def get_git_shas_for_service(service, deploy_groups, soa_dir):
    if service is None:
        return []
    git_url = get_git_url(service=service, soa_dir=soa_dir)
    all_deploy_groups = {config.get_deploy_group() for config in get_instance_config_for_service(
        service=service,
        soa_dir=soa_dir,
    )}
    deploy_groups, _ = validate_given_deploy_groups(all_deploy_groups, deploy_groups)
    previously_deployed_shas = {}
    for ref, sha in list_remote_refs(git_url).items():
        regex_match = extract_tags(ref)
        try:
            deploy_group = regex_match['deploy_group']
            tstamp = regex_match['tstamp']
        except KeyError:
            pass
        else:
            # note that all strings are greater than ''
            if deploy_group in deploy_groups and tstamp > previously_deployed_shas.get(sha, ''):
                previously_deployed_shas[sha] = tstamp
    return previously_deployed_shas.items()
Returns a list of 2-tuples of the form (sha, timestamp) for each deploy tag in a service's git
dataset/ETHPy150Open Yelp/paasta/paasta_tools/cli/cmds/rollback.py/get_git_shas_for_service