from datetime import date, datetime, time, timedelta

from dateutil.relativedelta import relativedelta
from dateutil.parser import parse as dateutil_parse
import pytz

from django.utils import timezone
from django.db.models import Sum

KFET_WAKES_UP_AT = time(7, 0)


def kfet_day(year, month, day, start_at=KFET_WAKES_UP_AT):
    """datetime wrapper with time offset."""
    naive = datetime.combine(date(year, month, day), start_at)
    return pytz.timezone('Europe/Paris').localize(naive, is_dst=None)


def to_kfet_day(dt, start_at=KFET_WAKES_UP_AT):
    kfet_dt = kfet_day(year=dt.year, month=dt.month, day=dt.day)
    if dt.time() < start_at:
        kfet_dt -= timedelta(days=1)
    return kfet_dt


class Scale(object):
    name = None
    step = None

    def __init__(self, n_steps=0, begin=None, end=None,
                 last=False, std_chunk=True):
        self.std_chunk = std_chunk
        if last:
            end = timezone.now()
        if std_chunk:
            if begin is not None:
                begin = self.get_chunk_start(begin)
            if end is not None:
                end = self.do_step(self.get_chunk_start(end))

        if begin is not None and n_steps != 0:
            self.begin = begin
            self.end = self.do_step(self.begin, n_steps=n_steps)
        elif end is not None and n_steps != 0:
            self.end = end
            self.begin = self.do_step(self.end, n_steps=-n_steps)
        elif begin is not None and end is not None:
            self.begin = begin
            self.end = end
        else:
            raise Exception('Two of these args must be specified: '
                            'n_steps, begin, end; '
                            'or use last and n_steps')

        self.datetimes = self.get_datetimes()

    @staticmethod
    def by_name(name):
        for cls in Scale.__subclasses__():
            if cls.name == name:
                return cls
        return None

    def get_from(self, dt):
        return self.std_chunk and self.get_chunk_start(dt) or dt

    def __getitem__(self, i):
        return self.datetimes[i], self.datetimes[i+1]

    def __len__(self):
        return len(self.datetimes) - 1

    def do_step(self, dt, n_steps=1):
        return dt + self.step * n_steps

    def get_datetimes(self):
        datetimes = [self.begin]
        tmp = self.begin
        while tmp < self.end:
            tmp = self.do_step(tmp)
            datetimes.append(tmp)
        return datetimes

    def get_labels(self, label_fmt=None):
        if label_fmt is None:
            label_fmt = self.label_fmt
        return [
            begin.strftime(label_fmt.format(i=i, rev_i=len(self)-i))
            for i, (begin, end) in enumerate(self)
        ]

    def chunkify_qs(self, qs, field=None):
        if field is None:
            field = 'at'
        begin_f = '{}__gte'.format(field)
        end_f = '{}__lte'.format(field)
        return [
            qs.filter(**{begin_f: begin, end_f: end})
            for begin, end in self
        ]

    def get_by_chunks(self, qs, field_callback=None, field_db='at'):
        """Objects of queryset ranked according to the scale.

        Returns a generator whose each item, corresponding to a scale chunk,
        is a generator of objects from qs for this chunk.

        Args:
            qs: Queryset of source objects, must be ordered *first* on the
                same field returned by `field_callback`.
            field_callback: Callable which gives value from an object used
                to compare against limits of the scale chunks.
                Default to: lambda obj: getattr(obj, field_db)
            field_db: Used to filter against `scale` limits.
                Default to 'at'.

        Examples:
            If queryset `qs` use `values()`, `field_callback` must be set and
                could be: `lambda d: d['at']`
            If `field_db` use foreign attributes (eg with `__`), it should be
                something like: `lambda obj: obj.group.at`.

        """
        if field_callback is None:
            def field_callback(obj):
                return getattr(obj, field_db)

        begin_f = '{}__gte'.format(field_db)
        end_f = '{}__lte'.format(field_db)

        qs = (
            qs
            .filter(**{begin_f: self.begin, end_f: self.end})
        )

        obj_iter = iter(qs)

        last_obj = None

        def _objects_until(obj_iter, field_callback, end):
            """Generator of objects until `end`.

            Ends if objects source is empty or when an object not verifying
            field_callback(obj) <= end is met.

            If this object exists, it is stored in `last_obj` which is found
            from outer scope.
            Also, if this same variable is non-empty when the function is
            called, it first yields its content.

