MDL-42671 EditPDF: Disable EditPDF is zlib is not available

Also put a warning on the admin page if this is the case.

lib/adminlib.php

@@ -8553,3 +8553,68 @@ class admin_setting_configmultiselect_modules extends admin_setting_configmultis
         return true;
     }
 }
+
+/**
+ * Admin setting to show if a php extension is enabled or not.
+ *
+ * @copyright 2013 Damyon Wiese
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class admin_setting_php_extension_enabled extends admin_setting {
+
+    /** @var string The name of the extension to check for */
+    private $extension;
+
+    /**
+     * Calls parent::__construct with specific arguments
+     */
+    public function __construct($name, $visiblename, $description, $extension) {
+        $this->extension = $extension;
+        $this->nosave = true;
+        parent::__construct($name, $visiblename, $description, '');
+    }
+
+    /**
+     * Always returns true, does nothing
+     *
+     * @return true
+     */
+    public function get_setting() {
+        return true;
+    }
+
+    /**
+     * Always returns true, does nothing
+     *
+     * @return true
+     */
+    public function get_defaultsetting() {
+        return true;
+    }
+
+    /**
+     * Always returns '', does not write anything
+     *
+     * @return string Always returns ''
+     */
+    public function write_setting($data) {
+        // Do not write any setting.
+        return '';
+    }
+
+    /**
+     * Outputs the html for this setting.
+     * @return string Returns an XHTML string
+     */
+    public function output_html($data, $query='') {
+        global $OUTPUT;
+
+        $o = '';
+        if (!extension_loaded($this->extension)) {
+            $warning = $OUTPUT->pix_icon('i/warning', '', '', array('role' => 'presentation')) . ' ' . $this->description;
+
+            $o .= format_admin_setting($this, $this->visiblename, $warning);
+        }
+        return $o;
+    }
+}

mod/assign/feedback/editpdf/lang/en/assignfeedback_editpdf.php

@@ -89,3 +89,5 @@ $string['unsavedchanges'] = 'Unsaved changes';
 $string['viewfeedbackonline'] = 'View annotated pdf...';
 $string['white'] = 'White';
 $string['yellow'] = 'Yellow';
+$string['zlibenabled'] = 'zlib enabled';
+$string['zlibnotavailable'] = 'Php extension "zlib" is not available. The annotate PDF feature relies on this php extension and will be disabled until zlib is installed and enabled.';

mod/assign/feedback/editpdf/locallib.php

@@ -266,6 +266,9 @@ class assign_feedback_editpdf extends assign_feedback_plugin {
      */
     public function is_enabled() {
         $testpath = assignfeedback_editpdf\pdf::test_gs_path();
+        if (!extension_loaded('zlib')) {
+            return false;
+        }
         if ($testpath->status == assignfeedback_editpdf\pdf::GSPATH_OK) {
             return true;
         }

mod/assign/feedback/editpdf/settings.php

@@ -36,7 +36,15 @@ $settings->add($setting);
 // Ghostscript setting.
 $settings->add(new admin_setting_configexecutable('assignfeedback_editpdf/gspath',
                                                   get_string('gspath', 'assignfeedback_editpdf'),
-                                            get_string('gspath_help', 'assignfeedback_editpdf'), '/usr/bin/gs'));
+                                                  get_string('gspath_help', 'assignfeedback_editpdf'),
+                                                  '/usr/bin/gs'));
+
+$setting = new admin_setting_php_extension_enabled('assignfeedback_editpdf/zlibenabled',
+                                                   get_string('zlibenabled', 'assignfeedback_editpdf'),
+                                                   get_string('zlibnotavailable', 'assignfeedback_editpdf'),
+                                                   'zlib');
+
+$settings->add($setting);
 
 $url = new moodle_url('/mod/assign/feedback/editpdf/testgs.php');
 $link = html_writer::link($url, get_string('testgs', 'assignfeedback_editpdf'));