"""oauth_account table; user.discord_only -> user.oauth_only

Generalises "sign in with Discord" to any provider (see accounts/oauth.py). Three
steps, each conditional so the revision is safe on a database created before or
after the ORM gained these definitions — revision 0001 builds the schema with
``Base.metadata.create_all`` off *live* model metadata, so a freshly created
database already has both the table and the renamed column, and an unconditional
DDL would fail there with duplicate-object errors.

The backfill is the load-bearing step. Discord identities used to live in
``user.discord_id``, and account resolution now keys on ``oauth_account``; without
copying the existing rows across, every already-linked user would silently stop
being recognised at login and would get a *second* account created on their next
sign-in. ``user.discord_id`` is deliberately left in place — it is the DM delivery
address notify.py reads, not merely an identity.

Revision ID: 0005_oauth_accounts
Revises: 0004_bookmarks
Create Date: 2026-07-26
"""
import time

import sqlalchemy as sa
from alembic import op
# The same UUID type the ORM uses for user.id — a plain sa.Uuid renders differently
# on SQLite and would not match the column create_all produces.
from fastapi_users_db_sqlalchemy.generics import GUID

revision = "0005_oauth_accounts"
down_revision = "0004_bookmarks"
branch_labels = None
depends_on = None


def _columns(table: str) -> set[str]:
    return {c["name"] for c in sa.inspect(op.get_bind()).get_columns(table)}


def _tables() -> set[str]:
    return set(sa.inspect(op.get_bind()).get_table_names())


def upgrade() -> None:
    cols = _columns("user")

    # 1. Rename the flag. It no longer means "Discord created this account", it
    #    means "no password its owner has ever seen, whichever provider made it".
    if "oauth_only" in cols:
        # A database built by 0001 already has oauth_only (create_all reads *current*
        # metadata), and 0003 then re-added an empty discord_only beside it, because
        # 0003 tests for the name it knew. Drop that vestige, or a fresh database
        # carries a column an upgraded one does not — schema drift that would only
        # surface much later. Safe: on this path the column was created empty
        # moments ago and nothing has ever read it.
        if "discord_only" in cols:
            op.drop_column("user", "discord_only")
    elif "discord_only" in cols:
        # The real upgrade path: a deployed database carrying live values. Renamed,
        # never dropped, so nothing is lost.
        op.alter_column("user", "discord_only", new_column_name="oauth_only")
    else:
        # Database predates even discord_only (never deployed with it).
        op.add_column("user", sa.Column("oauth_only", sa.Boolean(), nullable=False,
                                        server_default=sa.false()))

    # 2. The identity table.
    if "oauth_account" not in _tables():
        op.create_table(
            "oauth_account",
            sa.Column("id", sa.Integer(), primary_key=True, autoincrement=True),
            sa.Column("user_id", GUID(), sa.ForeignKey("user.id", ondelete="CASCADE"),
                      nullable=False),
            sa.Column("provider", sa.String(length=32), nullable=False),
            sa.Column("subject", sa.String(length=64), nullable=False),
            sa.Column("email", sa.String(length=320), nullable=True),
            sa.Column("created_at", sa.Float(), nullable=False),
            sa.UniqueConstraint("provider", "subject", name="uq_oauth_provider_subject"),
            sa.UniqueConstraint("user_id", "provider", name="uq_oauth_user_provider"),
        )
        op.create_index("idx_oauth_user", "oauth_account", ["user_id"])

    # 3. Backfill every existing Discord link. Guarded by NOT EXISTS so re-running
    #    (or running after create_all already produced the table) cannot violate
    #    either unique constraint.
    op.execute(sa.text("""
        INSERT INTO oauth_account (user_id, provider, subject, email, created_at)
        SELECT u.id, 'discord', u.discord_id, u.email, :now
        FROM "user" u
        WHERE u.discord_id IS NOT NULL
          AND NOT EXISTS (
            SELECT 1 FROM oauth_account o
            WHERE o.provider = 'discord'
              AND (o.subject = u.discord_id OR o.user_id = u.id)
          )
    """).bindparams(now=time.time()))


def downgrade() -> None:
    if "oauth_account" in _tables():
        op.drop_index("idx_oauth_user", table_name="oauth_account")
        op.drop_table("oauth_account")
    cols = _columns("user")
    if "oauth_only" in cols and "discord_only" not in cols:
        op.alter_column("user", "oauth_only", new_column_name="discord_only")