diff --git a/ChangeLog.md b/ChangeLog.md
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--- /dev/null
+++ b/ChangeLog.md
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+# Changelog for timeutils
+
+## Unreleased changes
diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,674 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
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+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    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/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/README.md b/README.md
new file mode 100644
--- /dev/null
+++ b/README.md
@@ -0,0 +1,68 @@
+# timeutils
+
+Copyright (C) 2019 Jonathan Lamothe
+<jlamothe1980@gmail.com>
+
+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/>.
+
+## Executive Summary
+
+This package contains some simple time-based tools, and consists of
+two parts: a library, and an executable.  The library should be fairly
+portable, and provides some simple timer/stopwatch functionality.  The
+executanle is a simple console-based program built on top of the
+[brick](http://hackage.haskell.org/package/brick) package, and as
+such, will presently only work on POSIX-compatible systems (sorry
+Windows users).
+
+## Library
+
+The library provides its functionalty through the `Data.Time.Utils`
+module, and is thoroughlly documented [on
+Hackage](http://hackage.haskell.org/package/timeutils).
+
+## Executable
+
+This package provides the `timeutils` executable, a console-based
+program with a rudimentary user interface.  It has two modes:
+stopwatch and countdown.  You can toggle between these modes by
+pressing the `<tab>` key. The program can be exited with the `<esc>`
+key, the `q` key, or by hitting `<ctrl-c>`.
+
+### Stopwatch Mode
+
+The following is a list of keys and their effects in stopwatch mode:
+
+Key | Effect
+--- | ------
+`<space>` | start/stop stopwatch
+`l` | start new lap
+`r` | reset stopwatch
+
+### Countdown Mode
+
+The following is a list of keys and their effects in countdown mode:
+
+Key | Effect
+--- | ------
+`n` | new countdown
+`<up>`/`<down>` | select countdown
+`<space>` | start/stop selected countdown
+`<del>` | delete selected countdown
+`r` | reset selected countdown
+`R` | delete all countdowns
+`d`/`D` | increment/deincrement days in current countdown
+`h`/`H` | increment/deincrement hours in current countdown
+`m`/`M` | increment/deincrement minutes in current countdown
+`s`/`S` | increment/deincrement seconds in current countdown
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/app/Logic.hs b/app/Logic.hs
new file mode 100644
--- /dev/null
+++ b/app/Logic.hs
@@ -0,0 +1,197 @@
+{-
+
+timeutils
+
+Copyright (C) 2019 Jonathan Lamothe
+<jlamothe1980@gmail.com>
+
+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 Logic (handleEvent) where
+
+import Brick.BChan (writeBChan)
+import Brick.Main (continue, halt)
+import Brick.Types (BrickEvent (..), EventM, Next)
+import Control.Concurrent (forkIO, threadDelay)
+import Control.Monad (void)
+import Control.Monad.IO.Class (liftIO)
+import Data.Time (NominalDiffTime, getCurrentTime)
+import Lens.Micro (over, sets)
+import Graphics.Vty.Input.Events
+  ( Event (..)
+  , Key (..)
+  , Modifier (..)
+  )
+
+import Data.Time.Utils
+import Types
+
+handleEvent
+  :: ProgState
+  -> BrickEvent () ()
+  -> EventM () (Next ProgState)
+handleEvent s ev = do
+  t <- liftIO getCurrentTime
+  let s' = s { currentTime = t }
+  case ev of
+    VtyEvent (EvKey (KChar 'q') [])      -> halt s'
+    VtyEvent (EvKey (KChar 'c') [MCtrl]) -> halt s'
+    VtyEvent (EvKey KEsc [])             -> halt s'
+    VtyEvent (EvKey (KChar '\t') [])     -> continue $ changeMode s'
+    AppEvent ()                          -> ping s' >> continue s'
+    VtyEvent ev'                         -> continue $
+      case progMode s of
+        StopwatchMode -> stopwatchEvent s' ev'
+        CountdownMode -> countdownEvent s' ev'
+    _ -> continue s'
+
+changeMode :: ProgState -> ProgState
+changeMode s = s
+  { progMode = case progMode s of
+    StopwatchMode -> CountdownMode
+    CountdownMode -> StopwatchMode
+  }
+
+ping :: ProgState -> EventM () ()
+ping s = void $ liftIO $ forkIO $ do
+  threadDelay 100000
+  writeBChan (channel s) ()
+
+stopwatchEvent
+  :: ProgState
+  -> Event
+  -> ProgState
+stopwatchEvent s (EvKey (KChar ' ') []) = let
+  t   = currentTime s
+  sw  = stopwatch s
+  sw' = if stopwatchIsRunning sw
+    then stopStopwatchAt t sw
+    else startStopwatchAt t sw
+  in s { stopwatch = sw' }
+stopwatchEvent s (EvKey (KChar 'l') []) = let
+  t   = currentTime s
+  sw  = stopwatch s
+  sw' = newLapAt t sw
+  in s { stopwatch = sw' }
+stopwatchEvent s (EvKey (KChar 'r') []) =
+  s { stopwatch = newStopwatch }
+stopwatchEvent s _ = s
+
+countdownEvent
+  :: ProgState
+  -> Event
+  -> ProgState
+countdownEvent s ev = case ev of
+  EvKey (KChar 'n') [] -> newCd s
+  EvKey KUp []         -> prevCd s
+  EvKey KDown []       -> nextCd s
+  EvKey (KChar ' ') [] -> startStopCd s
+  EvKey (KChar 'r') [] -> resetCd s
+  EvKey (KChar 'R') [] -> resetCds s
+  EvKey KDel []        -> deleteCd s
+  EvKey (KChar 'd') [] -> adjustCd day s
+  EvKey (KChar 'D') [] -> adjustCd (-day) s
+  EvKey (KChar 'h') [] -> adjustCd hour s
+  EvKey (KChar 'H') [] -> adjustCd (-hour) s
+  EvKey (KChar 'm') [] -> adjustCd minute s
