is close to 0, it is probably a bot; if it is close to 1, it is more likely that it is a human. The default score of <code>0.4</code> may be customized using the <code>min_score</code> argument.</p>
 <br>
 
+<h2>Math Captcha</h2>
+<p>Let users solve a simple math puzzle to verify if they are human.<br>
+	You can choose between a text or an image captcha. The image captcha is recommended because only more sophisticated bots have the ability to read text from images.
+</p>
+<pre><code class="language-php">$form->addField('my-captcha',  'math-captcha', [
+	'label'     => "What is &lt;challenge&gt;?",  // &lt;challenge&gt; will be replaced with the actual math question
+	'secret'    => 'YOUR_SECRET_KEY', 		  // secret salt for captcha (generate a random string)
+	'min'       => 1,												// optionally override the minimum number for the math puzzle
+	'max'       => 100,											// optionally override the maximum number for the math puzzle
+  'use_image' => true,										// use an image instead of text (recommended)
+	'font_path' => '...',										// -- optionally change the font (when using an image)
+	'font_size'	=> 24,											// -- optionally override font size (when using an image)
+	'color' 	  => [255, 0, 0],							// -- optionally override the text color using [R, G, B] (when using an image)
+]);
+</code></pre>
+
+<p>If you use the image based puzzle, you might want to add some CSS to shrink the image and align it with the label text.</p>
+<pre><code class="language-css">.form-wrap .img-puzzle {
+	position: relative;
+	display: inline-block;
+	height: 0.8em;
+	transform: translateY(0.1em); /* vertical alignment */
+}
+
+.form-wrap .img-puzzle img {
+	height: 100%;
+}
+</code></pre>
+<br><br>
+
+
 								<h2>Honeypot</h2>
 
