from __future__ import annotations

from django.contrib.auth import get_user_model
from django.contrib.contenttypes.models import ContentType
from django.db import transaction
from django.db.models import Q, QuerySet
from schedule.models import Calendar, CalendarRelation, Event, EventRelation

from employees.models import Department, EmployeeDepartment, RoleAssignment

from .models import CalendarBinding

User = get_user_model()


def get_calendar_binding(calendar: Calendar | None) -> CalendarBinding | None:
    if calendar is None:
        return None
    binding = getattr(calendar, "binding", None)
    if binding is not None:
        return binding
    return (
        CalendarBinding.objects.select_related("context_content_type")
        .filter(calendar=calendar)
        .first()
    )


def is_department_calendar(calendar: Calendar | None) -> bool:
    binding = get_calendar_binding(calendar)
    return bool(binding and binding.type == CalendarBinding.BindingType.DEPARTMENT)


def is_company_wide_calendar(calendar: Calendar | None) -> bool:
    binding = get_calendar_binding(calendar)
    return bool(
        binding
        and binding.type == CalendarBinding.BindingType.DEFAULT
        and binding.access_scope == CalendarBinding.AccessScope.ALL
    )


def get_department_calendar_binding(
    department: Department,
) -> CalendarBinding | None:
    dept_ct = ContentType.objects.get_for_model(Department)
    return (
        CalendarBinding.objects.select_related("calendar")
        .filter(
            type=CalendarBinding.BindingType.DEPARTMENT,
            context_content_type=dept_ct,
            context_object_id=department.id,
        )
        .first()
    )


def department_calendar_name(department: Department) -> str:
    return department.name


def department_calendar_slug(department: Department) -> str:
    return f"department-{department.id}"


def _unique_calendar_slug(base_slug: str) -> str:
    if not Calendar.objects.filter(slug=base_slug).exists():
        return base_slug

    counter = 1
    while Calendar.objects.filter(slug=f"{base_slug}-{counter}").exists():
        counter += 1
    return f"{base_slug}-{counter}"


def _find_existing_department_calendar(
    department: Department,
) -> Calendar | None:
    slug = department_calendar_slug(department)
    return (
        Calendar.objects.filter(slug=slug)
        .exclude(binding__isnull=False)
        .order_by("-id")
        .first()
    )


@transaction.atomic
def get_or_create_department_calendar(
    department: Department,
) -> tuple[Calendar, CalendarBinding]:
    binding = get_department_calendar_binding(department)
    if binding:
        sync_department_calendar_binding(department, binding=binding)
        return binding.calendar, binding

    calendar = _find_existing_department_calendar(department)
    if calendar is None:
        calendar = Calendar.objects.create(
            name=department_calendar_name(department),
            slug=_unique_calendar_slug(department_calendar_slug(department)),
        )

    dept_ct = ContentType.objects.get_for_model(Department)
    binding, _ = CalendarBinding.objects.get_or_create(
        calendar=calendar,
        defaults={
            "type": CalendarBinding.BindingType.DEPARTMENT,
            "context_content_type": dept_ct,
            "context_object_id": department.id,
        },
    )

    if (
        binding.type != CalendarBinding.BindingType.DEPARTMENT
        or binding.context_content_type_id != dept_ct.id
        or binding.context_object_id != department.id
    ):
        binding.type = CalendarBinding.BindingType.DEPARTMENT
        binding.context_content_type = dept_ct
        binding.context_object_id = department.id
        binding.save(
            update_fields=[
                "type",
                "context_content_type",
                "context_object_id",
                "updated_at",
            ]
        )

    sync_department_calendar_binding(department, binding=binding)
    return binding.calendar, binding


def _department_participant_ids(department: Department) -> set[int]:
    ids: set[int] = set(
        EmployeeDepartment.objects.filter(
            department=department,
            is_active=True,
            employee__is_active=True,
        ).values_list("employee_id", flat=True)
    )

    role_only_ids = RoleAssignment.objects.filter(
        role__department=department,
        is_active=True,
        employee__is_active=True,
    ).values_list("employee_id", flat=True)
    ids.update(role_only_ids)

    if department.head_id:
        ids.add(department.head_id)

