django-shared-utils/shared/utils/views/daterange.py

## UNFINISHED WORK IN PROGRESS

"""
Generic date range views.

Django's generic date views only deal with a single date per
model. The date range views replicate the API but deal with
a start and an end date.
"""

import datetime

from django.conf import settings
from django.core.exceptions import ImproperlyConfigured
from django.http import Http404
from django.utils import timezone
from django.utils.encoding import force_str, force_str
from django.utils.translation import ugettext as _
from django.views.generic.base import View
from django.views.generic.detail import (
    BaseDetailView, SingleObjectTemplateResponseMixin,
)
from django.views.generic.list import (
    MultipleObjectMixin, MultipleObjectTemplateResponseMixin,
)

from django.views.generic.dates import (
    YearMixin, MonthMixin, DayMixin, WeekMixin,
    DateMixin,
)

from .. import conf, preview


if conf.USE_PREVIEW_DATETIME:
    effective_datetime = preview.datetime
else:
    effective_datetime = timezone.datetime


class DateRangeMixin(DateMixin):
    """
    Mixin class for views manipulating date-based data.
    """
    date_field = None
    end_date_field = None
    allow_future = False

    def get_end_date_field(self):
        """
        Get the name of the end date field to be used to filter by.
        """
        if self.end_date_field is None:
            raise ImproperlyConfigured("%s.end_date_field is required." % self.__class__.__name__)
        return self.end_date_field

    # Note: the following three methods only work in subclasses that also
    # inherit SingleObjectMixin or MultipleObjectMixin.

    def _make_date_lookup_arg(self, value):
        """
        Convert a date into a datetime when the date field is a DateTimeField.

        When time zone support is enabled, `date` is assumed to be in the
        current time zone, so that displayed items are consistent with the URL.
        """
        if self.uses_datetime_field:
            value = datetime.datetime.combine(value, datetime.time.min)
            if settings.USE_TZ:
                value = timezone.make_aware(value, timezone.get_current_timezone())
        return value

    def _make_single_date_lookup(self, date):
        """
        Get the lookup kwargs for filtering on a single date.

        If the date field is a DateTimeField, we can't just filter on
        date_field=date because that doesn't take the time into account.
        """
        date_field = self.get_date_field()
        if self.uses_datetime_field:
            since = self._make_date_lookup_arg(date)
            until = self._make_date_lookup_arg(date + datetime.timedelta(days=1))
            return {
                '%s__gte' % date_field: since,
                '%s__lt' % date_field: until,
            }
        else:
            # Skip self._make_date_lookup_arg, it's a no-op in this branch.
            return {date_field: date}


class BaseDateListView(MultipleObjectMixin, DateMixin, View):
    """
    Abstract base class for date-based views displaying a list of objects.
    """
    allow_empty = False
    date_list_period = 'year'

    def get(self, request, *args, **kwargs):
        self.date_list, self.object_list, extra_context = self.get_dated_items()
        context = self.get_context_data(object_list=self.object_list,
                                        date_list=self.date_list)
        context.update(extra_context)
        return self.render_to_response(context)

    def get_dated_items(self):
        """
        Obtain the list of dates and items.
        """
        raise NotImplementedError('A DateView must provide an implementation of get_dated_items()')

    def get_ordering(self):
        """
        Returns the field or fields to use for ordering the queryset; uses the
        date field by default.
        """
        return self.get_date_field() if self.ordering is None else self.ordering

    def get_dated_queryset(self, **lookup):
        """
        Get a queryset properly filtered according to `allow_future` and any
        extra lookup kwargs.
        """
        qs = self.get_queryset().filter(**lookup)
        date_field = self.get_date_field()
        allow_future = self.get_allow_future()
        allow_empty = self.get_allow_empty()
        paginate_by = self.get_paginate_by(qs)

        if not allow_future:
            now = effective_datetime.now() if self.uses_datetime_field else effective_datetime.today()
            qs = qs.filter(**{'%s__lte' % date_field: now})

