#!/usr/bin/python
# vim: set fileencoding=utf-8 :
#
# Copyright 2014 Guido Guenther <agx@sigxcpu.org>
#
# Licesnse: GPLv3
#
# A munin plugin to measure temperature and humidity
#
#%# capabilities=autoconf
#%# family=contrib

import os
import sys
import math
import platform

# Useful to run from within the source tree
exe = os.path.abspath(os.path.dirname(os.path.realpath(sys.argv[0])))
dev_path='%s/Adafruit_Python_DHT/build/lib.linux-%s-2.7/' % (exe,
                                                             platform.machine())
if os.path.exists(dev_path):
    sys.path.insert(0, dev_path)

import Adafruit_DHT

sensortype = os.getenv('sensor', 'AM2302')
pin = os.getenv('pin', 4)

def print_config():
    where = os.getenv('where')
    if where is None:
        where = sys.argv[0].split('_', 1)[1]
    print """graph_title Humidity and Temperature in %(where)s
graph_category heating
graph_info Show temperature, humidity and dewpoint in %(where)s using a %(sensortype)s
temp.label Temperature
temp.type GAUGE
temp.max 100
temp.min -50
hum.label Humidity
hum.type GAUGE
hum.max 100
hum.min 0
hum.critical 60
hum.warning 50
dp.label Dewpoint
dp.type GAUGE
""" % dict(sensortype=sensortype, where=where)

K2 = 17.5043
K3 = 241.2

def calc_dewpoint(temp, hum):
    """
    See https://de.wikipedia.org/wiki/Taupunkt

    >>> calc_dewpoint(20, 100)
    20.0
    """
    phi = hum / 100.0
    theta = temp

    lnphi = math.log(phi)
    z = ((K2 * theta) /  (K3 + theta)) + lnphi
    n = ((K2 * K3) / (K3 + theta)) - lnphi

    return K3 * (z/n)
    

def fetch_values():
    sensor = eval('Adafruit_DHT.' + sensortype)
    hum, temp = Adafruit_DHT.read_retry(sensor, pin)

    dp = calc_dewpoint(temp, hum)
    print "temp.value %f" % temp
    print "hum.value %f" % hum
    print "dp.value %f" % dp


def main(args):
    if len(args) > 1:
        if args[1] in [ 'autoconf', 'detect' ]:
            try:
                fetch_raw()
                print "yes"
                return 0
            except:
                print "no"
                return 1
        elif args[1] == 'config':
            try:
                print_config()
            except Exception as e:
                print >>sys.stderr, "Failed to fetch config: '%s'" % e
                return 1
            return 0
    try:
        fetch_values()
    except Exception as e:
        print >>sys.stderr, "Failed to fetch values: '%s'" % e
        return 1
    return 0

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