Add lastfm adapter

app/adapters/lastfm_adapter.rb

@@ -0,0 +1,37 @@
+class LastfmAdapter < BaseAdapter
+  class << self
+    def required_keys
+      %i(username api_key)
+    end
+
+    def auth_type
+      :none
+    end
+
+    def website_link
+      "https://www.last.fm"
+    end
+
+    def title
+      "Last.fm"
+    end
+
+    def valid_credentials?(credentials)
+      username, api_key = credentials.values_at(:username, :api_key)
+      username.present? && api_key.present?
+    end
+  end
+
+  def scrobbles
+    username, api_key = credentials.values_at(:username, :api_key)
+    resp = Faraday.get("http://ws.audioscrobbler.com/2.0/?method=user.getinfo&user=#{username}&api_key=#{api_key}&format=json")
+
+    user_info = JSON.parse(resp.body)
+    if user_info
+      user_info.fetch("user.playcount").to_i
+    else
+      raise "Can't fetch user playcount"
+    end
+  end
+
+end

app/metrics/lastfm/scrobbles.rb

@@ -0,0 +1,8 @@
+PROVIDERS.fetch(:lastfm).register_metric :scrobbles do |metric|
+  metric.title = "Scrobbles"
+  metric.description = "Number of scrobbles"
+
+  metric.block = proc do |adapter|
+    Datapoint.new value: adapter.scrobbles
+  end
+end

config/initializers/providers.rb

@@ -1,5 +1,5 @@
 PROVIDERS = %i(
-    googlefit trello pocket beeminder bcycle stackoverflow
+    googlefit trello pocket beeminder bcycle stackoverflow lastfm
 ).map do |p_key|
     adapter = "#{p_key}_adapter".camelize.constantize
     [p_key, Provider.new(p_key, adapter)]