WordPress resize image on the fly

hello_resize_image.php

/**
 * @param $attach_id
 * @param $width
 * @param $height
 * @param bool $crop
 *
 * @return false|array Returns an array (url, width, height, is_intermediate), or false, if no image is available.
 */

function hello_image_resize( $attach_id, $width, $height, $crop = false ) {

	/**
	 * wrong attachment id
	 */

	if ( 'attachment' != get_post_type( $attach_id ) ) {
		return false;
	}

	$width  = intval( $width );
	$height = intval( $height );

	$src_img       = wp_get_attachment_image_src( $attach_id, 'full' );
	$src_img_ratio = $src_img[1] / $src_img[2];
	$src_img_path  = get_attached_file( $attach_id );

	/**
	 * error: somehow file does not exist ¯\_(ツ)_/¯
	 */

	if ( ! file_exists( $src_img_path ) ) {
		return false;
	}

	$src_img_info = pathinfo( $src_img_path );

	if ( $crop ) {
		$new_width  = $width;
		$new_height = $height;
	} elseif ( $width / $height <= $src_img_ratio ) {
		$new_width  = $width;
		$new_height = 1 / $src_img_ratio * $width;
	} else {
		$new_width  = $height * $src_img_ratio;
		$new_height = $height;
	}

	$new_width  = round( $new_width );
	$new_height = round( $new_height );

	/**
	 * return the source image if the requested is bigger than the original image
	 */

	if ( $new_width > $src_img[1] || $new_height > $src_img[2] ) {
		return $src_img;
	}

	$new_img_path = "{$src_img_info['dirname']}/{$src_img_info['filename']}-{$new_width}x{$new_height}.{$src_img_info['extension']}";
	$new_img_url  = str_replace( trailingslashit( ABSPATH ), trailingslashit( get_home_url() ), $new_img_path );

	/**
	 * return if already exists
	 */

	if ( file_exists( $new_img_path ) ) {
		return [
			$new_img_url,
			$new_width,
			$new_height,
		];
	}

	/**
	 * crop, save and return image
	 */

	$image = wp_get_image_editor( $src_img_path );
	if ( ! is_wp_error( $image ) ) {
		$image->resize( $width, $height, $crop );
		$image->save( $new_img_path );

		return [
			$new_img_url,
			$new_width,
			$new_height,
		];
	}

	return false;
}