from __future__ import unicode_literals

import datetime

from django.conf import settings
from django.core.exceptions import ImproperlyConfigured
from django.db import models
from django.http import Http404
from django.utils import timezone
from django.utils.encoding import force_str, force_text
from django.utils.functional import cached_property
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,
)


class YearMixin(object):
    """
    Mixin for views manipulating year-based data.
    """
    year_format = '%Y'
    year = None

    def get_year_format(self):
        """
        Get a year format string in strptime syntax to be used to parse the
        year from url variables.
        """
        return self.year_format

    def get_year(self):
        """
        Return the year for which this view should display data.
        """
        year = self.year
        if year is None:
            try:
                year = self.kwargs['year']
            except KeyError:
                try:
                    year = self.request.GET['year']
                except KeyError:
                    raise Http404(_("No year specified"))
        return year

    def get_next_year(self, date):
        """
        Get the next valid year.
        """
        return _get_next_prev(self, date, is_previous=False, period='year')

    def get_previous_year(self, date):
        """
        Get the previous valid year.
        """
        return _get_next_prev(self, date, is_previous=True, period='year')

    def _get_next_year(self, date):
        """
        Return the start date of the next interval.

        The interval is defined by start date <= item date < next start date.
        """
        return date.replace(year=date.year + 1, month=1, day=1)

    def _get_current_year(self, date):
        """
        Return the start date of the current interval.
        """
        return date.replace(month=1, day=1)


class MonthMixin(object):
    """
    Mixin for views manipulating month-based data.
    """
    month_format = '%b'
    month = None

    def get_month_format(self):
        """
        Get a month format string in strptime syntax to be used to parse the
        month from url variables.
        """
        return self.month_format

    def get_month(self):
        """
        Return the month for which this view should display data.
        """
        month = self.month
        if month is None:
            try:
                month = self.kwargs['month']
            except KeyError:
                try:
                    month = self.request.GET['month']
                except KeyError:
                    raise Http404(_("No month specified"))
        return month

    def get_next_month(self, date):
        """
        Get the next valid month.
        """
        return _get_next_prev(self, date, is_previous=False, period='month')

    def get_previous_month(self, date):
        """
        Get the previous valid month.
        """
        return _get_next_prev(self, date, is_previous=True, period='month')

    def _get_next_month(self, date):
        """
        Return the start date of the next interval.

        The interval is defined by start date <= item date < next start date.
        """
        if date.month == 12:
            return date.replace(year=date.year + 1, month=1, day=1)
        else:
            return date.replace(month=date.month + 1, day=1)

    def _get_current_month(self, date):
        """
        Return the start date of the previous interval.
        """
        return date.replace(day=1)


class DayMixin(object):
    """
    Mixin for views manipulating day-based data.
    """
    day_format = '%d'
    day = None

    def get_day_format(self):
        """
        Get a day format string in strptime syntax to be used to parse the day
        from url variables.
        """
        return self.day_format

    def get_day(self):
        """
        Return the day for which this view should display data.
        """
        day = self.day
        if day is None:
            try:
                day = self.kwargs['day']
            except KeyError:
                try:
                    day = self.request.GET['day']
                except KeyError:
                    raise Http404(_("No day specified"))
        return day

    def get_next_day(self, date):
        """
        Get the next valid day.
        """
        return _get_next_prev(self, date, is_previous=False, period='day')

    def get_previous_day(self, date):
        """
        Get the previous valid day.
        """
        return _get_next_prev(self, date, is_previous=True, period='day')

    def _get_next_day(self, date):
        """
        Return the start date of the next interval.

        The interval is defined by start date <= item date < next start date.
        """
        return date + datetime.timedelta(days=1)

    def _get_current_day(self, date):
        """
        Return the start date of the current interval.
        """
        return date


class WeekMixin(object):
    """
    Mixin for views manipulating week-based data.
    """
    week_format = '%U'
    week = None

    def get_week_format(self):
        """
        Get a week format string in strptime syntax to be used to parse the
        week from url variables.
        """
        return self.week_format

    def get_week(self):
        """
        Return the week for which this view should display data
        """
        week = self.week
        if week is None:
            try:
                week = self.kwargs['week']
            except KeyError:
                try:
                    week = self.request.GET['week']
                except KeyError:
                    raise Http404(_("No week specified"))
        return week

    def get_next_week(self, date):
        """
        Get the next valid week.
        """
        return _get_next_prev(self, date, is_previous=False, period='week')

    def get_previous_week(self, date):
        """
        Get the previous valid week.
        """
        return _get_next_prev(self, date, is_previous=True, period='week')

    def _get_next_week(self, date):
        """
        Return the start date of the next interval.

        The interval is defined by start date <= item date < next start date.
        """
        return date + datetime.timedelta(days=7 - self._get_weekday(date))

    def _get_current_week(self, date):
        """
        Return the start date of the current interval.
        """
        return date - datetime.timedelta(self._get_weekday(date))

    def _get_weekday(self, date):
        """
        Return the weekday for a given date.

        The first day according to the week format is 0 and the last day is 6.
        """
        week_format = self.get_week_format()
        if week_format == '%W':                 # week starts on Monday
            return date.weekday()
        elif week_format == '%U':               # week starts on Sunday
            return (date.weekday() + 1) % 7
        else:
            raise ValueError("unknown week format: %s" % week_format)


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

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

    def get_allow_future(self):
        """
        Returns `True` if the view should be allowed to display objects from
        the future.
        """
        return self.allow_future

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

    @cached_property
    def uses_datetime_field(self):
        """
        Return `True` if the date field is a `DateTimeField` and `False`
        if it's a `DateField`.
        """
        model = self.get_queryset().model if self.model is None else self.model
        field = model._meta.get_field(self.get_date_field())
        return isinstance(field, models.DateTimeField)

    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):