 								<p>

src/HazzelForms/Field/Captcha/MathCaptcha.php

@@ -0,0 +1,158 @@
+<?php
+
+namespace HazzelForms\Field\Captcha;
+
+use HazzelForms\Field\Field as Field;
+
+class MathCaptcha extends Captcha {
+  protected $fieldType = 'math-captcha';
+  protected $num1;
+  protected $num2;
+  protected $operator;
+  protected $answer;
+  protected $secret;
+  protected $useImage;
+  protected $fontPath;
+  protected $fontSize;
+  protected $color;
+  protected $ttl;
+
+  public function __construct($formName, $fieldName, $args = []) {
+    parent::__construct($formName, $fieldName, $args);
+
+    $min            = $args['min'] ?? 1;  // default to 1  if not specified
+    $max            = $args['max'] ?? 25; // default to 25 if not specified
+    $this->secret   = $args['secret'];
+    $this->ttl      =  isset($args['ttl']) && is_int($args['ttl']) ? $args['ttl'] : 10; // default to 10 minutes if not specified 
+    $this->useImage = ($args['use_image'] && extension_loaded('gd')) ?? false;
+    $this->fontPath = $args['font_path'] ?? realpath(__DIR__ . '/../../assets/font/OpenSans-Regular.ttf');
+    $this->fontSize = $args['font_size'] ?? 24;
+    $this->color    = $args['color'] ?? [0, 0, 0];
+
+    // Generate two random numbers and a random operator
+    $this->num1 = rand($min, $max);
+    $this->num2 = rand($min, $max);
+    $this->operator = rand(0, 1) ? '+' : '-';
+
+    if ($this->operator == '-' && $this->num2 > $this->num1) {
+      // Swap numbers to ensure a non-negative result
+      [$this->num1, $this->num2] = [$this->num2, $this->num1];
+    }
+
+    $this->answer = $this->operator == '+' ? ($this->num1 + $this->num2) : ($this->num1 - $this->num2);
+  }
+
+  // override label method to allow for custom label
+  public function returnLabel() {
+    // Get the challenge string (either image or text representation)
+    $challengeString = sprintf('%d %s %d', $this->num1, $this->operator, $this->num2);
+    $challenge = $this->useImage ? $this->generateImage($challengeString) : $challengeString;
+
+    // If the label contains the placeholder <challenge>, replace it
+    if (strpos($this->label, '<challenge>') !== false) {
+      $replacedLabel = str_replace('<challenge>', $challenge, $this->label);
+      return sprintf('<label for="%1$s-%2$s"><span class="label">%3$s</span></label>', $this->formName, $this->fieldSlug, $replacedLabel);
+    }
+
+    // If no placeholder is found or if label is not set, revert to the default behavior
+    return parent::returnLabel();
+  }
+
+  public function returnField() {
+    $currentTimestamp = date('Y-m-d H:i'); // Capture current timestamp
+
+    return sprintf(
+      '<input type="text" name="%1$s[%2$s]" id="%1$s-%2$s" class="%4$s" />
+             <input type="hidden" name="%1$s--math-verify" value="%3$s" />',
+      $this->formName,
+      $this->fieldSlug,
+      md5($this->answer . $this->secret . $currentTimestamp),
+      $this->classlist
+    );
+  }
+
+  // Build error message as html
+  public function returnError($lang) {
+    if (!empty($this->error)) {
+      return sprintf('<span class="error-msg">%1$s</span>', $lang->getMessage('submit', 'invalid_captcha'));
+    }
+  }
+
+  // Build error placeholder
+  public function returnErrorPlaceholder() {
+    return sprintf('<span class="error-msg" id="error--%1$s-%2$s"></span>', $this->formName, $this->fieldSlug);
+  }
+
+  // Get error message
+  public function getErrorMessage($lang) {
+    if (!empty($this->error)) {
+      return $lang->getMessage('submit', 'invalid_captcha');
+    }
+  }
+
+  protected function generateImage($text) {
+    $textBoundingBox = imagettfbbox($this->fontSize, 0, $this->fontPath, $text);
+
+    // Determine the width and height of the text box
+    $textWidth = $textBoundingBox[2] - $textBoundingBox[0];
+    $textHeight = $textBoundingBox[1] - $textBoundingBox[7];
+
+    // Add some padding around the text
+    $padding = 2;
+    $imageWidth = $textWidth + ($padding * 2);
+    $imageHeight = $textHeight + ($padding * 2);
+
+    // Create a true color image with transparency
+    $image = imagecreatetruecolor($imageWidth, $imageHeight);
+
+    // Enable alpha blending and save the alpha channel
+    imagesavealpha($image, true);
+    $backgroundColor = imagecolorallocatealpha($image, 0, 0, 0, 127);
+    imagefill($image, 0, 0, $backgroundColor);
+
+    // Allocate the color for the text (white)
+    $textColor = imagecolorallocate($image, $this->color[0], $this->color[1], $this->color[2]);
+
+    // Align the text at the bottom of the image
+    imagettftext($image, $this->fontSize, 0, $padding, $imageHeight - $padding, $textColor, $this->fontPath, $text);
+
+    ob_start();
+    imagepng($image);
+    $data = ob_get_contents();
+    ob_end_clean();
+
+    imagedestroy($image);
+
+    return '<span class="img-puzzle"><img src="data:image/png;base64,' . base64_encode($data) . '" alt="Math puzzle" /></span>';
+  }
+
+
+  public function validate() {
+    $oneValid = false;
+    $storedAnswer = $_POST[$this->formName . '--math-verify'] ?? '';
+
+    // loop over possible timestamps from last 10 minutes
+    for ($i = 0; $i < $this->ttl; $i++) {
+      $timestamp = date('Y-m-d H:i', strtotime('-' . $i . ' minutes')); // Capture current timestamp
+
+      // check if the answer is correct for any of the timestamps
+      if (md5($this->fieldValue . $this->secret . $timestamp) === $storedAnswer) {
+        $oneValid = true;
+        break;
+      }
+    }
+
+    if ($oneValid === false || $storedAnswer === '') {
+      $this->error = 'invalid';
+    } else {
+      $this->fieldValue = 'ok';
+    }
+
+    $this->validated = true;
+    return $this->isValid();
+  }
+
+  public function setValue($value) {
+    $this->fieldValue = $value;
+  }
+}

src/HazzelForms/HazzelForm.php

@@ -126,6 +126,9 @@ public function addField($fieldName, $type = 'text', $args = []) {
             case 'recaptcha-v3':
                 $this->fields->$fieldName = new Field\Captcha\RecaptchaV3($fieldName, $this->formName, $args);
                 break;
+            case 'math-captcha':
+                $this->fields->$fieldName = new Field\Captcha\MathCaptcha($fieldName, $this->formName, $args);
+                break;
             case 'honeypot':
                 $this->fields->$fieldName = new Field\Captcha\HoneyPot($fieldName, $this->formName, $args);
                 break;