// Actions Service Interface

/**
 * Executes multiple actions in the context of the user given by the user_id.
 * There are two modes of execution:
 * single_validation=false (default):
 *   All actions are validated in common, so if one action or one payload of
 *   one action fails, the request is aborted with an ActionException indicating
 *   the problematic action with both indices.
 * single_validation=true:
 *   Each action is validated by it's own. If there is an error, the error must
 *   be reported via an ActionError in the ActionsResponse. The actions result
 *   is not written into the Datastore. It might raise an ActionException if the
 *   single write request to the Datastore fails (e.g. because of locking there)
 *
 * For general, non specific action-related, errors an ActionException is used.
 *
 * @throws ActionException
 */
handle_request(payload: Action[], user_id: Id): ActionsResponse

interface Action {
    action: string;
    data: object[];
    single_validation?: boolean;
}

interace ActionsResponse {
    success: true;
    message: string;

    /**
     * This is a potentially double-array with entries for each action
     * and, if not null, an array for each data provided for each action.
     *
     * If an action does not produce a result, the inner array can be omitted and
     * null can be used. If the inner array is given, each entry must be an object
     * with the result (e.g. for a create action `{id: <the id>}`) or null.
     *
     * E.g. for valid arrays (two actions with two data entries each):
     * - [null, null]
     * - [null, [null, null]]
     * - [null, [{id: 2}, null]]
     * - [[{id: 2}, {id: 3}], [{id: 5}, {id: 8}]]
     *
     *
     * To report errors, use the ActionError format!
     **/
    results: ((object | ActionError | null)[] | null )[]
}

interface ActionError {
    success: false;
    message: string;
}

/**
 * JSON resonse with a status code of !=200. If a specific action raised the error,
 * use the action_error_index and action_payload_error_index to indicate the errored
 * action and payload. If there were general errors, both indices must be omitted.
 *
 * If the single_validation Flag was true in the request, it is not allowed to send
 * action-specific errors with this exception. It must be responded through ActionsResponse.
 */
Exception ActionException {
    success: false;
    message: string;
    action_error_index: number;
    action_payload_error_index: number;
}