add time formatting options to cron describe

src/System/Cron/Describe.hs

@@ -28,6 +28,7 @@ module System.Cron.Describe
       defaultOpts
     , twentyFourHourFormat
     , twelveHourFormat
+    , customFormat
     , verbose
     , notVerbose
     , OptionBuilder

src/System/Cron/Internal/Describe/Options.hs

@@ -16,6 +16,7 @@ import Data.Default.Class
 import Data.Semigroup as Semigroup
 -------------------------------------------------------------------------------
 import System.Cron.Internal.Describe.Types
+import Data.Time (TimeZone, TimeLocale)
 -------------------------------------------------------------------------------
 
 
@@ -46,6 +47,13 @@ twelveHourFormat :: OptionBuilder
 twelveHourFormat = Builder (\o -> o {timeFormat = Hour12} )
 
 
+-- | Return a builder that sets the options to use a custom time format.
+-- This takes in a time zone, a time locale, and a time formatting string defined by:
+-- https://hackage.haskell.org/package/time-1.12.2/docs/Data-Time-Format.html#t:FormatTime
+customFormat :: TimeZone -> TimeLocale -> String -> OptionBuilder
+customFormat z l f = Builder (\o -> o {timeFormat = CustomTimeFormat z l f} )
+
+
 -- | Return a builder that sets the options to be verbose. A verbose description
 -- doesn't eliminate unnecessary information. The only caveat being that month
 -- information is only ever displayed if it isn't "*".

src/System/Cron/Internal/Describe/Time.hs

@@ -1,20 +1,17 @@
 module System.Cron.Internal.Describe.Time where
 
 import System.Cron.Internal.Describe.Types
+import Data.Time (formatTime, TimeOfDay (TimeOfDay), defaultTimeLocale, TimeLocale, TimeZone, utc, utcToLocalTimeOfDay)
 
 newtype Minute = Minute Int
 newtype Hour   = Hour Int
 
 format :: TimeFormat -> Minute -> Hour -> String
-format t (Minute m) (Hour h) = leftPad (hour t) ++ ":" ++ leftPad m ++ suffix t
-  where leftPad n
-          | n < 10    = "0" ++ show n
-          | otherwise = show n
-        suffix Hour24 = ""
-        suffix Hour12
-          | h < 12    = " AM"
-          | otherwise = " PM"
-        hour Hour24 = h
-        hour Hour12
-          | h > 12 = h `mod` 12
-          | otherwise = h
+format Hour24 = fmtTime utc defaultTimeLocale "%R"
+format Hour12 = fmtTime utc defaultTimeLocale "%I:%M %p"
+format (CustomTimeFormat zone locale pattern) = fmtTime zone locale pattern
+
+fmtTime :: TimeZone -> TimeLocale -> String -> Minute -> Hour -> String
+fmtTime zone locale pattern (Minute m) (Hour h) = formatTime locale pattern tod
+  where
+    tod = snd . utcToLocalTimeOfDay zone $ TimeOfDay h m 0

src/System/Cron/Internal/Describe/Types.hs

@@ -4,6 +4,7 @@ module System.Cron.Internal.Describe.Types where
 
 import Data.List  (intercalate)
 import Data.Maybe (catMaybes)
+import Data.Time (TimeLocale, TimeZone)
 
 
 data Descriptor = Descriptor {
@@ -44,7 +45,7 @@ safeIntToWeekDay n
 data Verbosity = Verbose | NotVerbose
 
 
-data TimeFormat = Hour24 | Hour12
+data TimeFormat = Hour24 | Hour12 | CustomTimeFormat TimeZone TimeLocale String
 
 
 data DescribedValue = Concrete String