+  EvKey (KChar 'M') [] -> adjustCd (-minute) s
+  EvKey (KChar 's') [] -> adjustCd second s
+  EvKey (KChar 'S') [] -> adjustCd (-second) s
+  _                    -> s
+
+newCd :: ProgState -> ProgState
+newCd s = s
+  { countdowns   = newCountdown 0 : cds
+  , countdownSel = Just 0
+  } where cds = countdowns s
+
+prevCd :: ProgState -> ProgState
+prevCd s = s
+  { countdownSel = case countdownSel s of
+    Just 0  -> Nothing
+    Just n  -> Just $ pred n
+    Nothing -> if null $ countdowns s
+      then Nothing
+      else Just $ pred $ length $ countdowns s
+  }
+
+nextCd :: ProgState -> ProgState
+nextCd s = s
+  { countdownSel = case countdownSel s of
+    Nothing -> Just 0
+    Just n  -> let n' = succ n
+      in if n' >= length (countdowns s)
+        then Nothing
+        else Just n'
+  }
+
+startStopCd :: ProgState -> ProgState
+startStopCd s = let
+  t = currentTime s
+  in updateCd
+    (\cd -> if countdownIsRunning cd
+      then stopCountdownAt t cd
+      else startCountdownAt t cd)
+    s
+
+resetCd :: ProgState -> ProgState
+resetCd = updateCd $ \cd -> let
+  l = countdownLength cd
+  in newCountdown l
+
+resetCds :: ProgState -> ProgState
+resetCds s = s
+  { countdowns   = []
+  , countdownSel = Nothing
+  }
+
+deleteCd :: ProgState -> ProgState
+deleteCd s = s
+  { countdowns = foldr
+    (\(i, cd) cds -> if Just i == countdownSel s
+      then cds
+      else cd : cds)
+    []
+    (zip [0..] $ countdowns s)
+  , countdownSel = Nothing
+  }
+
+adjustCd :: NominalDiffTime -> ProgState -> ProgState
+adjustCd dt = over (sets updateCd . countdownLengthL) $
+  max 0 . (+dt)
+
+updateCd :: (Countdown -> Countdown) -> ProgState -> ProgState
+updateCd f s = s
+  { countdowns = map
+    (\(i, cd) -> if Just i == countdownSel s
+      then f cd
+      else cd)
+    (zip [0..] $ countdowns s)
+  }
+
+day :: NominalDiffTime
+day = hour * 24
+
+hour :: NominalDiffTime
+hour = minute * 60
+
+minute :: NominalDiffTime
+minute = second * 60
+
+second :: NominalDiffTime
+second = 1
+
+-- jl
diff --git a/app/Main.hs b/app/Main.hs
new file mode 100644
--- /dev/null
+++ b/app/Main.hs
@@ -0,0 +1,52 @@
+{-
+
+timeutils
+
+Copyright (C) 2019 Jonathan Lamothe
+<jlamothe1980@gmail.com>
+
+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 Main where
+
+import Brick.BChan (writeBChan)
+import Brick.Main (App (..), customMain, neverShowCursor)
+import Graphics.Vty (mkVty)
+import Graphics.Vty.Config (defaultConfig)
+import Control.Monad (void)
+
+import Logic
+import Types
+import UI
+
+app :: App ProgState () ()
+app = App
+  { appDraw         = draw
+  , appChooseCursor = neverShowCursor
+  , appHandleEvent  = handleEvent
+  , appStartEvent   = return
+  , appAttrMap      = mkAttrMap
+  }
+
+main :: IO ()
+main = do
+  s <- newProgState
+  writeBChan (channel s) ()
+  let buildVty = mkVty defaultConfig
+  vty <- buildVty
+  void $ customMain vty buildVty (Just $ channel s) app s
+
+-- jl
diff --git a/app/Types.hs b/app/Types.hs
new file mode 100644
--- /dev/null
+++ b/app/Types.hs
@@ -0,0 +1,59 @@
+{-
+
+timeutils
+
+Copyright (C) 2019 Jonathan Lamothe
+<jlamothe1980@gmail.com>
+
+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 Types
+  ( ProgState (..)
+  , ProgMode (..)
+  , newProgState
+  ) where
+
+import Brick.BChan (BChan, newBChan)
+import Data.Time (UTCTime, getCurrentTime)
+
+import Data.Time.Utils
+
+data ProgState = ProgState
+  { currentTime  :: UTCTime
+  , stopwatch    :: Stopwatch
+  , countdowns   :: [Countdown]
+  , progMode     :: ProgMode
+  , countdownSel :: Maybe Int
+  , channel      :: BChan ()
+  }
+
+data ProgMode = StopwatchMode | CountdownMode
+  deriving (Eq, Show)
+
+newProgState :: IO ProgState
+newProgState = do
+  t    <- getCurrentTime
+  chan <- newBChan 10
+  return ProgState
+    { currentTime  = t
+    , stopwatch    = newStopwatch
+    , countdowns   = []
+    , progMode     = StopwatchMode
+    , countdownSel = Nothing
+    , channel      = chan
+    }
+
+-- jl
diff --git a/app/UI.hs b/app/UI.hs
new file mode 100644
--- /dev/null
+++ b/app/UI.hs
@@ -0,0 +1,95 @@
+{-
+
+timeutils
+
+Copyright (C) 2019 Jonathan Lamothe
+<jlamothe1980@gmail.com>
+
+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 UI (draw, mkAttrMap) where
+
+import Brick.AttrMap (AttrMap, AttrName, attrMap, attrName)
+import Brick.Types (Widget)
+import Brick.Util (fg, on)
+import Brick.Widgets.Center (center)
+import Brick.Widgets.Core (hBox, str, vBox, withAttr)
+import qualified Graphics.Vty.Attributes as A
+
+import Data.Time.Utils
+import Types
+
+draw :: ProgState -> [Widget ()]
+draw s = [center $ case progMode s of
+    StopwatchMode -> stopwatchW s
+    CountdownMode -> countdownsW s]
+
+mkAttrMap :: ProgState -> AttrMap
+mkAttrMap _ = attrMap
+  (A.green `on` A.black)
+  [ ( titleAttr
+    , A.currentAttr `A.withStyle` (A.bold + A.reverseVideo)
+    )
+  , ( labelAttr
+    , A.currentAttr `A.withStyle` A.bold
+    )
+  , ( completedAttr
+    , fg A.red `A.withStyle` A.bold
+    )
+  ]
+
+stopwatchW :: ProgState -> Widget ()
+stopwatchW s = vBox $
+  [ withAttr titleAttr $ str "Stopwatch"
+  , hBox
+    [ withAttr labelAttr $ str "Total time: "
+    , str $ humanNDT $ totalStopwatchTimeAt t sw
+    ]
+  , withAttr labelAttr $ str "Laps:"
+  ] ++ map (str . humanNDT) (allLapsAt t sw)
+  where
+    t  = currentTime s
+    sw = stopwatch s
