package main

import "image"
import "image/color"
import "image/png"
import "os"
import "strings"

func main() {
    renderDragon(dragonString(20, "Fa"))
}

func dragonString(iterations int, dragon string) string {
    var outstr = strings.Split(dragon, "")
    for i := 0; i < iterations; i++ {
        var tmpout = []string{""}
        for _, s := range outstr {
            switch s {
            case "a":
                tmpout = append(tmpout, "a", "R", "b", "F", "R")
            case "b":
                tmpout = append(tmpout, "L", "F", "a", "L", "b")
            default:
                tmpout = append(tmpout, string(s))
            }
        }
        outstr = tmpout
    }
    return strings.Join(outstr, "")
}

type Point struct {
    x int
    y int
}

func renderDragon(dragon string) {
    var x, y int = 0, 0
    var dir int = 0
    var points []Point
    for _ , s := range dragon {
        switch s {
        case 76:
            if dir == 0 {
                dir = 3
            } else {
                dir -= 1
            }
        case 82:
            if dir == 3 {
                dir = 0
            } else {
                dir += 1
            }
        case 70:
            switch dir {
            case 0:
                y += 4
                points = append(points, Point{x, y - 3},Point{x, y - 2},Point{x, y - 1},Point{x, y})
            case 1:
                x += 4
                points = append(points, Point{x - 3, y},Point{x - 2, y},Point{x - 1, y},Point{x, y})
            case 2:
                y -= 4
                points = append(points, Point{x, y + 3},Point{x, y + 2},Point{x, y + 1},Point{x, y})
            case 3:
                x -= 4
                points = append(points, Point{x + 3, y},Point{x + 2, y},Point{x + 1, y},Point{x, y})
            }
        }
    }
    var minx, miny, maxx, maxy int
    for _, i := range points {
        if i.x < minx {
            minx = i.x
        }
        if i.y < miny {
            miny = i.y
        }
        if i.x > maxx {
            maxx = i.x
        }
        if i.y > maxy {
            maxy = i.y
        }
    }
    image := image.NewRGBA(image.Rect(minx, miny, maxx + 1, maxy + 1))
    white := color.NRGBA{254, 254, 254, 254}
    for _, i := range points {
        image.Set(i.x, i.y, white)

    }
    png.Encode(os.Stdout, image)
}