        if not allow_empty:
            # When pagination is enabled, it's better to do a cheap query
            # than to load the unpaginated queryset in memory.
            is_empty = len(qs) == 0 if paginate_by is None else not qs.exists()
            if is_empty:
                raise Http404(_("No %(verbose_name_plural)s available") % {
                    'verbose_name_plural': force_str(qs.model._meta.verbose_name_plural)
                })

        return qs

    def get_date_list_period(self):
        """
        Get the aggregation period for the list of dates: 'year', 'month', or 'day'.
        """
        return self.date_list_period

    def get_date_list(self, queryset, date_type=None, ordering='ASC'):
        """
        Get a date list by calling `queryset.dates/datetimes()`, checking
        along the way for empty lists that aren't allowed.
        """
        date_field = self.get_date_field()
        allow_empty = self.get_allow_empty()
        if date_type is None:
            date_type = self.get_date_list_period()

        if self.uses_datetime_field:
            date_list = queryset.datetimes(date_field, date_type, ordering)
        else:
            date_list = queryset.dates(date_field, date_type, ordering)

        if date_list is not None and not date_list and not allow_empty:
            name = force_str(queryset.model._meta.verbose_name_plural)
            raise Http404(_("No %(verbose_name_plural)s available") %
                          {'verbose_name_plural': name})

        return date_list


class BaseArchiveIndexView(BaseDateListView):
    """
    Base class for archives of date-based items.

    Requires a response mixin.
    """
    context_object_name = 'latest'

    def get_dated_items(self):
        """
        Return (date_list, items, extra_context) for this request.
        """
        qs = self.get_dated_queryset()
        date_list = self.get_date_list(qs, ordering='DESC')

        if not date_list:
            qs = qs.none()

        return (date_list, qs, {})


class ArchiveIndexView(MultipleObjectTemplateResponseMixin, BaseArchiveIndexView):
    """
    Top-level archive of date-based items.
    """
    template_name_suffix = '_archive'


class BaseYearArchiveView(YearMixin, BaseDateListView):
    """
    List of objects published in a given year.
    """
    date_list_period = 'month'
    make_object_list = False

    def get_dated_items(self):
        """
        Return (date_list, items, extra_context) for this request.
        """
        year = self.get_year()

        date_field = self.get_date_field()
        date = _date_from_string(year, self.get_year_format())

        since = self._make_date_lookup_arg(date)
        until = self._make_date_lookup_arg(self._get_next_year(date))
        lookup_kwargs = {
            '%s__gte' % date_field: since,
            '%s__lt' % date_field: until,
        }

        qs = self.get_dated_queryset(**lookup_kwargs)
        date_list = self.get_date_list(qs)

        if not self.get_make_object_list():
            # We need this to be a queryset since parent classes introspect it
            # to find information about the model.
            qs = qs.none()

        return (date_list, qs, {
            'year': date,
            'next_year': self.get_next_year(date),
            'previous_year': self.get_previous_year(date),
        })

    def get_make_object_list(self):
        """
        Return `True` if this view should contain the full list of objects in
        the given year.
        """
        return self.make_object_list


class YearArchiveView(MultipleObjectTemplateResponseMixin, BaseYearArchiveView):
    """
    List of objects published in a given year.
    """
    template_name_suffix = '_archive_year'


class BaseMonthArchiveView(YearMixin, MonthMixin, BaseDateListView):
    """
    List of objects published in a given month.
    """
    date_list_period = 'day'

    def get_dated_items(self):
        """
        Return (date_list, items, extra_context) for this request.
        """
        year = self.get_year()
        month = self.get_month()

        date_field = self.get_date_field()
        date = _date_from_string(year, self.get_year_format(),
                                 month, self.get_month_format())

        since = self._make_date_lookup_arg(date)
        until = self._make_date_lookup_arg(self._get_next_month(date))
        lookup_kwargs = {
            '%s__gte' % date_field: since,
            '%s__lt' % date_field: until,
        }

        qs = self.get_dated_queryset(**lookup_kwargs)
        date_list = self.get_date_list(qs)

