module Main where

import Prelude
import Char ( isSpace, toLower )
import IO
import IOExts ( IORef, modifyIORef, newIORef, readIORef, unsafePerformIO )

-- Bung everything inside a record, to save us multiple IORefs
data Config = Config
    { cfgSomeSetting :: String }

configRef = unsafePerformIO $ newIORef $ Config
    { cfgSomeSetting = "this is the default setting" }

config = unsafePerformIO $ readIORef configRef

-- as a shortcut / compatibility with existing code
someSetting = cfgSomeSetting config

-- returns lines in reverse order, I know, but it's irrelevant
hGetLines h = get [] where
    get ls = (hGetLine h >>= get . (: ls)) `catch` (const $ return ls)

-- *should* be called first thing in main (if at all);
-- otherwise madness ensues...
loadConfig :: FilePath -> IO ()
loadConfig conf = bracket (openFile conf ReadMode) hClose $ \ h -> do
    kvs <- fmap (map keyVal . filter isNotComment . lines) (hGetContents h)
    --kvs <- fmap (map keyVal . filter isNotComment) (hGetLines h)
    --mapM_ putStrLn kvs
    modifyIORef configRef (\ c -> foldl cfgLine c kvs) where
    keyVal s = (map toLower key, dropWhile isSpace rest)
        where (key, rest) = break isSpace s

    isNotComment ('#':_) = False
    isNotComment []      = False
    isNotComment _       = True

    cfgLine c ("setting", v) = c { cfgSomeSetting = v }
    cfgLine c _ = c -- ignore everything else

main = do
    loadConfig "prefs.conf"
    local <- readIORef configRef
    mapM_ putStrLn [ cfgSomeSetting local, cfgSomeSetting config, someSetting ]