#!/usr/bin/env python
# python 2.6.6 compatible
# Goes through list of customizable varnish metrics and reports to newrelic
# requires config in /etc/newrelic/newrelic_varnish_agent.ini
# sample config:
# [varnish]
# instance: ___varish_instance_name___
# metrics: sess_conn,client_req,backend_fail,cache_miss,threads,threads_created,threads_failed,threads_limited,sess_drop,n_lru_nuked,esi_errors,n_expired
# [newrelic]
# license_key: ___key___
# appname: ___newrelic_app_name___
# sudo pip install newrelic

import subprocess, json, os
import newrelic.agent
from ConfigParser import SafeConfigParser

class VarnishMetrics():
    """
    creates an instance to call metrics from varnishstat
    """
    def __init__(self, metrics=[], instance="lcache6"):
        self.instance = instance
        self.metrics = metrics
    def load_metrics(self):
        """
        load stats from varnishstat json output
        returns a dict
        """
        p = subprocess.Popen(["varnishstat", "-1", "-j", "-n", self.instance], stdout=subprocess.PIPE)
        stdout, err = p.communicate()
        return json.loads(stdout)
        #with open('example.txt', 'r') as myfile:
        #  out = myfile.read()
        #  return json.loads(out)

    def parse_metrics(self):
        """
        takes an itemized list of desired metrics to report and returns as list of dicts
        returns a list
        """
        raw_metrics = self.load_metrics()
        pstat = []
        for metricname in self.metrics:
            jsonmetric = "MAIN." + metricname
            metric = raw_metrics[jsonmetric]['value']
            pstat.append({metricname: metric})
        return pstat

def read_config():
    """
    loads the ini file
    varnish_instance = varnish instance to access with the stats command
    newrelic_appname = the appname to report in customo newrelic metric
    returns dict
    """
    parser = SafeConfigParser({'environment': 'development'})
    parser.read('/etc/newrelic/newrelic_varnish_agent.ini')
    config = {
        'newrelic_license_key': parser.get('newrelic', 'license_key'),
        'newrelic_environment': parser.get('newrelic', 'environment'),
        'newrelic_appname': parser.get('newrelic', 'appname'),
        'varnish_instance': parser.get('varnish', 'instance'),
        'varnish_metrics': parser.get('varnish', 'metrics').split(','),
        }
    os.environ["NEW_RELIC_LICENSE_KEY"] = config['newrelic_license_key']
    return config

def report_custom_metrics(label, value, application=None, appname="varnish"):
    """
    reports customized newrelic metrics
    returns none
    """
    print("Reporting metric {label} value {value} appname {appname}".format(label=label, value=value, appname=appname))
    metric = "Custom/{appname}/{label}".format(appname=appname, label=label)
    newrelic.agent.record_custom_metric(metric, value, application)

if __name__ == "__main__":
    config = read_config()

    newrelic.agent.initialize()
    application = newrelic.agent.register_application(name=config['newrelic_appname'])
    m = VarnishMetrics(instance=config['varnish_instance'], metrics=config['varnish_metrics'])
    varnish_metrics = m.parse_metrics()
    for metric in varnish_metrics:
        label, value = metric.items()[0]
        report_custom_metrics(label, value, application, config['newrelic_appname'])