        return (date_list, qs, {
            'month': date,
            'next_month': self.get_next_month(date),
            'previous_month': self.get_previous_month(date),
        })


class MonthArchiveView(MultipleObjectTemplateResponseMixin, BaseMonthArchiveView):
    """
    List of objects published in a given month.
    """
    template_name_suffix = '_archive_month'


class BaseWeekArchiveView(YearMixin, WeekMixin, BaseDateListView):
    """
    List of objects published in a given week.
    """

    def get_dated_items(self):
        """
        Return (date_list, items, extra_context) for this request.
        """
        year = self.get_year()
        week = self.get_week()

        date_field = self.get_date_field()
        week_format = self.get_week_format()
        week_start = {
            '%W': '1',
            '%U': '0',
        }[week_format]
        date = _date_from_string(year, self.get_year_format(),
                                 week_start, '%w',
                                 week, week_format)

        since = self._make_date_lookup_arg(date)
        until = self._make_date_lookup_arg(self._get_next_week(date))
        lookup_kwargs = {
            '%s__gte' % date_field: since,
            '%s__lt' % date_field: until,
        }

        qs = self.get_dated_queryset(**lookup_kwargs)

        return (None, qs, {
            'week': date,
            'next_week': self.get_next_week(date),
            'previous_week': self.get_previous_week(date),
        })


class WeekArchiveView(MultipleObjectTemplateResponseMixin, BaseWeekArchiveView):
    """
    List of objects published in a given week.
    """
    template_name_suffix = '_archive_week'


class BaseDayArchiveView(YearMixin, MonthMixin, DayMixin, BaseDateListView):
    """
    List of objects published on a given day.
    """

    def get_dated_items(self):
        """
        Return (date_list, items, extra_context) for this request.
        """
        year = self.get_year()
        month = self.get_month()
        day = self.get_day()

        date = _date_from_string(year, self.get_year_format(),
                                 month, self.get_month_format(),
                                 day, self.get_day_format())

        return self._get_dated_items(date)

    def _get_dated_items(self, date):
        """
        Do the actual heavy lifting of getting the dated items; this accepts a
        date object so that TodayArchiveView can be trivial.
        """
        lookup_kwargs = self._make_single_date_lookup(date)
        qs = self.get_dated_queryset(**lookup_kwargs)

        return (None, qs, {
            'day': date,
            'previous_day': self.get_previous_day(date),
            'next_day': self.get_next_day(date),
            'previous_month': self.get_previous_month(date),
            'next_month': self.get_next_month(date)
        })


class DayArchiveView(MultipleObjectTemplateResponseMixin, BaseDayArchiveView):
    """
    List of objects published on a given day.
    """
    template_name_suffix = "_archive_day"


class BaseTodayArchiveView(BaseDayArchiveView):
    """
    List of objects published today.
    """

    def get_dated_items(self):
        """
        Return (date_list, items, extra_context) for this request.
        """
        return self._get_dated_items(datetime.date.today())


class TodayArchiveView(MultipleObjectTemplateResponseMixin, BaseTodayArchiveView):
    """
    List of objects published today.
    """
    template_name_suffix = "_archive_day"


class BaseDateDetailView(YearMixin, MonthMixin, DayMixin, DateMixin, BaseDetailView):
    """
    Detail view of a single object on a single date; this differs from the
    standard DetailView by accepting a year/month/day in the URL.
    """

    def get_object(self, queryset=None):
        """
        Get the object this request displays.
        """
        year = self.get_year()
        month = self.get_month()
        day = self.get_day()
        date = _date_from_string(year, self.get_year_format(),
                                 month, self.get_month_format(),
                                 day, self.get_day_format())

        # Use a custom queryset if provided
        qs = self.get_queryset() if queryset is None else queryset

        if not self.get_allow_future() and date > datetime.date.today():
            raise Http404(_(
                "Future %(verbose_name_plural)s not available because "
                "%(class_name)s.allow_future is False."
            ) % {
                'verbose_name_plural': qs.model._meta.verbose_name_plural,
                'class_name': self.__class__.__name__,
            })

