From 944ef46d845bf0ed4fa063183bc9bf3d119e14fe Mon Sep 17 00:00:00 2001
From: Steffen Jost <jost@tcs.ifi.lmu.de>
Date: Tue, 15 Feb 2022 12:39:17 +0100
Subject: [PATCH] refactor(db): instance PersistField CalendarDiffDays

---
 src/Data/Time/Clock/Instances.hs | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/src/Data/Time/Clock/Instances.hs b/src/Data/Time/Clock/Instances.hs
index 36dc03b45..8ff9d721b 100644
--- a/src/Data/Time/Clock/Instances.hs
+++ b/src/Data/Time/Clock/Instances.hs
@@ -46,28 +46,35 @@ instance Csv.ToField UTCTime where
 instance Csv.FromField UTCTime where
   parseField = iso8601ParseM <=< Csv.parseField
 
-deriving instance Generic  CalendarDiffDays
+
+
+-- CalendarDiffDays
+--
+-- CalendarDiffDays is basically a pair of Integers, we are stored in the DB as an Array of Word (Word8 probably suffices already)
+type CDDdb = Word
+
+deriving instance Generic CalendarDiffDays
 --  deriving instance Hashable CalendarDiffDays
 
 instance PersistField CalendarDiffDays where
-  toPersistValue CalendarDiffDays{..} = toPersistValue $ both coerceI64 (cdMonths, cdDays)
+  toPersistValue CalendarDiffDays{..} = toPersistValue $ both coerceICcd (cdMonths, cdDays)
     where
-      coerceI64 :: Integer -> Word
-      coerceI64 = fromIntegral
+      coerceICcd :: Integer -> CDDdb
+      coerceICcd = fromIntegral
 
-      -- cannot be imported from utils due to cyclic dependencies and Data.Tuple.Extra is not yet a dependency
+      -- placement in Utils impossivle due to cyclic dependencies
+      -- Data.Tuple.Extra is not yet a dependency
+      -- both = join (***)  is still too cryptic for me
       both :: (a -> b) -> (a, a) -> (b, b)
       both f (x,y) = (f x, f y)
 
   fromPersistValue v =
     case fromPersistValue v of
-      Right (cdMonths, cdDays) -> Right CalendarDiffDays{cdMonths = coerce64I cdMonths, cdDays = coerce64I cdDays}
+      Right (coerceCcdI -> cdMonths, coerceCcdI -> cdDays) -> Right CalendarDiffDays{..}
       Left e -> Left e
     where
-      coerce64I :: Word -> Integer
-      coerce64I = toInteger
+      coerceCcdI :: CDDdb -> Integer
+      coerceCcdI = toInteger
 
-type WordPair = (Word, Word)
 instance PersistFieldSql CalendarDiffDays where
-  sqlType _ = sqlType (Proxy @WordPair)
-
+  sqlType _ = sqlType (Proxy @(CDDdb, CDDdb))