CREATE OR REPLACE FUNCTION delete_user(rolename text) RETURNS int
AS $$
DECLARE
    user_exists bool;
    is_admin    bool;
    has_imports bool;
BEGIN
    SELECT EXISTS (SELECT 1 FROM pg_roles
        WHERE rolname = rolename)
        INTO user_exists;

    IF NOT user_exists THEN
        RETURN 0;
    END IF;

    SELECT EXISTS (SELECT 1 FROM pg_roles
        WHERE pg_has_role(rolename, oid, 'member') AND
            rolname IN ('waterway_admin', 'sys_admin'))
        INTO is_admin;

    -- None admins can be deleted.
    IF NOT is_admin THEN
        DELETE FROM users.list_users WHERE username = rolename;
        RETURN 1;
    END IF;

    SELECT EXISTS (SELECT 1 FROM import.imports
        WHERE username = rolename)
        INTO has_imports;

    -- Admins w/o imports can be deleted.
    IF NOT has_imports THEN
        DELETE FROM users.list_users WHERE username = rolename;
        RETURN 1;
    END IF;

    -- Admins w/ imports have to be deactivated.
    UPDATE users.list_users
        SET (email_address, report_reciever, active) =
            ('nomail@example.com', false, false)
        WHERE username = rolename;

    -- Do not allow to login any more.
    EXECUTE format(
        'ALTER ROLE %I NOLOGIN', rolename);

    RETURN 2;
END;
$$
LANGUAGE plpgsql
SECURITY DEFINER;

GRANT EXECUTE ON FUNCTION delete_user to sys_admin;