// Written by xojoc <http://xojoc.pw>. Public domain.
package main

import (
	"github.com/lucasb-eyer/go-colorful"
	"image"
	"image/color"
	"image/png"
	"math"
	"math/cmplx"
	"os"
)

const (
	w    = 700
	h    = 500
	maxi = 50
)

func xhex(s string) colorful.Color {
	c, err := colorful.Hex(s)
	if err != nil {
		panic(err)
	}
	return c
}

func main() {
	img := image.NewRGBA(image.Rect(0, 0, w, h))
	palette1 := []colorful.Color{
		xhex("#ceecf7"),
		xhex("#5c87b2"),
		xhex("#7ea1bf"),
		xhex("#55708d"),
		xhex("#14222f"),
	}
	palette2 := []colorful.Color{
		xhex("#757577"),
		xhex("#546169"),
		xhex("#2D333F"),
		xhex("#902165"),
		xhex("#A30B3A"),
	}
	ncolors1 := len(palette1)
	ncolors2 := len(palette2)

	// Where the mandelbrot set intersects the x,y axis.
	setx := -2.5
	sety := -1.0
	// width/height of the set.
	setw := 3.5
	seth := 2.0
	for y := 0; y < h; y++ {
		for x := 0; x < w; x++ {
			// Scale in the range (-2.5,1.0) for x and (-1.0,1.0) for y.
			c := complex(float64(x)/float64(w)*setw+setx,
				float64(y)/float64(h)*seth+sety)
			z := 0i
			i := 0
			for ; cmplx.Abs(z) < 1<<16 && i < maxi; i++ {
				z = cmplx.Pow(z, 2) + c
			}
			var idx float64
			if i < maxi {
				idx = float64(i) - math.Log2(math.Log2(cmplx.Abs(z)))
			}

			palette := palette1
			ncolors := ncolors1
			if imag(z) < 0 {
				palette = palette2
				ncolors = ncolors2
			}
			c1 := palette[int(idx)%ncolors]
			c2 := palette[int(idx+1)%ncolors]
			_, f := math.Modf(idx)
			if i == maxi {
				img.Set(x, y, color.Black)
			} else {
				img.Set(x, y, c1.BlendLab(c2, f))
			}
		}
	}

	png.Encode(os.Stdout, img)
}