From 0b0fa3eb647707d6612519399511298d3e9d236c Mon Sep 17 00:00:00 2001
From: defanor <defanor@uberspace.net>
Date: Sun, 17 Dec 2017 00:52:34 +0300
Subject: Add Coalpit.DSV

---
 Coalpit/DSV.hs | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 Coalpit/DSV.hs

diff --git a/Coalpit/DSV.hs b/Coalpit/DSV.hs
new file mode 100644
index 0000000..f11f830
--- /dev/null
+++ b/Coalpit/DSV.hs
@@ -0,0 +1,65 @@
+{- |
+Module      :  Coalpit.DSV
+Description :  Argument parsing facilities
+Maintainer  :  defanor <defanor@uberspace.net>
+Stability   :  unstable
+Portability :  non-portable (uses GHC extensions)
+
+This module provides functions useful for argument parsing.
+-}
+
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE FlexibleInstances #-}
+
+module Coalpit.DSV (composeDSV, parseDSV) where
+
+import Data.List
+import Text.Megaparsec
+import Text.Megaparsec.Char
+import Data.Void
+
+
+composeDSVLine :: Char -> [String] -> String
+composeDSVLine fs = intercalate [fs] . map escapeVal
+  where
+    escapeVal :: String -> String
+    -- not great, but will do for now
+    escapeVal s = let inner = show s
+                  in if fs `elem` inner
+                     then inner
+                     else init $ tail inner
+
+-- | Composes DSV out of values.
+composeDSV :: Char
+           -- ^ Field separator.
+           -> [[String]]
+           -- ^ Lines of values.
+           -> String
+composeDSV fs = unlines . map (composeDSVLine fs)
+
+
+pStr :: Char -> Parsec Void String String
+pStr fs = do
+  s <- try (between (char '"') (char '"')
+            (concat <$> many (string "\\\\"
+                              <|> string "\\\""
+                              <|> pure <$> notChar '"')))
+    <|> many (notChar fs)
+  case reads (concat ["\"", s, "\""]) of
+    [(str, "")] -> pure str
+    other -> fail $ "Failed to read a string: " ++ show other ++ "(" ++ s ++ ")"
+
+pDSVLine :: Char -> Parsec Void String [String]
+pDSVLine fs = pStr fs `sepBy` char fs
+
+-- | Parses values out of DSV.
+parseDSV :: Char
+         -- ^ Field separator
+         -> String
+         -- ^ A string containing lines.
+         -> [Either String [String]]
+parseDSV fs = map parseLine . lines
+  where parseLine :: String -> Either String [String]
+        parseLine l = case parse (pDSVLine fs) "line" l of
+          Left err -> Left $ parseErrorPretty err
+          Right x -> Right x
-- 
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