feat(images): auto-resize OG images to 1200x630px (closes #2)

- New ImageHelper class with resize(), validate(), cleanup() methods
- Center-crop algorithm maintains aspect ratio to target dimensions
- GD-based processing, supports JPEG/PNG/GIF/WebP input, outputs JPEG
- Generated images cached in images/mokoog/generated/ with hash naming
- Skips resize if image already at or below target dimensions
- Skips regeneration if cached version is newer than source
- validate() checks minimum 200x200px (Facebook/WhatsApp requirement)
- cleanup() removes generated images when OG records are deleted
- Auto-resize toggle in system plugin advanced settings (default: on)
- Integrated into resolveImageUrl() in the system plugin

Authored-by: Moko Consulting

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/packages/plg_system_mokoog/language/en-GB/plg_system_mokoog.ini

@@ -23,3 +23,5 @@ PLG_SYSTEM_MOKOOG_FIELD_STRIP_HTML="Strip HTML from Description"
 PLG_SYSTEM_MOKOOG_FIELD_STRIP_HTML_DESC="Remove HTML tags from the auto-generated description."
 PLG_SYSTEM_MOKOOG_FIELD_DESC_LENGTH="Description Length"
 PLG_SYSTEM_MOKOOG_FIELD_DESC_LENGTH_DESC="Maximum character length for the auto-generated og:description."
+PLG_SYSTEM_MOKOOG_FIELD_AUTO_RESIZE="Auto-resize Images"
+PLG_SYSTEM_MOKOOG_FIELD_AUTO_RESIZE_DESC="Automatically resize images to 1200x630px (Facebook recommended) using center crop. Generated images are saved to images/mokoog/generated/."

src/packages/plg_system_mokoog/language/en-US/plg_system_mokoog.ini

@@ -23,3 +23,5 @@ PLG_SYSTEM_MOKOOG_FIELD_STRIP_HTML="Strip HTML from Description"
 PLG_SYSTEM_MOKOOG_FIELD_STRIP_HTML_DESC="Remove HTML tags from the auto-generated description."
 PLG_SYSTEM_MOKOOG_FIELD_DESC_LENGTH="Description Length"
 PLG_SYSTEM_MOKOOG_FIELD_DESC_LENGTH_DESC="Maximum character length for the auto-generated og:description."
+PLG_SYSTEM_MOKOOG_FIELD_AUTO_RESIZE="Auto-resize Images"
+PLG_SYSTEM_MOKOOG_FIELD_AUTO_RESIZE_DESC="Automatically resize images to 1200x630px (Facebook recommended) using center crop. Generated images are saved to images/mokoog/generated/."

src/packages/plg_system_mokoog/mokoog.xml

@@ -107,6 +107,17 @@
                     min="50"
                     max="300"
                 />
+                <field
+                    name="auto_resize"
+                    type="radio"
+                    label="PLG_SYSTEM_MOKOOG_FIELD_AUTO_RESIZE"
+                    description="PLG_SYSTEM_MOKOOG_FIELD_AUTO_RESIZE_DESC"
+                    default="1"
+                    class="btn-group"
+                >
+                    <option value="1">JYES</option>
+                    <option value="0">JNO</option>
+                </field>
             </fieldset>
         </fields>
     </config>

src/packages/plg_system_mokoog/src/Extension/MokoOG.php

@@ -17,6 +17,7 @@ use Joomla\CMS\Plugin\CMSPlugin;
 use Joomla\CMS\Uri\Uri;
 use Joomla\Event\Event;
 use Joomla\Event\SubscriberInterface;
+use Joomla\Plugin\System\MokoOG\Helper\ImageHelper;
 
 final class MokoOG extends CMSPlugin implements SubscriberInterface
 {
@@ -288,7 +289,7 @@ final class MokoOG extends CMSPlugin implements SubscriberInterface
     }
 
