#!/usr/bin/env ruby

require 'rmagick'

# [ ] load the image
# [ ] map each pixel to a 12 bit color, with pixels less than 25% transparent as mask
# [ ] sort the color counts
# [ ] transparent pixels become the mask
# [ ] turn the big color counts into three bitplames worth of data
# [ ] turn the little color counts into up to 8 sprites worth of data strips & color changes

image = Magick::Image.read('topaz.png').first

rows = []

class MaskPixel
  def initialize; end

  def color? = false
end

class Color
  attr_reader :red, :green, :blue

  def initialize(red:, green:, blue:)
    @red = red
    @green = green
    @blue = blue
  end

  def ==(other)
    red == other.red && green == other.green && blue == other.blue
  end

  alias eql? ==

  def hash
    red * 256 + green * 16 + blue
  end
end

class BitplanePixel
  attr_reader :color

  def initialize(color:)
    @color = color
  end

  def color? = true
end

MAX_ALPHA = Magick::QuantumRange * 0.25
BIT_SHIFT = Math.log2(Magick::QuantumRange + 1) - 4

class PixelRow
  def initialize
    @row = []
  end

  def add(pixel:, x:)
    @row[x] = pixel
  end

  def colors_with_usage
    @row.find_all(&:color?).each_with_object({}) do |pixel, obj|
      obj[pixel.color] ||= 0
      obj[pixel.color] += 1
    end
  end
end

image.each_pixel do |px, x, y|
  rows[y] ||= PixelRow.new

  pixel = if px.alpha < MAX_ALPHA
            MaskPixel.new
          else
            BitplanePixel.new(
              color: Color.new(
                red: px.red >> BIT_SHIFT,
                green: px.green >> BIT_SHIFT,
                blue: px.blue >> BIT_SHIFT
              )
            )
          end

  rows[y].add(pixel:, x:)
end

pp rows[50].colors_with_usage