import subprocess


def service_available(service_name):
    """Determine whether a system service is available"""
    try:
        subprocess.check_output(
            ['service', service_name, 'status'],
            stderr=subprocess.STDOUT).decode('UTF-8')
    except subprocess.CalledProcessError as e:
        return b'unrecognized service' not in e.output
    else:
        return True


def add_new_group(group_name, system_group=False, gid=None):
    cmd = ['addgroup']
    if gid:
        cmd.extend(['--gid', str(gid)])
    if system_group:
        cmd.append('--system')
    else:
        cmd.extend([
            '--group',
        ])
    cmd.append(group_name)
    subprocess.check_call(cmd)


def lsb_release():
    """Return /etc/lsb-release in a dict"""
    d = {}
    with open('/etc/lsb-release', 'r') as lsb:
        for l in lsb:
            k, v = l.split('=')
            d[k.strip()] = v.strip()
    return d


def cmp_pkgrevno(package, revno, pkgcache=None):
    """Compare supplied revno with the revno of the installed package.

    *  1 => Installed revno is greater than supplied arg
    *  0 => Installed revno is the same as supplied arg
    * -1 => Installed revno is less than supplied arg

    This function imports apt_cache function from charmhelpers.fetch if
    the pkgcache argument is None. Be sure to add charmhelpers.fetch if
    you call this function, or pass an apt_pkg.Cache() instance.
    """
    import apt_pkg
    if not pkgcache:
        from charmhelpers.fetch import apt_cache
        pkgcache = apt_cache()
    pkg = pkgcache[package]
    return apt_pkg.version_compare(pkg.current_ver.ver_str, revno)