factor out common code in database migration

Turns out that adding column is a pretty common and straighfordward migration. I originally intended to add a new column to the TxMeta table, hence the refactor. In the end, I've used a different table for withdrawals, but the refactor is still worth it as it is IMO.

lib/core/src/Cardano/Wallet/DB/Sqlite.hs

@@ -420,25 +420,9 @@ migrateManually tr defaultFieldValues =
     --   it is missing.
     --
     addActiveSlotCoefficientIfMissing :: Sqlite.Connection -> IO ()
-    addActiveSlotCoefficientIfMissing conn = do
-        isFieldPresent conn activeSlotCoeff >>= \case
-            TableMissing ->
-                traceWith tr $ MsgManualMigrationNotNeeded activeSlotCoeff
-            ColumnMissing -> do
-                traceWith tr $ MsgManualMigrationNeeded activeSlotCoeff value
-                addColumn <- Sqlite.prepare conn $ T.unwords
-                    [ "ALTER TABLE", tableName activeSlotCoeff
-                    , "ADD COLUMN", fieldName activeSlotCoeff
-                    , fieldType activeSlotCoeff, "NOT NULL", "DEFAULT", value
-                    , ";"
-                    ]
-                _ <- Sqlite.step addColumn
-                Sqlite.finalize addColumn
-            ColumnPresent ->
-                traceWith tr $ MsgManualMigrationNotNeeded activeSlotCoeff
-
+    addActiveSlotCoefficientIfMissing conn =
+        addColumn conn (DBField CheckpointActiveSlotCoeff) value
       where
-        activeSlotCoeff = DBField CheckpointActiveSlotCoeff
         value = toText
             $ W.unActiveSlotCoefficient
             $ defaultActiveSlotCoefficient defaultFieldValues
@@ -448,23 +432,8 @@ migrateManually tr defaultFieldValues =
     --
     addDesiredPoolNumberIfMissing :: Sqlite.Connection -> IO ()
     addDesiredPoolNumberIfMissing conn = do
-        isFieldPresent conn desiredPoolNumber >>= \case
-            TableMissing ->
-                traceWith tr $ MsgManualMigrationNotNeeded desiredPoolNumber
-            ColumnMissing -> do
-                traceWith tr $ MsgManualMigrationNeeded desiredPoolNumber value
-                addColumn <- Sqlite.prepare conn $ T.unwords
-                    [ "ALTER TABLE", tableName desiredPoolNumber
-                    , "ADD COLUMN", fieldName desiredPoolNumber
-                    , fieldType desiredPoolNumber, "NOT NULL", "DEFAULT", value
-                    , ";"
-                    ]
-                _ <- Sqlite.step addColumn
-                Sqlite.finalize addColumn
-            ColumnPresent ->
-                traceWith tr $ MsgManualMigrationNotNeeded desiredPoolNumber
+        addColumn conn (DBField ProtocolParametersDesiredNumberOfPools) value
       where
-        desiredPoolNumber = DBField ProtocolParametersDesiredNumberOfPools
         value = T.pack $ show $ defaultDesiredNumberOfPool defaultFieldValues
 
     -- | This table became @protocol_parameters@.
@@ -491,6 +460,30 @@ migrateManually tr defaultFieldValues =
                 | otherwise                       -> ColumnMissing
             _ -> TableMissing
 
+    -- | A migration for adding a non-existing column to a table. Factor out as
+    -- it's a common use-case.
+    addColumn
+        :: Sqlite.Connection
+        -> DBField
+        -> Text
+        -> IO ()
+    addColumn conn field value = do
+        isFieldPresent conn field >>= \case
+            TableMissing ->
+                traceWith tr $ MsgManualMigrationNotNeeded field
+            ColumnMissing -> do
+                traceWith tr $ MsgManualMigrationNeeded field value
+                query <- Sqlite.prepare conn $ T.unwords
+                    [ "ALTER TABLE", tableName field
+                    , "ADD COLUMN", fieldName field
+                    , fieldType field, "NOT NULL", "DEFAULT", value
+                    , ";"
+                    ]
+                _ <- Sqlite.step query
+                Sqlite.finalize query
+            ColumnPresent ->
+                traceWith tr $ MsgManualMigrationNotNeeded field
+
 -- | A set of default field values that can be consulted when performing a
 --   database migration.
 --