def generate_url(request, image_id, filter_spec):
    # Get the image
    Image = get_image_model()
    try:
        image = Image.objects.get(id=image_id)
    except Image.DoesNotExist:
        return JsonResponse({"error": "Cannot find image."}, status=404)

    # Check if this user has edit permission on this image
    if not permission_policy.user_has_permission_for_instance(request.user, "change", image):
        return JsonResponse({"error": "You do not have permission to generate a URL for this image."}, status=403)

    # Parse the filter spec to make sure its valid
    try:
        Filter(spec=filter_spec).operations
    except InvalidFilterSpecError:
        return JsonResponse({"error": "Invalid filter spec."}, status=400)

    # Generate url
    signature = generate_signature(image_id, filter_spec)
    url = reverse("wagtailimages_serve", args=(signature, image_id, filter_spec))

    # Get site root url
    try:
        site_root_url = Site.objects.get(is_default_site=True).root_url
    except Site.DoesNotExist:
        site_root_url = Site.objects.first().root_url

    # Generate preview url
    preview_url = reverse("wagtailimages:preview", args=(image_id, filter_spec))

    return JsonResponse({"url": site_root_url + url, "preview_url": preview_url}, status=200)

def edit(request, image_id, callback=None):
    Image = get_image_model()
    ImageForm = get_image_edit_form(Image)

    image = get_object_or_404(Image, id=image_id)

    if not request.is_ajax():
        return HttpResponseBadRequest("Cannot POST to this view without AJAX")

    if not permission_policy.user_has_permission_for_instance(request.user, 'change', image):
        raise PermissionDenied

    form = ImageForm(request.POST, request.FILES, instance=image, prefix='image-' + image_id)

    if form.is_valid():
        form.save()

        # Reindex the image to make sure all tags are indexed
        for backend in get_search_backends():
            backend.add(image)

        return JsonResponse({
            'success': True,
            'image_id': int(image_id),
        })
    else:
        return JsonResponse({
            'success': False,
            'image_id': int(image_id),
            'form': render_to_string('wagtailimages/multiple/edit_form.html', {
                'image': image,
                'form': form,
            }, request=request),
        })

def url_generator(request, image_id):
    image = get_object_or_404(get_image_model(), id=image_id)

    if not permission_policy.user_has_permission_for_instance(request.user, "change", image):
        return permission_denied(request)

    form = URLGeneratorForm(initial={"filter_method": "original", "width": image.width, "height": image.height})

    return render(request, "wagtailimages/images/url_generator.html", {"image": image, "form": form})

def delete(request, image_id):
    image = get_object_or_404(get_image_model(), id=image_id)

    if not permission_policy.user_has_permission_for_instance(request.user, "delete", image):
        return permission_denied(request)

    if request.POST:
        image.delete()
        messages.success(request, _("Image '{0}' deleted.").format(image.title))
        return redirect("wagtailimages:index")

    return render(request, "wagtailimages/images/confirm_delete.html", {"image": image})

def delete(request, image_id):
    image = get_object_or_404(get_image_model(), id=image_id)

    if not request.is_ajax():
        return HttpResponseBadRequest("Cannot POST to this view without AJAX")

    if not permission_policy.user_has_permission_for_instance(request.user, 'delete', image):
        raise PermissionDenied

    image.delete()

    return JsonResponse({
        'success': True,
        'image_id': int(image_id),
    })

def url_generator(request, image_id):
    image = get_object_or_404(get_image_model(), id=image_id)

    if not permission_policy.user_has_permission_for_instance(request.user, 'change', image):
        return permission_denied(request)

    form = URLGeneratorForm(initial={
        'filter_method': 'original',
        'width': image.width,
        'height': image.height,
    })

    return render(request, "wagtailimages/images/url_generator.html", {
        'image': image,
        'form': form,
    })

def delete(request, image_id):
    image = get_object_or_404(get_image_model(), id=image_id)

    if not permission_policy.user_has_permission_for_instance(request.user, 'delete', image):
        return permission_denied(request)

    if image.folder:
        parent_folder = image.folder
    else:
        parent_folder = False

    if request.method == 'POST':
        image.delete()
        messages.success(request, _("Image '{0}' deleted.").format(image.title))
        response = redirect('wagtailimages:index')

        if parent_folder:
            response['Location'] += '?folder={0}'.format(parent_folder.id)
        return response

    return render(request, "wagtailimages/images/confirm_delete.html", {
        'image': image,
    })

 def is_editable_by_user(self, user):
     from wagtail.wagtailimages.permissions import permission_policy
     return permission_policy.user_has_permission_for_instance(user, 'change', self)

def edit(request, image_id):
    Image = get_image_model()
    ImageForm = get_image_form(Image)

    image = get_object_or_404(Image, id=image_id)

    if not permission_policy.user_has_permission_for_instance(request.user, 'change', image):
        return permission_denied(request)

    if request.method == 'POST':
        original_file = image.file
        form = ImageForm(request.POST, request.FILES, instance=image, user=request.user)
        if form.is_valid():
            if 'file' in form.changed_data:
                # if providing a new image file, delete the old one and all renditions.
                # NB Doing this via original_file.delete() clears the file field,
                # which definitely isn't what we want...
                original_file.storage.delete(original_file.name)
                image.renditions.all().delete()

                # Set new image file size
                image.file_size = image.file.size

            form.save()

            # Reindex the image to make sure all tags are indexed
            for backend in get_search_backends():
                backend.add(image)

            messages.success(request, _("Image '{0}' updated.").format(image.title), buttons=[
                messages.button(reverse('wagtailimages:edit', args=(image.id,)), _('Edit again'))
            ])
            return redirect('wagtailimages:index')
        else:
            messages.error(request, _("The image could not be saved due to errors."))
    else:
        form = ImageForm(instance=image, user=request.user)

    # Check if we should enable the frontend url generator
    try:
        reverse('wagtailimages_serve', args=('foo', '1', 'bar'))
        url_generator_enabled = True
    except NoReverseMatch:
        url_generator_enabled = False

    if image.is_stored_locally():
        # Give error if image file doesn't exist
        if not os.path.isfile(image.file.path):
            messages.error(request, _(
                "The source image file could not be found. Please change the source or delete the image."
            ).format(image.title), buttons=[
                messages.button(reverse('wagtailimages:delete', args=(image.id,)), _('Delete'))
            ])

    return render(request, "wagtailimages/images/edit.html", {
        'image': image,
        'form': form,
        'url_generator_enabled': url_generator_enabled,
        'filesize': image.get_file_size(),
        'user_can_delete': permission_policy.user_has_permission_for_instance(
            request.user, 'delete', image
        ),
    })