from django.conf import settings
from rest_framework import permissions
from rest_framework.exceptions import PermissionDenied
from django.http import Http404


class ApiKeyHeaderPermission(permissions.BasePermission):
    def has_permission(self, request, view):
        """
        Check for permissions by matching the configured API key and header

        If settings.DEBUG is True and settings.EDX_API_KEY is not set or None,
        then allow the request. Otherwise, allow the request if and only if
        settings.EDX_API_KEY is set and the X-Edx-Api-Key HTTP header is
        present in the request and matches the setting.
        """
        api_key = getattr(settings, "EDX_API_KEY", None)
        return (
            (settings.DEBUG and api_key is None) or
            (api_key is not None and request.META.get("HTTP_X_EDX_API_KEY") == api_key)
        )


class IsAuthenticatedOrDebug(permissions.BasePermission):
    """
    Allows access only to authenticated users, or anyone if debug mode is enabled.
    """

    def has_permission(self, request, view):
        if settings.DEBUG:
            return True

        user = getattr(request, 'user', None)
        return user and user.is_authenticated()


class IsUserInUrl(permissions.BasePermission):
    """
    Permission that checks to see if the request user matches the user in the URL.
    """
    def has_permission(self, request, view):
        # Return a 404 instead of a 403 (Unauthorized). If one user is looking up
        # other users, do not let them deduce the existence of an account.
        if request.user.username != request.parser_context.get('kwargs', {}).get('username', None):
            raise Http404()
        return True


class IsUserInUrlOrStaff(IsUserInUrl):
    """
    Permission that checks to see if the request user matches the user in the URL or has is_staff access.
    """
    def has_permission(self, request, view):
        if request.user.is_staff:
            return True

        return super(IsUserInUrlOrStaff, self).has_permission(request, view)