-- Подписка «сообщить о поступлении»
CREATE TABLE IF NOT EXISTS product_stock_alerts (
  id SERIAL PRIMARY KEY,
  product_id INTEGER NOT NULL REFERENCES products(id) ON DELETE CASCADE,
  email TEXT NOT NULL,
  user_id INTEGER REFERENCES users(id) ON DELETE SET NULL,
  created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
  notified_at TIMESTAMPTZ,
  UNIQUE (product_id, email)
);

CREATE INDEX IF NOT EXISTS idx_stock_alerts_product_pending
  ON product_stock_alerts (product_id)
  WHERE notified_at IS NULL;