"""Tenant-scoped managers (``TENANCY.md`` §4).

* :class:`TenantManager` — default manager of every tenant-owned model; fails
  closed (empty queryset) when no tenant is bound.
* :class:`AllObjectsManager` — the ``all_objects`` escape hatch for migrations,
  admin, and platform staff. Never called from a view.
* :class:`GlobalOrTenantManager` — for resources that exist globally and can be
  overridden per tenant (roles, pipelines, templates, feature flags).
"""

from __future__ import annotations

from typing import TYPE_CHECKING, Any

from django.db import models
from django.db.models import Q

from .context import get_current_tenant

if TYPE_CHECKING:
    from django.db.models import QuerySet

__all__ = ["TenantManager", "AllObjectsManager", "GlobalOrTenantManager"]


class TenantManager(models.Manager):
    """Default manager on tenant-owned models. Scopes to the current tenant."""

    def get_queryset(self) -> QuerySet[Any]:
        tenant = get_current_tenant()
        if tenant is None:
            # Fail closed: no tenant context must never mean "all tenants".
            return super().get_queryset().none()
        return super().get_queryset().filter(tenant_id=tenant.pk)

    def unsafe_all(self) -> QuerySet[Any]:
        """Explicit, greppable escape hatch for system code. Never from a view."""
        return super().get_queryset()


class AllObjectsManager(models.Manager):
    """Unscoped manager exposed as ``all_objects`` (admin/migrations/staff)."""


class GlobalOrTenantManager(models.Manager):
    """Global rows (``tenant IS NULL``) plus the current tenant's overrides.

    Never exposes another tenant's rows. Use :meth:`resolve` to apply the
    documented precedence: tenant override → global default → ``None``.
    """

    def get_queryset(self) -> QuerySet[Any]:
        tenant = get_current_tenant()
        qs = super().get_queryset()
        if tenant is None:
            return qs.filter(tenant__isnull=True)
        return qs.filter(Q(tenant_id=tenant.pk) | Q(tenant__isnull=True))

    def resolve(self, **filters: Any) -> Any:
        """Returns the tenant override for ``filters``, else the global row."""
        tenant = get_current_tenant()
        if tenant is not None:
            override = self.get_queryset().filter(tenant_id=tenant.pk, **filters).first()
            if override is not None:
                return override
        return self.get_queryset().filter(tenant__isnull=True, **filters).first()

    def unsafe_all(self) -> QuerySet[Any]:
        return super().get_queryset()