Rewrite some of the grossUnitPrice stuff

frontend/Entry.elm

@@ -135,11 +135,11 @@ updateState msg globals state = case state of
       case find (\tg -> tg.id == searchResult.taxGroupId) globals.taxGroups of
         Nothing -> (state, Cmd.none)
         Just taxGroup ->
-          ( ItemEditor
+          ( ItemEditor <| updateGrossUnitPrice
             { barcode = searchResult.barcode
             , name = searchResult.name
             , netUnitPrice = NumberInput.fromFloat searchResult.netUnitPrice
-            , grossUnitPrice = NumberInput.fromFloat <| calculateGarfieldPrice searchResult.netUnitPrice taxGroup.percentage
+            , grossUnitPrice = NumberInput.fromFloat 0
             , salesUnits = NumberInput.fromInt searchResult.salesUnits
             , group = Select.init (.id >> String.fromInt) (.name) { id = searchResult.groupId, name = searchResult.groupName } globals.groups
             , location = Select.init (.id >> String.fromInt) (.name) { id = searchResult.locationId, name = searchResult.locationName } globals.locations
@@ -175,7 +175,7 @@ updateState msg globals state = case state of
 
 updateGrossUnitPrice model =
   { model
-  | grossUnitPrice = NumberInput.fromFloat <| calculateGarfieldPrice (NumberInput.get model.netUnitPrice) (Select.get model.taxGroup).percentage
+  | grossUnitPrice = Maybe.withDefault model.grossUnitPrice <| Maybe.map NumberInput.fromFloat <| calculateGarfieldPrice model
   }
 
 -- View stuff
@@ -238,15 +238,23 @@ view { globals, state } = case state of
           [ label [ for "snack-name" ] [ text "Name" ]
           , input [ value model.name, disabled True, id "snack-name" ] []
           ]
-        , div [ class "form-input" ]
-          [ label [ for "gross-unit-price" ]
-            [ text <| "Stückpreis (Brutto), Vorschlag: " ++ String.fromFloat (calculateGarfieldPrice (NumberInput.get model.netUnitPrice) (Select.get model.taxGroup).percentage)
-            ]
-          , input [ onInput SetGrossUnitPrice, value <| NumberInput.show model.grossUnitPrice, id "gross-unit-price", type_ "number", step "0.01" ] []
-          ]
+        , viewGrossUnitPriceInput model
         ]
       ]
 
+viewGrossUnitPriceInput model =
+  let
+    suggestedPriceStr = case calculateGarfieldPrice model of
+      Nothing -> "?"
+      Just suggestedPrice -> String.fromFloat suggestedPrice
+  in
+    div [ class "form-input" ]
+      [ label [ for "gross-unit-price" ]
+        [ text <| "Stückpreis (Brutto), Vorschlag: " ++ suggestedPriceStr
+        ]
+      , input [ onInput SetGrossUnitPrice, value <| NumberInput.show model.grossUnitPrice, id "gross-unit-price", type_ "number", step "0.01" ] []
+      ]
+
 searchResultHeaders =
   tr []
     [ th [] [ text "Barcode" ]
@@ -275,8 +283,10 @@ viewSearchResult model =
       ]
     ]
 
-calculateGarfieldPrice netUnitPrice taxPercentage =
-  roundTo 2 <| netUnitPrice * (1 + taxPercentage) + 0.01
+calculateGarfieldPrice model =
+  NumberInput.get model.netUnitPrice |> Maybe.map (\netUnitPrice ->
+    roundTo 2 <| netUnitPrice * (1 + (Select.get model.taxGroup).percentage) + 0.01
+  )
 
 roundTo places x = toFloat (round <| x * 10 ^ places) / 10 ^ places
 

frontend/NumberInput.elm

@@ -1,25 +1,29 @@
 module NumberInput exposing (..)
 
 type alias Model a =
-  { value : a
+  { value : Maybe a
   , original : String
   , convert : String -> Maybe a
   }
 
 fromFloat : Float -> Model Float
-fromFloat x = Model x (String.fromFloat x) String.toFloat
+fromFloat x = Model (Just x) (String.fromFloat x) String.toFloat
 
 fromInt : Int -> Model Int
-fromInt x = Model x (String.fromInt x) String.toInt
+fromInt x = Model (Just x) (String.fromInt x) String.toInt
 
-get : Model a -> a
+get : Model a -> Maybe a
 get = .value
 
+withDefault : a -> Model a -> a
+withDefault d = Maybe.withDefault d << get
+
+isValid : Model a -> Bool
+isValid model = model.value /= Nothing
+
 update : String -> Model a -> Model a
 update str model =
-  case model.convert str of
-    Nothing -> model
-    Just value -> { model | value = value, original = str }
+  { model | value = model.convert str, original = str }
 
 show : Model a -> String
 show = .original