     /**
-     * Resolve a relative image path to a full URL.
+     * Resolve a relative image path to a full URL, resizing for OG if needed.
      *
      * @param   string  $image  Image path
      *
@@ -300,6 +301,11 @@ final class MokoOG extends CMSPlugin implements SubscriberInterface
             return $image;
         }
 
+        // Auto-resize to OG recommended dimensions if enabled
+        if ($this->params->get('auto_resize', 1)) {
+            $image = ImageHelper::resize($image);
+        }
+
         return rtrim(Uri::root(), '/') . '/' . ltrim($image, '/');
     }
 }

src/packages/plg_system_mokoog/src/Helper/ImageHelper.php

@@ -0,0 +1,222 @@
+<?php
+
+/**
+ * @package     MokoOpenGraph
+ * @subpackage  plg_system_mokoog
+ * @author      Moko Consulting <hello@mokoconsulting.tech>
+ * @copyright   Copyright (C) 2026 Moko Consulting. All rights reserved.
+ * @license     GNU General Public License version 3 or later; see LICENSE
+ */
+
+namespace Joomla\Plugin\System\MokoOG\Helper;
+
+defined('_JEXEC') or die;
+
+use Joomla\CMS\Filesystem\File;
+use Joomla\CMS\Filesystem\Folder;
+
+class ImageHelper
+{
+    /**
+     * Target width for OG images (Facebook recommended).
+     */
+    private const TARGET_WIDTH = 1200;
+
+    /**
+     * Target height for OG images (Facebook recommended).
+     */
+    private const TARGET_HEIGHT = 630;
+
+    /**
+     * JPEG quality for generated images.
+     */
+    private const JPEG_QUALITY = 85;
+
+    /**
+     * Output directory relative to JPATH_ROOT.
+     */
+    private const OUTPUT_DIR = 'images/mokoog/generated';
+
+    /**
+     * Resize an image to OG-optimized dimensions if needed.
+     *
+     * Returns the path to the resized image relative to JPATH_ROOT,
+     * or the original path if no resize was needed or possible.
+     *
+     * @param   string  $imagePath    Image path relative to JPATH_ROOT
+     * @param   int     $targetWidth  Target width (default 1200)
+     * @param   int     $targetHeight Target height (default 630)
+     * @param   int     $quality      JPEG quality 1-100 (default 85)
+     *
+     * @return  string  Path to the output image (relative to JPATH_ROOT)
+     */
+    public static function resize(
+        string $imagePath,
+        int $targetWidth = self::TARGET_WIDTH,
+        int $targetHeight = self::TARGET_HEIGHT,
+        int $quality = self::JPEG_QUALITY
+    ): string {
+        // Resolve absolute path
+        $absPath = JPATH_ROOT . '/' . ltrim($imagePath, '/');
+
+        if (!is_file($absPath)) {
+            return $imagePath;
+        }
+
+        $imageInfo = @getimagesize($absPath);
+
+        if (!$imageInfo) {
+            return $imagePath;
+        }
+
+        [$origWidth, $origHeight, $type] = $imageInfo;
+
+        // Skip if already at or below target size
+        if ($origWidth <= $targetWidth && $origHeight <= $targetHeight) {
+            return $imagePath;
+        }
+
+        // Ensure output directory exists
+        $outputDir = JPATH_ROOT . '/' . self::OUTPUT_DIR;
+
+        if (!is_dir($outputDir)) {
+            Folder::create($outputDir);
+        }
+
+        // Generate output filename based on source hash + dimensions
+        $hash       = md5($imagePath . $targetWidth . $targetHeight);
+        $outputName = $hash . '.jpg';
+        $outputPath = $outputDir . '/' . $outputName;
+        $outputRel  = self::OUTPUT_DIR . '/' . $outputName;
+
+        // Skip if already generated
+        if (is_file($outputPath) && filemtime($outputPath) >= filemtime($absPath)) {
+            return $outputRel;
+        }
+
+        // Load source image
+        $source = self::loadImage($absPath, $type);
+
+        if (!$source) {
+            return $imagePath;
