str_replace doesn't replace accurately - php

Question

I am working on a multilingual wordpress website where I need to append a loclale in all internal url in a web page.
So I have all of the content of the webpage in the $content variable. now
preg_match_all( '/<a\s+(?:[^>]*?\s+)?href=([\"\'])(.*?)\1/', $content, $matches );
$localized_url_arr = [];
$url_arr = [];
if ( ! empty( $matches[2] ) ) {
$current_locale = get_current_locale();
foreach ( $matches[2] as $url ) {
if ( preg_match( '/\b[A-Z0-9._%+-]+#[A-Z0-9.-]+\.[A-Z]{2,4}\b/si', $url ) ) {
continue;
}
$new_url = add_locale_to_url( $url, $current_locale ); // this is adding locale to url eg => www.example.com --> www.example.com/us for us locale
if ( $new_url !== $url ) {
$localized_url_arr[] = [
$url => $new_url
];
}
}
}
$arr = array_merge(...$localized_url_arr);
$content = str_replace( array_keys($arr), array_values($arr), $content );
now Ideally this function should replace those to those urls which dosen;t have a locale in them. but it is appending locale in all the url, however the $arr has only those urls which needs to be appended with a locale but my str_replace is appending all urls that we have in matches[2] array.

Answer 1

When you replace www.example.com with www.example.com/us, it will replace it anywhere it appears, even if there's already /us after it.
You can use a regular expression with a negative lookahead to replace a string only if it's not followed by some other pattern.
preg_match_all( '/<a\s+(?:[^>]*?\s+)?href=([\"\'])(.*?)\1/', $content, $matches );
$localized_url_arr = [];
if ( ! empty( $matches[2] ) ) {
$current_locale = get_current_locale();
foreach ( $matches[2] as $url ) {
if ( preg_match( '/\b[A-Z0-9._%+-]+#[A-Z0-9.-]+\.[A-Z]{2,4}\b/si', $url ) ) {
continue;
}
$new_url = add_locale_to_url( $url, $current_locale ); // this is adding locale to url eg => www.example.com --> www.example.com/us for us locale
$url_pattern = "#$url(?!/us/#si";
if ( $new_url !== $url ) {
$localized_url_arr[$url] = $new_url
}
}
$content = preg_replace(array_keys($localized_url_arr), array_values($localized_url_arr), $content );
}
The regular expression matches each URL unless it's followed by /us/, and will replace it with $new_url.