import logging
import boto
import time

from Queue import Empty
from threading import Thread


logger = logging.getLogger(__name__)

MAX_BATCH_METRICS = 20

# Sleep for this much time between failed send requests.
# This prevents hammering cloudwatch when it's not available.
FAILED_SEND_SLEEP_SECS = 5

def start_cloudwatch_sender(metrics, app):
  """
  Starts sending from metrics to a new CloudWatchSender.
  """
  access_key = app.config.get('CLOUDWATCH_AWS_ACCESS_KEY')
  secret_key = app.config.get('CLOUDWATCH_AWS_SECRET_KEY')
  namespace = app.config.get('CLOUDWATCH_NAMESPACE')

  if not namespace:
    logger.debug('CloudWatch not configured')
    return

  sender = CloudWatchSender(metrics, access_key, secret_key, namespace)
  sender.start()

class CloudWatchSender(Thread):
  """
  CloudWatchSender loops indefinitely and pulls metrics off of a queue then sends it to CloudWatch.
  """
  def __init__(self, metrics, aws_access_key, aws_secret_key, namespace):
    Thread.__init__(self)
    self.daemon = True

    self._aws_access_key = aws_access_key
    self._aws_secret_key = aws_secret_key
    self._metrics = metrics
    self._namespace = namespace

  def run(self):
    try:
      logger.debug('Starting CloudWatch sender process.')
      connection = boto.connect_cloudwatch(self._aws_access_key, self._aws_secret_key)
    except:
      logger.exception('Failed to connect to CloudWatch.')
    self._metrics.enable()

    while True:
      metrics = {
        'name': [],
        'value': [],
        'unit': [],
        'timestamp': [],
        'dimensions': [],
      }

      metric = self._metrics.get()
      append_metric(metrics, metric)

      while len(metrics['name']) < MAX_BATCH_METRICS:
        try:
          metric = self._metrics.get_nowait()
          append_metric(metrics, metric)
        except Empty:
          break

      try:
        connection.put_metric_data(self._namespace, **metrics)
        logger.debug('Sent %d CloudWatch metrics', len(metrics['name']))
      except:
        for i in range(len(metrics['name'])):
          self._metrics.put(metrics['name'][i], metrics['value'][i],
            unit=metrics['unit'][i],
            dimensions=metrics['dimensions'][i],
            timestamp=metrics['timestamp'][i],
          )

        logger.exception('Failed to write to CloudWatch: %s', metrics)
        logger.debug('Attempted to requeue %d metrics.', len(metrics['name']))
        time.sleep(FAILED_SEND_SLEEP_SECS)

def append_metric(metrics, m):
  name, value, kwargs = m
  metrics['name'].append(name)
  metrics['value'].append(value)
  metrics['unit'].append(kwargs.get('unit'))
  metrics['dimensions'].append(kwargs.get('dimensions'))
  metrics['timestamp'].append(kwargs.get('timestamp'))