import datetime
import json
import logging

from Queue import Queue, Full, Empty
from threading import Thread

import requests


logger = logging.getLogger(__name__)

QUEUE_MAX = 1000
MAX_BATCH_SIZE = 100
REGISTER_WAIT = datetime.timedelta(hours=1)

class PrometheusPlugin(object):
  """ Application plugin for reporting metrics to Prometheus. """
  def __init__(self, app=None):
    self.app = app
    if app is not None:
      self.state = self.init_app(app)
    else:
      self.state = None

  def init_app(self, app):
    prom_url = app.config.get('PROMETHEUS_AGGREGATOR_URL')
    logger.debug('Initializing prometheus with aggregator url: %s', prom_url)
    prometheus = Prometheus(prom_url)

    # register extension with app
    app.extensions = getattr(app, 'extensions', {})
    app.extensions['prometheus'] = prometheus
    return prometheus

  def __getattr__(self, name):
    return getattr(self.state, name, None)


class Prometheus(object):
  """ Aggregator for collecting stats that are reported to Prometheus. """
  def __init__(self, url=None):
    self._metric_collectors = []
    self._url = url

    if url is not None:
      self._queue = Queue(QUEUE_MAX)
      self._sender = _QueueSender(self._queue, url, self._metric_collectors)
      self._sender.start()
      logger.debug('Prometheus aggregator sending to %s', url)
    else:
      self._queue = None
      logger.debug('Prometheus aggregator disabled')

  def enqueue(self, call, data):
    if not self._queue:
      return

    v = json.dumps({
      'Call': call,
      'Data': data,
    })

    if call == 'register':
      self._metric_collectors.append(v)
      return

    try:
      self._queue.put_nowait(v)
    except Full:
      # If the queue is full, it is because 1) no aggregator was enabled or 2)
      # the aggregator is taking a long time to respond to requests. In the case
      # of 1, it's probably enterprise mode and we don't care. In the case of 2,
      # the response timeout error is printed inside the queue handler. In either case,
      # we don't need to print an error here.
      pass

  def create_gauge(self, *args, **kwargs):
    return self._create_collector('Gauge', args, kwargs)

  def create_counter(self, *args, **kwargs):
    return self._create_collector('Counter', args, kwargs)

  def create_summary(self, *args, **kwargs):
    return self._create_collector('Summary', args, kwargs)

  def create_histogram(self, *args, **kwargs):
    return self._create_collector('Histogram', args, kwargs)

  def create_untyped(self, *args, **kwargs):
    return self._create_collector('Untyped', args, kwargs)

  def _create_collector(self, collector_type, args, kwargs):
    return _Collector(self.enqueue, collector_type, *args, **kwargs)


class _QueueSender(Thread):
  """ Helper class which uses a thread to asynchronously send metrics to the local Prometheus
      aggregator. """
  def __init__(self, queue, url, metric_collectors):
    Thread.__init__(self)
    self.daemon = True
    self.next_register = datetime.datetime.now()
    self._queue = queue
    self._url = url
    self._metric_collectors = metric_collectors

  def run(self):
    while True:
      reqs = []
      reqs.append(self._queue.get())

      while len(reqs) < MAX_BATCH_SIZE:
        try:
          req = self._queue.get_nowait()
          reqs.append(req)
        except Empty:
          break

      try:
        resp = requests.post(self._url + '/call', '\n'.join(reqs))
        if resp.status_code == 500 and self.next_register <= datetime.datetime.now():
          resp = requests.post(self._url + '/call', '\n'.join(self._metric_collectors))
          self.next_register = datetime.datetime.now() + REGISTER_WAIT
          logger.debug('Register returned %s for %s metrics; setting next to %s', resp.status_code,
                       len(self._metric_collectors), self.next_register)
        elif resp.status_code != 200:
          logger.debug('Failed sending to prometheus: %s: %s: %s', resp.status_code, resp.text,
                       ', '.join(reqs))
        else:
          logger.debug('Sent %d prometheus metrics', len(reqs))
      except:
        logger.exception('Failed to write to prometheus aggregator: %s', reqs)


class _Collector(object):
  """ Collector for a Prometheus metric. """
  def __init__(self, enqueue_method, collector_type, collector_name, collector_help,
               namespace='', subsystem='', **kwargs):
    self._enqueue_method = enqueue_method

    self._base_args = {
      'Name': collector_name,
      'Namespace': namespace,
      'Subsystem': subsystem,
      'Type': collector_type,
    }

    registration_params = dict(kwargs)
    registration_params.update(self._base_args)
    registration_params['Help'] = collector_help

    self._enqueue_method('register', registration_params)

  def __getattr__(self, method):
    def f(value=0, labelvalues=()):
      data = dict(self._base_args)
      data.update({
        'Value': value,
        'LabelValues': [str(i) for i in labelvalues],
        'Method': method,
      })

      self._enqueue_method('put', data)

    return f