def serialize_transaction(transaction):
    """
    Serializes a transaction to a data structure that is equivalent to the stored JSON format.
    :param transaction: the transaction to serialize (an instance of dnf.db.history.TransactionWrapper)
    """

    data = {
        "version": VERSION,
    }
    rpms = []
    groups = []
    environments = []

    if transaction is None:
        return data

    for tsi in transaction.packages():
        if tsi.is_package():
            rpms.append({
                "action": tsi.action_name,
                "nevra": tsi.nevra,
                "reason": libdnf.transaction.TransactionItemReasonToString(tsi.reason),
                "repo_id": tsi.from_repo
            })

        elif tsi.is_group():
            group = tsi.get_group()

            group_data = {
                "action": tsi.action_name,
                "id": group.getGroupId(),
                "packages": [],
                "package_types": libdnf.transaction.compsPackageTypeToString(group.getPackageTypes())
            }

            for pkg in group.getPackages():
                group_data["packages"].append({
                    "name": pkg.getName(),
                    "installed": pkg.getInstalled(),
                    "package_type": libdnf.transaction.compsPackageTypeToString(pkg.getPackageType())
                })

            groups.append(group_data)

        elif tsi.is_environment():
            env = tsi.get_environment()

            env_data = {
                "action": tsi.action_name,
                "id": env.getEnvironmentId(),
                "groups": [],
                "package_types": libdnf.transaction.compsPackageTypeToString(env.getPackageTypes())
            }

            for grp in env.getGroups():
                env_data["groups"].append({
                    "id": grp.getGroupId(),
                    "installed": grp.getInstalled(),
                    "group_type": libdnf.transaction.compsPackageTypeToString(grp.getGroupType())
                })

            environments.append(env_data)

    if rpms:
        data["rpms"] = rpms

    if groups:
        data["groups"] = groups

    if environments:
        data["environments"] = environments

    return data