update-smart-playlists.rb

require "nokogiri"
require "pry"

doc = Nokogiri::XML(File.read("collection.nml"))

def update_playlist(doc, playlist_name, xpath)
  playlist = doc.xpath("/NML/PLAYLISTS//NODE[@TYPE='PLAYLIST'][@NAME='#{playlist_name}']/PLAYLIST").first

  playlist.children.remove

  entry_nodes = doc.xpath(xpath).map { |entry|
    loc = entry.xpath("LOCATION").first
    "#{loc["VOLUME"]}#{loc["DIR"]}#{loc["FILE"]}"
  }.map { |key|
    doc.create_element("ENTRY") do |entry|
      entry.add_child(doc.create_element("PRIMARYKEY", "", "TYPE" => "TRACK", "KEY" => key))
      entry.add_child(doc.create_text_node("\n"))
    end
  }

  entry_nodes.each do |entry|
    playlist.add_child(entry)
    playlist.add_child(doc.create_text_node("\n"))
  end

  playlist.attribute("ENTRIES").value = entry_nodes.count.to_s
end

# Set Cued playlist to tracks with the second cuepoint set
update_playlist(doc, "Cued", "/NML/COLLECTION/ENTRY[CUE_V2[@HOTCUE='1']]")

# Set Uncued playlist to tracks without the second cuepoint set
update_playlist(doc, "Uncued", "/NML/COLLECTION/ENTRY[not(CUE_V2[@HOTCUE='1'])]")

nml = doc.to_xml(:save_with => Nokogiri::XML::Node::SaveOptions::NO_EMPTY_TAGS)

# traktor puts a space before ?>, but nokogiri doesn't
# fix that up to avoid unnecessary diffs
nml.sub!("\"?>", "\" ?>")

File.write("collection.nml", nml)