How many songs does Spotify hide from me?

require "rspotify"
require "rspotify/oauth"
require "omniauth"
require "webrick"
require "rack"

auth_url = "http://localhost:8080/auth/spotify"
puts "==> Please visit #{auth_url}"

$rack = Rack::Server.new(
  Port:   8080,
  server: "webrick",
  app: Rack::Builder.new do
    # OmniAuth requires a Rack session to be available
    use Rack::Session::Cookie, secret: "Some secret"

    use OmniAuth::Builder do
      provider :spotify,
               ENV.fetch("SPOTIFY_CLIENT_ID"), ENV.fetch("SPOTIFY_CLIENT_SECRET"),
               # We want to read our library (i.e. saved songs) and private playlists
               scope: "user-library-read playlist-read-private"
    end

    run(lambda do |env|
      case env["PATH_INFO"]
      when "/auth/spotify/callback"
        $omniauth_auth = env["omniauth.auth"]
        $rack.server.shutdown
        [200, { "Content-Type" => "text/html" },
         ["Code received.  Check your terminal."]]
      else
        [200, { "Content-Type" => "text/html" },
         [%(Please visit <a href="#{auth_url}">#{auth_url}</a>.)]]
      end
    end)
  end
)
$rack.start

me = RSpotify::User.new($omniauth_auth)

# For debugging purposes:
binding.irb

irb(main):001:0> me.id  # get the User ID/screen name
=> "nilsding"
irb(main):002:0> me.saved_tracks.first.name  # get the name of the first track
=> "The Dark Side"
irb(main):003:0> me.saved_tracks.first.artists.map(&:name)  # get the artists of the first track
=> ["Muse"]

irb(main):004:0> me.saved_tracks(market: "AT").first.is_playable
Traceback (most recent call last):
        5: from ./spotify-availability.rb:78:in `<main>'
        4: from <internal:prelude>:145:in `irb'
        3: from (irb):20:in `<main>'
        2: from (irb):20:in `rescue in <main>'
        1: from /home/nilsding/.rbenv/versions/2.6.5/lib64/ruby/gems/2.6.0/gems/rspotify-2.7.0/lib/rspotify/user.rb:316:in `saved_tracks'
ArgumentError (unknown keyword: market)

irb(main):001:0> me.saved_tracks(market: "AT").first.is_playable
=> true

irb(main):002:0> def me.first_non_playable_track(market)
irb(main):003:1>   (0..500).step(50).flat_map do |offset|
irb(main):004:2*     self.saved_tracks(market: market, limit: 50, offset: offset)
irb(main):005:2>   end.find { |track| !track.is_playable }.tap do |track|
irb(main):006:2*     return [track.artists.map(&:name).join(", "), track.name].join(" - ")
irb(main):007:2>   end
irb(main):008:1> end
=> :first_non_playable_track
irb(main):009:0> me.first_non_playable_track "AT"  # first non-playable track in Austria
=> "Solid Globe - North Pole - Original mix"
irb(main):010:0> me.first_non_playable_track "US"  # first non-playable track in the USA
=> "Rainhard Fendrich - Haben Sie Wien schon bei Nacht geseh'n"

songs = []
offset = 0
page_size = 50
loop do
  saved_tracks_part = me.saved_tracks(market: "AT", limit: page_size, offset: offset)
  break if saved_tracks_part.empty?

  songs.concat(saved_tracks_part)
  offset += page_size
rescue RestClient::BadGateway
  # Apparently Spotify's API returns a 502 Bad Gateway if there are no more songs available.
  # Fine, just rescue this error and move on ...
  break
end

puts "Found #{songs.count} songs."

# Group songs by playable (true) or not playable (false)
grouped_songs = songs.group_by(&:is_playable)

puts "Playable songs: #{grouped_songs[true].count}"
puts "Unplayable songs: #{grouped_songs[false].count}"
print "That's "
print ((grouped_songs[false].count.to_f / songs.count) * 100).round(3)
puts "% unplayable songs!"

irb(main):042:0> me.saved_tracks(limit: 1, offset: 390000)
Traceback (most recent call last):
        [traceback omitted]
RestClient::BadGateway (502 Bad Gateway)