factoring.elm

-- Read all about this program in the official Elm guide:
-- https://guide.elm-lang.org/architecture/user_input/text_fields.html

import Html exposing (Html, Attribute, beginnerProgram, text, div, input)
import Html.Attributes exposing (..)
import Html.Events exposing (onInput)
import List
import String
import Regex
import Result
import Debug

main =
  beginnerProgram { model = {polynomial = [], divisor = []}, view = view, update = update }


-- UPDATE

type Msg = PolynomialChanged String | DivisorChanged String

update event oldState =
  case event of
    PolynomialChanged newPolynomial ->
      { oldState | polynomial = toExpression newPolynomial }
    DivisorChanged newDivisor ->
      { oldState | divisor = toExpression newDivisor }

type alias Term = { constant: Int, exponent: Int }
type alias Expression = List Term

toExpression: String -> Expression
toExpression input =
  List.map toTerm (termInputs input)

toTerm: String -> Term
toTerm input =
  {constant = extractConstant input, exponent = extractExponent input}

extractConstant input =
  if String.contains "x" input
  then
    let matches = Regex.find (Regex.AtMost 1) (Regex.regex "[-]?\\d+") input in
    matches |> List.head |> Maybe.map .match |> Maybe.map (\match -> String.toInt (Debug.log "constant match" match) |> Result.toMaybe) |> Maybe.withDefault (Just 1) |> Maybe.withDefault 1
  else
    String.toInt input |> Result.withDefault 0

extractExponent input =
  if String.contains "x" input
  then
    let matches = Regex.find (Regex.AtMost 1) (Regex.regex "\\d+$") input in
      matches |> List.head |> Maybe.map .match |> Maybe.map (\match -> String.toInt (Debug.log "exponent match" match) |> Result.toMaybe) |> Maybe.withDefault (Just 1) |> Maybe.withDefault 1
  else
    0

termInputs: String -> List String
termInputs input = String.split " " input

termToString: Term -> String
termToString term =
  "constant: " ++ toString term.constant ++ "."
  ++ " exponent: " ++ toString term.exponent ++ "."

result: Expression -> Expression -> String
result polynomial divisor =
  "Result:"

-- VIEW

view state =
  div []
    [ input [ placeholder "polynomial", onInput PolynomialChanged, myStyle ] []
    , input [ placeholder "divisor", onInput DivisorChanged, myStyle ] []
    , div [ myStyle ] [ text ("polynomial: " ++ (state.polynomial |> List.map termToString |> String.join ", ")) ]
    , div [ myStyle ] [ text ("divisor: " ++ (state.divisor |> List.map termToString |> String.join ", ")) ]
    , div [ myStyle ] [ text (result (state.polynomial) (state.divisor)) ]
    ]

myStyle =
  style
    [ ("width", "100%")
    , ("height", "40px")
    , ("padding", "10px 0")
    , ("font-size", "2em")
    , ("text-align", "center")
    ]