Main.elm

module Main exposing (..)

import Browser
import Html exposing (div, input, p, span, strong, text)
import Html.Attributes exposing (value)
import Html.Events exposing (onInput)


type alias Model =
    String


type Msg
    = Input String


type Balance
    = Balanced
    | Stagger ( Int, Int, Int ) -- ( [ { respectively
    | Unbalanced


balance : ( Int, Int, Int ) -> Balance
balance ( n1, n2, n3 ) =
    if n1 > 0 || n2 > 0 || n3 > 0 then
        Stagger ( n1, n2, n3 )

    else if n1 < 0 || n2 < 0 || n3 < 0 then
        Unbalanced

    else
        -- 0,0,0
        Balanced


delta : Char -> ( Int, Int, Int )
delta c =
    case c of
        '(' ->
            ( 1, 0, 0 )

        '[' ->
            ( 0, 1, 0 )

        '{' ->
            ( 0, 0, 1 )

        ')' ->
            ( -1, 0, 0 )

        ']' ->
            ( 0, -1, 0 )

        '}' ->
            ( 0, 0, -1 )

        _ ->
            -- skip invalid char?
            ( 0, 0, 0 )


add : Char -> Balance -> Balance
add c b =
    let
        ( d1, d2, d3 ) =
            delta c
    in
    case b of
        Unbalanced ->
            Unbalanced

        Balanced ->
            balance ( d1, d2, d3 )

        Stagger ( n1, n2, n3 ) ->
            balance ( n1 + d1, n2 + d2, n3 + d3 )


check s =
    List.foldl add Balanced (String.toList s) == Balanced


init =
    ""


update msg model =
    case msg of
        Input s ->
            s


view model =
    div []
        [ p [] [ input [ onInput Input, value model ] [] ]
        , p []
            [ if check model then
                strong [] [ text "BALANCED" ]

              else
                span [] [ text "nope." ]
            ]
        ]


main =
    Browser.sandbox
        { init = init
        , view = view
        , update = update
        }