package main

import (
	"crypto/md5"
	"math"
	"slices"

	"github.com/fogleman/gg"
)

// Translated to Go from: https://github.com/dgraham/identicon
func GitHub(dc *gg.Context, userId string) {
	hash := md5.Sum([]byte(userId))
	w := 800
	h := 800
	cols := 5
	rows := 5
	pw := w / cols
	ph := h / rows

	// Background
	dc.SetRGB255(240, 240, 240)
	dc.DrawRectangle(0, 0, float64(w), float64(h))
	dc.Fill()

	dc.SetRGB255(foreground(hash[:]))

	// Foreground
	enabledVertices := make([]bool, 25)
	for i := range 15 {
		byte := hash[i/2]
		var nibble uint8 // 4 bits are called a nibble
		if i % 2 == 0 {
			nibble = (byte & 0xf0) >> 4 // left side
		} else {
			nibble = byte & 0x0f // right side
		}
		painted := nibble % 2 == 0

		rowIdx := i % 5
		colIdx := 2 - i / 5
		mirrColIdx := 2 + i / 5

		enabledVertices[rowIdx * 5 + colIdx] = painted
		enabledVertices[rowIdx * 5 + mirrColIdx] = painted
	}

	for row, pix := range slices.Collect(slices.Chunk(enabledVertices, 5)) {
		for col, painted := range pix {
			if painted {
				x := col * pw
				y := row * ph

				dc.DrawRectangle(float64(x), float64(y), float64(pw), float64(ph))
				dc.Fill()
			}
		}
	}
}


func hue_to_rgb(a float32, b float32, hue float32) float32 {
	var h float32
	if hue < 0.0 {
		h = hue + 1.0
	} else if hue > 1.0 {
		h = hue - 1.0
	} else {
		h = hue
	}

	if h < 1.0 / 6.0 {
		return a + (b - a) * 6.0 * h
	}

	if h < 1.0 / 2.0 {
		return b
	}

	if h < 2.0 / 3.0 {
		return a + (b - a) * (2.0 / 3.0 - h) * 6.0
	}

	return a
}

func foreground(source []uint8) (int, int, int) {
	h1 := (uint16(source[12]) & 0x0f) << 8;
	h2 := uint16(source[13])

	h := uint32(h1 | h2)
	s := uint32(source[14])
	l := uint32(source[15])

	hue := float32(h * 360) / float32(4095)
	sat := float32(s * 20) / float32(255)
	lum := float32(l * 20) / float32(255)

	sat = 65.0 - sat
	lum = 75.0 - lum

	hue = hue / 360.0
	sat = sat / 100.0
	lum = lum / 100.0

	var b float32
	if lum <= 0.5 {
		b = lum * (sat + 1.0)
	} else {
		b = lum + sat - lum * sat
	}
	a := lum * 2.0 - b

	r := hue_to_rgb(a, b, hue + 1.0 / 3.0)
	g := hue_to_rgb(a, b, hue)
	b = hue_to_rgb(a, b, hue - 1.0 / 3.0)

	return int(math.Round(float64(r * 255))), int(math.Round(float64(g * 255))), int(math.Round(float64(b * 255)))
}