+
+countdownsW :: ProgState -> Widget ()
+countdownsW s = vBox $
+  withAttr titleAttr (str "Countdowns") :
+  if null cds
+    then [str "(no countdowns)"]
+    else map (uncurry display) cds
+  where
+    t            = currentTime s
+    cds          = zip [0..] $ countdowns s
+    display i cd = let
+      selected = countdownSel s == Just i
+      left     = str $ if selected then ">" else " "
+      right    = str $ if selected then "<" else " "
+      subW     = str $ humanNDT $ timeRemainingAt t cd
+      mainW    = if countdownIsCompletedAt t cd
+        then withAttr completedAttr subW
+        else subW
+      in hBox [left, mainW, right]
+
+titleAttr :: AttrName
+titleAttr = attrName "title"
+
+labelAttr :: AttrName
+labelAttr = attrName "label"
+
+completedAttr :: AttrName
+completedAttr = attrName "completed"
+
+-- jl
diff --git a/src/Data/Time/Utils.hs b/src/Data/Time/Utils.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/Time/Utils.hs
@@ -0,0 +1,611 @@
+{- |
+
+timeutils
+
+Copyright (C) 2019 Jonathan Lamothe
+<jlamothe1980@gmail.com>
+
+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 Data.Time.Utils (
+  -- * Types
+  Timer (..),
+  TimeParts (..),
+  Countdown (..),
+  Stopwatch (..),
+  -- * Lenses
+  -- ** Timer Lenses
+  timerOffsetL,
+  timerStartTimeL,
+  -- ** TimeParts Lenses
+  tpDaysL,
+  tpHoursL,
+  tpMinutesL,
+  tpSecondsL,
+  tpMillisL,
+  -- ** Countdown Lenses
+  countdownLengthL,
+  countdownTimerL,
+  -- ** Stopwatch Lenses
+  stopwatchTimerL,
+  stopwatchLapsL,
+  -- * Constructors
+  newTimer,
+  newTimeParts,
+  newCountdown,
+  newStopwatch,
+  -- * Impure Functions
+  -- ** Timer Functions
+  startTimer,
+  stopTimer,
+  timeElapsed,
+  -- ** Countdown Functions
+  startCountdown,
+  stopCountdown,
+  timeRemaining,
+  countdownIsCompleted,
+  -- ** Stopwatch Functions
+  startStopwatch,
+  stopStopwatch,
+  newLap,
+  currentLap,
+  allLaps,
+  totalStopwatchTime,
+  -- * Pure Functions
+  decomposeNDT,
+  composeNDT,
+  humanNDT,
+  -- ** Timer Functions
+  timerIsRunning,
+  timerIsStarted,
+  startTimerAt,
+  stopTimerAt,
+  timeElapsedAt,
+  -- ** Countdown Functions
+  countdownIsRunning,
+  countdownIsStarted,
+  startCountdownAt,
+  stopCountdownAt,
+  timeRemainingAt,
+  countdownIsCompletedAt,
+  -- ** Stopwatch Functions
+  stopwatchIsRunning,
+  stopwatchIsStarted,
+  startStopwatchAt,
+  stopStopwatchAt,
+  newLapAt,
+  currentLapAt,
+  allLapsAt,
+  totalStopwatchTimeAt
+) where
+
+import Data.Maybe (isJust, isNothing)
+import Data.Time.Clock
+  ( NominalDiffTime
+  , UTCTime
+  , diffUTCTime
+  , getCurrentTime
+  )
+import Lens.Micro (Lens', lens)
+
+-- | A type that keeps track of the passage of time
+data Timer = Timer
+  { timerOffset    :: NominalDiffTime
+    -- ^ The amount of time previously logged
+  , timerStartTime :: Maybe UTCTime
+    -- ^ The time the 'Timer' was last started ('Nothing' if not
+    -- currently running)
+  } deriving (Eq, Show)
+
+-- | Lens for the 'timerOffset' attribute
+timerOffsetL :: Lens' Timer NominalDiffTime
+timerOffsetL = lens timerOffset $
+  \t o -> t { timerOffset = o }
+
+-- | Lens for the 'timerStartTime' attribute
+timerStartTimeL :: Lens' Timer (Maybe UTCTime)
+timerStartTimeL = lens timerStartTime $
+  \t st -> t { timerStartTime = st }
+
+-- | Represents a 'NominalDiffTime' broken down into days, hours,
+-- minutes, seconds and milliseconds
+data TimeParts = TimeParts
+  { tpDays    :: Int
+    -- ^ The number of days
+  , tpHours   :: Int
+    -- ^ The number of hours
+  , tpMinutes :: Int
+    -- ^ The number of minutes
+  , tpSeconds :: Int
+    -- ^ The number of seconds
+  , tpMillis  :: Int
+    -- ^ The number of milliseconds
+  } deriving (Eq, Show)
+
+-- | Lens for the 'tpDays' attribute
+tpDaysL :: Lens' TimeParts Int
+tpDaysL = lens tpDays $
+  \tp d -> tp { tpDays = d }
+
+-- | Lens for the 'tpHours' attribute
+tpHoursL :: Lens' TimeParts Int
+tpHoursL = lens tpHours $
+  \tp h -> tp { tpHours = h }
+
+-- | Lens for the 'tpMinutes' attribute
+tpMinutesL :: Lens' TimeParts Int
+tpMinutesL = lens tpMinutes $
+  \tp m -> tp { tpMinutes = m }
+
+-- | Lens for the 'tpSeconds' attribute
+tpSecondsL :: Lens' TimeParts Int
+tpSecondsL = lens tpSeconds $
+  \tp s -> tp { tpSeconds = s }
+
+-- | Lens for the 'tpMillis' attribute
+tpMillisL :: Lens' TimeParts Int
+tpMillisL = lens tpMillis $
+  \tp ms -> tp { tpMillis = ms }
+
+-- | Represents a timed countdown
+data Countdown = Countdown
+  { countdownLength :: NominalDiffTime
+  -- ^ The length of time
+  , countdownTimer  :: Timer
+  -- ^ The timer which runs the 'Countdown'
+  } deriving (Eq, Show)
+
+-- | Lens for the 'countdownLength' attribute
+countdownLengthL :: Lens' Countdown NominalDiffTime
+countdownLengthL = lens countdownLength $
+  \cd l -> cd { countdownLength = l }
+
+-- | Lens for the 'countdownTimer' attribute
+countdownTimerL :: Lens' Countdown Timer
+countdownTimerL = lens countdownTimer $
+  \cd t -> cd { countdownTimer = t }
+
+-- | Tracks the time of multiple laps
+data Stopwatch = Stopwatch
+  { stopwatchTimer :: Timer
+  -- ^ The 'Timer' for the current lap
+  , stopwatchLaps  :: [NominalDiffTime]
+  -- ^ The times of previous laps (most recent first)
+  } deriving (Eq, Show)
+
+-- | Lens for the 'stopwatchTimer' attribute
+stopwatchTimerL :: Lens' Stopwatch Timer
