defmodule Identicon do

  @doc """
  Create a Identicon by providing the name to the main function

  ## Examples

      iex> Identicon.main "your_name"

  """
  def main(input) do
    input
    |> hash_input
    |> pick_color
    |> build_grid
    |> filter_odd_squares
    |> build_pixel_map
    |> draw_image
    |> save_image(input)
  end

  def save_image(image, input) do
    File.write("#{input}.png", image)
  end

  def draw_image(%Identicon.Image{color: color, pixel_map: pixel_map}) do
    image = :egd.create(250,250)
    fill = :egd.color(color)
    Enum.each(pixel_map, fn({start, stop}) ->
      :egd.filledRectangle(image,start,stop,fill)
    end)

    :egd.render(image)
  end

  def pick_color(%Identicon.Image{hex: [r,g,b | _tail]} = image) do
    %Identicon.Image{image | color: {r,g,b}}
  end

  def build_grid(%Identicon.Image{hex: hex} = image) do
    grid =
      hex
      |> Enum.chunk_every(3,3,:discard)
      |> Enum.map(&mirror_row/1)
      |> List.flatten
      |> Enum.with_index
    %Identicon.Image{image | grid: grid}
  end

  def mirror_row([a,b | _tail] = grid) do
    grid ++ [a,b]
  end

  def filter_odd_squares(%Identicon.Image{grid: grid} = image) do
    grid = Enum.filter(grid, fn {num, _index} -> rem(num,2) == 0 end)
    %Identicon.Image{image | grid: grid}
  end

  def hash_input(input) do
    hex = :crypto.hash(:md5, input)
    |> :binary.bin_to_list

    %Identicon.Image{hex: hex}
  end

  def build_pixel_map(%Identicon.Image{grid: grid} = image) do
    pixel_map = Enum.map(grid, fn ({_num, index }) ->
      horizontal = rem(index,5) * 50
      vertical = div(index,5) * 50
      top_left = {horizontal,vertical}
      bottom_right = {horizontal + 50, vertical + 50}
      {top_left,bottom_right}
    end)

    %Identicon.Image{image | pixel_map: pixel_map}
  end
end