package main

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

func main() {
        iterations := flag.Int("iterations", 0, "The number of iterations of the curve.")
        filename := flag.String("file", "dragon.png", "The filename of the resulting image.")
        encode := flag.Bool("png", true, "Whether to encode into png.")
        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.")
        if *encode {
                render := time.Now()
                drag.render(*filename)
                fmt.Println(time.Since(render), "to render.")
        }
        fmt.Println(drag.Points[10^12])
        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(filename string) {
    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(filename)
    defer file.Close()
    png.Encode(file, image)
}