+stopwatchTimerL = lens stopwatchTimer $
+  \sw t -> sw { stopwatchTimer = t }
+
+-- | Lens for the 'stopwatchLaps' attribute
+stopwatchLapsL :: Lens' Stopwatch [NominalDiffTime]
+stopwatchLapsL = lens stopwatchLaps $
+  \sw l -> sw { stopwatchLaps = l }
+
+-- | New instance of a 'Timer'
+newTimer :: Timer
+newTimer = Timer 0 Nothing
+
+-- | New instance of a 'TimeParts' value
+newTimeParts :: TimeParts
+newTimeParts = TimeParts 0 0 0 0 0
+
+-- | New instance of a 'Countdown'
+newCountdown
+  :: NominalDiffTime
+  -- ^ The time length
+  -> Countdown
+newCountdown l = Countdown l newTimer
+
+-- | New instance of a stopwatch
+newStopwatch :: Stopwatch
+newStopwatch = Stopwatch
+  { stopwatchTimer = newTimer
+  , stopwatchLaps  = []
+  }
+
+-- | Starts a 'Timer'
+startTimer
+  :: Timer
+  -- ^ The 'Timer' being started
+  -> IO Timer
+  -- ^ The modified 'Timer'
+startTimer timer = startTimerAt
+  <$> getCurrentTime
+  <*> return timer
+
+-- | Stops a 'Timer'
+stopTimer
+  :: Timer
+  -- ^ The 'Timer' being stopped
+  -> IO Timer
+  -- ^ The modified 'Timer'
+stopTimer timer = stopTimerAt
+  <$> getCurrentTime
+  <*> return timer
+
+-- | Calculates the amount of time elapsed on a 'Timer'
+timeElapsed
+  :: Timer
+  -- ^ The 'Timer' being checked
+  -> IO NominalDiffTime
+  -- ^ The amount of time elapsed
+timeElapsed timer = timeElapsedAt
+  <$> getCurrentTime
+  <*> return timer
+
+-- | Starts a 'Countdown'
+startCountdown
+  :: Countdown
+  -- ^ The 'Countdown' being started
+  -> IO Countdown
+  -- ^ Returns the modified 'Countdown'
+startCountdown countdown = startCountdownAt
+  <$> getCurrentTime
+  <*> return countdown
+
+-- | Stops a 'Countdown'
+stopCountdown
+  :: Countdown
+  -- ^ The 'Countdown' being stopped
+  -> IO Countdown
+  -- ^ Returns the modified 'Countdown'
+stopCountdown countdown = stopCountdownAt
+  <$> getCurrentTime
+  <*> return countdown
+
+-- | Calculates the amount of time remaining in a 'Countdown'
+timeRemaining
+  :: Countdown
+  -- ^ The 'Countdown' being checked
+  -> IO NominalDiffTime
+  -- ^ The amount of time remaining
+timeRemaining countdown = timeRemainingAt
+  <$> getCurrentTime
+  <*> return countdown
+
+-- | Determines whether or not a 'Countdown' has completed.
+countdownIsCompleted
+  :: Countdown
+  -- ^ The 'Countdown' being checked
+  -> IO Bool
+  -- ^ Returns 'True' if the 'Countdown' has completed, 'False'
+  -- otherwise
+countdownIsCompleted countdown = countdownIsCompletedAt
+  <$> getCurrentTime
+  <*> return countdown
+
+-- | Starts a 'Stopwatch'
+startStopwatch
+  :: Stopwatch
+  -- ^ The 'Stopwatch' being started
+  -> IO Stopwatch
+  -- ^ Returns the modified 'Stopwatch'
+startStopwatch stopwatch = startStopwatchAt
+  <$> getCurrentTime
+  <*> return stopwatch
+
+-- | Stops a 'Stopwatch'
+stopStopwatch
+  :: Stopwatch
+  -- ^ The 'Stopwatch' being stopped
+  -> IO Stopwatch
+  -- ^ Returns the modified 'Stopwatch'
+stopStopwatch stopwatch = stopStopwatchAt
+  <$> getCurrentTime
+  <*> return stopwatch
+
+-- | Starts a new lap
+newLap
+  :: Stopwatch
+  -- ^ The 'Stopwatch' being modified
+  -> IO Stopwatch
+  -- ^ Returns the 'Stopwatch' being modified
+newLap stopwatch = newLapAt
+  <$> getCurrentTime
+  <*> return stopwatch
+
+-- | Returns the time of the current lap from a 'Stopwatch'
+currentLap
+  :: Stopwatch
+  -- ^ The 'Stopwatch' being checked
+  -> IO NominalDiffTime
+  -- ^ Returns the amount of time elapsed in the current lap
+currentLap stopwatch = currentLapAt
+  <$> getCurrentTime
+  <*> return stopwatch
+
+-- | Returns the lap times for a 'Stopwatch'
+allLaps
+  :: Stopwatch
+  -- ^ The 'Stopwatch' being checked
+  -> IO [NominalDiffTime]
+  -- ^ Returns the lap times (most recent first)
+allLaps stopwatch = allLapsAt
+  <$> getCurrentTime
+  <*> return stopwatch
+
+-- | Calculates the total run time of a 'Stopwatch'
+totalStopwatchTime
+  :: Stopwatch
+  -- ^ The 'Stopwatch' being checked
+  -> IO NominalDiffTime
+  -- ^ Returns the total run time
+totalStopwatchTime stopwatch = totalStopwatchTimeAt
+  <$> getCurrentTime
+  <*> return stopwatch
+
+-- | Converts a 'NominalDiffTime' to a 'TimeParts' value
+decomposeNDT :: NominalDiffTime -> TimeParts
+decomposeNDT t = TimeParts
+  { tpDays    = days
+  , tpHours   = hours
+  , tpMinutes = minutes
+  , tpSeconds = seconds
+  , tpMillis  = millis
+  }
+  where
+    days    = h `quot` 24
+    hours   = h - days * 24
+    minutes = m - h * 60
+    seconds = s - m * 60
+    millis  = ms - s * 1000
+    h       = m `quot` 60
+    m       = s `quot` 60
+    s       = ms `quot` 1000
+    ms      = floor $ t * 1000
+
+-- | Converts a 'TimeParts' value to a 'NominalDiffTime'
+composeNDT :: TimeParts -> NominalDiffTime
+composeNDT tp = fromInteger millis / 1000
+  where
+    millis  = seconds * 1000 + toInteger (tpMillis tp)
+    seconds = minutes * 60 + toInteger (tpSeconds tp)
+    minutes = hours * 60 + toInteger (tpMinutes tp)
+    hours   = toInteger (tpDays tp) * 24 + toInteger (tpHours tp)
+
+-- | Converts a 'NominalDiffTime' into a more human-readable format
+humanNDT :: NominalDiffTime -> String
+humanNDT t = sign ++ d ++ h ++ m ++ s ++ ms
+  where
+    sign    = if t < 0 then "-" else ""
+    d       = show (tpDays tp) ++ "d "
+    h       = fix 2 (tpHours tp) ++ "h "
+    m       = fix 2 (tpMinutes tp) ++ "m "
+    s       = fix 2 (tpSeconds tp) ++ "."
