from __future__ import annotations

from dataclasses import dataclass, replace
from datetime import datetime
from enum import Enum
from typing import Literal

# ADR-0013: onboarding-risk / entity-shape grouping. Orthogonal to
# capability role (below) -- neither axis constrains the other except
# through guardrail policy, which is a reserved, unimplemented concern.
GROUPINGS = frozenset(
    {
        "trial",
        "friendly",
        "single",
        "small",
        "medium",
        "large",
        "enterprise",
        "consumer",
        "family",
        "community",
        "association",
        "agentic",
    }
)

# tenant:platform and tenant:coulomb predate the grouping taxonomy and stay
# reserved, ungrouped identifiers (ADR-0013's Tenant Claim rationale).
RESERVED_IDENTIFIERS = frozenset({"tenant:platform", "tenant:coulomb"})


class InvalidTenantIdentifierError(ValueError):
    """A tenant identifier does not match `tenant:<grouping>:<name>` or a reserved form."""


class InvalidGrantError(ValueError):
    """A role grant violates a domain invariant (ADR-0014)."""


class InvalidLifecycleTransitionError(ValueError):
    """A lifecycle transition is not legal from the tenant's current state."""


class ImmutableFieldError(ValueError):
    """An update tried to change a field that is immutable by contract."""


class EmptyUpdateError(ValueError):
    """An update carried no allow-listed field changes."""


class TenantRetiredError(ValueError):
    """A mutation was attempted on a retired tenant that only active tenants allow."""


class TenantLifecycle(str, Enum):
    """TEN-WP-0005: tenant existence is reversible, never hard-deleted.

    Retirement suspends a tenant's ability to take on new capability or plan
    state; it deliberately preserves the tenant record, its grant history,
    and its plan history so audit correlation and recovery stay intact.
    """

    ACTIVE = "active"
    RETIRED = "retired"


# The only tenant fields a PATCH may change. tenant_id, identifier, and
# grouping are immutable: the identifier is the IAM Profile `tenant` claim
# value that key-cape mints into tokens and flex-auth authorizes against, so
# mutating it would silently invalidate every issued token referencing it.
MUTABLE_METADATA_FIELDS = frozenset({"display_name", "contact_email"})


class CapabilityRole(str, Enum):
    """ADR-0014: non-exclusive capability roles a tenant may hold."""

    PLTF = "PLTF"
    IAM = "IAM"
    VEN = "VEN"
    CUS = "CUS"


GrantReason = Literal["plan_assignment", "manual_grant", "platform_default"]


def parse_tenant_identifier(identifier: str) -> tuple[str | None, str]:
    """Return (grouping, name). grouping is None only for reserved identifiers."""
    if identifier in RESERVED_IDENTIFIERS:
        return None, identifier.split(":", 1)[1]

    parts = identifier.split(":")
    if len(parts) != 3 or parts[0] != "tenant":
        raise InvalidTenantIdentifierError(
            f"Malformed tenant identifier: {identifier!r} (expected tenant:<grouping>:<name>)"
        )
    _, grouping, name = parts
    if grouping not in GROUPINGS:
        raise InvalidTenantIdentifierError(f"Unknown tenant grouping: {grouping!r}")
    if not name:
        raise InvalidTenantIdentifierError("Tenant name segment is empty")
    return grouping, name


@dataclass(frozen=True, slots=True)
class Tenant:
    tenant_id: str
    identifier: str
    grouping: str | None
    # -- TEN-WP-0005 lifecycle and mutable metadata. All default so that
    # pre-lifecycle construction sites (and migrated rows) keep working.
    display_name: str | None = None
    contact_email: str | None = None
    lifecycle: TenantLifecycle = TenantLifecycle.ACTIVE
    version: int = 1
    created_at: datetime | None = None
    updated_at: datetime | None = None
    retired_at: datetime | None = None
    reactivated_at: datetime | None = None

    @classmethod
    def create(
        cls,
        *,
        tenant_id: str,
        identifier: str,
        display_name: str | None = None,
        contact_email: str | None = None,
        created_at: datetime | None = None,
    ) -> "Tenant":
        grouping, _name = parse_tenant_identifier(identifier)
        return cls(
            tenant_id=tenant_id,
            identifier=identifier,
            grouping=grouping,
            display_name=display_name,
            contact_email=contact_email,
            created_at=created_at,
            updated_at=created_at,
        )

    @property
    def is_reserved(self) -> bool:
        return self.grouping is None

    @property
    def is_active(self) -> bool:
        return self.lifecycle is TenantLifecycle.ACTIVE

    def with_metadata(self, changes: dict[str, object], *, at: datetime) -> "Tenant":
        """Apply an allow-listed metadata change, bumping the record version.

        Fails closed on anything ambiguous: unknown fields, attempts to change
        an immutable field, an empty change set, or a no-op change set. A no-op
        is rejected rather than silently accepted so a caller never reads a
        version bump as evidence that a value actually changed.
        """
        if self.lifecycle is not TenantLifecycle.ACTIVE:
            raise InvalidLifecycleTransitionError(
                "metadata of a retired tenant cannot be updated; reactivate first"
            )

        unknown = set(changes) - MUTABLE_METADATA_FIELDS
        immutable = unknown & {"tenant_id", "identifier", "grouping", "version", "lifecycle"}
        if immutable:
            raise ImmutableFieldError(f"immutable field(s): {', '.join(sorted(immutable))}")
        if unknown:
            raise ImmutableFieldError(f"unknown field(s): {', '.join(sorted(unknown))}")
        if not changes:
            raise EmptyUpdateError("update carried no fields")
        if all(getattr(self, field) == value for field, value in changes.items()):
            raise EmptyUpdateError("update would not change any field")

        return replace(self, version=self.version + 1, updated_at=at, **changes)  # type: ignore[arg-type]

    def with_grouping(self, grouping: str, *, at: datetime) -> "Tenant":
        """Reclassify the tenant (TEN-WP-0010).

