module Browse where

import Directory
import Maybe (catMaybes)


-- shorter names for some imported utilities

getDir = getDirectoryContents
isFile = doesFileExist
isDir  = doesDirectoryExist


--------------------
-- a Tree type for picture files and directories
-- (Show instance below gives outlines, or derive it if you prefer)

data DTree = Pic FilePath | Dir FilePath [DTree]  -- deriving Show


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-- the main computation returns Just a DTree (or Nothing)
-- (we will store full paths at each node for ease of use,
-- although it is redundant and thus wasteful of space)

dirtree :: FilePath -> IO (Maybe DTree)

dirtree fp = when (not (dotted fp))
             (do f <- isFile fp
                 if f then when (isGIF fp) (return (Just (Pic fp)))
                      else do d <- isDir fp
                              when d (subtrees fp))

subtrees fp = do dlist <- getDir fp
                 trees <- mapM dirtree (map (path fp) dlist)
                 return (Just (Dir fp (catMaybes trees)))


--------------------
-- put a nested directory of pictures on your 
-- H drive and adjust this path to point to it

test = dirtree path >>= print
       where    path = "/Users/fruehr/hugs/pics"
       -- where path = "H:\\public_html\\pictures"


--------------------
-- some utility functions for readability

-- for unix directories (and Windows?) with "dot" links

dotted fp = take 1 (reverse fp) == "."

-- expand this definition if you use JPEGs, PNGs, etc.

isGIF  fp = ".gif" == snd (break (=='.') fp)

path p f = p ++ '/' : f

when b p = if b then p else return Nothing


-- outline-style show function for DTrees

instance Show (DTree) where
  show = sh "" where sh i (Pic f)     = i ++ f
                     sh i (Dir d [])  = i ++ d ++ " [D]"
                     sh i (Dir d ds)  = i ++ d ++ " [D] \n" ++ 
                                        unline (map (sh ('\t':i)) ds)

unline = foldr1 (\x y->x++'\n':y)