+    ms      = fix 3 (tpMillis tp) ++ "s"
+    tp      = decomposeNDT $ abs t
+    fix n x = let
+      str  = show x
+      slen = length str
+      plen = n - slen
+      pad  = replicate plen '0'
+      in pad ++ str
+
+-- | Determines whether or not a 'Timer' is running
+timerIsRunning
+  :: Timer
+  -- ^ The 'Timer' being checked
+  -> Bool
+timerIsRunning = isJust . timerStartTime
+
+-- | Determines whether or not a 'Timer' has been started (even if it
+-- is currently stopped)
+timerIsStarted
+  :: Timer
+  -- ^ The 'Timer' being checked
+  -> Bool
+  -- ^ 'True' if the timer has been started, 'False' otherwise
+timerIsStarted timer = timerIsRunning timer ||
+  timerOffset timer /= 0
+
+-- | Starts a 'Timer' from a given time
+startTimerAt
+  :: UTCTime
+  -- ^ The current time
+  -> Timer
+  -- ^ The 'Timer' being started
+  -> Timer
+  -- ^ The modified 'Timer'
+startTimerAt t timer
+  | isNothing (timerStartTime timer) =
+    timer { timerStartTime = Just t }
+  | otherwise = timer
+
+-- | Stops a 'Timer' from a given time
+stopTimerAt
+  :: UTCTime
+  -- ^ The current time
+  -> Timer
+  -- ^ The 'Timer' being stopped
+  -> Timer
+  -- ^ The modified 'Timer'
+stopTimerAt t timer = newTimer { timerOffset = offset }
+  where offset = timeElapsedAt t timer
+
+-- | Calculates the amount of time elapsed on a 'Timer' from a given
+-- time
+timeElapsedAt
+  :: UTCTime
+  -- ^ The current time
+  -> Timer
+  -- ^ The 'Timer' being checked
+  -> NominalDiffTime
+  -- ^ The amount of time elapsed
+timeElapsedAt t timer = case timerStartTime timer of
+  Nothing -> timerOffset timer
+  Just st -> timerOffset timer + diffUTCTime t st
+
+-- | Determines whether or not a 'Countdown' is running
+countdownIsRunning
+  :: Countdown
+  -- ^ The 'Countdown' being checked
+  -> Bool
+  -- ^ 'True' if running, 'False' otherwise
+countdownIsRunning countdown = timerIsRunning timer
+  where timer = countdownTimer countdown
+
+-- | Determines whether or not a 'Countdown' has been started (even if
+-- subsequently stopped)
+countdownIsStarted
+  :: Countdown
+  -- ^ The 'Countdown' being checked
+  -> Bool
+  -- ^ 'True' if it has been started, 'False' otherwise
+countdownIsStarted countdown = timerIsStarted timer
+  where timer = countdownTimer countdown
+
+-- | Starts a 'Countdown' using a given time
+startCountdownAt
+  :: UTCTime
+  -- ^ The current time
+  -> Countdown
+  -- ^ The 'Countdown' being started
+  -> Countdown
+  -- ^ The modified 'Countdown'
+startCountdownAt t countdown =
+  countdown { countdownTimer = timer' }
+  where
+    timer' = startTimerAt t timer
+    timer  = countdownTimer countdown
+
+-- | Stops a 'Countdown' using a given time
+stopCountdownAt
+  :: UTCTime
+  -- ^ The current time
+  -> Countdown
+  -- ^ The 'Countdown' being stopped
+  -> Countdown
+  -- ^ The modified 'Countdown'
+stopCountdownAt t countdown =
+  countdown { countdownTimer = timer' }
+  where
+    timer' = stopTimerAt t timer
+    timer  = countdownTimer countdown
+
+-- | Calculates the amount of time remaining in a 'Countdown' at a
+-- given time
+timeRemainingAt
+  :: UTCTime
+  -- ^ The current time
+  -> Countdown
+  -- ^ The 'Countdown' being checked
+  -> NominalDiffTime
+  -- ^ The amount of time remaining
+timeRemainingAt t countdown = len - timeElapsedAt t timer
+  where
+    len   = countdownLength countdown
+    timer = countdownTimer countdown
+
+-- | Determines if a 'Countdown' is completed at a given time
+countdownIsCompletedAt
+  :: UTCTime
+  -- ^ The current time
+  -> Countdown
+  -- ^ The 'Countdown' being checked
+  -> Bool
+  -- ^ Returns 'True' if the 'Countdown' has completed, 'False'
+  -- otherwise.
+countdownIsCompletedAt t countdown =
+  timeRemainingAt t countdown <= 0
+
+-- | Determines whether or not a 'Stopwatch' is running
+stopwatchIsRunning
+  :: Stopwatch
+  -- ^ The 'Stopwatch' being checked
+  -> Bool
+  -- ^ 'True' if the 'Stopwatch' is running, 'False' otherwise
+stopwatchIsRunning = timerIsRunning . stopwatchTimer
+
+-- | Determines whether or not a stopwatch has been started (even if
+-- subsequently stopped)
+stopwatchIsStarted
+  :: Stopwatch
+  -- ^ The 'Stopwatch' being checked
+  -> Bool
+  -- ^ 'True' if started, 'False' otherwise
+stopwatchIsStarted = (/= newStopwatch)
+
+-- | Starts a 'Stopwatch' at a given time
+startStopwatchAt
+  :: UTCTime
+  -- ^ The current time
+  -> Stopwatch
+  -- ^ The 'Stopwatch' being started
+  -> Stopwatch
+  -- ^ The modified 'Stopwatch'
+startStopwatchAt t stopwatch = stopwatch { stopwatchTimer = timer }
+  where timer = startTimerAt t $ stopwatchTimer stopwatch
+
+-- | Stops a 'Stopwatch' at a given time
+stopStopwatchAt
+  :: UTCTime
+  -- ^ The current time
+  -> Stopwatch
+  -- ^ The 'Stopwatch' being stopped
+  -> Stopwatch
+  -- ^ The modified 'Stopwatch'
+stopStopwatchAt t stopwatch = stopwatch { stopwatchTimer = timer }
+  where timer = stopTimerAt t $ stopwatchTimer stopwatch
+
+-- | Starts a new lap at a given time
+newLapAt
+  :: UTCTime
+  -- ^ The currebt time
+  -> Stopwatch
+  -- ^ The 'Stopwatch' being modified
+  -> Stopwatch
+  -- ^ The modified 'Stopwatch'
+newLapAt t stopwatch = Stopwatch
+  { stopwatchTimer = startTimerAt t newTimer
+  , stopwatchLaps  = allLapsAt t stopwatch
+  }
+
+-- | Determines the length of the current lap given a time
+currentLapAt
+  :: UTCTime
+  -- ^ The current time
+  -> Stopwatch
+  -- ^ The 'Stopwatch' being checkwd
+  -> NominalDiffTime
+  -- ^ The elapsed time for the current lap
+currentLapAt t stopwatch = timeElapsedAt t timer
+  where timer = stopwatchTimer stopwatch
+
+-- | Returns the lap times from a 'Stopwatch' given a time
+allLapsAt
+  :: UTCTime
+  -- ^ The current time
+  -> Stopwatch
+  -- ^ The 'Stopwatch' being checked
+  -> [NominalDiffTime]
+  -- ^ The lap times (most recent first)
+allLapsAt t stopwatch = currentLapAt t stopwatch :
+  stopwatchLaps stopwatch
+
+-- | Calculates the total runtime of a 'Stopwatch' given a time
+totalStopwatchTimeAt
+  :: UTCTime
+  -- ^ The current time
+  -> Stopwatch
+  -- ^ The 'Stopwatch' being checked
+  -> NominalDiffTime
+  -- ^ The total run time
+totalStopwatchTimeAt t stopwatch =
+  sum $ allLapsAt t stopwatch
+
+-- jl
diff --git a/test/Spec.hs b/test/Spec.hs
new file mode 100644
--- /dev/null
+++ b/test/Spec.hs
@@ -0,0 +1,493 @@
+{-
+
+timeutils
+
+Copyright (C) 2019 Jonathan Lamothe
+<jlamothe1980@gmail.com>
+
+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/>.
