#!/usr/bin/python

import commands
import os
import sys
import re
import socket
import struct
import time

#import ctypes
# TODO: maybe when there's more time; for better readability.
#class History(Structure):
#    _fields_ = [ ("version", c_int),
#                 ("index", c_int),
#                 ("history", c_float * HISTORY_LENGTH), ]

# allocate fixed space on disk to save persistent state.
# what to store in this file?
# slice_history : x,x,x,x,x,...
# root_history : y,y,y,y,y,y...

HISTORY_LENGTH = 24*30  # 30 days, if checked once an hour
HISTORY_fmt = ('ii', 'f'*HISTORY_LENGTH )
HISTORY_version = 1


def get_network_bytes(interface):
    for line in open('/proc/net/dev', 'r'):
        if interface in line:
            data = line.split('%s:' % interface)[1].split()
            rx_bytes, tx_bytes = (data[0], data[8])
            return (float(rx_bytes), float(tx_bytes))
    return None

def get_uptime():
    for line in open('/proc/uptime', 'r'):
        data = line.split()[0]
        return float(data)
    return None

def read_safe_history(filename):
    """
        This function guarantees that space is preserved.
        If one of the file operations fail, it will throw an exception.
    """
    if os.path.exists(filename):
        # read existing data
        fd = os.open(filename, os.O_RDONLY)
        a = os.read(fd, os.path.getsize(filename))
        try:
            (version, i) = struct.unpack_from(HISTORY_fmt[0], a, 0)
            assert version == HISTORY_version
            history = struct.unpack_from(HISTORY_fmt[1], a, struct.calcsize(HISTORY_fmt[0]))
            history = [ h for h in history ]
        except:
            # TODO: in the future a more clever version migration might be nice.
            os.remove(filename) # just nuke the old version
            # create for the first time, with empty data
            (i, history) = (0, [0]*HISTORY_LENGTH)
            write_safe_history(filename, (i, history), False)

        os.close(fd)
            
    else:
        # create for the first time, with empty data
        (i, history) = (0, [0]*HISTORY_LENGTH)
        write_safe_history(filename, (i, history), False)

    return (i, history)

def write_safe_history(filename, (i, history), check_for_file=True):
    # length should match, and the file should already exist
    assert len(history) == HISTORY_LENGTH
    if check_for_file:
        assert os.path.exists(filename)

    # open without TRUNC nor APPEND, then seek to beginning to preserve space on disk
    fd = os.open(filename, os.O_WRONLY|os.O_CREAT)
    os.lseek(fd, 0, 0)
    ret  = os.write(fd, struct.pack(HISTORY_fmt[0], HISTORY_version, i ))
    ret += os.write(fd, struct.pack(HISTORY_fmt[1], *history))
    os.close(fd)
    return ret

def add_to_history((i, history), data):
    try:
        assert data > 0.0
        history[i] = data
        i += 1
        i = i % HISTORY_LENGTH
    except:
        # do not record data if data <= 0
        pass
    return (i, history)

def record_data(filename, data):
    rh = read_safe_history(filename)
    return write_safe_history(filename, add_to_history(rh, data))

def get_avg_uptime(filename):
    (idx, history) = read_safe_history(filename)
    summary = history[idx:] + history[:idx]
    measured = filter(lambda x: x != 0, summary)
    if len(measured) == 0: 
        return 0
    return float(sum(measured))/float(len(measured))

def timed(method):

    def timeit(*args, **kw):
        ts = time.time()
        result = method(*args, **kw)
        te = time.time()

        #print '%r (%r, %r) %2.2f sec' % \
        #      (method.__name__, args, kw, te-ts)
        return (result, te-ts)

    return timeit

@timed
def check_dns(ip, protocol='udp'):
    try:
        #ip = ip[:-1] + "0"
        ro = DNS.Request(name="www.yahoo.com", qtype="A", server=ip)
        r = ro.req(protocol=protocol)
        r = "OK"
    except DNS.Base.DNSError, e:
        r = "Error: %s" % e
    return r
        
def get_nameserver_ips(filename):
    ip_re = re.compile("\d+\.\d+\.\d+\.\d+")
    ret = {}
    if not os.path.exists(filename):
        return ret

    f = open(filename, 'r')

    if 'resolv' in filename:
        for l in f:
            for field in l.strip().split():
                if ip_re.match(field) and field not in ret:
                    ret[field] = 0

    if 'ifcfg' in filename:
        for l in f:
            if 'DNS' not in l:
                continue
            for field in l.strip().split('='):
                field = field.replace('"', '')
                field = field.replace("'", '')
                if ip_re.match(field) and field not in ret:
                    ret[field] = 0
    return ret

def main():

    ut = get_uptime()
    if ut == None:
        # massive fail.  cannot continue.
        sys.exit(1)

    record_data("uptime_history.dat", ut)

    print get_avg_uptime("uptime_history.dat"),
    
    print ""


if __name__ == "__main__":
    main()


# TODO: comon?
#url = """http://comon.cs.princeton.edu/status/tabulator.cgi?table=table_nodeviewshort&select='dns1udp>80 && dns2udp>80&&name=="%s"'&format=formatcsv&dumpcols='dns1udp,dns1tcp,dns2udp,dns2tcp'""" % os.popen("hostname").read().strip()