add track stats

app/services/stats/tracks_stat.rb

@@ -0,0 +1,58 @@
+module Stats
+  class TracksStat
+
+    # X Wortanteil / period / show
+    # * Uniq Artists / period / show (via track counts by artist)
+    # * Uniq Song / period / show (via song counts)
+    # * Track counts by Artist / period /show
+    # * Song counts / period / show
+    #
+    # X Broadcast hours / period / show
+
+    attr_reader :date_range
+
+    def initialize(date_range)
+      @date_range = date_range
+    end
+
+    def tracks
+      Track.within(date_range.first, date_range.last).joins(:broadcast)
+    end
+
+    def broadcast
+      Broadcast.within(date_range.first, date_range.last)
+    end
+
+    def track_durations
+      @track_durations ||=
+        tracks.group(:show_id).sum(duration_in_seconds('tracks'))
+    end
+
+    def broadcast_durations
+      @broadcast_durations ||=
+        broadcasts.group(:show_id).sum(duration_in_seconds('broadcasts'))
+    end
+
+    def track_ratios
+      broadcast_durations.each_with_object do |(show_id, value), hash|
+        hash[show_id] = track_durations[show_id] / value.to_f
+      end
+    end
+
+    def duration_in_seconds(table)
+      case db_adapter
+      when /postgres/
+        "extract(epoch from (#{table}.finished_at - #{table}.started_at))"
+      when /sqlite/
+        "strftime('%s', #{table}.finished_at) - strftime('%s', #{table}.started_at)"
+      else
+        raise "Unsupported DB adapter #{db_adapter}"
+      end
+    end
+
+    def db_adapter
+      Track.connection.adapter_name.downcase
+    end
+
+  end
+end