# make / work consistently between python 2.x and 3.x
# https://www.python.org/dev/peps/pep-0238/
from __future__ import division
from functools import reduce
import math


def safeSum(values):
  safeValues = [v for v in values if v is not None]
  if safeValues:
    return sum(safeValues)


def safeDiff(values):
  safeValues = [v for v in values if v is not None]
  if safeValues:
    values = list(map(lambda x: x*-1, safeValues[1:]))
    values.insert(0, safeValues[0])
    return sum(values)


def safeLen(values):
  return len([v for v in values if v is not None])


def safeDiv(a, b):
  if a is None: return None
  if b in (0,None): return None
  return a / b


def safeExp(a):
    try:
        return math.exp(a)
    except TypeError:
        return None


def safePow(a, b):
  if a is None: return None
  if b is None: return None
  try:
    result = math.pow(a, b)
  except (ValueError, OverflowError):
    return None
  return result


def safeMul(*factors):
  if None in factors:
    return None

  factors = [float(x) for x in factors]
  product = reduce(lambda x,y: x*y, factors)
  return product


def safeSubtract(a,b):
    if a is None or b is None: return None
    return float(a) - float(b)


def safeAvg(values):
  safeValues = [v for v in values if v is not None]
  if safeValues:
    return sum(safeValues) / len(safeValues)


def safeAvgZero(values):
  if values:
    return sum([0 if v is None else v for v in values]) / len(values)


def safeMedian(values):
  safeValues = [v for v in values if v is not None]
  if safeValues:
    sortedVals = sorted(safeValues)
    mid = len(sortedVals) // 2
    if len(sortedVals) % 2 == 0:
      return float(sortedVals[mid-1] + sortedVals[mid]) / 2
    else:
      return sortedVals[mid]


def safeStdDev(a):
  sm = safeSum(a)
  ln = safeLen(a)
  avg = safeDiv(sm,ln)
  if avg is None: return None
  sum = 0
  safeValues = [v for v in a if v is not None]
  for val in safeValues:
     sum = sum + (val - avg) * (val - avg)
  return math.sqrt(sum/ln)


def safeLast(values):
  for v in reversed(values):
    if v is not None: return v


def safeMin(values, default=None):
  safeValues = [v for v in values if v is not None]
  if safeValues:
    return min(safeValues)
  else:
    return default


def safeMax(values, default=None):
  safeValues = [v for v in values if v is not None]
  if safeValues:
    return max(safeValues)
  else:
    return default


def safeMap(function, values):
  safeValues = [v for v in values if v is not None]
  if safeValues:
    return [function(x) for x in safeValues]


def safeAbs(value):
  if value is None: return None
  return abs(value)
