Reddit ranking algorithm in Ruby

gistfile1.rb

#!/Users/dustyeike/.rvm/rubies/ruby-1.9.2-p290/bin/ruby
require "rubygems"
require "test/unit"
require "date"

EPOCH = Date.new(1970, 1, 1)

#
# Returns the number of seconds from the epoch to date
def epoch_seconds date
  td = date - EPOCH
  Time.at(td).day * 86400 + Time.at(td).sec + (Time.at(td).usec).to_f / 1000000
end

def score ups, down
  ups - down
end

#
# The hot formula. Should match the equivalent function in postgres.
def hot ups, down, date
  s = score ups, down
  order = Math.log([s.abs, 1].max, 10)
  
  if s > 0
    sign = 1
  elsif s < 0
    sign = -1
  else
    sign = 0
  end

  seconds = epoch_seconds(date) - 1134028003
  (order + sign * seconds / 45000).round
end

class TestRedditAlgoritym < Test::Unit::TestCase
  def setup
    today = DateTime.now
    @now = Date.new(today.year, today.month, today.day)
  end
  
  def test_epoch_seconds
    assert_equal(epoch_seconds(@now), 2678403.0)
  end
  
  def test_score
    assert_equal(score(10, 5), 5)
  end
  
  def test_hot
    assert_equal(hot(10,5,@now), -25140)
  end
end