-- this program imput numbers and calculate their factorials. The workflow control a record all the inputs and outputs
-- so that when the program restart, all the previous results are shown.
-- if the program abort by a runtime error or a power failure, the program will still work
-- enter 0 for exit and finalize the workflow (all the intermediate data will be erased)
-- enter any alphanumeric character for aborting and then re-start.

module Main where
import Control.Workflow
import Data.TCache

fact 0 =1
fact n= n * fact (n-1)

{-
this is the origina program without workflow

factorials= do
    print "give me a number"
    str<-  getLine
    let n= read str :: Integer
    let fct=  fact n
    print fct
    factorials

    
main1=  factorials
-}


-- now the  workflow versión
data Fact= Fact Integer Integer deriving (Read, Show)

instance IResource Fact where
  keyResource _= "lastfact"
  serialize= undefined
  deserialize= undefined

factorialsWF _= do
    all <- getAll
    unsafeIOtoWF $ putStrLn "Factorials calculated so far:"
    unsafeIOtoWF $ putStrLn $ concatMap (\(Fact n fct)-> "number "++ show n ++ " factorial is "++ show fct++ "\n") all
    factLoop (Fact 0 0)
  where

  factLoop fct=  do

    nf <- step (\_ -> do 
             putStrLn "give me a number if you enter a letter, the program will abort. please restart"
             str<-  getLine
             let n= read str :: Integer   -- if you enter alphanumeric characters the program will abort. please restart
             let fct=  fact n
             print fct
             return $ Fact n fct)  fct
             
    case nf of
     Fact 0 _ -> do
                  unsafeIOtoWF $ print "bye" 
                  return (Fact 0 0)
     _ -> factLoop nf


main = startWF "factorials"  (Fact 0 0) [("factorials",factorialsWF)]