-- Copyright 2003 Mike MacHenry

-- This program is free software; you can redistribute it and/or modify
-- it under the terms of the GNU General Public License as published by
-- the Free Software Foundation; either version 2 of the License, or
-- (at your option) any later version.

-- This program is distributed in the hope that it will be useful,
-- but WITHOUT ANY WARRANTY; without even the implied warranty of
-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-- GNU General Public License for more details.

-- You should have received a copy of the GNU General Public License
-- along with this program; if not, write to the Free Software
-- Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

-- The license is at <http://www.gnu.org/licenses/gpl.txt>.

-- sneaker.hs v0.0.1
-- dskippy 2003/02/04
-- Mike MacHenry <dskippy@ccs.neu.edu>

-----------------------------------------------------------------------
-- This is my version of the sneaker program written in Haskell. I
-- wrote it in Haskell simply to learn Haskell because it is so cool
-- and to contribute to the ever growing collection of sneaker programs
-- (see http://www.netgeek.ws) There are a few difference about this
-- sneaker program from the rest (most due to it's Haskellian nature)
--
-- One important thing to note is that it improves on a previously
-- unnoticed bug in existing sneaker programs. Psuedo-random number
-- generators are ment to be seeded in a program to give it determinism
-- but then applied over and over again (often using a next operation)
-- They are not intened to be reseeded over and over again. It has been
-- show that the function f(n) = seed n; rand; does not exhibit random
-- behavior where as f(n) = rand; does. As a result I wrote this sneaker
-- program fixing it in a very Haskellian way. I get the current date
-- and seed the random number generator with the year. Then I get
-- generate an infinite list of pairs of sneakers and index it with the
-- number of days since the begining of the year. This gives a more
-- random distribution of the sneakers to be worn on each day
----------------------------------------------------------------------

-- TODO: make work for any given date, not just current.

import Random
import Time

data Color = Blue | Red | Green | Khaki | White | Black | Orange | Yellow
  deriving (Enum, Show, Bounded)
data Pair  = Pair Color Color

instance Random Color where
  random              = randomR (minBound,maxBound)
  randomR (lo,hi) gen = (toEnum val, gen')
    where (val,gen') = randomR (fromEnum lo, fromEnum hi) gen

instance Show Pair where
  show (Pair left right) = "Left: " ++ show left ++ "\nRight: " ++ show right

today :: IO CalendarTime
today = getClockTime >>= toCalendarTime

randomPairs :: RandomGen g => g -> [Pair]
randomPairs gen = zipWith Pair (randoms lgen) (randoms rgen)
  where (lgen, rgen) = split gen

main :: IO ()
main = do day <- today
          putStrLn (calendarTimeToString day)
          print (randomPairs (mkStdGen (ctYear day)) !! ctYDay day)