    return ids


def _set_relation_role(calendar: Calendar, user_id: int, distinction: str) -> None:
    user_ct = ContentType.objects.get_for_model(User)
    relations = list(
        CalendarRelation.objects.filter(
            calendar=calendar,
            content_type=user_ct,
            object_id=user_id,
        ).order_by("id")
    )
    if relations:
        primary = relations[0]
        changed = False
        if primary.distinction != distinction:
            primary.distinction = distinction
            changed = True
        if primary.inheritable is not True:
            primary.inheritable = True
            changed = True
        if changed:
            primary.save(update_fields=["distinction", "inheritable"])
        if len(relations) > 1:
            CalendarRelation.objects.filter(
                id__in=[relation.id for relation in relations[1:]]
            ).delete()
        return

    calendar.create_relation(
        User.objects.get(pk=user_id),
        distinction=distinction,
        inheritable=True,
    )


def sync_department_calendar_owner(
    department: Department, *, binding: CalendarBinding | None = None
) -> Calendar | None:
    binding = binding or get_department_calendar_binding(department)
    if not binding:
        return None

    calendar = binding.calendar
    desired_owner_id = department.head_id
    user_ct = ContentType.objects.get_for_model(User)

    owner_relations = CalendarRelation.objects.filter(
        calendar=calendar,
        content_type=user_ct,
        distinction="owner",
    ).order_by("id")

    if desired_owner_id is None:
        owner_relations.delete()
        return calendar

    _set_relation_role(calendar, desired_owner_id, "owner")

    owner_relations.exclude(object_id=desired_owner_id).delete()
    return calendar


def sync_department_calendar_members(
    department: Department, *, binding: CalendarBinding | None = None
) -> Calendar | None:
    binding = binding or get_department_calendar_binding(department)
    if not binding:
        return None

    calendar = binding.calendar
    desired_ids = _department_participant_ids(department)
    owner_id = department.head_id
    user_ct = ContentType.objects.get_for_model(User)

    existing_relations = list(
        CalendarRelation.objects.filter(
            calendar=calendar,
            content_type=user_ct,
        ).order_by("id")
    )
    if owner_id:
        _set_relation_role(calendar, owner_id, "owner")

    for user_id in sorted(desired_ids):
        if user_id == owner_id:
            continue
        _set_relation_role(calendar, user_id, "editor")

    stale_relation_ids = [
        relation.id
        for relation in existing_relations
        if relation.object_id not in desired_ids
    ]
    if stale_relation_ids:
        CalendarRelation.objects.filter(id__in=stale_relation_ids).delete()

    return calendar


def sync_department_calendar_binding(
    department: Department, *, binding: CalendarBinding | None = None
) -> Calendar | None:
    binding = binding or get_department_calendar_binding(department)
    if not binding:
        return None

    calendar = binding.calendar
    desired_name = department_calendar_name(department)
    if calendar.name != desired_name:
        calendar.name = desired_name
        calendar.save(update_fields=["name"])

    sync_department_calendar_owner(department, binding=binding)
    sync_department_calendar_members(department, binding=binding)
    return calendar


def sync_department_calendar_if_bound(department: Department) -> None:
    binding = get_department_calendar_binding(department)
    if not binding:
        return
    sync_department_calendar_binding(department, binding=binding)


def sync_department_calendar_binding_by_department_id(department_id: int) -> None:
    try:
        department = Department.objects.get(pk=department_id)
    except Department.DoesNotExist:
        return
    sync_department_calendar_if_bound(department)


def delete_department_calendar(department_id: int) -> None:
    try:
        department = Department.objects.get(pk=department_id)
    except Department.DoesNotExist:
        department = None

    if department:
        binding = get_department_calendar_binding(department)
    else:
        dept_ct = ContentType.objects.get_for_model(Department)
        binding = (
            CalendarBinding.objects.filter(
                type=CalendarBinding.BindingType.DEPARTMENT,
                context_content_type=dept_ct,
                context_object_id=department_id,
            )
            .select_related("calendar")
            .first()
        )

    if binding:
        binding.calendar.delete()


