fix: LAG() returns jankie time

Author: cskartikey

app/controllers/api/v1/stats_controller.rb

@@ -71,7 +71,14 @@ def user_stats
         query = query.where(project: filter_by_project)
       end
 
-      total_seconds = query.duration_seconds || 0
+      # do the boundary thingie if requested
+      use_boundary_aware = params[:boundary_aware] == "true"
+      total_seconds = if use_boundary_aware
+        Heartbeat.duration_seconds_boundary_aware(query, start_date.to_f, end_date.to_f) || 0
+      else
+        query.duration_seconds || 0
+      end
+
       return render json: { total_seconds: total_seconds }
     end
 

app/models/concerns/heartbeatable.rb

@@ -235,5 +235,60 @@ def duration_seconds(scope = all)
         connection.select_value("SELECT COALESCE(SUM(diff), 0)::integer FROM (#{capped_diffs.to_sql}) AS diffs").to_i
       end
     end
+
+    def duration_seconds_boundary_aware(scope, start_time, end_time)
+      scope = scope.with_valid_timestamps
+
+      model_class = scope.model
+      base_scope = model_class.all.with_valid_timestamps
+
+      if scope.where_values_hash["user_id"]
+        base_scope = base_scope.where(user_id: scope.where_values_hash["user_id"])
+      end
+
+      if scope.where_values_hash["category"]
+        base_scope = base_scope.where(category: scope.where_values_hash["category"])
+      end
+
+      if scope.where_values_hash["project"]
+        base_scope = base_scope.where(project: scope.where_values_hash["project"])
+      end
+
+      if scope.where_values_hash["deleted_at"]
+        base_scope = base_scope.where(deleted_at: scope.where_values_hash["deleted_at"])
+      end
+
+      # get the heartbeat before the start_time
+      boundary_heartbeat = base_scope
+        .where("time < ?", start_time)
+        .order(time: :desc)
+        .limit(1)
+        .first
+
+      # if it's not NULL, we'll use it
+      if boundary_heartbeat
+        combined_scope = base_scope
+          .where("time >= ? OR time = ?", start_time, boundary_heartbeat.time)
+          .where("time <= ?", end_time)
+      else
+        combined_scope = base_scope
+          .where(time: start_time..end_time)
+      end
+
+      # we calc w/ the boundary heartbeat, but we only sum within the orignal constraint
+      capped_diffs = combined_scope
+        .select("time, CASE
+          WHEN LAG(time) OVER (ORDER BY time) IS NULL THEN 0
+          ELSE LEAST(EXTRACT(EPOCH FROM (to_timestamp(time) - to_timestamp(LAG(time) OVER (ORDER BY time)))), #{heartbeat_timeout_duration.to_i})
+        END as diff")
+        .where.not(time: nil)
+        .order(time: :asc)
+
+      connection.select_value(
+        "SELECT COALESCE(SUM(diff), 0)::integer
+         FROM (#{capped_diffs.to_sql}) AS diffs
+         WHERE time >= #{start_time}"
+      ).to_i
+    end
   end
 end