-- n:m-Verknüpfung Bankbuchung <-> Belege mit zugewiesenem Betrag
CREATE TABLE IF NOT EXISTS bank_transaction_belege (
    id          INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    bank_tx_id  INT UNSIGNED NOT NULL,
    beleg_id    INT UNSIGNED NOT NULL,
    betrag      DECIMAL(12,2) NOT NULL DEFAULT 0.00,
    created_at  TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    UNIQUE KEY uq_tx_beleg (bank_tx_id, beleg_id),
    FOREIGN KEY (bank_tx_id) REFERENCES bank_transactions(id) ON DELETE CASCADE,
    FOREIGN KEY (beleg_id)   REFERENCES belege(id)            ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

-- Bestehende 1:1-Verknüpfungen migrieren
INSERT IGNORE INTO bank_transaction_belege (bank_tx_id, beleg_id, betrag)
SELECT bt.id, bt.beleg_id, ABS(bt.wert)
FROM bank_transactions bt
WHERE bt.beleg_id IS NOT NULL;

-- Neuer Status 'teilweise'
ALTER TABLE bank_transactions
    MODIFY COLUMN status ENUM('offen','teilweise','gebucht','ignoriert') NOT NULL DEFAULT 'offen';

-- Altes Einzelfeld entfernen
ALTER TABLE bank_transactions DROP COLUMN beleg_id;