from flask import request, current_app, url_for
from urllib.parse import urlsplit, urlunsplit


def prefixed_url_for(endpoint, **values):
    prefix = request.headers.get('X-Forwarded-Prefix', '')
    scheme = request.headers.get('X-Forwarded-Proto', request.scheme)
    host = request.headers.get('Host', request.host)

    external = values.pop('_external', False)
    generated_url = url_for(endpoint, **values)

    if external:
        path, query, fragment = urlsplit(generated_url)[2:5]
        # Check if the prefix is already present in the path
        if prefix and not path.startswith(prefix):
            new_path = prefix + path
        else:
            new_path = path
        return urlunsplit((scheme, host, new_path, query, fragment))
    else:
        # Check if the prefix is already present in the generated URL
        if prefix and not generated_url.startswith(prefix):
            return prefix + generated_url
        else:
            return generated_url