+
+-}
+
+import Test.Hspec (Spec, context, describe, hspec, it, shouldBe)
+
+import Data.Time.Clock
+  ( NominalDiffTime
+  , UTCTime
+  , addUTCTime
+  , getCurrentTime
+  )
+
+import Data.Time.Utils
+
+main :: IO ()
+main = hspec $ do
+  timeElapsedAtSpec
+  startTimerAtSpec
+  stopTimerAtSpec
+  decomposeNDTSpec
+  composeNDTSpec
+  timerIsRunningSpec
+  timerIsStartedSpec
+  timeRemainingAtSpec
+  countdownIsCompletedAtSpec
+  countdownIsRunningSpec
+  countdownIsStartedSpec
+  startCountdownSpec
+  stopCountdownSpec
+  currentLapAtSpec
+  allLapsAtSpec
+  totalStopwatchTimeAtSpec
+  stopwatchIsRunningSpec
+  stopwatchIsStartedSpec
+  startStopwatchSpec
+  stopStopwatchSpec
+  newLapAtSpec
+  humanNDTSpec
+
+timeElapsedAtSpec :: Spec
+timeElapsedAtSpec = describe "timeElapsedAt" $ do
+
+  context "newTimer" $
+    it "should be 0" $ do
+      t <- getCurrentTime
+      timeElapsedAt t newTimer `shouldBe` 0
+
+  context "started, no previous" $
+    it "should be 1 minute" $ do
+      (t, t') <- times 60
+      let timer = newTimer { timerStartTime = Just t }
+      timeElapsedAt t' timer `shouldBe` 60
+
+  context "stopped, with previous" $
+    it "should be 1 minute" $ do
+      t <- getCurrentTime
+      let timer = newTimer { timerOffset = 60 }
+      timeElapsedAt t timer `shouldBe` 60
+
+  context "started, with previous" $
+    it "should be 2 minutes" $ do
+      (t, t') <- times 60
+      let
+        timer = newTimer
+          { timerOffset    = 60
+          , timerStartTime = Just t
+          }
+      timeElapsedAt t' timer `shouldBe` 120
+
+startTimerAtSpec :: Spec
+startTimerAtSpec = describe "startTimerAt" $ do
+
+  context "newTimer" $
+    it "should set the start time" $ do
+      t <- getCurrentTime
+      let expected = newTimer { timerStartTime = Just t }
+      startTimerAt t newTimer `shouldBe` expected
+
+  context "already started" $
+    it "should not modify the timer" $ do
+      (t, t') <- times 60
+      let timer = newTimer { timerStartTime = Just t }
+      startTimerAt t' timer `shouldBe` timer
+
+  context "stopped" $
+    it "should resume the timer" $ do
+      t <- getCurrentTime
+      let
+        timer = newTimer { timerOffset = 60 }
+        expected = timer { timerStartTime = Just t }
+      startTimerAt t timer `shouldBe` expected
+
+stopTimerAtSpec :: Spec
+stopTimerAtSpec = describe "stopTimerAt" $ do
+
+  context "newTimer" $
+    it "should not change the timer" $ do
+      t <- getCurrentTime
+      stopTimerAt t newTimer `shouldBe` newTimer
+
+  context "stopped timer" $
+    it "should not change the timer" $ do
+      t <- getCurrentTime
+      let timer = newTimer { timerOffset = 60 }
+      stopTimerAt t timer `shouldBe` timer
+
+  context "running timer" $
+    it "should stop the timer, and calculate the new offset" $ do
+      (t, t') <- times 60
+      let
+        timer = newTimer
+          { timerOffset    = 60
+          , timerStartTime = Just t
+          }
+        expected = newTimer { timerOffset = 120 }
+      stopTimerAt t' timer `shouldBe` expected
+
+decomposeNDTSpec :: Spec
+decomposeNDTSpec = describe "decomposeNDT" $ do
+  let
+    days    = 1
+    hours   = days * 24 + 2
+    minutes = hours * 60 + 3
+    seconds = minutes * 60 + 4
+    millis  = seconds * 1000 + 5
+    time    = millis / 1000
+
+  context "zero" $
+    it "should be zero" $
+      decomposeNDT 0 `shouldBe` newTimeParts
+
+  context "positive" $
+    it "should calculate the time parts" $ let
+      expected = TimeParts
+        { tpDays    = 1
+        , tpHours   = 2
+        , tpMinutes = 3
+        , tpSeconds = 4
+        , tpMillis  = 5
+        }
+      in decomposeNDT time `shouldBe` expected
+
+  context "negative" $
+    it "should calculate the time parts" $ let
+      expected = TimeParts
+        { tpDays    = -1
+        , tpHours   = -2
+        , tpMinutes = -3
+        , tpSeconds = -4
+        , tpMillis  = -5
+        }
+      in decomposeNDT (-time) `shouldBe` expected
+
+composeNDTSpec :: Spec
+composeNDTSpec = describe "composeNDT" $
+  it "should compose correctly" $ let
+    parts = TimeParts
+      { tpDays    = 1
+      , tpHours   = 2
+      , tpMinutes = 3
+      , tpSeconds = 4
+      , tpMillis  = 5
+      }
+    t = composeNDT parts
+    in decomposeNDT t `shouldBe` parts
+
+timerIsRunningSpec :: Spec
+timerIsRunningSpec = describe "timerIsRunning" $ do
+
+  context "not running" $
+    it "should return False" $
+      timerIsRunning newTimer `shouldBe` False
+
+  context "running" $
+    it "should return True" $ do
+      timer <- startTimer newTimer
+      timerIsRunning timer `shouldBe` True
+
+timerIsStartedSpec :: Spec
+timerIsStartedSpec = describe "timerIsStarted" $ do
+
+  context "newTimer" $
+    it "should be False" $
+      timerIsStarted newTimer `shouldBe` False
+
+  context "started" $
+    it "should be True" $ do
+      timer <- startTimer newTimer
+      timerIsStarted timer `shouldBe` True
+
+  context "started, then stopped" $
+    it "should be True" $ do
+      (t, t') <- times 60
+      let
+        timer  = startTimerAt t newTimer
+        timer' = stopTimerAt t' timer
+      timerIsStarted timer' `shouldBe` True
+
+timeRemainingAtSpec :: Spec
+timeRemainingAtSpec = describe "timeRemainingAt" $ do
+
+  context "not started" $
+    it "should be one minute" $ do
+      t <- getCurrentTime
