module Graphics.Collage
    ( collage, Form
    , toForm, filled, textured, gradient, outlined, traced, text, outlinedText
    , move, moveX, moveY, scale, rotate, alpha
    , group, groupTransform
    , Shape, rect, oval, square, circle, ngon, polygon
    , Path, segment, path
    , solid, dashed, dotted, LineStyle, LineCap(..), LineJoin(..), defaultLine
    , backbuffer, Backbuffer, getAt
    ) where

{-| The collage API is for freeform graphics. You can move, rotate, scale, etc.
all sorts of forms including lines, shapes, images, and elements.

Collages use the same coordinate system you might see in an algebra or physics
problem. The origin (0,0) is at the center of the collage, not the top left
corner as in some other graphics libraries. Furthermore, the y-axis points up,
so moving a form 10 units in the y-axis will move it up on screen.

# Unstructured Graphics
@docs collage

# Creating Forms
@docs toForm, filled, textured, gradient, outlined, traced, text, outlinedText

# Transforming Forms
@docs move, moveX, moveY, scale, rotate, alpha

# Grouping Forms
Grouping forms makes it easier to write modular graphics code. You can create
a form that is a composite of many subforms. From there it is easy to transform
it as a single unit.

@docs group, groupTransform

# Shapes
@docs rect, oval, square, circle, ngon, polygon

# Paths
@docs segment, path

# Line Styles
@docs solid, dashed, dotted, LineStyle, LineCap, LineJoin, defaultLine

-}

import Basics exposing (..)
import List
import Transform2D exposing (Transform2D)
import Transform2D as T
import Maybe exposing (Maybe)
import Native.Graphics.Collage
import Graphics.Element exposing (Element)
import Color exposing (Color, black, Gradient)
import Text exposing (Text)


type alias Form =
    { theta : Float
    , scale : Float
    , x : Float
    , y : Float
    , alpha : Float
    , form : BasicForm
    }


type FillStyle
    = Solid Color
    | Texture String
    | Grad Gradient


{-| The shape of the ends of a line. -}
type LineCap = Flat | Round | Padded


{-| The shape of the “joints” of a line, where each line segment
meets. `Sharp` takes an argument to limit the length of the joint. This
defaults to 10.
-}
type LineJoin = Smooth | Sharp Float | Clipped


{-| All of the attributes of a line style. This lets you build up a line style
however you want. You can also update existing line styles with record updates.
-}
type alias LineStyle =
    { color : Color
    , width : Float
    , cap   : LineCap
    , join  : LineJoin
    , dashing : List Int
    , dashOffset : Int
    }


{-| The default line style, which is solid black with flat caps and sharp joints.
You can use record updates to build the line style you
want. For example, to make a thicker line, you could say:

    { defaultLine | width <- 10 }
-}
defaultLine : LineStyle
defaultLine =
    { color = black
    , width = 1
    , cap   = Flat
    , join  = Sharp 10
    , dashing = []
    , dashOffset = 0
    }


{-| Create a solid line style with a given color. -}
solid : Color -> LineStyle
solid  clr =
  { defaultLine | color <- clr }


{-| Create a dashed line style with a given color. Dashing equals `[8,4]`. -}
dashed : Color -> LineStyle
dashed clr =
  { defaultLine | color <- clr, dashing <- [8,4] }


{-| Create a dotted line style with a given color. Dashing equals `[3,3]`. -}
dotted : Color -> LineStyle
dotted clr =
  { defaultLine | color <- clr, dashing <- [3,3] }


type BasicForm
    = FPath LineStyle Path
    | FShape ShapeStyle Shape
    | FOutlinedText LineStyle Text
    | FText Text
    | FImage Int Int (Int,Int) String
    | FElement Element
    | FGroup Transform2D (List Form)


type ShapeStyle
    = Line LineStyle
    | Fill FillStyle


form : BasicForm -> Form
form f =
  { theta=0, scale=1, x=0, y=0, alpha=1, form=f }


fill style shape =
  form (FShape (Fill style) shape)


{-| Create a filled in shape. -}
filled : Color -> Shape -> Form
filled color shape =
  fill (Solid color) shape


{-| Create a textured shape. The texture is described by some url and is
tiled to fill the entire shape.
-}
textured : String -> Shape -> Form
textured src shape =
  fill (Texture src) shape


{-| Fill a shape with a [gradient](Color#linear). -}
gradient : Gradient -> Shape -> Form
gradient grad shape =
  fill (Grad grad) shape


{-| Outline a shape with a given line style. -}
outlined : LineStyle -> Shape -> Form
outlined style shape =
  form (FShape (Line style) shape)


{-| Trace a path with a given line style. -}
traced : LineStyle -> Path -> Form
traced style path =
  form (FPath style path)


{-| Create a sprite from a sprite sheet. It cuts out a rectangle
at a given position.
-}
sprite : Int -> Int -> (Int,Int) -> String -> Form
sprite w h pos src =
  form (FImage w h pos src)


{-| Turn any `Element` into a `Form`. This lets you use text, gifs, and video
in your collage. This means you can move, rotate, and scale
an `Element` however you want.
-}
toForm : Element -> Form
toForm e =
  form (FElement e)


{-| Flatten many forms into a single `Form`. This lets you move and rotate them
as a single unit, making it possible to build small, modular components.
-}
group : List Form -> Form
group fs =
  form (FGroup T.identity fs)


{-| Flatten many forms into a single `Form` and then apply a matrix
transformation.
-}
groupTransform : Transform2D -> List Form -> Form
groupTransform matrix fs =
  form (FGroup matrix fs)


