ckgpt-1.0.0-alpha1/src/Form/CkGptSettingsForm.php

<?php
namespace Drupal\ckgpt\Form;

use Drupal\Core\Form\ConfigFormBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Class CkGptSettingsForm.
 */
class CkGptSettingsForm extends ConfigFormBase {

  /**
   * {@inheritdoc}
   */
  protected function getEditableConfigNames() {
    return [
      'ckgpt.settings',
    ];
  }

  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'ckgpt_settings_form';
  }

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $config = $this->config('ckgpt.settings');

    $form['openai_api_key'] = [
      '#type' => 'textfield',
      '#title' => $this->t('OpenAI API Key'),
      '#description' => $this->t('Enter the API key for accessing the OpenAI API.'),
      '#default_value' => $config->get('openai_api_key'),
      '#required' => TRUE,
    ];

    return parent::buildForm($form, $form_state);
  }

  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $values = $form_state->getValues();
    $this->config('ckgpt.settings')
      ->set('openai_api_key', $values['openai_api_key'])
      ->save();
    parent::submitForm($form, $form_state);
  }

}