+      let countdown = newCountdown 60
+      timeRemainingAt t countdown `shouldBe` 60
+
+  context "started" $ mapM_
+    (\(len, dt, expected) -> let
+      label = "length: " ++ show len ++
+        ", elapsed: " ++ show dt
+      expectation = "should be " ++ show expected
+      in
+        context label $
+          it expectation $ do
+            (t, t') <- times dt
+            let
+              timer     = startTimerAt t newTimer
+              countdown = Countdown
+                { countdownLength = len
+                , countdownTimer  = timer
+              }
+            timeRemainingAt t' countdown `shouldBe` expected)
+    --  length, elapsed, expected
+    [ ( 60,     30,      30       )
+    , ( 60,     60,      0        )
+    , ( 30,     60,      -30      )
+    ]
+
+countdownIsCompletedAtSpec :: Spec
+countdownIsCompletedAtSpec = describe "countdownIsCompletedAt" $ do
+
+  context "not started" $ mapM_
+    (\(label, dt, expected) ->
+      context label $
+        it ("should be " ++ show expected) $ do
+          t <- getCurrentTime
+          let cd = newCountdown dt
+          countdownIsCompletedAt t cd `shouldBe` expected)
+    --  label,               length, expected
+    [ ( "negative length",   -60,    True     )
+    , ( "zero length",       0,      True     )
+    , ( "posititive length", 60,     False    )
+    ]
+
+  context "started" $ mapM_
+    (\(len, dt, expected) -> let
+      label = "length: " ++ show len ++
+        ", elapsed: " ++ show dt
+      in context label $
+        it ("should be " ++ show expected) $ do
+          t1 <- getCurrentTime
+          let
+            t2        = addUTCTime dt t1
+            timer     = startTimerAt t1 newTimer
+            countdown = (newCountdown len) { countdownTimer = timer }
+          countdownIsCompletedAt t2 countdown `shouldBe` expected)
+    --  length, elapsed, expected
+    [ ( 60,     0,       False    )
+    , ( 60,     30,      False    )
+    , ( 60,     60,      True     )
+    , ( 0,      0,       True     )
+    , ( 30,     60,      True     )
+    ]
+
+countdownIsRunningSpec :: Spec
+countdownIsRunningSpec = describe "countdownIsRunning" $ do
+
+  context "not running" $
+    it "should return False" $ let
+      countdown = newCountdown 60
+      in countdownIsRunning countdown `shouldBe` False
+
+  context "running" $
+    it "should return True" $ do
+      timer <- startTimer newTimer
+      let countdown = (newCountdown 60) { countdownTimer = timer }
+      countdownIsRunning countdown `shouldBe` True
+
+countdownIsStartedSpec :: Spec
+countdownIsStartedSpec = describe "countdownIsStarted" $ do
+
+  context "new countdown" $
+    it "should be False" $
+      countdownIsStarted (newCountdown 60) `shouldBe` False
+
+  context "countdown started" $
+    it "should be True" $ do
+      countdown <- startCountdown $ newCountdown 60
+      countdownIsStarted countdown `shouldBe` True
+
+  context "countdown started, then stopped" $
+    it "should be True" $ do
+      (t, t') <- times 30
+      let
+        countdown  = startCountdownAt t $ newCountdown 60
+        countdown' = stopCountdownAt t' countdown
+      countdownIsStarted countdown' `shouldBe` True
+
+startCountdownSpec :: Spec
+startCountdownSpec = describe "startCountdown" $
+  it "should start the countdown" $ do
+    let countdown = newCountdown 60
+    countdown' <- startCountdown countdown
+    countdownIsRunning countdown' `shouldBe` True
+
+stopCountdownSpec :: Spec
+stopCountdownSpec = describe "stopCountdown" $
+  it "should stop the countdown" $ do
+    countdown  <- startCountdown $ newCountdown 60
+    countdown' <- stopCountdown countdown
+    countdownIsRunning countdown' `shouldBe` False
+
+currentLapAtSpec :: Spec
+currentLapAtSpec = describe "currentLapAt" $ do
+
+  context "newStopwatch" $
+    it "should be zero" $ do
+      t <- getCurrentTime
+      currentLapAt t newStopwatch ` shouldBe` 0
+
+  context "running" $
+    it "should be 1 minute" $ do
+      (t, t') <- times 60
+      let stopwatch = runningStopwatch t
+      currentLapAt t' stopwatch `shouldBe` 60
+
+allLapsAtSpec :: Spec
+allLapsAtSpec = describe "allLapsAt" $ do
+
+  context "newStopwatch" $
+    it "should return a lap of zero length" $ do
+      t <- getCurrentTime
+      allLapsAt t newStopwatch `shouldBe` [0]
+
+  context "single lap" $
+    it "should return a single lap of 1 minute" $ do
+      (t, t') <- times 60
+      let stopwatch = runningStopwatch t
+      allLapsAt t' stopwatch `shouldBe` [60]
+
+  context "multiple laps" $
+    it "should return the lap times" $ do
+      (t, t') <- times 60
+      let
+        timer     = startTimerAt t newTimer
+        stopwatch = Stopwatch
+          { stopwatchTimer = timer
+          , stopwatchLaps  = [10, 20, 30]
+          }
+      allLapsAt t' stopwatch `shouldBe` [60, 10, 20, 30]
+
+totalStopwatchTimeAtSpec :: Spec
+totalStopwatchTimeAtSpec = describe "totalStopwatchTimeAt" $ do
+
+  context "newStopwatch" $
+    it "should be zero" $ do
+      t <- getCurrentTime
+      totalStopwatchTimeAt t newStopwatch `shouldBe` 0
+
+  context "single lap" $
+    it "should be 1 minute" $ do
+      (t, t') <- times 60
+      let stopwatch = runningStopwatch t
+      totalStopwatchTimeAt t' stopwatch `shouldBe` 60
+
+  context "multiple laps" $
+    it "should be 90 seconds" $ do
