Now list artists, albums and songs.

Gemfile

@@ -1,6 +1,7 @@
 source 'https://rubygems.org'
 
 gem 'sinatra'
+gem 'sinatra-contrib'
 gem 'foreman'
 
 gem 'ruby-mpd'

Gemfile.lock

@@ -1,15 +1,19 @@
 GEM
   remote: https://rubygems.org/
   specs:
+    backports (3.3.3)
     daemons (1.1.9)
     dotenv (0.8.0)
     eventmachine (1.0.3)
     foreman (0.63.0)
       dotenv (>= 0.7)
       thor (>= 0.13.6)
+    multi_json (1.7.9)
     rack (1.5.2)
     rack-protection (1.5.0)
       rack
+    rack-test (0.6.2)
+      rack (>= 1.0)
     ruby-mpd (0.2.4)
     shotgun (0.9)
       rack (>= 1.0)
@@ -17,6 +21,13 @@ GEM
       rack (~> 1.4)
       rack-protection (~> 1.4)
       tilt (~> 1.3, >= 1.3.4)
+    sinatra-contrib (1.4.1)
+      backports (>= 2.0)
+      multi_json
+      rack-protection
+      rack-test
+      sinatra (~> 1.4.0)
+      tilt (~> 1.3)
     thin (1.5.1)
       daemons (>= 1.0.9)
       eventmachine (>= 0.12.6)
@@ -32,4 +43,5 @@ DEPENDENCIES
   ruby-mpd
   shotgun
   sinatra
+  sinatra-contrib
   thin

mpd_client.rb

@@ -1,14 +1,49 @@
 require 'sinatra'
+require "sinatra/namespace"
 require 'json'
 require 'ruby-mpd'
+require 'cgi'
 
 class MPDClient < Sinatra::Base
-  before do
-    @mpd = MPD.new
-    @mpd.connect
+  register Sinatra::Namespace
+
+  namespace '/api' do
+
+    get '/albums' do
+      JSON mpd.albums
+    end
+
+    get '/artists/:artist' do
+      JSON mpd.albums(CGI.unescape(params[:artist]))
+    end
+
+    get '/albums/:album' do
+      JSON get_songs_by_album(CGI.unescape(params[:album]))
+    end
+
+    get '/artists/:artist/:album' do
+      JSON get_songs_by_album(CGI.unescape(params[:album]))
+    end
+
+    get '/artists' do
+      JSON mpd.artists
+    end
+
   end
 
-  get '/api/albums' do
-    @mpd.albums
+  private
+
+  def get_songs_by_album(album)
+    mpd.search(:album, album).map do |song|
+      { tracknumber: song.track,
+        title: song.title }
+    end
   end
+
+  def mpd
+    @mpd ||= MPD.new
+    @mpd.connect unless @mpd.connected?
+    @mpd
+  end
+
 end