BEGIN;

ALTER TABLE stock_lot
  ADD COLUMN IF NOT EXISTS next_active BOOLEAN NOT NULL DEFAULT FALSE;

CREATE UNIQUE INDEX IF NOT EXISTS uq_stock_lot_one_next_active_per_product
  ON stock_lot(product_id)
  WHERE status = 'open' AND next_active = TRUE;

CREATE OR REPLACE FUNCTION fn_auto_switch_lot_when_depleted()
RETURNS TRIGGER
LANGUAGE plpgsql
AS $$
DECLARE
  v_product_id BIGINT;
  v_open_lot_id BIGINT;
  v_qualified_count INTEGER;
  v_current_net NUMERIC;
  v_event_key TEXT;
BEGIN
  SELECT product_id
  INTO v_product_id
  FROM stock_lot
  WHERE id = NEW.lot_id;

  IF NOT EXISTS (
    SELECT 1 FROM stock_lot WHERE id = NEW.lot_id AND status = 'current'
  ) THEN
    RETURN NEW;
  END IF;

  SELECT qty_net
  INTO v_current_net
  FROM v_stock_lot_balance
  WHERE stock_lot_id = NEW.lot_id;

  IF COALESCE(v_current_net, 0) > 0 THEN
    RETURN NEW;
  END IF;

  PERFORM 1
  FROM stock_lot
  WHERE product_id = v_product_id
  FOR UPDATE;

  IF NOT EXISTS (
    SELECT 1 FROM stock_lot WHERE id = NEW.lot_id AND status = 'current'
  ) THEN
    RETURN NEW;
  END IF;

  SELECT sl.id
  INTO v_open_lot_id
  FROM stock_lot sl
  INNER JOIN v_stock_lot_balance v ON v.stock_lot_id = sl.id
  WHERE sl.product_id = v_product_id
    AND sl.status = 'open'
    AND sl.next_active = TRUE
    AND NULLIF(TRIM(sl.lot_number), '') IS NOT NULL
    AND sl.manufacturer_party_id IS NOT NULL
    AND NULLIF(TRIM(sl.manufacturer_lot_number), '') IS NOT NULL
    AND sl.mfg_date IS NOT NULL
    AND sl.expiry_date IS NOT NULL
    AND sl.purchase_date IS NOT NULL
    AND v.qty_net > 0
  LIMIT 1;

  IF v_open_lot_id IS NULL THEN
    SELECT COUNT(*), MIN(sl.id)
    INTO v_qualified_count, v_open_lot_id
    FROM stock_lot sl
    INNER JOIN v_stock_lot_balance v ON v.stock_lot_id = sl.id
    WHERE sl.product_id = v_product_id
      AND sl.status = 'open'
      AND NULLIF(TRIM(sl.lot_number), '') IS NOT NULL
      AND sl.manufacturer_party_id IS NOT NULL
      AND NULLIF(TRIM(sl.manufacturer_lot_number), '') IS NOT NULL
      AND sl.mfg_date IS NOT NULL
      AND sl.expiry_date IS NOT NULL
      AND sl.purchase_date IS NOT NULL
      AND v.qty_net > 0;

    IF v_qualified_count <> 1 THEN
      RETURN NEW;
    END IF;

    UPDATE stock_lot
    SET next_active = TRUE, updated_at = NOW()
    WHERE id = v_open_lot_id;
  END IF;

  UPDATE stock_lot
  SET status = 'closed', updated_at = NOW()
  WHERE id = NEW.lot_id;

  UPDATE stock_lot
  SET status = 'current', next_active = FALSE, updated_at = NOW()
  WHERE id = v_open_lot_id;

  v_event_key := format('lot.auto_switched:%s:%s', v_product_id, txid_current());

  PERFORM fn_enqueue_event(
    'lot.auto_switched',
    v_event_key,
    'stock_lot',
    NEW.lot_id::TEXT,
    jsonb_build_object(
      'productId', v_product_id,
      'closedLotId', NEW.lot_id,
      'newCurrentLotId', v_open_lot_id,
      'occurredAt', NOW()
    )
  );

  RETURN NEW;
END;
$$;

COMMIT;