nbconvert-markdown-image-embed.rb

#!ruby

require "tmpdir"
require "pathname"
require "base64"

target_nb = ARGF.read
cmd = %w(jupyter nbconvert --to markdown)
png_optimizer_cmd = ["optipng", "-quiet"] # or nil

Dir.mktmpdir("nbconvert-embed-image") do |dir|
  path = Pathname.new(dir).relative_path_from(__dir__)

  prefix = "target"
  tmp_file = path + "#{prefix}.ipynb"
  md_file = path + "#{prefix}.md"

  tmp_file.open("w") { |f| f.puts target_nb }

  cmd = cmd + [tmp_file.to_s]
  warn cmd.join(" ")
  system(*cmd)

  unless png_optimizer_cmd&.empty?
    path.glob("**/*.png").each do |png|
      opt_cmd = [png_optimizer_cmd, png.to_s].flatten
      warn opt_cmd.join(" ")
      system(*opt_cmd)
    end
  end

  body = md_file.read
  body.gsub!(/!\[svg\]\((.+)\)/) {
    filepath = path.join($1)
    data = IO.binread(filepath.sub(".svg", ".png"))
    b64 = Base64.encode64(data).gsub("\n", "")
    src = "data:image/png;base64,#{b64}"
    # "<img alt='notebook image' src='#{src}' />"
    "![img](#{src})"
  }

  puts body
end