module Util exposing (..)

import Html.Events exposing (on, keyCode)
import Html exposing (Attribute)
import Json.Decode as Json


{-| Conditionally emit msg defined by `tagger` if the
key pressed was the enter key
-}
onEnter : msg -> Attribute msg
onEnter tagger =
    onKeyDown tagger <| \key -> key == 13


{-| Conditionally emit msg defined by `tagger` based
on return value of `pred`.
-}
onKeyDown : msg -> (Int -> Bool) -> Attribute msg
onKeyDown tagger pred =
    on "keydown"
        (keyCode
            |> Json.map pred
            |> Json.andThen
                (\result ->
                    if result then
                        Json.succeed tagger
                    else
                        Json.fail ""
                )
        )