"""platform_membership — the learned roster of what the account actually pays for.

Milestone 387, phase C. FabledCurator knows which creators it has been TOLD to
follow (`source`), and nothing about which ones the operator is actually
subscribed to. Those two sets drift in both directions and the app cannot
currently see either drift:

* A subscription the operator pays for that FC does not track is content they
  believe they are archiving and are not.
* A source FC keeps walking after the subscription lapsed is requests spent on
  a wall, reported as a creator who has gone quiet.

This table is the memory that makes both visible — every membership the account
has been observed to hold, and when it was last seen.

## Why a learned roster rather than a live lookup

Same reasoning as `service_seen` (milestone 365), and the same shape: an
absence is only observable against a record of presence. A membership that
stops appearing in a sweep is the signal — "you were subscribed to this, now
you aren't" — and there is nowhere to read that from a live call, because a
live call returns what IS, never what stopped being.

It also means the reconciliation surface keeps working when Patreon is
unreachable, degraded to a stale roster with a visible age rather than an empty
page (rule 164).

## Roster truth, NOT per-post truth

The single most important thing about this table: `tier_names` says which tiers
the account holds. It does **not** say which posts those tiers unlock. A
creator can gate a post behind an access rule that maps onto no tier name at
all.

`current_user_can_view` — read per post by `patreon_client.post_is_gated` — is
the authoritative signal, and phase A already turned it into a durable
per-source state. This roster EXPLAINS that state ("you are no longer a patron"
vs "your tier doesn't cover these posts"). It must never be used to decide
whether to fetch something. Getting that backwards would make FC silently stop
fetching content the operator is paying for, which is the worst failure
available in this milestone.

## status is a plain String, and deliberately the platform's own word

Not a Postgres ENUM, not CHECK-gated — matching `service_seen.kind`,
`gpu_job.status` and `source.error_type`. Two reasons, and the first is the
real one:

1. **The vocabulary is not ours to invent.** Patreon says `active_patron` /
   `former_patron` / `declined_patron`; SubscribeStar and FANBOX will say
   something else. Storing each platform's own word verbatim and mapping to
   FC's meaning at the READ site keeps this table a record of what was
   observed rather than a lossy translation of it. A lowest-common-denominator
   enum picked before any platform has been characterised (step C0) would be a
   guess baked into the schema.
2. A constraint swap per new value (rule 36) would be cost with no invariant
   behind it, exactly as `service_seen.kind` records.

The service layer owns the whitelist and the mapping; the column owns the
evidence.

## Retention: aged out, never deleted on disappearance

A membership that stops appearing in a sweep is NOT removed. Its disappearance
is the fact the reconciliation surface reads, and deleting the row would
destroy the signal at the moment it became interesting. `last_seen_at` is what
makes "gone" decidable, and a retention policy ages rows out on time rather
than on absence.
"""

from datetime import datetime

from sqlalchemy import JSON, DateTime, Integer, String, Text, UniqueConstraint, func
from sqlalchemy.orm import Mapped, mapped_column

from .base import Base


class PlatformMembership(Base):
    __tablename__ = "platform_membership"
    __table_args__ = (
        # The natural key the sweep's upsert conflicts on. Named explicitly
        # because `touch_membership` references it by name in ON CONFLICT.
        UniqueConstraint(
            "platform", "external_campaign_id",
            name="uq_platform_membership_platform_campaign",
        ),
    )

    id: Mapped[int] = mapped_column(Integer, primary_key=True)

    platform: Mapped[str] = mapped_column(String(64), nullable=False)
    # The platform's own id for the thing subscribed to — a Patreon campaign
    # id, whatever SubscribeStar and FANBOX call theirs. Text rather than a
    # bounded String: these are opaque upstream identifiers and guessing a
    # ceiling for a value we do not mint is how a walk dies on a truncation.
    external_campaign_id: Mapped[str] = mapped_column(Text, nullable=False)

    # For the reconciliation UI, and for matching against Source.url — the
    # vanity/URL is what the two sides actually have in common.
    display_name: Mapped[str | None] = mapped_column(Text, nullable=True)
    url: Mapped[str | None] = mapped_column(Text, nullable=True)

    # The platform's own word. See the module docstring — this is evidence,
    # not a normalised FC status.
    status: Mapped[str | None] = mapped_column(String(32), nullable=True)

    # Nullable throughout: a free follow has no tier and no money attached, and
    # a platform may not expose an amount at all. Absent must stay
    # distinguishable from zero — "free" and "we don't know" are different
    # answers to "what is this costing".
    tier_names: Mapped[list | None] = mapped_column(JSON, nullable=True)
    amount_cents: Mapped[int | None] = mapped_column(Integer, nullable=True)
    currency: Mapped[str | None] = mapped_column(String(8), nullable=True)

    # NEVER updated after insert. The one field that answers "has this ever
    # been true", which is what makes a disappearance readable rather than
    # indistinguishable from never having existed. `touch_membership`
    # deliberately excludes it from the ON CONFLICT update set.
    first_seen_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True), nullable=False, server_default=func.now(),
    )
    last_seen_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True), nullable=False, server_default=func.now(),
    )

    # The raw membership as the platform returned it, so a later question can
    # be answered without re-fetching — and so a field we did not think to
    # model is not lost. Displayed and never queried, like service_seen.details.
    details: Mapped[dict] = mapped_column(JSON, nullable=False, default=dict)