module Useful where 

import List ( intersperse, tails )
import Numeric ( readHex )
import Char ( chr )

-------------------------------
-- Really useful functions

hex2num :: (Num a) => String -> a
hex2num s = let (result, _):_ = readHex s in result

toEnv s = let cleanup = replace "; " ";" s in map tuple (split ';' cleanup)

tuple :: String -> (String, String)
tuple line = case split '=' line of
   a:b:_ -> (a,b)
   a:_   -> (a,"")
   _     -> ("","") -- not good, probably won't happen...

tabtuple :: String -> (String, String)
tabtuple line = case split '\t' line of
   a:b:_ -> (a,b)
   a:_   -> (a,"")
   _     -> ("","") -- not good, probably won't happen...

-------------------------------
-- Titles and tags
tagencode s = concat $ intersperse "_" $ map fix (words s)
    where fix "&" = "N"
          fix x   = x

tagdecode s = concat $ intersperse " " $ map unfix (split '_' s)
    where unfix "N" = "&"
          unfix x   = x

-------------------------------
-- Strings

split       :: Char -> String -> [String]
split _ ""  =  []
split c s   =  let (l, s') = break (== c) s
                 in  l : case s' of
                           []      -> []
                           (_:s'') -> split c s''

beginsWith []       []     = True
beginsWith _        []     = True
beginsWith []       _      = False
beginsWith (a:aa)   (b:bb)
    | a == b               = aa `beginsWith` bb
    | otherwise            = False

dropping []     []     = []
dropping []     _      = []
dropping x      []     = x
dropping s@(a:aa) (b:bb) | a == b    = dropping aa bb
                         | otherwise = s

-- replace all occurrences of 'this' with 'that' in the string 'str'
-- like Python replace
replace _    _    []  = []
replace this that str
    | str `beginsWith` this = let after = (str `dropping` this)
                               in  that ++ replace this that after
    | otherwise             =
        let x:xs = str
          in x : replace this that xs

eat s = replace s ""

-- sometimes newlines get out of hand on the end of form POST submissions,
-- so trim all the end newlines and add a single newline
fixEndingNewlines = reverse . ('\n':) . dropWhile (=='\n') . reverse . filter (/= '\r')

endsWith a b = beginsWith (reverse a) (reverse b)

a `contains` b = any (`beginsWith` b) $ tails a