"""Utility functions for querying CPU, memory, disk, etc."""

from __future__ import absolute_import
import os


NET_DIRECTION_RX = 0
NET_DIRECTION_TX = 1

_NET_STAT_ROOT = '/sys/class/net/'
_NET_STAT_BYTES = {
    NET_DIRECTION_RX: 'rx_bytes',
    NET_DIRECTION_TX: 'tx_bytes'
}


def get_free_disk_fraction(directory=None):
  """Returns free disk space. From 0.0 (disk is full) to 1.0 (disk is empty)."""
  if not directory:
    directory = os.getcwd()
  statvfs = os.statvfs(directory)
  return float(statvfs.f_bavail) / float(statvfs.f_blocks)


def get_network_if():
  """Returns list of network interfaces on host."""
  try:
    return [net_if for net_if in os.listdir(_NET_STAT_ROOT) if net_if != 'lo']
  except OSError:
    return []


def get_current_directional_traffic(if_list=None, direction=NET_DIRECTION_RX):
  """Returns current network interfaces directional statistic in bytes."""
  if not if_list:
    if_list = get_network_if()
  bytes_count = 0
  for net_if in if_list:
    stat_path = os.path.join(
        _NET_STAT_ROOT, net_if, 'statistics', _NET_STAT_BYTES[direction])
    try:
      with open(stat_path) as stat:
        bytes_count += int(stat.read())
    except OSError:
      pass
  return bytes_count


def get_current_total_traffic(if_list=None):
  """Returns current rx, tx and total network interfaces statistic in bytes."""
  rx_bytes = get_current_directional_traffic(if_list, NET_DIRECTION_RX)
  tx_bytes = get_current_directional_traffic(if_list, NET_DIRECTION_TX)
  return rx_bytes, tx_bytes, rx_bytes + tx_bytes