implemented SubFix.Internal.decodeTime function

package.yaml

@@ -28,6 +28,8 @@ dependencies:
 
 library:
   source-dirs: src
+  dependencies:
+  - transformers >=0.5.6.2 && <0.6
 
 executables:
   subfix:

src/SubFix/Internal.hs

@@ -25,11 +25,13 @@ along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 -}
 
-module SubFix.Internal (encodeTime, decodeTime, timestamp) where
+{-# LANGUAGE LambdaCase #-}
 
--- | Encodes a timestamp from a number of milliseconds
-encodeTime :: Integer -> String
-encodeTime = undefined
+module SubFix.Internal (decodeTime, encodeTime, timestamp) where
+
+import Control.Monad (when)
+import Control.Monad.Trans.State (StateT (..), get, put)
+import Data.Char (isDigit, ord)
 
 -- | Decodes a timestamp to a number of milliseconds and the unused
 -- input
@@ -38,7 +40,19 @@ decodeTime
   -- ^ The encoded timestamp
   -> Maybe (Integer, String)
   -- ^ The number of milliseconds and unused input (if available)
-decodeTime = undefined
+decodeTime = runStateT $ do
+  hours <- getNum 2
+  dropChar ':'
+  mins <- getNum 2
+  dropChar ':'
+  secs <- getNum 2
+  dropChar ','
+  ms <- getNum 3
+  return $ timestamp hours mins secs ms
+
+-- | Encodes a timestamp from a number of milliseconds
+encodeTime :: Integer -> String
+encodeTime = undefined
 
 -- | Converts hours, minutes, seconds and milliseconds into the total
 -- number of milliseconds
@@ -57,4 +71,32 @@ timestamp h m s ms = let
   s' = m' * 60 + s
   in s' * 1000 + ms
 
+getNum :: MonadFail m => Int -> StateT String m Integer
+getNum = f 0 where
+  f val digits
+    | digits <= 0 = return val
+    | otherwise   = do
+      digit <- nextDigit
+      f (val * 10 + digit) (pred digits)
+
+dropChar :: MonadFail m => Char -> StateT String m ()
+dropChar expected = do
+  ch <- nextChar
+  when (ch /= expected) $
+    fail "incorrect character"
+
+nextDigit :: MonadFail m => StateT String m Integer
+nextDigit = do
+  ch <- nextChar
+  if isDigit ch
+    then return $ toInteger $ ord ch - ord '0'
+    else fail "missing digit"
+
+nextChar :: MonadFail m => StateT String m Char
+nextChar = get >>= \case
+  ""       -> fail "no character available"
+  (ch:str) -> do
+    put str
+    return ch
+
 --jl

subfix.cabal

@@ -4,7 +4,7 @@ cabal-version: 1.12
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: abd53b387d0bc7d910539fc83efe7b2fa75fe55deb728293cb25b78a7475d4cb
+-- hash: 475ccf2c735b96ddd94fc9281d9e8e97ecf64c4b60cd6645112a6ffb72165873
 
 name:           subfix
 version:        0.0.0
@@ -38,6 +38,7 @@ library
   ghc-options: -Wall -Werror
   build-depends:
       base >=4.7 && <5
+    , transformers >=0.5.6.2 && <0.6
   default-language: Haskell2010
 
 executable subfix
@@ -57,6 +58,7 @@ test-suite subfix-test
   main-is: Spec.hs
   other-modules:
       SubFix.ConvertSpec
+      SubFix.Internal.DecodeTimeSpec
       SubFix.Internal.TimestampSpec
       SubFix.InternalSpec
       SubFixSpec

test/SubFix/Internal/DecodeTimeSpec.hs

@@ -0,0 +1,45 @@
+{-
+
+subfix
+Copyright (C) Jonathan Lamothe <jonathan@jlamothe.net>
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or (at
+your option) any later version.
+
+This program is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+-}
+
+module SubFix.Internal.DecodeTimeSpec (spec) where
+
+import Test.Hspec (Spec, context, describe, it, shouldBe)
+
+import SubFix.Internal (decodeTime, timestamp)
+
+spec :: Spec
+spec = describe "decodeTime" $ mapM_
+  ( \(input, expected) ->
+    context input $
+      it ("should be " ++ show expected) $
+        decodeTime input `shouldBe` expected
+  )
+
+  --  input,             expected
+  [ ( "",                Nothing                            )
+  , ( "abc",             Nothing                            )
+  , ( "00:00:00,000",    Just (0, "")                       )
+  , ( "01:02:03,004",    Just (timestamp 1 2 3 4, "")       )
+  , ( "1:2:3,4",         Nothing                            )
+  , ( "10:20:30,400",    Just (timestamp 10 20 30 400, "" ) )
+  , ( "01:02:03,004abc", Just (timestamp 1 2 3 4, "abc")    )
+  ]
+
+--jl

test/SubFix/InternalSpec.hs

@@ -22,9 +22,12 @@ module SubFix.InternalSpec (spec) where
 
 import Test.Hspec (Spec, describe)
 
+import qualified SubFix.Internal.DecodeTimeSpec as DecodeTime
 import qualified SubFix.Internal.TimestampSpec as Timestamp
 
 spec :: Spec
-spec = describe "Internal" Timestamp.spec
+spec = describe "Internal" $ do
+  DecodeTime.spec
+  Timestamp.spec
 
 --jl