ALTER TABLE vendors
    ADD COLUMN IF NOT EXISTS is_internet_provider BOOLEAN NOT NULL DEFAULT FALSE;

ALTER TABLE internet_connections_connections
    ADD COLUMN IF NOT EXISTS vendor_id INTEGER REFERENCES vendors(id) ON DELETE SET NULL;

CREATE INDEX IF NOT EXISTS idx_vendors_internet_provider
    ON vendors(is_internet_provider, is_active);

CREATE INDEX IF NOT EXISTS idx_internet_connections_vendor
    ON internet_connections_connections(vendor_id)
    WHERE deleted_at IS NULL;

-- Link existing provider text only when it identifies exactly one vendor.
UPDATE internet_connections_connections connection
SET vendor_id = candidate.vendor_id
FROM (
    SELECT LOWER(BTRIM(connection.provider)) AS provider_key, MIN(vendor.id) AS vendor_id
    FROM internet_connections_connections connection
    JOIN vendors vendor ON LOWER(BTRIM(vendor.name)) = LOWER(BTRIM(connection.provider))
    WHERE connection.deleted_at IS NULL AND NULLIF(BTRIM(connection.provider), '') IS NOT NULL
    GROUP BY LOWER(BTRIM(connection.provider))
    HAVING COUNT(DISTINCT vendor.id) = 1
) candidate
WHERE connection.deleted_at IS NULL
  AND connection.vendor_id IS NULL
  AND LOWER(BTRIM(connection.provider)) = candidate.provider_key;

CREATE OR REPLACE FUNCTION assign_internet_connection_vendor()
RETURNS TRIGGER AS $$
DECLARE
    matched_vendor_id INTEGER;
BEGIN
    IF NEW.vendor_id IS NULL AND NULLIF(BTRIM(NEW.provider), '') IS NOT NULL THEN
        SELECT id INTO matched_vendor_id
        FROM vendors
        WHERE is_active = TRUE
          AND is_internet_provider = TRUE
          AND regexp_replace(
                regexp_replace(LOWER(name), '(denmark|danmark|a/s|as)', '', 'g'),
                '[^a-z0-9]', '', 'g'
              ) = regexp_replace(
                regexp_replace(LOWER(NEW.provider), '(denmark|danmark|a/s|as)', '', 'g'),
                '[^a-z0-9]', '', 'g'
              )
        ORDER BY id
        LIMIT 1;
        NEW.vendor_id := matched_vendor_id;
    END IF;
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

DROP TRIGGER IF EXISTS internet_connections_assign_vendor ON internet_connections_connections;
CREATE TRIGGER internet_connections_assign_vendor
    BEFORE INSERT OR UPDATE OF provider, vendor_id
    ON internet_connections_connections
    FOR EACH ROW
    EXECUTE FUNCTION assign_internet_connection_vendor();