        # Filter down a queryset from self.queryset using the date from the
        # URL. This'll get passed as the queryset to DetailView.get_object,
        # which'll handle the 404
        lookup_kwargs = self._make_single_date_lookup(date)
        qs = qs.filter(**lookup_kwargs)

        return super(BaseDetailView, self).get_object(queryset=qs)


class DateDetailView(SingleObjectTemplateResponseMixin, BaseDateDetailView):
    """
    Detail view of a single object on a single date; this differs from the
    standard DetailView by accepting a year/month/day in the URL.
    """
    template_name_suffix = '_detail'


def _date_from_string(year, year_format, month='', month_format='', day='', day_format='', delim='__'):
    """
    Helper: get a datetime.date object given a format string and a year,
    month, and day (only year is mandatory). Raise a 404 for an invalid date.
    """
    format = delim.join((year_format, month_format, day_format))
    datestr = delim.join((year, month, day))
    try:
        return datetime.datetime.strptime(force_str(datestr), format).date()
    except ValueError:
        raise Http404(_("Invalid date string '%(datestr)s' given format '%(format)s'") % {
            'datestr': datestr,
            'format': format,
        })


def _get_next_prev(generic_view, date, is_previous, period):
    """
    Helper: Get the next or the previous valid date. The idea is to allow
    links on month/day views to never be 404s by never providing a date
    that'll be invalid for the given view.

    This is a bit complicated since it handles different intervals of time,
    hence the coupling to generic_view.

    However in essence the logic comes down to:

        * If allow_empty and allow_future are both true, this is easy: just
          return the naive result (just the next/previous day/week/month,
          regardless of object existence.)

        * If allow_empty is true, allow_future is false, and the naive result
          isn't in the future, then return it; otherwise return None.

        * If allow_empty is false and allow_future is true, return the next
          date *that contains a valid object*, even if it's in the future. If
          there are no next objects, return None.

        * If allow_empty is false and allow_future is false, return the next
          date that contains a valid object. If that date is in the future, or
          if there are no next objects, return None.
    """
    date_field = generic_view.get_date_field()
    allow_empty = generic_view.get_allow_empty()
    allow_future = generic_view.get_allow_future()

    get_current = getattr(generic_view, '_get_current_%s' % period)
    get_next = getattr(generic_view, '_get_next_%s' % period)

    # Bounds of the current interval
    start, end = get_current(date), get_next(date)

    # If allow_empty is True, the naive result will be valid
    if allow_empty:
        if is_previous:
            result = get_current(start - datetime.timedelta(days=1))
        else:
            result = end

        if allow_future or result <= effective_datetime.today():
            return result
        else:
            return None

    # Otherwise, we'll need to go to the database to look for an object
    # whose date_field is at least (greater than/less than) the given
    # naive result
    else:
        # Construct a lookup and an ordering depending on whether we're doing
        # a previous date or a next date lookup.
        if is_previous:
            lookup = {'%s__lt' % date_field: generic_view._make_date_lookup_arg(start)}
            ordering = '-%s' % date_field
        else:
            lookup = {'%s__gte' % date_field: generic_view._make_date_lookup_arg(end)}
            ordering = date_field

        # Filter out objects in the future if appropriate.
        if not allow_future:
            # Fortunately, to match the implementation of allow_future,
            # we need __lte, which doesn't conflict with __lt above.
            if generic_view.uses_datetime_field:
                now = effective_datetime.now()
            else:
                now = effective_datetime.today()
            lookup['%s__lte' % date_field] = now

        qs = generic_view.get_queryset().filter(**lookup).order_by(ordering)

        # Snag the first object from the queryset; if it doesn't exist that
        # means there's no next/previous link available.
        try:
            result = getattr(qs[0], date_field)
        except IndexError:
            return None

        # Convert datetimes to dates in the current time zone.
        if generic_view.uses_datetime_field:
            if settings.USE_TZ:
                result = effective_datetime.localtime(result)
            result = result.date()

        # Return the first day of the period.
        return get_current(result)