elm-twitch/src/Twitch.elm

module Twitch exposing (Playlist, Video, fetchPlaylists)

import Html.Parser
import Http
import Json.Decode as Decode
import Task exposing (Task)


type alias Playlist =
    { name : String
    , videos : List Video
    }


type alias Video =
    { name : String
    , url : String
    , duration : Float
    }


get : { url : String, resolver : Http.Resolver x a } -> Task x a
get { url, resolver } =
    Http.task
        { body = Http.emptyBody
        , headers = []
        , method = "GET"
        , resolver = resolver
        , timeout = Nothing
        , url = url
        }


fetchPlaylists : Task x (List Playlist)
fetchPlaylists =
    fetchPlaylistPath |> Task.andThen fetchPlaylistsMapper


fetchPlaylistPath : Task x (List String)
fetchPlaylistPath =
    get
        { url = "/videos"
        , resolver = Http.stringResolver parsePlaylistPath
        }


fetchPlaylist : String -> Task x Playlist
fetchPlaylist name =
    get
        { url = "/videos/" ++ name ++ "/description.json"
        , resolver = Http.stringResolver parsePlaylistName
        }
        |> Task.andThen
            (\a ->
                Task.map (\b -> Playlist a b)
                    (get
                        { url = "/videos/" ++ name
                        , resolver = Http.stringResolver parsePlaylistVideoPaths
                        }
                        |> Task.andThen (\c -> fetchVideos name c)
                    )
            )


fetchVideo : String -> String -> Task x Video
fetchVideo playlist video =
    let
        url =
            "/videos/" ++ playlist ++ video
    in
    get
        { url = "/videos/" ++ playlist ++ "/" ++ video ++ "/description.json"
        , resolver = Http.stringResolver (parseVideo url)
        }


fetchVideos : String -> List String -> Task x (List Video)
fetchVideos playlist videos =
    Task.sequence (List.map (fetchVideo playlist) videos)


parseVideo : String -> Http.Response String -> Result x Video
parseVideo url result =
    case result of
        Http.GoodStatus_ _ content ->
            case Decode.decodeString (decodeVideo url) content of
                Ok v ->
                    Ok v

                _ ->
                    Ok { name = "", url = url, duration = 0 }

        _ ->
            Ok { name = "", url = url, duration = 0 }


fetchPlaylistsMapper : List String -> Task x (List Playlist)
fetchPlaylistsMapper names =
    Task.sequence (List.map fetchPlaylist names)


parsePlaylistName : Http.Response String -> Result x String
parsePlaylistName result =
    case result of
        Http.GoodStatus_ _ content ->
            case Decode.decodeString decodePlaylistName content of
                Ok p ->
                    Ok p

                _ ->
                    Ok ""

        _ ->
            Ok ""


parsePlaylistVideoPaths : Http.Response String -> Result x (List String)
parsePlaylistVideoPaths result =
    case result of
        Http.GoodStatus_ _ content ->
            let
                withoutDoctype =
                    if String.startsWith "<!doctype" (String.toLower content) then
                        String.lines content |> List.drop 1 |> String.join "\n"

                    else
                        content

                decoded =
                    Html.Parser.run withoutDoctype

                hrefs =
                    Result.map findHrefs decoded
            in
            case hrefs of
                Ok h ->
                    Ok (List.filter (String.endsWith "/") h)

                _ ->
                    Ok []

        _ ->
            Ok []


parsePlaylistPath : Http.Response String -> Result x (List String)
parsePlaylistPath result =
    case result of
        Http.GoodStatus_ _ content ->
            let
                withoutDoctype =
                    if String.startsWith "<!doctype" (String.toLower content) then
                        String.lines content |> List.drop 1 |> String.join "\n"

                    else
                        content

                decoded =
                    Html.Parser.run withoutDoctype

                hrefs =
                    Result.map findHrefs decoded
            in
            case hrefs of
                Ok h ->
                    Ok h

                _ ->
                    Ok []

        _ ->
            Ok []


findHrefsAux : List String -> Html.Parser.Node -> List String
findHrefsAux acc node =
    case node of
        Html.Parser.Element string (( key, value ) :: t) nodes ->
            let
                newAcc =
                    if key == "href" then
                        value :: acc

                    else
                        acc
            in
            findHrefsAux newAcc (Html.Parser.Element string t nodes)

        Html.Parser.Element string [] (h :: t) ->
            let
                attrs =
                    findHrefsAux [] h
            in
            findHrefsAux (acc ++ attrs) (Html.Parser.Element string [] t)

        _ ->
            acc


findHrefs : List Html.Parser.Node -> List String
findHrefs x =
    findHrefsAux [] (Html.Parser.Element "" [] x)


decodePlaylistName : Decode.Decoder String
decodePlaylistName =
    Decode.field "title" Decode.string


decodeVideo : String -> Decode.Decoder Video
decodeVideo url =
    Decode.map2 (\x y -> Video x url y)
        (Decode.field "title" Decode.string)
        (Decode.field "duration" Decode.float)