locale_translation_context.module

<?php

/**
 * @file
 * Contains hooks for the Locale Translation Context module.
 */

use Drupal\Component\Gettext\PoStreamWriter;
use Drupal\Core\Database\Database;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Language\LanguageInterface;
use Drupal\locale_translation_context\PoDatabaseReader;
use Symfony\Component\HttpFoundation\BinaryFileResponse;

/**
 * Implements hook_form_FORM_ID_alter().
 */
function locale_translation_context_form_locale_translate_export_form_alter(&$form, FormStateInterface $form_state) {

  $form['context'] = [
    '#title' => t("Context"),
    '#type' => 'select',
    '#options' => locale_translation_context_get_context_options(),
    '#empty_option' => t('All contexts'),
  ];

  // Change the form's submit function.
  $original_submit_function_key = array_search('::submitForm', $form['#submit']);
  $form['#submit'][$original_submit_function_key] = 'locale_translation_context_export_form_submit';
}

/**
 * Get the available context list.
 *
 * @return array
 *   Array of the available contexts.
 */
function locale_translation_context_get_context_options() {
  $context_options = [];

  $connection = Database::getConnection();
  $data = $connection->select('locales_source', 'ls');
  $data->fields('ls', ['context']);
  $data->isNotNull('context');
  $data->groupBy('context');
  $data->orderBy('context');
  $results = $data->execute();

  foreach ($results as $result) {
    if (!empty($result->context)) {
      $context_options[$result->context] = $result->context;
    }
  }

  return $context_options;
}

/**
 * Alters the Drupal\locale\Form\ExportForm submitForm method.
 *
 * @param array $form
 *   Contains the form array.
 * @param \Drupal\Core\Form\FormStateInterface $form_state
 *   Form state object.
 */
function locale_translation_context_export_form_submit(array &$form, FormStateInterface $form_state) {
  // If template is required, language code is not given.
  if ($form_state->getValue('langcode') != LanguageInterface::LANGCODE_SYSTEM) {
    $language = \Drupal::languageManager()->getLanguage($form_state->getValue('langcode'));
  }
  else {
    $language = NULL;
  }
  $content_options = $form_state->getValue('content_options', []);
  $context = $form_state->getValue('context');
  $reader = new PoDatabaseReader();
  $language_name = '';
  if ($language != NULL) {
    $reader->setLangcode($language->getId());
    $reader->setOptions($content_options);
    $languages = \Drupal::languageManager()->getLanguages();
    $language_name = isset($languages[$language->getId()]) ? $languages[$language->getId()]->getName() : '';
    $filename = $language->getId() . '.po';
  }
  else {
    // Template required.
    $filename = 'drupal.pot';
  }

  // Set context option.
  if (!empty($context)) {
    $options = $reader->getOptions();
    $options['context'] = $context;
    $reader->setOptions($options);
  }

  $item = $reader->readItem();
  if (!empty($item)) {
    $uri = \Drupal::service('file_system')->tempnam('temporary://', 'po_');
    $header = $reader->getHeader();
    $header->setProjectName(\Drupal::config('system.site')->get('name'));
    $header->setLanguageName($language_name);

    $writer = new PoStreamWriter();
    $writer->setURI($uri);
    $writer->setHeader($header);

    $writer->open();
    $writer->writeItem($item);
    $writer->writeItems($reader);
    $writer->close();

    $response = new BinaryFileResponse($uri);
    $response->setContentDisposition('attachment', $filename);
    $form_state->setResponse($response);
  }
  else {
    \Drupal::messenger()->addStatus(t('Nothing to export.'));
  }
}