"""Closed, server-derived tenant scope for the conditional WP10 foundation."""

from __future__ import annotations

import re
from collections.abc import Mapping
from dataclasses import dataclass
from enum import StrEnum


class TenantContextError(ValueError):
    """A tenant boundary was absent, unapproved, or contradicted by input."""


class DeliveryMode(StrEnum):
    PRIVATE_SINGLE_TENANT = "private_single_tenant"
    SHARED_CONTROL_PLANE = "shared_control_plane"
    SAAS = "saas"


_TENANT_ID = re.compile(r"^[a-z][a-z0-9-]{0,62}$")
_HOST = re.compile(r"^[a-z0-9][a-z0-9.-]{0,252}$")
_EVENT_TYPE = re.compile(r"^[a-z][a-z0-9_.-]{0,80}$")
_DIGEST = re.compile(r"^[0-9a-f]{64}$")


def _tenant_id(value: str) -> str:
    if not isinstance(value, str) or not _TENANT_ID.fullmatch(value):
        raise TenantContextError("tenant_scope_denied")
    return value


@dataclass(frozen=True)
class TenantScope:
    tenant_id: str
    mode: DeliveryMode
    version: int = 1

    def __post_init__(self) -> None:
        _tenant_id(self.tenant_id)
        if self.version != 1:
            raise TenantContextError("tenant_context_version_denied")

    def require_background_scope(self, declared_tenant_id: str | None) -> str:
        if declared_tenant_id is None:
            raise TenantContextError("tenant_scope_required")
        if _tenant_id(declared_tenant_id) != self.tenant_id:
            raise TenantContextError("tenant_scope_denied")
        return self.tenant_id

    def require_admin_scope(self, declared_tenant_id: str | None) -> str:
        return self.require_background_scope(declared_tenant_id)


TenantContext = TenantScope


def validate_tenant_event_envelope(scope: TenantScope, envelope: Mapping[str, object]) -> dict[str, object]:
    """Reject task/event dispatch unless its scope is explicit and server-matched."""
    required = {"schema_version", "tenant_id", "event_type", "payload_digest"}
    if set(envelope) - required:
        raise TenantContextError("tenant_event_closed")
    tenant_id = envelope.get("tenant_id")
    if tenant_id is None:
        raise TenantContextError("tenant_scope_required")
    if set(envelope) != required:
        raise TenantContextError("tenant_event_closed")
    if not isinstance(tenant_id, str) or _tenant_id(tenant_id) != scope.tenant_id:
        raise TenantContextError("tenant_scope_denied")
    if envelope.get("schema_version") != 1 or not isinstance(envelope.get("event_type"), str) or not _EVENT_TYPE.fullmatch(envelope["event_type"]):
        raise TenantContextError("tenant_event_closed")
    if not isinstance(envelope.get("payload_digest"), str) or not _DIGEST.fullmatch(envelope["payload_digest"]):
        raise TenantContextError("tenant_event_closed")
    return dict(envelope)


class TenantContextResolver:
    """Resolve scope only from server-held delivery configuration and host mapping."""

    def __init__(
        self,
        *,
        mode: DeliveryMode,
        approved_default_tenant: str | None,
        route_tenants: Mapping[str, str],
        activated_modes: frozenset[DeliveryMode] | None = None,
    ) -> None:
        self.mode = DeliveryMode(mode)
        self.approved_default_tenant = (
            _tenant_id(approved_default_tenant)
            if approved_default_tenant is not None
            else None
        )
        self.route_tenants = {
            self._host(host): _tenant_id(tenant_id)
            for host, tenant_id in route_tenants.items()
        }
        self.activated_modes = activated_modes or frozenset(
            {DeliveryMode.PRIVATE_SINGLE_TENANT}
        )

    @staticmethod
    def _host(host: str) -> str:
        if not isinstance(host, str) or not _HOST.fullmatch(host.lower()):
            raise TenantContextError("tenant_route_denied")
        return host.lower()

    def resolve_request(
        self,
        *,
        host: str,
        claimed_tenant_id: str | None,
        principal_id: str,
    ) -> TenantContext:
        if not isinstance(principal_id, str) or not principal_id:
            raise TenantContextError("tenant_principal_required")
        if self.mode not in self.activated_modes:
            raise TenantContextError("delivery_mode_not_approved")
        self._host(host)
        if self.mode is DeliveryMode.PRIVATE_SINGLE_TENANT:
            if self.approved_default_tenant is None:
                raise TenantContextError("tenant_default_not_approved")
            # Client claim is intentionally ignored: it never selects a tenant.
            return TenantContext(self.approved_default_tenant, self.mode)
        resolved = self.route_tenants.get(self._host(host))
        if resolved is None:
            raise TenantContextError("tenant_route_denied")
        if claimed_tenant_id is not None and _tenant_id(claimed_tenant_id) != resolved:
            raise TenantContextError("tenant_spoof_denied")
        return TenantContext(resolved, self.mode)