            Args:
                obj_iter: Source used to get objects.
                field_callback: Returned value, when it is called on an object
                    will be used to test ordering against `end`.
                end

            """
            nonlocal last_obj

            if last_obj is not None:
                yield last_obj
                last_obj = None

            for obj in obj_iter:
                if field_callback(obj) <= end:
                    yield obj
                else:
                    last_obj = obj
                    return

        for begin, end in self:
            # forward last seen object, if it exists, to the right chunk,
            # and fill with empty generators for intermediate chunks of scale
            if last_obj is not None:
                if field_callback(last_obj) > end:
                    yield iter(())
                    continue

            # yields generator for this chunk
            # this set last_obj to None if obj_iter reach its end, otherwise
            # it's set to the first met object from obj_iter which doesn't
            # belong to this chunk
            yield _objects_until(obj_iter, field_callback, end)


class DayScale(Scale):
    name = 'day'
    step = timedelta(days=1)
    label_fmt = '%A'

    @classmethod
    def get_chunk_start(cls, dt):
        return to_kfet_day(dt)


class WeekScale(Scale):
    name = 'week'
    step = timedelta(days=7)
    label_fmt = 'Semaine %W'

    @classmethod
    def get_chunk_start(cls, dt):
        dt_kfet = to_kfet_day(dt)
        offset = timedelta(days=dt_kfet.weekday())
        return dt_kfet - offset


class MonthScale(Scale):
    name = 'month'
    step = relativedelta(months=1)
    label_fmt = '%B'

    @classmethod
    def get_chunk_start(cls, dt):
        return to_kfet_day(dt).replace(day=1)


def stat_manifest(scales_def=None, scale_args=None, scale_prefix=None,
                  **other_url_params):
    if scale_prefix is None:
        scale_prefix = 'scale_'
    if scales_def is None:
        scales_def = []
    if scale_args is None:
        scale_args = {}
    manifest = []
    for label, cls in scales_def:
        url_params = {scale_prefix+'name': cls.name}
        url_params.update({scale_prefix+key: value
                           for key, value in scale_args.items()})
        url_params.update(other_url_params)
        manifest.append(dict(
            label=label,
            url_params=url_params,
        ))
    return manifest


def last_stats_manifest(scales_def=None, scale_args=None, scale_prefix=None,
                        **url_params):
    scales_def = [
        ('Derniers mois', MonthScale, ),
        ('Dernières semaines', WeekScale, ),
        ('Derniers jours', DayScale, ),
    ]
    if scale_args is None:
        scale_args = {}
    scale_args.update(dict(
        last=True,
        n_steps=7,
    ))
    return stat_manifest(scales_def=scales_def, scale_args=scale_args,
                         scale_prefix=scale_prefix, **url_params)


# Étant donné un queryset d'operations
# rend la somme des article_nb
def tot_ventes(queryset):
    res = queryset.aggregate(Sum('article_nb'))['article_nb__sum']
    return res and res or 0


class ScaleMixin(object):
    scale_args_prefix = 'scale_'

    def get_scale_args(self, params=None, prefix=None):
        """Retrieve scale args from params.

        Should search the same args of Scale constructor.

        Args:
            params (dict, optional): Scale args are searched in this.
                Default to GET params of request.
            prefix (str, optional): Appended at the begin of scale args names.
                Default to `self.scale_args_prefix`.

        """
        if params is None:
            params = self.request.GET
        if prefix is None:
            prefix = self.scale_args_prefix

        scale_args = {}

        name = params.get(prefix+'name', None)
        if name is not None:
            scale_args['name'] = name

        n_steps = params.get(prefix+'n_steps', None)
        if n_steps is not None:
            scale_args['n_steps'] = int(n_steps)

        begin = params.get(prefix+'begin', None)
        if begin is not None:
            scale_args['begin'] = dateutil_parse(begin)

        end = params.get(prefix+'send', None)
        if end is not None:
            scale_args['end'] = dateutil_parse(end)

        last = params.get(prefix+'last', None)
        if last is not None:
            scale_args['last'] = (
                last in ['true', 'True', '1'] and True or False)

        return scale_args

    def get_context_data(self, *args, **kwargs):
        context = super().get_context_data(*args, **kwargs)

        scale_args = self.get_scale_args()
        scale_name = scale_args.pop('name', None)
        scale_cls = Scale.by_name(scale_name)

        if scale_cls is None:
            scale = self.get_default_scale()
        else:
            scale = scale_cls(**scale_args)

        self.scale = scale
        context['labels'] = scale.get_labels()
        return context

    def get_default_scale(self):
        return DayScale(n_steps=7, last=True)