module Main exposing (main)
    module Main exposing (main)
    
    import Browser
    import Browser.Events exposing (onAnimationFrame)
    import Html exposing (Html)
    import Html.Attributes as Attr
    import Random
    import Svg exposing (circle, g, svg)
    import Svg.Attributes exposing (cx, cy, fill, height, opacity, r, transform, viewBox, width)
    import Time
    
    
    
    -- MAIN
    
    
    main : Program () Model Msg
    main =
        Browser.element
            { init = init
            , view = view
            , update = update
            , subscriptions = subscriptions
            }
    
    
    
    -- MODEL
    
    
    type alias Model =
        { time : Float
        , stars : List Star
        }
    
    
    type alias Star =
        { x : Float
        , y : Float
        , vx : Float
        , vy : Float
        , lifetime : Float
        }
    
    
    init : () -> ( Model, Cmd Msg )
    init _ =
        ( { time = 0
          , stars = []
          }
        , generateStar
        )
    
    
    
    -- UPDATE
    
    
    type Msg
        = Tick Float
        | NewStar Star
    
    
    update : Msg -> Model -> ( Model, Cmd Msg )
    update msg model =
        case msg of
            Tick delta ->
                ( { model
                    | time = model.time + delta
                    , stars = updateStars model.stars
                  }
                , generateStar
                )
    
            NewStar star ->
                ( { model
                    | stars = star :: model.stars
                  }
                , Cmd.none
                )
    
    
    updateStars : List Star -> List Star
    updateStars stars =
        stars
            |> List.filter (\p -> p.lifetime > 0)
            |> List.map updateStar
    
    
    updateStar : Star -> Star
    updateStar star =
        { star
            | x = star.x + star.vx
            , y = star.y + star.vy
            , lifetime = star.lifetime - 5
        }
    
    
    generateStar : Cmd Msg
    generateStar =
        Random.generate NewStar starGenerator
    
    
    starGenerator : Random.Generator Star
    starGenerator =
        Random.map5 Star
            (Random.float -4 4)
            --x
            (Random.float -4 4)
            --y
            (Random.float -0.05 0.05)
            --vx
            (Random.float -0.05 0.05)
            --vy
            (Random.float 50 300)
    
    
    
    -- Lifetime
    -- SUBSCRIPTIONS
    
    
    subscriptions : Model -> Sub Msg
    subscriptions _ =
        onAnimationFrame (\time -> Tick (Time.posixToMillis time |> toFloat))
    
    
    
    -- VIEW
    
    
    view : Model -> Html Msg
    view model =
        svg
            [ width "100%"
            , height "100%"
            , viewBox "0 0 100 100"
            ]
            [ g [ transform "translate(48, 32)" ]
                [ circle
                    [ cx "0"
                    , cy "100"
                    , r "20"
                    , fill "black"
                    , opacity "0.9"
                    ]
                    []
                , g [] (List.map viewStar model.stars)
                ]
            ]
    
    
    viewStar : Star -> Svg.Svg msg
    viewStar star =
        circle
            [ cx (String.fromFloat star.x)
            , cy (String.fromFloat star.y)
            , r "0.25"
            , fill "white"
            , opacity (String.fromFloat (star.lifetime / 100))
            ]
            []