-- Cities are independent transport networks. Existing Polotsk data is moved to
-- the default city so a second city can use the same route numbers and stop names.
CREATE TABLE IF NOT EXISTS cities (
    id SERIAL PRIMARY KEY,
    slug VARCHAR(64) NOT NULL UNIQUE,
    name VARCHAR(120) NOT NULL UNIQUE,
    emblem VARCHAR(64) NOT NULL DEFAULT '🏙️',
    center_lat NUMERIC(9, 6),
    center_lon NUMERIC(9, 6),
    schedule_source_url TEXT,
    is_active BOOLEAN NOT NULL DEFAULT true,
    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
    updated_at TIMESTAMPTZ NOT NULL DEFAULT now(),
    CONSTRAINT cities_slug_format CHECK (slug ~ '^[a-z0-9]+(?:-[a-z0-9]+)*$'),
    CONSTRAINT cities_center_pair CHECK (
      (center_lat IS NULL AND center_lon IS NULL)
      OR (center_lat BETWEEN -90 AND 90 AND center_lon BETWEEN -180 AND 180)
    )
);

INSERT INTO cities (slug, name, emblem, center_lat, center_lon, schedule_source_url)
VALUES
  ('polotsk', 'Полоцк', '🏛️', 55.4869, 28.7856, 'https://ap2polotsk.of.by/ap2/'),
  ('novopolotsk', 'Новополоцк', '🏙️', 55.5318, 28.5987, NULL)
ON CONFLICT (slug) DO NOTHING;

ALTER TABLE routes ADD COLUMN IF NOT EXISTS city_id INTEGER;
ALTER TABLE stops ADD COLUMN IF NOT EXISTS city_id INTEGER;
ALTER TABLE alerts ADD COLUMN IF NOT EXISTS city_id INTEGER;

UPDATE routes SET city_id = (SELECT id FROM cities WHERE slug = 'polotsk') WHERE city_id IS NULL;
UPDATE stops SET city_id = (SELECT id FROM cities WHERE slug = 'polotsk') WHERE city_id IS NULL;
UPDATE alerts SET city_id = (SELECT id FROM cities WHERE slug = 'polotsk') WHERE city_id IS NULL;

ALTER TABLE routes ALTER COLUMN city_id SET NOT NULL;
ALTER TABLE stops ALTER COLUMN city_id SET NOT NULL;
ALTER TABLE alerts ALTER COLUMN city_id SET NOT NULL;

DO $$
BEGIN
  IF NOT EXISTS (SELECT 1 FROM pg_constraint WHERE conname = 'routes_city_id_fkey') THEN
    ALTER TABLE routes ADD CONSTRAINT routes_city_id_fkey
      FOREIGN KEY (city_id) REFERENCES cities(id) ON DELETE RESTRICT;
  END IF;
  IF NOT EXISTS (SELECT 1 FROM pg_constraint WHERE conname = 'stops_city_id_fkey') THEN
    ALTER TABLE stops ADD CONSTRAINT stops_city_id_fkey
      FOREIGN KEY (city_id) REFERENCES cities(id) ON DELETE RESTRICT;
  END IF;
  IF NOT EXISTS (SELECT 1 FROM pg_constraint WHERE conname = 'alerts_city_id_fkey') THEN
    ALTER TABLE alerts ADD CONSTRAINT alerts_city_id_fkey
      FOREIGN KEY (city_id) REFERENCES cities(id) ON DELETE RESTRICT;
  END IF;
END $$;

CREATE INDEX IF NOT EXISTS idx_routes_city ON routes(city_id, is_active, route_number);
CREATE INDEX IF NOT EXISTS idx_stops_city ON stops(city_id, is_active, name);
CREATE INDEX IF NOT EXISTS idx_alerts_city_active ON alerts(city_id, is_active, start_time, end_time);

-- Incremental mobile sync must not leak even delete identifiers between cities.
ALTER TABLE sync_log ADD COLUMN IF NOT EXISTS city_id INTEGER REFERENCES cities(id) ON DELETE SET NULL;

UPDATE sync_log l SET city_id = r.city_id
FROM routes r
WHERE l.table_name = 'routes' AND l.record_id = r.id AND l.city_id IS NULL;
UPDATE sync_log l SET city_id = s.city_id
FROM stops s
WHERE l.table_name = 'stops' AND l.record_id = s.id AND l.city_id IS NULL;
UPDATE sync_log l SET city_id = r.city_id
FROM route_stops rs JOIN routes r ON r.id = rs.route_id
WHERE l.table_name = 'route_stops' AND l.record_id = rs.id AND l.city_id IS NULL;
UPDATE sync_log l SET city_id = r.city_id
FROM schedules s JOIN routes r ON r.id = s.route_id
WHERE l.table_name = 'schedules' AND l.record_id = s.id AND l.city_id IS NULL;

CREATE INDEX IF NOT EXISTS idx_sync_log_city_timestamp ON sync_log(city_id, timestamp DESC);

CREATE OR REPLACE FUNCTION log_sync_changes()
RETURNS TRIGGER AS $$
DECLARE
    sync_city_id INTEGER;
    related_route_id INTEGER;
BEGIN
    IF TG_TABLE_NAME IN ('routes', 'stops', 'alerts') THEN
        sync_city_id := CASE WHEN TG_OP = 'DELETE' THEN OLD.city_id ELSE NEW.city_id END;
    ELSIF TG_TABLE_NAME IN ('route_stops', 'schedules') THEN
        related_route_id := CASE WHEN TG_OP = 'DELETE' THEN OLD.route_id ELSE NEW.route_id END;
        SELECT city_id INTO sync_city_id FROM routes WHERE id = related_route_id;
    END IF;

    IF (TG_OP = 'DELETE') THEN
        INSERT INTO sync_log (table_name, record_id, action, city_id)
        VALUES (TG_TABLE_NAME, OLD.id, 'delete', sync_city_id);
        RETURN OLD;
    ELSIF (TG_OP = 'UPDATE') THEN
        INSERT INTO sync_log (table_name, record_id, action, city_id)
        VALUES (TG_TABLE_NAME, NEW.id, 'update', sync_city_id);
        RETURN NEW;
    ELSIF (TG_OP = 'INSERT') THEN
        INSERT INTO sync_log (table_name, record_id, action, city_id)
        VALUES (TG_TABLE_NAME, NEW.id, 'insert', sync_city_id);
        RETURN NEW;
    END IF;
    RETURN NULL;
END;
$$ LANGUAGE plpgsql;

DO $$
BEGIN
  IF NOT EXISTS (SELECT 1 FROM pg_trigger WHERE tgname = 'update_cities_updated_at') THEN
    CREATE TRIGGER update_cities_updated_at BEFORE UPDATE ON cities
      FOR EACH ROW EXECUTE FUNCTION update_updated_at_column();
  END IF;
END $$;