Add warning to Export page

lib/Subscribers/ImportExport/ImportExportFactory.php

@@ -150,6 +150,7 @@ class ImportExportFactory {
       $data['maxPostSizeBytes'] = Helpers::getMaxPostSize('bytes');
       $data['maxPostSize'] = Helpers::getMaxPostSize();
     }
+    $data['zipExtensionLoaded'] = extension_loaded('zip');
     return $data;
   }
 }

views/subscribers/importExport/export.html

@@ -6,6 +6,11 @@
     <%= __('Export') %>
     <a class="page-title-action" href="?page=mailpoet-subscribers#/"><%= __('Back to Subscribers') %></a>
   </h1>
+  <%if not zipExtensionLoaded %>
+    <div class="error">
+      <p><%= __('ZIP extension is required to create Excel files. Please refer to the [link]official PHP ZIP installation guide[/link] or contact your hosting provider’s technical support for instructions on how to install and load the ZIP extension.' | replaceLinkTags('http://php.net/manual/en/zip.installation.php')) %></p>
+    </div>
+  <%endif%>
   <% if segments is empty %>
   <div class="error">
     <p><%= __("Yikes! Couldn't find any subscribers") %></p>
@@ -72,7 +77,7 @@
         &nbsp;
         <label>
           <input type="radio" name="option_format"
-           value="xlsx"><%= __('Excel file') %>
+           value="xlsx" <%if not zipExtensionLoaded %> disabled="disabled" <%endif%>><%= __('Excel file') %>
         </label>
       </td>
     </tr>