#!/usr/bin/python

'''
Calculate disk space required for given graphite retention policy and number of
metrics
'''

#######################################

# retention policy
retentions = '10s:6h,1m:7d,10m:2y'

# number of metrics to be stored
num_metrics = 3000

#######################################

# time translations
second = 1
minute = 60 * second
hour = 60 * minute
day = 24 * hour
week = 7 * day
month = 30 * day
year = 52 * week
time_map = {
   's': second,
   'h': hour,
   'd': day,
   'w': week,
   'm': minute,
   'y': year
}

datapoint_size = 12 # 12 bytes per datapoint

def get_num_datapoints(retention):
   '''
   calculate number of datapoints based on the given retention policy string
   '''
   total_datapoints = 0
   for policy in retentions.split(','):
      resolution, period = policy.split(':')
      resolution_num, resolution_type = resolution[:-1], resolution[-1]
      period_num, period_type = period[:-1], period[-1]
      resolution_points = int(resolution_num) * time_map[resolution_type]
      period_points = int(period_num) * time_map[period_type]
      points = period_points / resolution_points
      print '%s for %s => %s data points' % (resolution, period, points)
      total_datapoints += points
   return total_datapoints

datapoints = get_num_datapoints(retentions)
disk_required_per_metric = (datapoints * datapoint_size * 1.0) / (1024 * 1024)
total_disk_required = disk_required_per_metric * num_metrics

print '=' * 30
print 'Number of metrics: %s' % num_metrics
print 'Retention policy: %s' % retentions
print 'Num datapoints per metric: %s' % datapoints
print 'Disk space per metric: %s MB' % disk_required_per_metric
print 'Total disk space for %s metrics: %s MB' % (num_metrics, total_disk_required)
print '=' * 30