cooking.hs

-- * Stuff

import Database.SQL (connectDB, dbquery)
import Database.Cache (cacheGet, cacheSet)
import Network.SOAP (soap)

import Control.Monad (guard)

type Oven = String
type Product = String
type HaveGas = Bool

data Recipe = Recipe { getOven :: Oven
                     , getProduct :: Product
                     , executeWith :: HaveGas -> Maybe Product
                     }

haveOven :: Oven -> IO Bool
haveOven oven = (elem oven . lines) `fmap` readFile "ovens.txt"

haveProduct :: Product -> IO Bool
haveProduct prod = connectDB >>= ((> 0) . length) `fmap` dbquery "SELECT 1 FROM products WHERE alias=%s" [prod]

gasReady :: IO HaveGas
gasReady = cached "gas" 10 $ soap "GasProvider" "gasReady"

create :: Recipe -> IO (Maybe Product)
create recipe = do
    haveOven (getOven recipe) >>= guard
    haveProduct (getProduct recipe) >>= guard

    gas <- gasReady
    return $ recipe `executeWith` gas

-- * Helpers

cached :: String -> Int -> IO a -> a
cached key time refresh = do
    cached <- cacheGet key
    case cached of
        Just value -> return value
        Nothing    -> refresh >>= cacheSet key time >>= return