def user_relation_distinction(calendar: Calendar, user) -> str | None:
    if not getattr(user, "is_authenticated", False):
        return None
    if user.is_staff or user.is_superuser:
        return "owner"

    user_ct = ContentType.objects.get_for_model(User)
    relation = (
        CalendarRelation.objects.filter(
            calendar=calendar,
            content_type=user_ct,
            object_id=user.id,
        )
        .order_by("id")
        .first()
    )
    return relation.distinction if relation else None


def user_can_view_calendar(user, calendar: Calendar) -> bool:
    if not getattr(user, "is_authenticated", False):
        return False
    if user.is_staff or user.is_superuser:
        return True
    if is_department_calendar(calendar):
        return True
    if is_company_wide_calendar(calendar):
        return True
    return user_relation_distinction(calendar, user) is not None


def filter_events_for_user(
    queryset: QuerySet,
    user,
    *,
    allow_admin_all: bool = False,
) -> QuerySet:
    """Ограничить события календарями и персональными приглашениями пользователя."""
    if not getattr(user, "is_authenticated", False):
        return queryset.none()
    if allow_admin_all and (user.is_staff or user.is_superuser):
        return queryset

    user_content_type = ContentType.objects.get_for_model(User)
    calendar_ids = CalendarRelation.objects.filter(
        content_type=user_content_type,
        object_id=user.id,
    ).values_list("calendar_id", flat=True)
    participant_event_ids = EventRelation.objects.filter(
        content_type=user_content_type,
        object_id=user.id,
    ).values_list("event_id", flat=True)
    return queryset.filter(
        Q(calendar_id__in=calendar_ids)
        | Q(id__in=participant_event_ids)
        | Q(
            calendar__binding__type=CalendarBinding.BindingType.DEFAULT,
            calendar__binding__access_scope=CalendarBinding.AccessScope.ALL,
        )
    ).distinct()


def user_can_view_event(user, event: Event) -> bool:
    if not event:
        return False
    if user_can_view_calendar(user, event.calendar):
        return True
    user_content_type = ContentType.objects.get_for_model(User)
    return EventRelation.objects.filter(
        event=event,
        content_type=user_content_type,
        object_id=user.id,
    ).exists()


def user_can_create_event(user, calendar: Calendar) -> bool:
    if not getattr(user, "is_authenticated", False):
        return False
    if user.is_staff or user.is_superuser:
        return True
    if is_department_calendar(calendar):
        return True
    return user_relation_distinction(calendar, user) in {"owner", "editor"}


def user_can_edit_calendar(user, calendar: Calendar) -> bool:
    if not getattr(user, "is_authenticated", False):
        return False
    if user.is_staff or user.is_superuser:
        return True
    return user_relation_distinction(calendar, user) == "owner"


def user_can_manage_participants(user, calendar: Calendar) -> bool:
    if not getattr(user, "is_authenticated", False):
        return False
    if user.is_staff or user.is_superuser:
        return True
    if is_department_calendar(calendar):
        return False
    return user_relation_distinction(calendar, user) == "owner"


def user_can_manage_calendar_notifications(user, calendar: Calendar) -> bool:
    """Проверить право менять общие правила уведомлений календаря."""
    if not getattr(user, "is_authenticated", False):
        return False
    if user.is_staff or user.is_superuser:
        return True
    return user_relation_distinction(calendar, user) in {"owner", "editor"}


def calendar_notification_enabled(calendar: Calendar | None, field: str) -> bool:
    """Вернуть настройку уведомления, сохраняя прежнее поведение без binding."""
    binding = get_calendar_binding(calendar)
    if binding is None:
        return True
    return bool(getattr(binding, field, True))


def user_can_edit_event(user, event: Event) -> bool:
    if not getattr(user, "is_authenticated", False):
        return False
    if user.is_staff or user.is_superuser:
        return True

    calendar = event.calendar
    if is_department_calendar(calendar):
        relation = user_relation_distinction(calendar, user)
        if relation in {"owner", "editor"}:
            return True
        return event.creator_id == user.id

    return user_relation_distinction(calendar, user) in {"owner", "editor"}


def user_can_delete_event(user, event: Event) -> bool:
    return user_can_edit_event(user, event)