"""
Helper functions for the accounts API.
"""
import hashlib

from django.conf import settings
from django.core.exceptions import ObjectDoesNotExist
from django.core.files.storage import get_storage_class
from staticfiles.storage import staticfiles_storage

from microsite_configuration import microsite

from student.models import UserProfile
from ..errors import UserNotFound


PROFILE_IMAGE_FILE_EXTENSION = 'jpg'   # All processed profile images are converted to JPEGs
PROFILE_IMAGE_SIZES_MAP = {
    'full': 500,
    'large': 120,
    'medium': 50,
    'small': 30
}
_PROFILE_IMAGE_SIZES = PROFILE_IMAGE_SIZES_MAP.values()


def get_profile_image_storage():
    """
    Configures and returns a django Storage instance that can be used
    to physically locate, read and write profile images.
    """
    config = settings.PROFILE_IMAGE_BACKEND
    storage_class = get_storage_class(config['class'])
    return storage_class(**config['options'])


def _make_profile_image_name(username):
    """
    Returns the user-specific part of the image filename, based on a hash of
    the username.
    """
    return hashlib.md5(settings.PROFILE_IMAGE_SECRET_KEY + username).hexdigest()


def _get_profile_image_filename(name, size, file_extension=PROFILE_IMAGE_FILE_EXTENSION):
    """
    Returns the full filename for a profile image, given the name and size.
    """
    return '{name}_{size}.{file_extension}'.format(name=name, size=size, file_extension=file_extension)


def _get_profile_image_urls(name, storage, file_extension=PROFILE_IMAGE_FILE_EXTENSION, version=None):
    """
    Returns a dict containing the urls for a complete set of profile images,
    keyed by "friendly" name (e.g. "full", "large", "medium", "small").
    """
    def _make_url(size):  # pylint: disable=missing-docstring
        url = storage.url(
            _get_profile_image_filename(name, size, file_extension=file_extension)
        )
        return '{}?v={}'.format(url, version) if version is not None else url

    return {size_display_name: _make_url(size) for size_display_name, size in PROFILE_IMAGE_SIZES_MAP.items()}


def get_profile_image_names(username):
    """
    Returns a dict containing the filenames for a complete set of profile
    images, keyed by pixel size.
    """
    name = _make_profile_image_name(username)
    return {size: _get_profile_image_filename(name, size) for size in _PROFILE_IMAGE_SIZES}


def get_profile_image_urls_for_user(user):
    """
    Return a dict {size:url} for each profile image for a given user.
    Notes:
      - this function does not determine whether the set of profile images
    exists, only what the URLs will be if they do exist.  It is assumed that
    callers will use `_get_default_profile_image_urls` instead to provide
    a set of urls that point to placeholder images, when there are no user-
    submitted images.
      - based on the value of django.conf.settings.PROFILE_IMAGE_BACKEND,
    the URL may be relative, and in that case the caller is responsible for
    constructing the full URL if needed.

    Arguments:
        user (django.contrib.auth.User): the user for whom we are getting urls.

    Returns:
        dictionary of {size_display_name: url} for each image.

    """
    if user.profile.has_profile_image:
        return _get_profile_image_urls(
            _make_profile_image_name(user.username),
            get_profile_image_storage(),
            version=user.profile.profile_image_uploaded_at.strftime("%s"),
        )
    else:
        return _get_default_profile_image_urls()


def _get_default_profile_image_urls():
    """
    Returns a dict {size:url} for a complete set of default profile images,
    used as a placeholder when there are no user-submitted images.

    TODO The result of this function should be memoized, but not in tests.
    """
    return _get_profile_image_urls(
        microsite.get_value('PROFILE_IMAGE_DEFAULT_FILENAME', settings.PROFILE_IMAGE_DEFAULT_FILENAME),
        staticfiles_storage,
        file_extension=settings.PROFILE_IMAGE_DEFAULT_FILE_EXTENSION,
    )


def set_has_profile_image(username, is_uploaded, upload_dt=None):
    """
    System (not user-facing) API call used to store whether the user has
    uploaded a profile image, and if so, when.  Used by profile_image API.

    Arguments:
        username (django.contrib.auth.User.username): references the user who
            uploaded an image.

        is_uploaded (bool): whether or not the user has an uploaded profile
            image.

        upload_dt (datetime.datetime): If `is_uploaded` is True, this should
            contain the server-side date+time of the upload.  If `is_uploaded`
            is False, the parameter is optional and will be ignored.

    Raises:
        ValueError: is_uploaded was True, but no upload datetime was supplied.
        UserNotFound: no user with username `username` exists.
    """
    if is_uploaded and upload_dt is None:
        raise ValueError("No upload datetime was supplied.")
    elif not is_uploaded:
        upload_dt = None
    try:
        profile = UserProfile.objects.get(user__username=username)
    except ObjectDoesNotExist:
        raise UserNotFound()

    profile.profile_image_uploaded_at = upload_dt
    profile.save()
