module Codec ( avCod, avArr )where

-- (c) 2007 Hans van Thiel
-- Version 0.1 License GPL

-- Note: extended Haskell because of dependent parameters
 
{- module: code a table of strings into:
    attribute-value lists, with the attributes in the heads
    lists of tuples, fst indexing att, snd indexing val 
        attribute indexes av-list of lists, start 0
        value indexes value in av-list, start 1
   string table has: attribute names in first line
                     attribute values in following lines
-}

import Data.List (transpose, elemIndex)
import Control.Monad.State
import Data.Array

-- get unique value-list and code strings as indices
-- Note: index incremented by 1, index 0 is the attribute

repl1 :: String -> [String] -> (Int, [String])
repl1 x tb  = case elemIndex x tb of
                 Nothing -> ((length tb) + 1, tb ++ [x] )
                 Just i -> (i + 1, tb)

toState :: String -> State [String] Int
toState x = State (repl1 x)

getVals :: [String] -> ([Int],[String])
getVals x = (runState (getState x)) [] where
                  getState = sequence . (map toState)

getInds :: [String] -> [Int]
getInds  =  fst . getVals

getTb :: [String] -> [String]
getTb = snd . getVals

-- get attribute-value lists from the table
-- Note: see comment at start for indexing scheme

avLs :: [[String]] -> [[String]]
avLs (x:xs) = zipWith (:)  x (values xs) where 
        values  = (map getTb) . transpose 

-- replace table, except first line, with:
-- tuples representing attribute-value pair
-- Note: see comment at start for indexing scheme

avCod :: [[String]] -> [[(Int, Int)]]
avCod (x:xs) = map (zip [0..]) (values xs) 
  where  values = transpose . (map getInds) . transpose

-- make an array of attribute-value lists from the 
-- table, instead of a list of lists of Strings

avArr :: [[String]] -> Array Int [String]
avArr tb = listArray (0, (length attvals) -1) attvals where
      attvals = avLs tb