Manipulate and list the Finder tags on an MacOS file.

tagger.rb

#!/usr/bin/env ruby

require "ffi-xattr"
require "cfpropertylist"
require "pry"

class Tag
  COLORS = {
    white: 0,
    gray: 1,
    green: 2,
    purple: 3,
    blue: 4,
    yellow: 5,
    red: 6,
    orange: 7
  }.freeze

  INVERSE_COLORS = COLORS.values.zip(COLORS.keys).to_h.freeze

  attr_accessor :name, :color

  def initialize name:, color: :white
    color = INVERSE_COLORS[ color ] if color.is_a? Numeric

    fail ArgumentError, "Color must be one of #{ COLORS.keys }, got `#{ color }' instead!" unless COLORS.key? color

    @name = name.to_s
    @color = color
  end

  def to_s
    [name, COLORS[ color ]].join("\n")
  end

  def to_binary binary
    CFPropertyList::CFString.new(to_s).to_binary(binary)
  end
end

class TaggedFile
  attr_reader :pathname

  def initialize pathname
    @pathname = pathname
  end

  def tags_plist
    CFPropertyList::List.new(data: xattrs["com.apple.metadata:_kMDItemUserTags"])
  end

  def xattrs
    Xattr.new(pathname.to_s)
  end

  def get_tags
    tags_plist
      .value
      .value
      .map do |attr|
        tag_tuples = attr.value.split "\n"
        Tag.new(name: tag_tuples[0], color: tag_tuples[1].to_i)
      end
  end

  def set_tag name:, color:
    tags = get_tags
    tags << Tag.new(name: name, color: color)

    set_tags tags: tags
  end

  def remove_tag name:
    tags = get_tags
    tags.delete_if { |tag| tag.name == name }

    set_tags tags: tags
  end

  def set_tags tags:
    xattrs["com.apple.metadata:_kMDItemUserTags"] = tags_plist.tap do |plist|
      plist.value = CFPropertyList::CFArray.new(tags)
    end.to_str
  end
end

class Runner
  def run
    file = TaggedFile.new Pathname.new("tagtest/1")

    tags = [
      Tag.new(name: "Test", color: :red),
      Tag.new(name: "Other Test", color: :gray)
    ]

    file.set_tags tags: tags
  end
end

Runner.new.run