Generates an excerpt from the content, if needed.

Returns a maximum of 55 words with an ellipsis appended if necessary.

The 55 word limit can be modified by plugins/themes using the {@see ‘excerpt_length’} filter
The ‘ […]’ string can be modified by plugins/themes using the {@see ‘excerpt_more’} filter

function wp_trim_excerpt( $text = '', $post = null ) {
	$raw_excerpt = $text;

	if ( '' === trim( $text ) ) {
		$post = get_post( $post );
		$text = get_the_content( '', false, $post );

		$text = strip_shortcodes( $text );
		$text = excerpt_remove_blocks( $text );

		/** This filter is documented in wp-includes/post-template.php */
		$text = apply_filters( 'the_content', $text );
		$text = str_replace( ']]>', ']]>', $text );

		/* translators: Maximum number of words used in a post excerpt. */
		$excerpt_length = (int) _x( '55', 'excerpt_length' );

		/**
		 * Filters the maximum number of words in a post excerpt.
		 *
		 * @since 2.7.0
		 *
		 * @param int $number The maximum number of words. Default 55.
		 */
		$excerpt_length = (int) apply_filters( 'excerpt_length', $excerpt_length );

		/**
		 * Filters the string in the "more" link displayed after a trimmed excerpt.
		 *
		 * @since 2.9.0
		 *
		 * @param string $more_string The string shown within the more link.
		 */
		$excerpt_more = apply_filters( 'excerpt_more', ' ' . '[…]' );
		$text         = wp_trim_words( $text, $excerpt_length, $excerpt_more );
	}

	/**
	 * Filters the trimmed excerpt string.
	 *
	 * @since 2.8.0
	 *
	 * @param string $text        The trimmed text.
	 * @param string $raw_excerpt The text prior to trimming.
	 */
	return apply_filters( 'wp_trim_excerpt', $text, $raw_excerpt );
}