BEGIN;

ALTER TABLE employee_kandangs
    DROP CONSTRAINT IF EXISTS fk_employee_kandangs_kandang;

ALTER TABLE employee_kandangs
    DROP CONSTRAINT IF EXISTS uq_employee_kandangs;

CREATE TEMP TABLE tmp_kandang_group_to_kandang_map (
    kandang_group_id BIGINT PRIMARY KEY,
    kandang_id BIGINT NOT NULL
) ON COMMIT DROP;

INSERT INTO tmp_kandang_group_to_kandang_map (kandang_group_id, kandang_id)
SELECT
    k.kandang_group_id,
    MIN(k.id) AS kandang_id
FROM kandangs k
WHERE k.kandang_group_id IS NOT NULL
GROUP BY k.kandang_group_id;

DO $$
BEGIN
    IF EXISTS (
        SELECT 1
        FROM employee_kandangs ek
        LEFT JOIN tmp_kandang_group_to_kandang_map m ON m.kandang_group_id = ek.kandang_id
        WHERE m.kandang_id IS NULL
    ) THEN
        RAISE EXCEPTION 'Cannot rollback employee_kandangs migration: kandang_group_id has no kandang mapping';
    END IF;
END $$;

UPDATE employee_kandangs ek
SET kandang_id = m.kandang_id,
    updated_at = NOW()
FROM tmp_kandang_group_to_kandang_map m
WHERE m.kandang_group_id = ek.kandang_id;

DELETE FROM employee_kandangs ek1
USING employee_kandangs ek2
WHERE ek1.id > ek2.id
  AND ek1.employee_id = ek2.employee_id
  AND ek1.kandang_id = ek2.kandang_id;

ALTER TABLE employee_kandangs
    ADD CONSTRAINT fk_employee_kandangs_kandang
        FOREIGN KEY (kandang_id) REFERENCES kandangs (id)
            ON DELETE CASCADE;

ALTER TABLE employee_kandangs
    ADD CONSTRAINT uq_employee_kandangs UNIQUE (employee_id, kandang_id);

COMMIT;