from __future__ import annotations

from typing import TYPE_CHECKING

from django.contrib.auth import get_user_model
from django.contrib.postgres.fields import DateTimeRangeField
from django.db import models
from django.db.models import F, Q, QuerySet
from django.utils import timezone

from model_utils.managers import InheritanceQuerySetMixin
from psycopg.types.range import Range

if TYPE_CHECKING:
    from collections.abc import Iterable
    from datetime import datetime


class Resource(models.Model):
    name = models.CharField(max_length=256)
    parent = models.ForeignKey(
        "Resource",
        on_delete=models.CASCADE,
        blank=True,
        null=True,
        related_name="children",
    )
    min_length = models.DurationField()
    max_length = models.DurationField()
    google_calendar = models.CharField(max_length=1024, unique=True)

    def __str__(self) -> str:
        if self.parent:
            return f"{self.parent} / {self.name}"
        else:
            return self.name

    def get_recursive_parents(self) -> Iterable[Resource]:
        if self.parent:
            yield self.parent
            yield from self.parent.get_recursive_parents()

    def get_recursive_children(self) -> Iterable[Resource]:
        for child in self.children.all():
            yield child
            yield from child.get_recursive_children()

    def get_related(self) -> Iterable[Resource]:
        yield self
        yield from self.get_recursive_parents()
        yield from self.get_recursive_children()


class ReservationQuerySet(InheritanceQuerySetMixin, QuerySet):
    def filter_after(self, start: datetime) -> ReservationQuerySet:
        """
        Selects events that are after the specified datetime, including
        overlaps but excluding exactly matching endpoints.
        """
        return self.filter(timespan__overlap=Range(start, None))

    def filter_before(self, end: datetime) -> ReservationQuerySet:
        """
        Selects events that are before the specified datetime, including
        overlaps but excluding exactly matching endpoints.
        """
        return self.filter(timespan__overlap=Range(None, end))

    def filter_between(self, start: datetime, end: datetime) -> ReservationQuerySet:
        """
        Selects events that are between the specified datetime, including
        overlaps but excluding exactly matching endpoints.
        """
        return self.filter(timespan__overlap=Range(start, end))


class Reservation(models.Model):
    resources = models.ManyToManyField(Resource, blank=True)
    start = models.DateTimeField()
    end = models.DateTimeField()
    timespan = models.GeneratedField(
        expression=models.Func(F("start"), F("end"), function="tstzrange"),
        output_field=DateTimeRangeField(),
        db_persist=True,
    )
    google_calendar_event_id = models.CharField(
        max_length=1024, null=True, blank=True, unique=True
    )

    duration = models.GeneratedField(
        expression=F("end") - F("start"),
        output_field=models.DurationField(),
        db_persist=True,
    )

    objects = ReservationQuerySet.as_manager()

    class Meta:
        constraints = [
            models.CheckConstraint(check=Q(end__gt=F("start")), name="end_after_start"),
        ]

    def __str__(self) -> str:
        resources = ", ".join(str(resource) for resource in self.resources.all())
        return f"{resources}: {self.start} - {self.end}"

    def get_title(self) -> str:
        return "Unknown Reservation"

    def make_google_calendar_event(self):
        event = {
            "summary": "CMSManage Reservation",
            "start": {
                "dateTime": self.start.isoformat(),
                "timeZone": timezone.get_default_timezone_name(),
            },
            "end": {
                "dateTime": self.end.isoformat(),
                "timeZone": timezone.get_default_timezone_name(),
            },
            "extendedProperties": {"private": {"cmsmanage": "1"}},
            "status": "confirmed",
        }

        # use existing id if it exists, otherwise let Google generate it
        if self.google_calendar_event_id:
            event["id"] = self.google_calendar_event_id

        return event


class UserReservation(Reservation):
    user = models.ForeignKey(
        get_user_model(), on_delete=models.CASCADE, null=True, blank=True
    )

    def __str__(self) -> str:
        return f"{self.user} | {super().__str__()}"

    def get_title(self) -> str:
        return str(self.user)

    def make_google_calendar_event(self):
        return super().make_google_calendar_event() | {
            "summary": str(self.user),
        }


class ExternalReservation(Reservation):
    """Reservations created by something else in Google Calendar"""

    title = models.CharField(max_length=1024)

    def __str__(self) -> str:
        return f'External "{self.title}" | {super().__str__()}'

    def get_title(self) -> str:
        return str(self.title)

    def make_google_calendar_event(self):
        """This should never be called, as these are reservations from Google Calendar and shouldn't be synced back"""
        raise AttributeError(
            "External Reservations should not be pushed back to Google Calendar"
        )