+        }
+
+        // Calculate crop dimensions (center crop to target aspect ratio)
+        $targetRatio = $targetWidth / $targetHeight;
+        $sourceRatio = $origWidth / $origHeight;
+
+        if ($sourceRatio > $targetRatio) {
+            // Source is wider — crop sides
+            $cropHeight = $origHeight;
+            $cropWidth  = (int) round($origHeight * $targetRatio);
+            $cropX      = (int) round(($origWidth - $cropWidth) / 2);
+            $cropY      = 0;
+        } else {
+            // Source is taller — crop top/bottom
+            $cropWidth  = $origWidth;
+            $cropHeight = (int) round($origWidth / $targetRatio);
+            $cropX      = 0;
+            $cropY      = (int) round(($origHeight - $cropHeight) / 2);
+        }
+
+        // Create output canvas and resample
+        $output = imagecreatetruecolor($targetWidth, $targetHeight);
+
+        imagecopyresampled(
+            $output,
+            $source,
+            0,
+            0,
+            $cropX,
+            $cropY,
+            $targetWidth,
+            $targetHeight,
+            $cropWidth,
+            $cropHeight
+        );
+
+        // Save as JPEG
+        imagejpeg($output, $outputPath, $quality);
+
+        imagedestroy($source);
+        imagedestroy($output);
+
+        return $outputRel;
+    }
+
+    /**
+     * Remove a generated image file.
+     *
+     * @param   string  $generatedPath  Path relative to JPATH_ROOT
+     *
+     * @return  void
+     */
+    public static function cleanup(string $generatedPath): void
+    {
+        if (empty($generatedPath) || !str_starts_with($generatedPath, self::OUTPUT_DIR)) {
+            return;
+        }
+
+        $absPath = JPATH_ROOT . '/' . $generatedPath;
+
+        if (is_file($absPath)) {
+            File::delete($absPath);
+        }
+    }
+
+    /**
+     * Check if an image meets minimum OG size requirements.
+     *
+     * @param   string  $imagePath  Image path relative to JPATH_ROOT
+     *
+     * @return  array{valid: bool, width: int, height: int, message: string}
+     */
+    public static function validate(string $imagePath): array
+    {
+        $absPath = JPATH_ROOT . '/' . ltrim($imagePath, '/');
+
+        if (!is_file($absPath)) {
+            return ['valid' => false, 'width' => 0, 'height' => 0, 'message' => 'File not found'];
+        }
+
+        $imageInfo = @getimagesize($absPath);
+
+        if (!$imageInfo) {
+            return ['valid' => false, 'width' => 0, 'height' => 0, 'message' => 'Not a valid image'];
+        }
+
+        [$width, $height] = $imageInfo;
+
+        // Facebook minimum: 200x200, recommended: 1200x630
+        // WhatsApp minimum: 300x200
+        if ($width < 200 || $height < 200) {
+            return [
+                'valid'   => false,
+                'width'   => $width,
+                'height'  => $height,
+                'message' => "Image too small ({$width}x{$height}). Minimum: 200x200px.",
+            ];
+        }
+
+        return ['valid' => true, 'width' => $width, 'height' => $height, 'message' => 'OK'];
+    }
+
+    /**
+     * Load an image resource from a file.
+     *
+     * @param   string  $path  Absolute file path
+     * @param   int     $type  IMAGETYPE_* constant
+     *
+     * @return  \GdImage|false
+     */
+    private static function loadImage(string $path, int $type)
+    {
+        return match ($type) {
+            IMAGETYPE_JPEG => @imagecreatefromjpeg($path),
+            IMAGETYPE_PNG  => @imagecreatefrompng($path),
+            IMAGETYPE_GIF  => @imagecreatefromgif($path),
+            IMAGETYPE_WEBP => @imagecreatefromwebp($path),
+            default        => false,
+        };
+    }
+}