package main

import ("image"
    "image/color"
    "image/png"
    "os"
    "time"
    "fmt"
    "flag")

func main() {
    var iterations = flag.Int("iterations", 0, "The number of iterations of the curve.")
    flag.Parse()
    drag := Dragon{0, 0, 0, 0, 0, 0, 0, []image.Point{}}
    start := time.Now()
    drag.generate(*iterations)
    fmt.Println(time.Since(start), "to generate.")
    render := time.Now()
    drag.render()
    fmt.Println(time.Since(render), "to render.")
    fmt.Println("\n", time.Since(start), "total.")
}

type Dragon struct {
    Dir, X, Y, Maxx, Maxy, Minx, Miny int
    Points []image.Point
}

func (d *Dragon) right() {
    if d.Dir == 3 {
        d.Dir = 0
    } else {
        d.Dir += 1
    }
}

func (d *Dragon) left() {
    if d.Dir == 0 {
        d.Dir = 3
    } else {
        d.Dir -= 1
    }
}

func (d *Dragon) forward() {
    switch d.Dir {
    case 0:
        d.Y += 4
        d.Points = append(d.Points, image.Point{d.X, d.Y - 3}, image.Point{d.X, d.Y - 2}, image.Point{d.X, d.Y - 1}, image.Point{d.X, d.Y})
    case 1:
        d.X += 4
        d.Points = append(d.Points, image.Point{d.X - 3, d.Y}, image.Point{d.X - 2, d.Y}, image.Point{d.X - 1, d.Y}, image.Point{d.X, d.Y})
    case 2:
        d.Y -= 4
        d.Points = append(d.Points, image.Point{d.X, d.Y + 3}, image.Point{d.X, d.Y + 2}, image.Point{d.X, d.Y + 1}, image.Point{d.X, d.Y})
    case 3:
        d.X -= 4
        d.Points = append(d.Points, image.Point{d.X + 3, d.Y}, image.Point{d.X + 2, d.Y}, image.Point{d.X + 1, d.Y}, image.Point{d.X, d.Y})
    }
    if d.X > d.Maxx {
        d.Maxx = d.X
    }
    if d.X < d.Minx {
        d.Minx = d.X
    }
    if d.Y > d.Maxy {
        d.Maxy = d.Y
    }
    if d.Y < d.Miny {
        d.Miny = d.Y
    }
}

func (d *Dragon) a (iterations int) {
    if iterations == 0 {
        return
    }
    d.a(iterations - 1)
    d.right()
    d.b(iterations - 1)
    d.forward()
    d.right()
}

func (d *Dragon) b (iterations int) {
    if iterations == 0 {
        return
    }
    d.left()
    d.forward()
    d.a(iterations - 1)
    d.left()
    d.b(iterations - 1)
}

func (d *Dragon) generate (iterations int) {
    d.forward()
    d.a(iterations)
}

func (d *Dragon) render () {
    white := color.NRGBA{255, 255, 255, 255}
    image := image.NewGray(image.Rect(d.Minx, d.Miny, d.Maxx + 1, d.Maxy + 1))
    for _, p := range d.Points {
        image.Set(p.X, p.Y, white)
    }
    file, _ := os.Create("dragon.png")
    defer file.Close()
    png.Encode(file, image)