{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ViewPatterns #-}

module Util (
    relativeDirFromPieces,
    defaultMkRedirect,
    replace,
    remove,
    dropLastIfNull,
) where

import Data.ByteString (ByteString)
import qualified Data.ByteString.Char8 as S8
import qualified Data.Text as T
import qualified Data.Text.Encoding as TE
import WaiAppStatic.Types

-- alist helper functions
replace :: Eq a => a -> b -> [(a, b)] -> [(a, b)]
replace k v [] = [(k, v)]
replace k v (x : xs)
    | fst x == k = (k, v) : xs
    | otherwise = x : replace k v xs

remove :: Eq a => a -> [(a, b)] -> [(a, b)]
remove _ [] = []
remove k (x : xs)
    | fst x == k = xs
    | otherwise = x : remove k xs

-- | Turn a list of pieces into a relative path to the root folder.
relativeDirFromPieces :: Pieces -> T.Text
relativeDirFromPieces pieces = T.concat $ map (const "../") (drop 1 pieces) -- last piece is not a dir

-- | Construct redirects with relative paths.
defaultMkRedirect :: Pieces -> ByteString -> S8.ByteString
defaultMkRedirect pieces newPath
    | S8.null newPath
        || S8.null relDir
        || S8.last relDir /= '/'
        || S8.head newPath /= '/' =
        relDir `S8.append` newPath
    | otherwise = relDir `S8.append` S8.tail newPath
  where
    relDir = TE.encodeUtf8 (relativeDirFromPieces pieces)

dropLastIfNull :: [Piece] -> [Piece]
dropLastIfNull pieces = case pieces of
    [fromPiece -> ""] -> []
    (a : r) -> a : dropLastIfNull r
    [] -> []