Add some basic error handling

src/Yore/DB.hs

@@ -1,10 +1,15 @@
 {-# LANGUAGE DeriveAnyClass #-}
 {-# LANGUAGE DuplicateRecordFields #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# OPTIONS_GHC -Wno-deriving-defaults #-}
 
 module Yore.DB
-  ( DayIndex (..)
+  ( DB
+  , Error (..)
+  , initDB
+  , withConn
+  , DayIndex (..)
   , DayFile (..)
   , createDayFile
   , createDayIndex
@@ -12,25 +17,44 @@ module Yore.DB
   , readDayPaths
   , getDayFileByIssue
   , getNumberOfIssues
-  , Table (..)
-  , getTables
   ) where
 
+import Control.Concurrent (getNumCapabilities)
 import Data.Functor.Identity (Identity (..))
+import Data.Pool (Pool, defaultPoolConfig, newPool, withResource)
 import Data.Text (Text)
 import Data.Time (Day)
 import GHC.Generics (Generic)
 
 import qualified Database.PostgreSQL.Opium as Opium
 
-data Table = Table
-  { schema :: String
-  , name :: String
-  }
-  deriving (Show, Generic, Opium.FromRow)
+newtype DB = DB (Pool (Either Opium.ConnectionError Opium.Connection))
 
-getTables :: Opium.Connection -> IO (Either Opium.Error [Table])
-getTables = Opium.fetch_ "SELECT table_schema AS schema, table_name AS name FROM information_schema.tables"
+data Error
+  = ConnectionError Opium.ConnectionError
+  | Error Opium.Error
+  deriving (Show)
+
+initDB :: Text -> IO DB
+initDB connString = do
+  capabilities <- getNumCapabilities
+  let maxResources = capabilities
+  DB
+    <$> newPool
+      ( defaultPoolConfig
+          (Opium.connect connString)
+          (either (const $ pure ()) Opium.close)
+          10
+          maxResources
+      )
+
+withConn :: DB -> (Opium.Connection -> IO (Either Opium.Error a)) -> IO (Either Error a)
+withConn (DB connPool) f =
+  withResource connPool $ \case
+    Left connectionError ->
+      pure $ Left $ ConnectionError connectionError
+    Right conn ->
+      either (Left . Error) Right <$> f conn
 
 data DayIndex = DayIndex
   { day_index_id :: Int

src/Yore/Log.hs

@@ -1,4 +1,4 @@
-module Yore.Log (info) where
+module Yore.Log (Yore.Log.error, info) where
 
 import Data.Time (getZonedTime)
 import GHC.Stack (HasCallStack, SrcLoc (..), callStack, getCallStack)
@@ -7,6 +7,9 @@ import Text.Printf (printf)
 info :: (HasCallStack) => String -> IO ()
 info = doLog "INF"
 
+error :: (HasCallStack) => String -> IO ()
+error = doLog "ERR"
+
 doLog :: (HasCallStack) => String -> String -> IO ()
 doLog level msg = do
   now <- getZonedTime