Config form from schema

mymodule.schema.yml

block.settings.mymodule_my_schema_form_block:
  type: block_settings
  label: 'MySchemaFormBlock block settings'
  mapping:
    svcid:
      type: string
      label: 'Service ID'
      constraints:
        Regex:
          pattern: '/^[a-zA-Z0-9_\-]+$/'
          message: "The Service ID can only contain simple letters, numbers, underscores or hyphens."
      # The following two properties are custom.
      default: 'abcde'
      locked: true
    envid:
      type: string
      label: 'Environment ID'
      constraints:
        Regex:
          pattern: '/^[a-zA-Z0-9_\-]+$/'
          message: "The Environment ID can only contain simple letters, numbers, underscores or hyphens."
      # This is a custom property.
      default: 'x-j9WsahRe_1An51DhErab-C'

MySchemaFormBlock.php

<?php

namespace Drupal\MYMODULE\Plugin\Block;

use Drupal\Core\Block\Attribute\Block;
use Drupal\Core\Block\BlockBase;
use Drupal\Core\Config\TypedConfigManagerInterface;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
use Drupal\Core\StringTranslation\TranslatableMarkup;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
 * Provides a 'MySchemaFormBlock' embed widget block.
 */
#[Block(
  id: "mymodule_my_schema_form_block",
  admin_label: new TranslatableMarkup("MyBlock embed widget")
)]
class MySchemaFormBlock extends BlockBase implements ContainerFactoryPluginInterface {

  /**
   * The typed config manager.
   *
   * @var \Drupal\Core\Config\TypedConfigManagerInterface
   */
  protected $typedConfigManager;

  /**
   * Constructs a new MySchemaFormBlock.
   *
   * @param array $configuration
   *   A configuration array containing information about the plugin instance.
   * @param string $plugin_id
   *   The plugin ID for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\Core\Config\TypedConfigManagerInterface $typed_config_manager
   *   The typed config manager.
   */
  public function __construct(
    array $configuration,
    $plugin_id,
    $plugin_definition,
    TypedConfigManagerInterface $typed_config_manager
  ) {
    // Typed config manager must be set first, because the parent constructor
    // will set configuration, which involves pulling defaults from the schema.
    $this->typedConfigManager = $typed_config_manager;
    parent::__construct($configuration, $plugin_id, $plugin_definition);
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static(
      $configuration,
      $plugin_id,
      $plugin_definition,
      $container->get('config.typed')
    );
  }

  /**
   * Return the configurable parameters for this donation widget.
   */
  protected function getConfigurables(): array {
    $specific_schema = $this->typedConfigManager->getDefinition('block.settings.' . $this->getBaseId());
    $parent_schema = $this->typedConfigManager->getDefinition('block_settings');
    $own_properties = array_diff_key(
      $specific_schema['mapping'],
      $parent_schema['mapping']
    );
    return $own_properties;
  }

  /**
   * {@inheritdoc}
   */
  public function defaultConfiguration() {
    return [
      'label_display' => FALSE,
    ] + array_map(function ($schema_info) {
      return $schema_info['default'] ?? NULL;
    }, $this->getConfigurables());
  }

  /**
   * {@inheritdoc}
   */
  public function blockForm($form, FormStateInterface $form_state) {
    foreach ($this->getConfigurables() as $key => $schema_info) {
      $form[$key] = [
        // Explicit support for certain types only. This is a bit like what
        // config_translation_config_schema_info_alter() helps achieve.
        '#type' => match ($schema_info['type']) {
          'string', 'label' => 'textfield',
          'text' => 'textarea',
          'boolean' => 'checkbox',
          'integer', 'float' => 'number',
          'email' => 'email',
        },
        '#title' => $schema_info['label'],
        '#default_value' => $this->configuration[$key],
        '#required' => empty($schema_info['nullable']),
        // The 'locked' property is not specified in core.
        '#disabled' => $schema_info['locked'] ?? FALSE,
      ];

      // Convert general regex in schema into whole-string regex for HTML.
      if (!empty($schema_info['constraints']['Regex']['pattern'])) {
        $pattern = $schema_info['constraints']['Regex']['pattern'];
        // Extract the pattern within delimiters, ignore any regex modifiers,
        // and strip off string start & end characters. The HTML pattern spec
        // does not cater for any of these.
        $delimiter = $pattern[0];
        $last_delimiter_position = strrpos($pattern, $delimiter);
        $pattern = substr($pattern, 1, $last_delimiter_position - 1);
        if (str_starts_with($pattern, '^')) {
          $pattern = substr($pattern, 1);
        }
        if (
          str_ends_with($pattern, '$') &&
          // Some basic detection of escaped dollar signs at the end.
          (!str_ends_with($pattern, '\$') || str_ends_with($pattern, '\\\\\$'))
        ) {
          $pattern = substr($pattern, 0, -1);
        }
        $form[$key]['#pattern'] = $pattern;

        if (!empty($schema_info['constraints']['Regex']['message'])) {
          $form[$key]['#attributes']['title'] = $schema_info['constraints']['Regex']['message'];
        }
      }
    }

    return $form;
  }

  /**
   * {@inheritdoc}
   */
  public function blockSubmit($form, FormStateInterface $form_state) {
    foreach (array_keys($this->getConfigurables()) as $key) {
      $this->configuration[$key] = $form_state->getValue($key);
    }
  }

  /**
   * {@inheritdoc}
   */
  public function build() {
    foreach ($this->getConfigurables() as $key => $schema_info) {
      $params[$key] = $this->configuration[$key] ?? $schema_info['default'] ?? '';
    }

    // Double-check parameters are safe (though this should have been enforced
    // by the config schema).
    $params = array_map(function ($value) {
      return preg_replace('/[^a-zA-Z0-9_-]/', '', $value);
    }, $params);

    $build = [
      'placeholder' => [
        '#type' => 'container',
      ],
      'loader' => [
        '#type' => 'html_tag',
        '#tag' => 'script',
        '#attributes' => [
          'src' => 'https://example.com/embed-script-thing.js',
        ],
      ],
    ];

    $imploded_params = "'" . implode("', '", $params) . "'";
    $build['initialiser'] = [
      '#type' => 'html_tag',
      '#tag' => 'script',
      '#value' => 'SomeGlobal.someMethod(' . $imploded_params . ')',
    ];

    return $build;
  }

}