{-| Move a form by the given amount. This is a relative translation so
`(move (10,10) form)` would move `form` ten pixels up and ten pixels to the
right.
-}
move : (Float,Float) -> Form -> Form
move (x,y) f =
  { f | x <- f.x + x, y <- f.y + y }


{-| Move a shape in the x direction. This is relative so `(moveX 10 form)` moves
`form` 10 pixels to the right.
-}
moveX : Float -> Form -> Form
moveX x f =
  { f | x <- f.x + x }


{-| Move a shape in the y direction. This is relative so `(moveY 10 form)` moves
`form` upwards by 10 pixels.
-}
moveY : Float -> Form -> Form
moveY y f =
  { f | y <- f.y + y }


{-| Scale a form by a given factor. Scaling by 2 doubles both dimensions,
and quadruples the area.
-}
scale : Float -> Form -> Form
scale s f =
  { f | scale <- f.scale * s }


{-| Rotate a form by a given angle. Rotate takes standard Elm angles (radians)
and turns things counterclockwise. So to turn `form` 30&deg; to the left
you would say, `(rotate (degrees 30) form)`.
-}
rotate : Float -> Form -> Form
rotate t f =
  { f | theta <- f.theta + t }


{-| Set the alpha of a `Form`. The default is 1, and 0 is totally transparent. -}
alpha : Float -> Form -> Form
alpha a f =
  { f | alpha <- a }


{-| A collage is a collection of 2D forms. There are no strict positioning
relationships between forms, so you are free to do all kinds of 2D graphics.
-}
collage : Int -> Int -> List Form -> Element
collage =
  Native.Graphics.Collage.collage


type alias Path = List (Float,Float)


{-| Create a path that follows a sequence of points. -}
path : List (Float,Float) -> Path
path ps =
  ps


{-| Create a path along a given line segment. -}
segment : (Float,Float) -> (Float,Float) -> Path
segment p1 p2 =
  [p1,p2]


type alias Shape = List (Float,Float)


{-| Create an arbitrary polygon by specifying its corners in order.
`polygon` will automatically close all shapes, so the given list
of points does not need to start and end with the same position.
-}
polygon : List (Float,Float) -> Shape
polygon points =
  points

{-| A rectangle with a given width and height. -}
rect : Float -> Float -> Shape
rect w h =
  let hw = w/2
      hh = h/2
  in
      [ (0-hw,0-hh), (0-hw,hh), (hw,hh), (hw,0-hh) ]


{-| A square with a given edge length. -}
square : Float -> Shape
square n =
  rect n n


{-| An oval with a given width and height. -}
oval : Float -> Float -> Shape
oval w h =
  let n = 50
      t = 2 * pi / n
      hw = w/2
      hh = h/2
      f i = (hw * cos (t*i), hh * sin (t*i))
  in
      List.map f [0..n-1]


{-| A circle with a given radius. -}
circle : Float -> Shape
circle r =
  oval (2*r) (2*r)


{-| A regular polygon with N sides. The first argument specifies the number
of sides and the second is the radius. So to create a pentagon with radius
30 you would say:

    ngon 5 30
-}
ngon : Int -> Float -> Shape
ngon n r =
  let m = toFloat n
      t = 2 * pi / m
      f i = ( r * cos (t*i), r * sin (t*i) )
  in
      List.map f [0..m-1]

{-| Create some text. Details like size and color are part of the `Text` value
itself, so you can mix colors and sizes and fonts easily.
-}
text : Text -> Form
text t =
  form (FText t)


{-| Create some outlined text. Since we are just outlining the text, the color
is taken from the `LineStyle` attribute instead of the `Text`.
-}
outlinedText : LineStyle -> Text -> Form
outlinedText ls t =
  form (FOutlinedText ls t)

colorFor : Int -> Color
colorFor i = Color.rgb 1 (i // 256) (i % 256) -- works for up to 65536 forms

numberForm : Int -> Form -> Form
numberForm i frm =
    let clr = colorFor i
        base = case frm.form of
            FPath lStyle pairs -> FPath {lStyle| color <- clr} pairs
            FShape sStyle pairs -> case sStyle of
                                        Line lStyle -> FShape (Line {lStyle| color <- clr}) pairs
                                        Fill lStyle -> FShape (Fill (Solid clr)) pairs
            FOutlinedText lStyle txt -> FOutlinedText {lStyle| color <- clr} txt
            FText txt -> FText (Text.color clr txt)
            FImage w h _ _ -> rect (toFloat w) (toFloat h) |> filled clr |> .form
            FElement elem -> rect (toFloat <| Graphics.Element.widthOf elem) (toFloat <| Graphics.Element.heightOf elem)
                                |> filled clr |> .form
            FGroup trans frms -> FGroup trans (List.map (numberForm i) frms)
    in {frm| alpha <- 1, form <- base}


{-| Create a backbuffer used for mouse detection. You should pass the same arguments that you do to `collage`.
-}
backbuffer : Int -> Int -> List Form -> Backbuffer
backbuffer w h frms =
    B <| collage w h <| List.indexedMap numberForm frms

{-| Determine which form (if any) is underneath the mouse, identified by index in the array that created that
backbuffer. Note that the point is in mouse coordinates, with the origin at the top-left of the collage.
-}
getAt : (Int, Int) -> Backbuffer -> Maybe Int
getAt = Native.Graphics.Collage.getAt

{-| The opaque type of the backbuffer.
-}
type Backbuffer = B Element