"""An avatar service used as a fallback to show something basic for a user."""

from django.template.loader import render_to_string
from django.utils.translation import gettext_lazy as _

from djblets.avatars.services.base import AvatarService


class FallbackService(AvatarService):
    """An avatar service used as a fallback.

    This will display a simple avatar showing the first two characters of the
    user's username, displayed on top of a background with a color based on the
    username.

    This will automatically be used as a fallback if no other avatar backends
    are usable for the user.
    """

    avatar_service_id = 'fallback'
    name = _('Fallback')
    template_name = 'avatars/fallback.html'
    hidden = True

    def render(self, request, user, size, template_name=None):
        """Render a user's avatar to HTML.

        Args:
            request (django.http.HttpRequest):
                The HTTP request.

            user (django.contrib.auth.models.User):
                The user for whom the avatar is to be rendered.

            size (int):
                The requested avatar size (height and width) in pixels.

            template_name (unicode, optional):
                The name of the template to use for rendering.

        Returns:
            django.utils.safestring.SafeText:
            The rendered avatar HTML.
        """
        return render_to_string(template_name or self.template_name, {
            'bg': self.get_bg_color(user),
            'font_size': '%spx' % (size // 3),
            'size': size,
            'text': user.username[:2].upper(),
            'user': user,
        })

    def get_bg_color(self, user):
        """Return a background color for the avatar.

        This will compute a basic HSL color for the avatar, based on the
        username.

        Args:
            user (django.contrib.auth.models.User):
                The user to generate the color for.

        Returns:
            unicode:
            The resulting HSL color definition.
        """
        i = 0

        for c in user.username:
            i = ord(c) + ((i << 5) - i)

        i = i % 360

        return 'hsl(%s, 60%%, 80%%)' % i

    def get_avatar_urls_uncached(self, user, size):
        """Return the Gravatar URLs for the requested user.

        Args:
            user (django.contrib.auth.models.User):
                The user whose avatar URLs are to be fetched.

            size (int):
                The size (in pixels) the avatar is to be rendered at.

        Returns
            dict:
            A dictionary containing the URLs of the user's avatars at normal-
            and high-DPI.
        """
        return {
            '1x': '',
            '2x': '',
            '3x': '',
        }

    def get_etag_data(self, user):
        """Return the ETag data for the user's avatar.

        Args:
            user (django.contrib.auth.models.User):
                The user.

        Returns:
            list of unicode:
            The uniquely identifying information for the user's avatar.
        """
        return [self.avatar_service_id, user.username]
