Cap sensor readings to 5,000 count

app/controllers/api/sensor_readings_controller.rb

@@ -1,7 +1,10 @@
 module Api
   class SensorReadingsController < Api::AbstractController
+    LIMIT = 5000
+    before_action :clean_old
+
     def create
-        mutate SensorReadings::Create.run(raw_json, device: current_device)
+      mutate SensorReadings::Create.run(raw_json, device: current_device)
     end
 
     def index
@@ -17,10 +20,23 @@ module Api
       render json: ""
     end
 
-  private
+    private
+
+    def clean_old
+      if current_device.sensor_readings.count > LIMIT
+        current_device
+          .sensor_readings
+          .where
+          .not(id: readings.pluck(:id))
+          .delete_all
+      end
+    end
 
     def readings
-      SensorReading.where(device: current_device)
+      @readings ||= SensorReading
+        .where(device: current_device)
+        .order(created_at: :desc)
+        .limit(LIMIT)
     end
 
     def reading

spec/controllers/api/sensor_readings/controller_spec.rb

@@ -18,7 +18,7 @@ describe Api::SensorReadingsController do
           x: nil,
           y: 1,
           z: 2,
-          mode: 1
+          mode: 1,
         }.to_json,
         params: { format: :json }
 
@@ -40,7 +40,7 @@ describe Api::SensorReadingsController do
           y: 1,
           z: 2,
           mode: 1,
-          read_at: read_at
+          read_at: read_at,
         }.to_json,
         params: { format: :json }
 
@@ -105,5 +105,20 @@ describe Api::SensorReadingsController do
       post :create, body: {}.to_json
       expect(response.status).to eq(401)
     end
+
+    it "cleans up excess logs" do
+      const_reassign(Api::SensorReadingsController, :LIMIT, 5)
+      sign_in user
+      10.times do |n|
+        FactoryBot.create(:sensor_reading,
+                          device: user.device,
+                          created_at: n.minutes.ago)
+      end
+      expect(user.device.sensor_readings.count).to eq(10)
+      get :index, params: { format: :json }
+      expect(json.count).to eq(5)
+      expect(user.device.sensor_readings.count).to eq(5)
+      const_reassign(Api::SensorReadingsController, :LIMIT, 5000)
+    end
   end
 end