"""storefronts — the storefront + membership service (SD-0001 §6.5).

Owns the storefront entity, the account<->storefront membership (INV-5), the entry-routing
answer (storefront_for), and INV-4's one-storefront guard — the single deletable check that
makes one-per-account an MVP rule, not a schema law. Never mints identity: the BFF passes
account_id and email down.
"""
from __future__ import annotations

import psycopg

from .errors import AlreadyOwnsStorefront
from .models import Storefront


def _default_name(email: str) -> str:
    """§6.3: a blank name stores a generated default — never NULL (corpus 14.01.0026)."""
    return f"{email.split('@', 1)[0]}'s storefront"


def storefront_for(conn: psycopg.Connection, account_id: int) -> Storefront | None:
    """The entry-routing answer (§6.5): which storefront, if any, this account has."""
    row = conn.execute(
        "SELECT s.id, s.name FROM storefront s"
        " JOIN storefront_membership m ON m.storefront_id = s.id"
        " WHERE m.account_id = %s ORDER BY m.created_at LIMIT 1",
        (account_id,),
    ).fetchone()
    return Storefront(id=row[0], name=row[1]) if row else None


def create_storefront(
    conn: psycopg.Connection, account_id: int, email: str, name: str | None
) -> Storefront:
    """Create the account's one storefront + owner membership (PUC-4; INV-4, INV-5).

    Guard + insert run as one atomic unit: a transaction-scoped advisory lock keyed by
    account_id serializes concurrent creates for the same account, so the second of two
    racing requests sees the first's committed membership and is refused (§6.5).
    """
    conn.execute("SELECT pg_advisory_xact_lock(%s)", (account_id,))
    existing = storefront_for(conn, account_id)
    if existing is not None:
        conn.rollback()  # release the advisory lock; nothing was written
        raise AlreadyOwnsStorefront()
    final_name = (name or "").strip() or _default_name(email)
    sf_id = conn.execute(
        "INSERT INTO storefront (name) VALUES (%s) RETURNING id", (final_name,)
    ).fetchone()[0]
    conn.execute(
        "INSERT INTO storefront_membership (account_id, storefront_id, role)"
        " VALUES (%s, %s, 'owner')",
        (account_id, sf_id),
    )
    conn.commit()
    return Storefront(id=sf_id, name=final_name)