        Deliberately *not* part of `with_metadata`. `display_name` and
        `contact_email` are cosmetic; grouping resolves spend ceilings, so a
        change here moves money. It gets its own method, its own route, and its
        own flex-auth action so policy can permit a rename without permitting
        a reclassification, and so the audit trail shows which one happened.

        The identifier's grouping segment is *historical* -- onboarding-time,
        immutable, and not authoritative for current grouping (ADR-0013
        amendment proposed under TEN-WP-0010-T01). This field is the
        authoritative one, which is why it may diverge from the identifier.
        """
        if self.is_reserved:
            # tenant:platform and tenant:coulomb are ungrouped by design and
            # resolve guardrails through the reserved profile. Giving one a
            # grouping would silently move the platform's own identity onto
            # the grouping ladder.
            raise ImmutableFieldError(
                "reserved tenants are ungrouped and cannot be reclassified"
            )
        if self.lifecycle is not TenantLifecycle.ACTIVE:
            raise InvalidLifecycleTransitionError(
                "grouping of a retired tenant cannot be changed; reactivate first"
            )
        if grouping not in GROUPINGS:
            raise InvalidTenantIdentifierError(f"Unknown tenant grouping: {grouping!r}")
        if grouping == self.grouping:
            raise EmptyUpdateError("update would not change the grouping")

        return replace(self, grouping=grouping, version=self.version + 1, updated_at=at)

    def retire(self, *, at: datetime) -> "Tenant":
        if self.lifecycle is TenantLifecycle.RETIRED:
            raise InvalidLifecycleTransitionError("tenant is already retired")
        return replace(
            self,
            lifecycle=TenantLifecycle.RETIRED,
            version=self.version + 1,
            updated_at=at,
            retired_at=at,
        )

    def reactivate(self, *, at: datetime) -> "Tenant":
        """Return the tenant to active. Deliberately narrow: it restores the
        tenant's ability to receive new grants and plan changes, and does not
        resurrect revoked grants or invent plan state -- those stay exactly as
        retirement left them.
        """
        if self.lifecycle is TenantLifecycle.ACTIVE:
            raise InvalidLifecycleTransitionError("tenant is already active")
        return replace(
            self,
            lifecycle=TenantLifecycle.ACTIVE,
            version=self.version + 1,
            updated_at=at,
            reactivated_at=at,
        )


@dataclass(frozen=True, slots=True)
class RoleGrant:
    """Audited role grant record -- the Tenant Role & Plan Grant Contract shape.

    Append-only: revocation produces a new record via `revoke()`, it never
    deletes the original.
    """

    grant_id: str
    tenant_id: str
    role: CapabilityRole
    grant_reason: GrantReason
    plan_id: str | None
    granted_by: str
    granted_at: datetime
    correlation_id: str
    revoked_at: datetime | None = None

    @property
    def active(self) -> bool:
        return self.revoked_at is None

    def revoke(self, *, at: datetime) -> "RoleGrant":
        if self.revoked_at is not None:
            raise InvalidGrantError(f"Grant {self.grant_id!r} is already revoked")
        return replace(self, revoked_at=at)


@dataclass(frozen=True, slots=True)
class PlanAssignment:
    """A tenant's current plan, referenced by id only -- never resolved or

    duplicated locally. Plan term definitions belong to adaptive-pricing.
    """

    tenant_id: str
    plan_id: str
    assigned_at: datetime


def create_role_grant(
    *,
    tenant: Tenant,
    grant_id: str,
    role: CapabilityRole,
    grant_reason: GrantReason,
    plan_id: str | None,
    granted_by: str,
    correlation_id: str,
    granted_at: datetime,
) -> RoleGrant:
    """Construct a RoleGrant, enforcing ADR-0014's domain invariants.

    - `plan_assignment` grants always require a `plan_id`.
    - `platform_default` grants never carry a `plan_id`, and are only valid
      for `trial`-grouped tenants (ADR-0014: trial may hold any role,
      unrestricted, for showcase purposes) or the reserved, ungrouped
      `tenant:platform`/`tenant:coulomb` tenants (their baseline roles were
      never purchased either).
    - `manual_grant` carries no grouping restriction and an optional
      `plan_id`.
    """
    if grant_reason == "plan_assignment" and plan_id is None:
        raise InvalidGrantError("plan_assignment grants require a plan_id")

    if grant_reason == "platform_default":
        if plan_id is not None:
            raise InvalidGrantError("platform_default grants must not carry a plan_id")
        if tenant.grouping not in (None, "trial"):
            raise InvalidGrantError(
                "platform_default is only valid for trial-grouped or reserved tenants, "
                f"got grouping={tenant.grouping!r}"
            )

    return RoleGrant(
        grant_id=grant_id,
        tenant_id=tenant.tenant_id,
        role=role,
        grant_reason=grant_reason,
        plan_id=plan_id,
        granted_by=granted_by,
        granted_at=granted_at,
        correlation_id=correlation_id,
    )