from django.core.exceptions import PermissionDenied
from django.http import HttpResponse
from django.shortcuts import get_object_or_404

from wagtail.models import Page


def set_page_position(request, page_to_move_id):
    page_to_move = get_object_or_404(Page, id=page_to_move_id)
    parent_page = page_to_move.get_parent()

    if not parent_page.permissions_for_user(request.user).can_reorder_children():
        raise PermissionDenied

    if request.method == "POST":
        # Get position parameter
        position = request.GET.get("position", None)

        # Find page that's already in this position
        position_page = None
        if position is not None:
            try:
                position_page = parent_page.get_children()[int(position)]
            except (IndexError, ValueError):
                pass  # No page in this position

        # Move page

        # any invalid moves *should* be caught by the permission check above,
        # so don't bother to catch InvalidMoveToDescendant

        if position_page:
            # If the page has been moved to the right, insert it to the
            # right. If left, then left.
            old_position = list(parent_page.get_children()).index(page_to_move)
            if int(position) < old_position:
                page_to_move.move(position_page, pos="left", user=request.user)
            elif int(position) > old_position:
                page_to_move.move(position_page, pos="right", user=request.user)
        else:
            # Move page to end
            page_to_move.move(parent_page, pos="last-child", user=request.user)

    return HttpResponse("")
