Basic concepts

1 files changed, 43 insertions, 0 deletions

diff --git a/lib/Postdelay/Scan.hs b/lib/Postdelay/Scan.hs
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+++ b/lib/Postdelay/Scan.hs
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+{-# LANGUAGE OverloadedStrings, ScopedTypeVariables, FlexibleContexts #-}
+
+module Postdelay.Scan
+  ( scan
+  , Delay(..)
+  , ParseError(..)
+  ) where
+
+import Postdelay.Types
+import Postdelay.Utils
+import Postdelay.TimeSpec
+
+import Control.Monad
+import Control.Monad.IO.Class
+import Control.Monad.Error.Class
+
+import Text.Parsec.Char
+import Text.Parsec.Prim
+import Text.Parsec.Combinator
+import Text.Parsec.Error (ParseError(..))
+import Text.ParserCombinators.Parsec.Rfc2822
+
+import Data.CaseInsensitive (CI)
+import qualified Data.CaseInsensitive as CI
+
+import Data.Either
+import Data.Foldable
+import Data.Semigroup
+
+
+scan :: (MonadIO m, MonadError ParseError m) => String -> m (Maybe Delay)
+scan = fmap getOption . extractDelay <=< either throwError return . parse message ""
+
+extractDelay :: forall m. (MonadIO m, MonadError ParseError m) => Message -> m (Option Delay)
+extractDelay (Message headers _) = foldMap pure <$> mapM parseDelay delayHeaders
+  where
+    delayHeaders :: [Field]
+    delayHeaders = do
+      h@(OptionalField field content) <- headers
+      guard $ CI.mk field == "X-Delay"
+      return h
+    parseDelay :: Field -> m Delay
+    parseDelay (OptionalField field content) = either throwError return =<< runParserT (Until <$> pTimeSpec) () field content