module Factorise

# File lib/factorise.rb, line 6
def factorise
  number = self.to_s.dup.to_i
  factors = []

  primes_below = Prime.take_while { |p| p <= number / 2 }

  # keep if divisible
  primes_below.each do |p|
    until number % p != 0
      factors << p
      number = number / p
    end
  end

  # if no factors (=> num is prime) return num
  if factors.length == 0
    return [self]
  else
    return factors
  end
end

# File lib/factorise.rb, line 29
def factoriseh
  array = self.factorise
  hash = {}

  # count each factor
  array.each do |factor|
    if hash.has_key? factor
      hash[factor] += 1
    else
      hash[factor] = 1
    end
  end

  return hash
end

# File lib/factorise.rb, line 54
def factorpairs
  num = self.to_s.dup.to_i
  pairs = []
  factors = num.nonprime

  # include or not include middle value
  if factors.length % 2 == 0
    firsthalf = factors.first(factors.length / 2)
  else
    firsthalf = factors.first((factors.length / 2) + 1)
  end

  # get pairs
  firsthalf.each_with_index do |factor, index|
    pairs[index] = [factor, num/factor]
  end

  return pairs
end

# File lib/factorise.rb, line 46
def nonprime
  num = self.to_s.dup.to_i

  # nice oneline
  return (1..num).select { |n| num % n == 0 }
end