Issue #3452355 by andileco: Make filter selector and sort selector based on the headers

Closes #3452355

src/Plugin/views/filter/ViewsCsvFilter.php

@@ -4,6 +4,7 @@ namespace Drupal\views_csv_source\Plugin\views\filter;
 
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\views\Plugin\views\filter\FilterPluginBase;
+use Drupal\views_csv_source\Plugin\views\query\ViewsCsvQuery;
 
 /**
  * Base filter handler for views_csv_source.
@@ -223,10 +224,22 @@ class ViewsCsvFilter extends FilterPluginBase {
     $form['key'] = [
       '#title' => $this->t('Column Selector'),
       '#description' => $this->t('Choose a column'),
-      '#type' => 'textfield',
       '#default_value' => $this->options['key'],
       '#required' => TRUE,
     ];
+    // Get the query.
+    $query = $this->view->query;
+    assert($query instanceof ViewsCsvQuery, 'Query must be of type ViewsCsvQuery');
+
+    // Ensure the query is of the correct type.
+    if ($headers = $query->getCsvHeader()) {
+      $form['key']['#type'] = 'select';
+      $form['key']['#options'] = array_combine($headers, $headers);
+    }
+    else {
+      // Fall back to text value if CSV has not been selected.
+      $form['key']['#type'] = 'textfield';
+    }
   }
 
   /**