class ImageStyleMappings

class ImageStyleMappings extends ProcessPluginBase {
    
    /**
     * {@inheritdoc}
     */
    public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
        if (!is_array($value)) {
            throw new MigrateException('Input should be an array');
        }
        [
            $mappings,
            $breakpoint_group,
        ] = $value;
        $new_value = [];
        foreach ($mappings as $mapping_id => $mapping) {
            // The id is in the key with the form
            // "breakpoints.theme.my_theme_id.image_style_machine_name". We want the
            // identifier after the last period.
            preg_match('/\\.([a-z0-9_]+)$/', $mapping_id, $matches);
            foreach ($mapping as $multiplier => $multiplier_settings) {
                if ($multiplier_settings['mapping_type'] == '_none') {
                    continue;
                }
                $image_style = [
                    'breakpoint_id' => $breakpoint_group . '.' . $matches[1],
                    'multiplier' => $multiplier,
                    'image_mapping_type' => $multiplier_settings['mapping_type'],
                    'image_mapping' => $this->getMultiplierSettings($multiplier_settings),
                ];
                $new_value[] = $image_style;
            }
        }
        return $new_value;
    }
    
    /**
     * Extracts multiplier settings based on its type.
     *
     * @param array[] $multiplier_settings
     *   The multiplier settings.
     *
     * @return array
     *   The multiplier settings.
     */
    protected function getMultiplierSettings(array $multiplier_settings) {
        $settings = [];
        if ($multiplier_settings['mapping_type'] == 'image_style') {
            $settings = $multiplier_settings['image_style'];
        }
        elseif ($multiplier_settings['mapping_type'] == 'sizes') {
            $settings = [
                'sizes' => $multiplier_settings['sizes'],
                'sizes_image_styles' => array_values($multiplier_settings['sizes_image_styles']),
            ];
        }
        return $settings;
    }

}