Implement price calculator

frontend/Entry.elm

@@ -90,6 +90,35 @@ type alias Globals =
   , taxGroups : List TaxGroup
   }
 
+type CalculatorTax = Net | Gross
+
+ctToInt ct = case ct of
+  Gross -> 0
+  Net -> 1
+
+ctShow ct = case ct of
+  Gross -> "Brutto"
+  Net -> "Netto"
+
+type alias CalculatorModel =
+  { tax : Select.Model CalculatorTax
+  , bundlePrice : NumberInput.Model Float
+  , bundleSize : NumberInput.Model Int
+  }
+
+type CalculatorMsg
+  = SetTax String
+  | SetBundlePrice String
+  | SetBundleSize String
+
+updateCalculator msg model = case msg of
+  SetTax key ->
+    { model | tax = Select.update key model.tax }
+  SetBundlePrice str ->
+    { model | bundlePrice = NumberInput.update str model.bundlePrice }
+  SetBundleSize str ->
+    { model | bundleSize = NumberInput.update str model.bundleSize }
+
 type State
   = ItemSearch
     { searchTerm : String
@@ -99,6 +128,7 @@ type State
     { barcode : String
     , name : String
     , salesUnits : NumberInput.Model Int
+    , calculator : CalculatorModel
     , netUnitPrice : NumberInput.Model Float
     , grossUnitPrice : NumberInput.Model Float
     , group : Select.Model Group
@@ -114,6 +144,7 @@ type Msg
   | SetBarcode String
   | SetName String
   | SetSalesUnits String
+  | CalculatorMsg CalculatorMsg
   | SetNetUnitPrice String
   | SetGrossUnitPrice String
   | SetGroup String
@@ -148,6 +179,11 @@ updateState msg globals state = case state of
           ( ItemEditor
             { barcode = searchResult.barcode
             , name = searchResult.name
+            , calculator =
+              { tax = Select.init ctShow ctShow Net [Net, Gross]
+              , bundlePrice = NumberInput.fromFloat searchResult.netUnitPrice
+              , bundleSize = NumberInput.fromInt 1
+              }
             , netUnitPrice = NumberInput.fromFloat searchResult.netUnitPrice
             , grossUnitPrice = NumberInput.fromFloat
               (suggestedGrossPrice searchResult.netUnitPrice taxGroup.percentage)
@@ -167,6 +203,8 @@ updateState msg globals state = case state of
       (ItemEditor { model | name = name }, Cmd.none)
     SetSalesUnits str ->
       (ItemEditor { model | salesUnits = NumberInput.update str model.salesUnits }, Cmd.none)
+    CalculatorMsg msg_ ->
+      (ItemEditor { model | calculator = updateCalculator msg_ model.calculator }, Cmd.none)
     SetNetUnitPrice str ->
       ( ItemEditor { model | netUnitPrice = NumberInput.update str model.netUnitPrice }
       , Cmd.none
@@ -227,6 +265,11 @@ view { globals, state } = case state of
           [ label [ for "location" ] [ text "Raum" ]
           , Select.view SetLocation model.location
           ]
+        , div [ class "form-input" ]
+          [ label [ for "tax-group" ] [ text "Steuergruppe" ]
+          , Select.view SetTaxGroup model.taxGroup
+          ]
+        , Html.map CalculatorMsg <| viewCalculator model.calculator (Select.get model.taxGroup)
         , div [ class "form-input" ]
           [ label [ for "net-unit-price" ] [ text "Einkaufspreis (Netto)" ]
           , input
@@ -237,10 +280,7 @@ view { globals, state } = case state of
             , step "0.01"
             ]
             []
-          ]
-        , div [ class "form-input" ]
-          [ label [ for "tax-group" ] [ text "Steuergruppe" ]
-          , Select.view SetTaxGroup model.taxGroup
+          , viewSetCalculatedPriceButton model
           ]
         , div [ class "form-input" ]
           [ label [ for "gross-unit-price" ] [ text "Verkaufspreis (Brutto)" ]
@@ -257,6 +297,81 @@ view { globals, state } = case state of
         ]
       ]
 
+viewCalculator model taxGroup =
+  let
+    mainPart =
+      [ text "("
+      , input
+        [ class "formula-input", placeholder "Gebindepreis"
+        , value <| NumberInput.show model.bundlePrice
+        , onInput SetBundlePrice
+        ]
+        []
+      , text " ÷ "
+      , input
+        [ class "formula-input", placeholder "Gebindegröße"
+        , value <| NumberInput.show model.bundleSize
+        , onInput SetBundleSize
+        ]
+        []
+      , text ") "
+      ]
+    taxPart =
+      [ text " ÷ "
+      , input
+        [ class "formula-input"
+        , disabled True
+        , value <| String.fromFloat <| 1 + taxGroup.percentage
+        ]
+        []
+      ]
+    resultPart =
+      [ text " = "
+      , input
+        [ class "formula-input"
+        , disabled True
+        , value <| Maybe.withDefault "?" <| Maybe.map String.fromFloat <| calculatorResult model taxGroup
+        ]
+        []
+      ]
+  in
+    fieldset []
+      [ legend [] [ text "Preisrechner" ]
+      , div [] <| List.concat <| List.filterMap identity
+        [ Just mainPart
+        , if Select.get model.tax == Gross then Just taxPart else Nothing
+        , Just resultPart
+        ]
+      , div [ class "form-input" ]
+        [ label [ for "calculator-tax" ] [ text "Gebindepreis ist" ]
+        , Select.view SetTax model.tax
+        ]
+      ]
+
+calculatorResult model taxGroup =
+  case (NumberInput.get model.bundlePrice, NumberInput.get model.bundleSize) of
+    (Just bundlePrice, Just bundleSize) ->
+      Just <| roundTo 2 <|
+        if Select.get model.tax == Gross then
+          (bundlePrice / toFloat bundleSize) / (1 + taxGroup.percentage)
+        else
+          bundlePrice / toFloat bundleSize
+    _ ->
+      Nothing
+
+viewSetCalculatedPriceButton model =
+  case calculatorResult model.calculator (Select.get model.taxGroup) of
+    Nothing ->
+      button [ disabled True ] [ text "Auf ? setzen" ]
+    Just calculatedPrice ->
+      button
+        [ onClick <| SetNetUnitPrice <| String.fromFloat calculatedPrice
+        -- Prevent submitting the form
+        , type_ "button"
+        ]
+        [ text <| "Auf " ++ String.fromFloat calculatedPrice ++ " setzen"
+        ]
+
 viewSetSuggestedPriceButton model =
   case NumberInput.get model.netUnitPrice of
     Nothing ->