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

VISIBLE_PREFIXES = ('/admin', '/api', '/chat-client')

def _derive_visible_prefix():
    # 1) Edge-provided header (beste en meest expliciete bron)
    xfp = request.headers.get('X-Forwarded-Prefix')
    if xfp and any(xfp.startswith(p) for p in VISIBLE_PREFIXES):
        return xfp.rstrip('/')

    # 2) Referer fallback: haal het top-level segment uit de Referer path
    ref = request.headers.get('Referer') or ''
    try:
        ref_path = urlsplit(ref).path or ''
        m = re.match(r'^/(admin|api|chat-client)(?:\b|/)', ref_path)
        if m:
            return f"/{m.group(1)}"
    except Exception:
        pass

    # 3) Geen prefix bekend
    return ''


def prefixed_url_for(endpoint, **values):
    """
    Gedrag:
    - Default (_external=False, for_redirect=False): retourneer relatief pad (zonder leading '/')
      voor templates/JS. De dynamische <base> zorgt voor correcte resolutie onder het zichtbare prefix.
    - _external=True: bouw absolute URL (schema/host). Als X-Forwarded-Prefix aanwezig is,
      prefixeer de path daarmee (handig voor e-mails/deeplinks).
    - for_redirect=True: geef root-absoluut pad inclusief zichtbaar top-prefix, geschikt
      voor HTTP Location headers. Backwards compat: _as_location=True wordt behandeld als for_redirect.
    """
    external = values.pop('_external', False)
    # Backwards compatibility met oudere paramnaam
    if values.pop('_as_location', False):
        values['for_redirect'] = True
    for_redirect = values.pop('for_redirect', False)

    generated_url = url_for(endpoint, **values)      # bv. "/user/tenant_overview"
    path, query, fragment = urlsplit(generated_url)[2:5]

    if external:
        scheme = request.headers.get('X-Forwarded-Proto', request.scheme)
        host = request.headers.get('Host', request.host)
        xfp = request.headers.get('X-Forwarded-Prefix', '') or ''
        new_path = (xfp.rstrip('/') + path) if (xfp and not path.startswith(xfp)) else path
        return urlunsplit((scheme, host, new_path, query, fragment))

    if for_redirect:
        visible_prefix = _derive_visible_prefix()
        if visible_prefix and not path.startswith(visible_prefix):
            return f"{visible_prefix}{path}"
        # root-absoluut pad, zonder prefix als onbekend
        return path

    # Default: relatief pad
    return path[1:] if path.startswith('/') else path