+      (t, t') <- times 60
+      let
+        stopwatch = (runningStopwatch t)
+          { stopwatchLaps = [10, 20] }
+      totalStopwatchTimeAt t' stopwatch `shouldBe` 90
+
+stopwatchIsRunningSpec :: Spec
+stopwatchIsRunningSpec = describe "stopwatchIsRunning" $ do
+
+  context "newStopwatch" $
+    it "should be False" $
+      stopwatchIsRunning newStopwatch `shouldBe` False
+
+  context "running" $
+    it "should be True" $ do
+      t <- getCurrentTime
+      let stopwatch = runningStopwatch t
+      stopwatchIsRunning stopwatch `shouldBe` True
+
+stopwatchIsStartedSpec :: Spec
+stopwatchIsStartedSpec = describe "stopwatchIsStarted" $ do
+
+  context "newStopwatch" $
+    it "should be False" $
+      stopwatchIsStarted newStopwatch `shouldBe` False
+
+  context "started" $
+    it "should be True" $ do
+      (t, t') <- times 60
+      let
+        timer     = startTimerAt t newTimer
+        stopwatch = newStopwatch { stopwatchTimer = timer }
+      stopwatchIsStarted stopwatch `shouldBe` True
+
+  context "previous laps" $
+    it "should be True" $ let
+      stopwatch = newStopwatch { stopwatchLaps = [60] }
+      in stopwatchIsStarted stopwatch `shouldBe` True
+
+startStopwatchSpec = describe "startStopwatch" $
+  it "should start the stopwatch" $ do
+    stopwatch <- startStopwatch newStopwatch
+    stopwatchIsRunning stopwatch `shouldBe` True
+
+stopStopwatchSpec = describe "stopStopwatch" $
+  it "should stop the Stopwatch" $ do
+    stopwatch  <- startStopwatch newStopwatch
+    stopwatch' <- stopStopwatch stopwatch
+    stopwatchIsRunning stopwatch' `shouldBe` False
+
+newLapAtSpec :: Spec
+newLapAtSpec = describe "newLapAt" $ do
+
+  context "newStopwatch" $
+    it "should record a zero length lap, and start a new one" $ do
+      (t, t') <- times 60
+      let stopwatch = newLapAt t newStopwatch
+      allLapsAt t' stopwatch `shouldBe` [60, 0]
+
+  context "running" $
+    it "should start a new lap" $ do
+      (t, t') <- times 60
+      let
+        stopwatch  = runningStopwatch t
+        stopwatch' = newLapAt t' stopwatch
+      allLapsAt t' stopwatch' `shouldBe` [0, 60]
+
+  context "previous lap" $
+    it "should start a new lap" $ do
+      (t, t') <- times 60
+      let
+        stopwatch  = (runningStopwatch t)
+          { stopwatchLaps = [30] }
+        stopwatch' = newLapAt t' stopwatch
+      allLapsAt t' stopwatch' `shouldBe` [0, 60, 30]
+
+humanNDTSpec :: Spec
+humanNDTSpec = describe "humanNDT" $ mapM_
+  (\(val, expected) ->
+    context (show val) $
+      it ("should be " ++ expected) $
+        humanNDT val `shouldBe` expected)
+  --  value,    expected
+  [ ( 0,        "0d 00h 00m 00.000s"  )
+  , ( single,   "1d 02h 03m 04.005s"  )
+  , ( double,   "11d 12h 13m 14.015s" )
+  , ( triple,   "11d 12h 13m 14.123s" )
+  , ( negative, "-1d 02h 03m 04.005s" )
+  ]
+  where
+    single   = composeNDT $ TimeParts 1 2 3 4 5
+    double   = composeNDT $ TimeParts 11 12 13 14 15
+    triple   = composeNDT $ TimeParts 11 12 13 14 123
+    negative = -single
+
+times :: NominalDiffTime -> IO (UTCTime, UTCTime)
+times dt = do
+  t <- getCurrentTime
+  let t' = addUTCTime dt t
+  return (t, t')
+
+runningStopwatch :: UTCTime -> Stopwatch
+runningStopwatch t = newStopwatch { stopwatchTimer = timer }
+  where timer = startTimerAt t newTimer
+
+-- jl
diff --git a/timeutils.cabal b/timeutils.cabal
new file mode 100644
--- /dev/null
+++ b/timeutils.cabal
@@ -0,0 +1,76 @@
+cabal-version: 1.12
+
+-- This file has been generated from package.yaml by hpack version 0.31.2.
+--
+-- see: https://github.com/sol/hpack
+--
+-- hash: 9ae94588d222d19f2faf581e2466ad3f9af3ab5702b91bceae56a8a156092153
+
+name:           timeutils
+version:        0.1.0
+synopsis:       Time utilities
+description:    Please see the README on GitHub at <https://github.com/jlamothe/timeutils#readme>
+category:       Time
+homepage:       https://github.com/jlamothe/timeutils#readme
+bug-reports:    https://github.com/jlamothe/timeutils/issues
+author:         Jonathan Lamothe
+maintainer:     jlamothe1980@gmail.com
+copyright:      Jonathan Lamothe
+license:        GPL-3
+license-file:   LICENSE
+build-type:     Simple
+extra-source-files:
+    README.md
+    ChangeLog.md
+
+source-repository head
+  type: git
+  location: https://github.com/jlamothe/timeutils
+
+library
+  exposed-modules:
+      Data.Time.Utils
+  other-modules:
+      Paths_timeutils
+  hs-source-dirs:
+      src
+  build-depends:
+      base >=4.7 && <5
+    , microlens >=0.4.10 && <0.5
+    , time >=1.8.0.2 && <1.9
+  default-language: Haskell2010
+
+executable timeutils
+  main-is: Main.hs
+  other-modules:
+      Logic
+      Types
+      UI
+      Paths_timeutils
+  hs-source-dirs:
+      app
+  ghc-options: -threaded -rtsopts -with-rtsopts=-N
+  build-depends:
+      base >=4.7 && <5
+    , brick >=0.47.1 && <0.48
+    , microlens >=0.4.10 && <0.5
+    , time >=1.8.0.2 && <1.9
+    , timeutils
+    , vty
+  default-language: Haskell2010
+
+test-suite timeutils-test
+  type: exitcode-stdio-1.0
+  main-is: Spec.hs
+  other-modules:
+      Paths_timeutils
+  hs-source-dirs:
+      test
+  ghc-options: -threaded -rtsopts -with-rtsopts=-N
+  build-depends:
+      base >=4.7 && <5
+    , hspec >=2.6.1 && <2.7
+    , microlens >=0.4.10 && <0.5
+    , time >=1.8.0.2 && <1.9
+    , timeutils
+  default-language: Haskell2010
