module Util.List exposing
    ( distinct
    , find
    , findIndexed
    , findNext
    , findPrev
    , get
    )


get : List a -> Int -> Maybe a
get list index =
    if index < 0 then
        Nothing

    else
        case list of
            [] ->
                Nothing

            x :: xs ->
                if index == 0 then
                    Just x

                else
                    get xs (index - 1)


find : (a -> Bool) -> List a -> Maybe a
find pred list =
    findIndexed pred list |> Maybe.map Tuple.first


findIndexed : (a -> Bool) -> List a -> Maybe ( a, Int )
findIndexed pred list =
    findIndexed1 pred list 0


findIndexed1 : (a -> Bool) -> List a -> Int -> Maybe ( a, Int )
findIndexed1 pred list index =
    case list of
        [] ->
            Nothing

        x :: xs ->
            if pred x then
                Just ( x, index )

            else
                findIndexed1 pred xs (index + 1)


distinct : List a -> List a
distinct list =
    List.reverse <|
        List.foldl
            (\a ->
                \r ->
                    if List.member a r then
                        r

                    else
                        a :: r
            )
            []
            list


findPrev : (a -> Bool) -> List a -> Maybe a
findPrev pred list =
    findIndexed pred list
        |> Maybe.map Tuple.second
        |> Maybe.map (\i -> i - 1)
        |> Maybe.andThen (get list)


findNext : (a -> Bool) -> List a -> Maybe a
findNext pred list =
    findIndexed pred list
        |> Maybe.map Tuple.second
        |> Maybe.map (\i -> i + 1)
        |> Maybe.andThen (get list)
