from django.http import Http404
from django.shortcuts import get_object_or_404
from guardian.shortcuts import get_objects_for_user

from customers.models import Customer


def td_format(td_object):
    """A helper function to convert time deltas to a human readable format.
    Taken from here."""
    seconds = int(td_object.total_seconds())
    periods = [
        ("year", 60 * 60 * 24 * 365),
        ("month", 60 * 60 * 24 * 30),
        ("day", 60 * 60 * 24),
        ("hour", 60 * 60),
        ("minute", 60),
        ("second", 1),
    ]

    strings = []
    for period_name, period_seconds in periods:
        if seconds >= period_seconds:
            period_value, seconds = divmod(seconds, period_seconds)
            has_s = "s" if period_value > 1 else ""
            strings.append("%s %s%s" % (period_value, period_name, has_s))

    return ", ".join(strings)


def _get_customers(user):
    """
    Returns a queryset of customers the user is allowed to view.

    user : django.contrib.auth.models.User
    """
    return get_objects_for_user(user, "customers.view_customer", klass=Customer)


def get_object_with_view_permission(model, user=None, pk=None):
    requested_object = get_object_or_404(model, id=pk)
    permission = "customers.view_customer"
    if model.__name__ == "Customer":
        customer = requested_object
    else:
        customer = get_object_or_404(Customer, name=requested_object.customer)
    if user.has_perm(permission, customer):
        return requested_object
    raise Http404()


def objects_for_allowed_customers(model, user=None):
    customers = _get_customers(user)
    if model.__name__ == "Customer":
        return customers
    objects = model.objects.filter(customer__in=customers)
    return objects


def get_objects_for_customer(model, user=None, customer_pk=None):
    customer = get_object_or_404(Customer, id=customer_pk)
    if user.has_perm("customers.view_customer", customer):
        objects = model.objects.filter(customer=customer)
        return objects
    raise Http404