#!/usr/bin/python

DESCRIPTION='''check disk usage,
stand alone command line tool and module for monitoring framework'''

USAGE='no command line options at this time, just execute it and watch the output'

SENSOR_SHELL_COMMAND='df'
ALERT_CRITERIA=85 #minimum this % usage -> alert

import re,os,sys

def main(HOST='',TARGETS=[]):   #output to stdout/stderr, use exit status to indicate problem
    EXITSTATUS=0
    for report in sensor(HOST,TARGETS): #call sensor from another python app
        print report['logmessage']
        if report['alert']:
            EXITSTATUS=1
            if report.has_key('alertmessage'):
                sys.stderr.write( report['alertmessage'] + '\n' )
    sys.exit(EXITSTATUS)

def sensor(HOST='',TARGETS=[]): #call this from another python app to get list of dictionaries
    disks=[]
    for disk in getdisks(HOST):
        if not TARGETS:
            if re.search('^/', disk['device']): #simple assumption: lines starting with / are local disks
                disks.append( evaluate_disk(disk) )
        elif disk['device'] in TARGETS or disk['mountpoint'] in TARGETS:
            disks.append( evaluate_disk(disk) )
    return disks

def evaluate_disk(disk):
    disk['logmessage']= logmessage( disk['device'],disk['mountpoint'],disk['usage'] )
    percentusage= int( re.sub('%','', disk['usage']) )
    if percentusage < ALERT_CRITERIA:
        disk['alert']=0
    else:
        disk['alert']=1
        disk['alertmessage']= alertmessage( disk['device'],disk['mountpoint'],disk['usage'] )
    return disk

def getdisks(HOST=''):
    disks=[]
    if not HOST:
        DF_STD_OUT=os.popen(SENSOR_SHELL_COMMAND).read().strip()
    else:
        DF_STD_OUT='' #TODO remote exec through module

    for dfline in DF_STD_OUT.split('\n')[1:]: #[1:] means throw away first element (first line in this case)
        disk={}
        dfline=dfline.strip()
        dfline=re.sub('\t',' ',dfline) #no tabs as whitespace
        dfline=re.sub('  *',' ',dfline) #not more than one space as separator
        disk['device']=       dfline.split(' ')[0]
        disk['mountpoint']=   dfline.split(' ')[-1]
        disk['usage']=        dfline.split(' ')[-2]
        disks.append( disk )

    return disks

def alertmessage(SRC,DST,USAGE):
    return 'disk nearly full ('+USAGE+'): '+DST+' ('+SRC+')'

def logmessage(SRC,DST,USAGE):
    return USAGE+' usage on '+DST+' ('+SRC+')'

if __name__ == "__main__":
    main()