#!/usr/bin/env python
"""
Gathers availability data for the VM host it's running on.
"""

from subprocess import PIPE, Popen, call
import sys
import yaml

# return the amount of memory in kilobytes represented by s
def parseUnits(s):
    num, unit = s.split(' ')
    return int(num) * {'kb':1, 'mb':1024}[unit.lower()]

def main(argv):
    p = Popen(['/usr/sbin/xm', 'info'], stdout=PIPE)
    output = p.communicate()[0]
    if p.returncode != 0:
        raise RuntimeError("Command '%s' returned non-zero exit status %d"
                           % ('invirt-availability', p.returncode)) 
    xminfo = yaml.load(output, yaml.CSafeLoader)

    # In kilobytes
    free_memory = int(xminfo['free_memory']) * 1024

    f = open('/proc/xen/balloon', 'r')
    ballooninfo = yaml.load(f.read())
    f.close()
    currentallocation = parseUnits(ballooninfo['Current allocation'])
    minimumtarget = parseUnits(ballooninfo['Minimum target'])

    p = Popen(['/usr/sbin/xm', 'info', '-c'], stdout=PIPE)
    output = p.communicate()[0]
    if p.returncode != 0:
        raise RuntimeError("Command '%s' returned non-zero exit status %d"
                           % ('invirt-availability', p.returncode)) 
    xminfoc = yaml.load(output, yaml.CSafeLoader)

    # In kilobytes
    dom0minmem = int(xminfoc['dom0-min-mem']) * 1024

    dom0_spare_memory = currentallocation - max(minimumtarget, dom0minmem)
    print int((free_memory + dom0_spare_memory)/1024)
    return 0

if __name__ == '__main__':
    sys.exit(main(sys.argv))