vbob

import Graphics.Element exposing (..)
import Graphics.Collage exposing (..)
import Mouse
import Color exposing (..)
import Time
import Keyboard


type alias Vec2 = (Float, Float)

type alias Particle = {pos: Vec2, vel: Vec2, acc: Vec2, color: Color}
type alias Model = List Particle
type Action = Step Float Vec2 | AddParticle Vec2 | Explode Vec2

model: Model
model = []


scene: Model -> Element
scene model =
  collage (fst size) (snd size) (List.map renderParticle model)

newParticle: Vec2 -> Color -> Particle
newParticle pos color =
      {pos = pos, vel = (0,0), acc = (1,0), color = (hsla (fst pos) (snd pos) 0.6 0.7)}


clickPosition: Signal (Float, Float)
clickPosition = Signal.sampleOn  Mouse.clicks realMouse

renderParticle: Particle -> Form
renderParticle particle =
  circle 5
    |> filled particle.color
    |> move particle.pos



size = (500, 500)

mouseToScene (w,h) (x,y) =
  (toFloat x -  w/2, h/2 - toFloat y)

addVec: Vec2 -> Vec2 -> Vec2
addVec (a,b) (c,d) = (a + c, b + d)


mulVec: Vec2 -> Float -> Vec2
mulVec (a,b) m = (a*m, b*m)


subVec: Vec2 -> Vec2 -> Vec2
subVec a b = addVec a (mulVec b -1)


gravity: Float -> Particle -> Particle
gravity dt p =
--  {p | acc = (fst p.acc, -9.8)}
  {p | acc = (fst p.acc, -55.8)}

physics: Float -> Particle -> Particle
physics dt p =
  {p | pos = addVec p.pos (mulVec p.vel (1/dt)), vel = addVec p.vel (mulVec p.acc (1/dt)), acc = (0,0)}



explode: Vec2 -> Model -> Model
explode pos model =
    List.map (\p -> {p | vel = mulVec (subVec p.pos pos) 2}) model

slowDown: Particle -> Particle
slowDown p = {p | vel = mulVec p.vel 0.99}

mousePull pos dt p =
  {p | acc = addVec p.acc (subVec pos p.pos)}

stepUpdate dt pos model =
  List.map (\m -> m |> physics dt |> gravity dt |> mousePull pos dt |> slowDown) model

addParticle: Vec2 -> Model -> Model
addParticle clickPos model =
  (newParticle clickPos red) :: model

realMouse = Signal.map (mouseToScene size) Mouse.position


spaceLocation: Signal Vec2
spaceLocation = Signal.sampleOn Keyboard.space realMouse

--timeAndPosition: Signal Step Float Vec2
timeAndPosition =
  Signal.map2 Step (Time.fps 50) realMouse


input: Signal Action
input =
  Signal.mergeMany [
      (Signal.sampleOn (Time.fps 50) timeAndPosition),
      (Signal.map AddParticle clickPosition),
      (Signal.map Explode spaceLocation)]

update: Action -> Model -> Model
update action model =
    case action of
      AddParticle pos -> addParticle pos model
      Step dt pos -> stepUpdate dt pos model
      Explode pos -> explode pos model

modelSignal: Signal Model
modelSignal =
  Signal.foldp update model input

main : Signal Element
main =
  Signal.map scene modelSignal