-- Migration: Shared Vehicle Config (car-config-centric architecture)
-- Converts per-user vehicle records to shared vehicle configs with junction table.
-- IMPORTANT: Take a DB backup before running. Execute inside a transaction.

BEGIN;

-- 1. Create user_vehicles junction table
CREATE TABLE user_vehicles (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
  vehicle_id UUID NOT NULL,
  created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
  last_accessed_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

-- 2. For each VIN, pick the canonical record (most recently updated)
-- and migrate all userId-vehicleId pairs into the junction table
INSERT INTO user_vehicles (user_id, vehicle_id, created_at, last_accessed_at)
SELECT
  v.user_id,
  canonical.id,
  v.created_at,
  v.updated_at
FROM vehicles v
JOIN (
  SELECT DISTINCT ON (vin) id, vin
  FROM vehicles
  ORDER BY vin, updated_at DESC NULLS LAST
) canonical ON canonical.vin = v.vin;

-- 3. Delete categories on NON-canonical vehicles that already exist on the
--    canonical vehicle (same name+source), so the UPDATE in step 4 won't
--    hit the unique constraint.
WITH canonical AS (
  SELECT DISTINCT ON (vin) id AS cid, vin
  FROM vehicles ORDER BY vin, updated_at DESC NULLS LAST
)
DELETE FROM categories
WHERE id IN (
  SELECT c_dup.id
  FROM categories c_dup
  JOIN vehicles v ON c_dup.vehicle_id = v.id
  JOIN canonical can ON can.vin = v.vin
  WHERE v.id != can.cid
    AND EXISTS (
      SELECT 1 FROM categories c_can
      WHERE c_can.vehicle_id = can.cid
        AND c_can.name = c_dup.name
        AND c_can.source = c_dup.source
    )
);

-- 4. Move remaining categories from non-canonical vehicles to canonical
WITH canonical AS (
  SELECT DISTINCT ON (vin) id AS cid, vin
  FROM vehicles ORDER BY vin, updated_at DESC NULLS LAST
)
UPDATE categories c
SET vehicle_id = can.cid
FROM vehicles v JOIN canonical can ON can.vin = v.vin
WHERE c.vehicle_id = v.id AND v.id != can.cid;

-- 5. Delete parts on non-canonical vehicles that would conflict after move
--    (parts don't have a unique constraint, but let's keep data clean by
--     removing duplicates — same oemCode+categoryId on canonical vehicle)
WITH canonical AS (
  SELECT DISTINCT ON (vin) id AS cid, vin
  FROM vehicles ORDER BY vin, updated_at DESC NULLS LAST
)
DELETE FROM parts
WHERE id IN (
  SELECT p_dup.id
  FROM parts p_dup
  JOIN vehicles v ON p_dup.vehicle_id = v.id
  JOIN canonical can ON can.vin = v.vin
  WHERE v.id != can.cid
    AND EXISTS (
      SELECT 1 FROM parts p_can
      WHERE p_can.vehicle_id = can.cid
        AND p_can.category_id = p_dup.category_id
        AND p_can.oem_code = p_dup.oem_code
    )
);

-- 6. Move remaining parts from non-canonical vehicles to canonical
WITH canonical AS (
  SELECT DISTINCT ON (vin) id AS cid, vin
  FROM vehicles ORDER BY vin, updated_at DESC NULLS LAST
)
UPDATE parts p
SET vehicle_id = can.cid
FROM vehicles v JOIN canonical can ON can.vin = v.vin
WHERE p.vehicle_id = v.id AND v.id != can.cid;

-- 7. Delete non-canonical vehicle records (duplicates)
DELETE FROM vehicles WHERE id NOT IN (
  SELECT DISTINCT ON (vin) id FROM vehicles
  ORDER BY vin, updated_at DESC NULLS LAST
);

-- 8. Drop old user-specific indexes and column
DROP INDEX IF EXISTS vehicles_user_vin_idx;
DROP INDEX IF EXISTS vehicles_user_id_idx;
ALTER TABLE vehicles DROP COLUMN user_id;

-- 9. Add unique index on VIN (one record per VIN globally)
CREATE UNIQUE INDEX vehicles_vin_unique_idx ON vehicles (vin);

-- 10. Add FK and indexes on junction table
ALTER TABLE user_vehicles
  ADD CONSTRAINT user_vehicles_vehicle_id_fkey
  FOREIGN KEY (vehicle_id) REFERENCES vehicles(id) ON DELETE CASCADE;
CREATE UNIQUE INDEX user_vehicles_user_vehicle_idx ON user_vehicles (user_id, vehicle_id);
CREATE INDEX user_vehicles_user_id_idx ON user_vehicles (user_id);

-- 11. Drop unused vehicle_categories table
DROP TABLE IF EXISTS vehicle_categories;

-- Also drop the old vin-only index if it exists (replaced by unique)
DROP INDEX IF EXISTS vehicles_vin_idx;

COMMIT;