market.elm

import Html exposing (..)
import Html.Attributes exposing (..)
import Html.Events exposing (..)

type alias Product = { name : String, singular : String, amount : Int, price : Int }

type alias Model =
  { products : List Product, cash : Int }
  
model : Model
model =
  { products = [
  { name = "Tomatoes", singular = "Tomato", amount = 0, price = 10 }
  , { name = "Potatoes", singular = "Potato", amount = 0, price = 5 }
  , { name = "Beetroots", singular = "Beetroot", amount = 0, price = 7 }
  ], cash = 100 }
  
type Action =
  Buy Product | Sell Product

updateProducts products product =
  let
    newProducts =
      List.map (\p ->
        if p.name == product.name then
          product
        else
          p) products
  in
    newProducts
        
update : Action -> Model -> Model
update action model =
  case action of
    Buy product ->
      { model | products = (updateProducts model.products product), cash = model.cash - product.price }
    Sell product ->
      { model | products = (updateProducts model.products product), cash = model.cash + product.price }

pluralize : String -> String -> Int -> String
pluralize singular plural quantity =
  if quantity == 1 then
    singular
   else
     plural
     
view model =
  let
    caption amount productName productSingular =
      (toString amount)
         ++ " "
         ++ pluralize productSingular productName amount
         
    productButton actionType label disable =
        button [ disabled disable, onClick actionType ] [ text label ]
    
    moneyText val =
      text ("£" ++ (toString val))
      
    getProduct productName = 
    List.head (List.filter (\m -> m.name == productName) model.products)
        |> Maybe.withDefault { name = "", singular = "", amount = 0, price = 0 }
      
    updateProductAmount product amountChange =
      { product | amount = product.amount + amountChange }
      
    buySell product =
      div [] [
        moneyText product.price
        , productButton (Buy (updateProductAmount product 1)) "Buy" ((model.cash - product.price) < 0)
        , productButton (Sell (updateProductAmount product -1)) "Sell" (product.amount <= 0)
        , text (caption product.amount product.name product.singular)
      ]
   
    productsDisplay =
      List.map (buySell) model.products
      
  in 
  div []
    ([ h1 [] [ text "Market" ]
    , div [] [ moneyText model.cash ]
    ] ++ productsDisplay)
    
main = beginnerProgram { model = model, update = update, view = view }