traverse_and_serialize_blocks

WordPress Version: 6.4

/**
 * Given an array of parsed block trees, applies callbacks before and after serializing them and
 * returns their concatenated output.
 *
 * Recursively traverses the blocks and their inner blocks and applies the two callbacks provided as
 * arguments, the first one before serializing a block, and the second one after serializing.
 * If either callback returns a string value, it will be prepended and appended to the serialized
 * block markup, respectively.
 *
 * The callbacks will receive a reference to the current block as their first argument, so that they
 * can also modify it, and the current block's parent block as second argument. Finally, the
 * `$pre_callback` receives the previous block, whereas the `$post_callback` receives
 * the next block as third argument.
 *
 * Serialized blocks are returned including comment delimiters, and with all attributes serialized.
 *
 * This function should be used when there is a need to modify the saved blocks, or to inject markup
 * into the return value. Prefer `serialize_blocks` when preparing blocks to be saved to post content.
 *
 * This function is meant for internal use only.
 *
 * @since 6.4.0
 * @access private
 *
 * @see serialize_blocks()
 *
 * @param array[]  $blocks        An array of parsed blocks. See WP_Block_Parser_Block.
 * @param callable $pre_callback  Callback to run on each block in the tree before it is traversed and serialized.
 *                                It is called with the following arguments: &$block, $parent_block, $previous_block.
 *                                Its string return value will be prepended to the serialized block markup.
 * @param callable $post_callback Callback to run on each block in the tree after it is traversed and serialized.
 *                                It is called with the following arguments: &$block, $parent_block, $next_block.
 *                                Its string return value will be appended to the serialized block markup.
 * @return string Serialized block markup.
 */
function traverse_and_serialize_blocks($blocks, $pre_callback = null, $post_callback = null)
{
    $result = '';
    $parent_block = null;
    // At the top level, there is no parent block to pass to the callbacks; yet the callbacks expect a reference.
    foreach ($blocks as $index => $block) {
        if (is_callable($pre_callback)) {
            $prev = (0 === $index) ? null : $blocks[$index - 1];
            $result .= call_user_func_array($pre_callback, array(&$block, &$parent_block, $prev));
        }
        if (is_callable($post_callback)) {
            $next = (count($blocks) - 1 === $index) ? null : $blocks[$index + 1];
            $post_markup = call_user_func_array($post_callback, array(&$block, &$parent_block, $next));
        }
        $result .= traverse_and_serialize_block($block, $pre_callback, $post_callback);
        $result .= isset($post_markup) ? $post_markup : '';
    }
    return $result;
}