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.functional import cached_property
from django.utils.translation import gettext 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:
    """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.
        """
        try:
            return date.replace(year=date.year + 1, month=1, day=1)
        except ValueError:
            raise Http404(_("Date out of range"))

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


class MonthMixin:
    """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:
            try:
                return date.replace(year=date.year + 1, month=1, day=1)
            except ValueError:
                raise Http404(_("Date out of range"))
        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:
    """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:
    """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.
        """
        try:
            return date + datetime.timedelta(days=7 - self._get_weekday(date))
        except OverflowError:
            raise Http404(_("Date out of range"))

    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 in {'%W', '%V'}:         # 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:
    """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):
        """
        Return `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)
        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,
            **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):
        """
        Return the field or fields to use for ordering the queryset; use the
        date field by default.
        """
        return '-%s' % 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 = timezone.now() if self.uses_datetime_field else timezone_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 = not qs if paginate_by is None else not qs.exists()
            if is_empty:
                raise Http404(_("No %(verbose_name_plural)s available") % {
                    'verbose_name_plural': 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:
            raise Http404(
                _("No %(verbose_name_plural)s available") % {
                    'verbose_name_plural': queryset.model._meta.verbose_name_plural,
                }
            )

        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_choices = {'%W': '1', '%U': '0', '%V': '1'}
        try:
            week_start = week_choices[week_format]
        except KeyError:
            raise ValueError('Unknown week format %r. Choices are: %s' % (
                week_format,
                ', '.join(sorted(week_choices)),
            ))
        year_format = self.get_year_format()
        if week_format == '%V' and year_format != '%G':
            raise ValueError(
                "ISO week directive '%s' is incompatible with the year "
                "directive '%s'. Use the ISO year '%%G' instead." % (
                    week_format, year_format,
                )
            )
        date = _date_from_string(year, 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().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='__'):
    """
    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 = year_format + delim + month_format + delim + day_format
    datestr = str(year) + delim + str(month) + delim + str(day)
    try:
        return datetime.datetime.strptime(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):
    """
    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 <= timezone_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 = timezone.now()
            else:
                now = timezone_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 = timezone.localtime(result)
            result = result.date()

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


def timezone_today():
    """Return the current date in the current time zone."""
    if settings.USE_TZ:
        return timezone.localdate()
    else:
        return datetime.date.today()
