attribute difference agent

app/models/agents/attribute_difference_agent.rb

@@ -0,0 +1,109 @@
+module Agents
+  class AttributeDifferenceAgent < Agent
+    cannot_be_scheduled!
+
+    description <<-MD
+      The Attribute Difference Agent receives events and emits a new event with
+      the difference or change of a specific attribute in comparison to the previous
+      event received.
+
+      `path` specifies the JSON path of the attribute to be used from the event.
+
+      `output` specifies the new attribute name that will be created on the original payload
+      and it will contain the difference or change.
+
+      `method` specifies if it should be...
+
+      * `percentage_change` eg. Previous value was `160`, new value is `116`. Percentage change is `-27.5`
+      * `decimal_difference` eg. Previous value was `5.5`, new value is `15.2`. Difference is `9.7`
+      * `integer_difference` eg. Previous value was `50`, new value is `40`. Difference is `-10`
+
+      `decimal_precision` defaults to `3`, but you can override this if you want.
+
+      `expected_update_period_in_days` is used to determine if the Agent is working.
+
+      The resulting event will be a copy of the received event with the difference
+      or change added as an extra attribute. If you use the `percentage_change` the
+      attribute will be formatted as such `{{attribute}}_change`, otherwise it will
+      be `{{attribute}}_diff`.
+    MD
+
+    event_description <<-MD
+      This will change based on the source event.
+    MD
+
+    def default_options
+      {
+        'path' => '.data.rate',
+        'output' => 'rate_diff',
+        'method' => 'integer_difference',
+        'expected_update_period_in_days' => 1
+      }
+    end
+
+    def validate_options
+      unless options['path'].present? && options['method'].present? && options['output'].present? && options['expected_update_period_in_days'].present?
+        errors.add(:base, 'The attribute, method and expected_update_period_in_days fields are all required.')
+      end
+    end
+
+    def working?
+      event_created_within?(interpolated['expected_update_period_in_days']) && !recent_error_logs?
+    end
+
+    def receive(incoming_events)
+      incoming_events.each do |event|
+        handle(interpolated(event), event)
+      end
+    end
+
+    private
+
+    def handle(opts, event)
+      opts['decimal_precision'] ||= 3
+      attribute_value = Utils.value_at(event.payload, opts['path'])
+      attribute_value = attribute_value.nil? ? 0 : attribute_value
+      payload = event.payload.deep_dup
+
+      if opts['method'] == 'percentage_change'
+        change = calculate_percentage_change(attribute_value, opts['decimal_precision'])
+        payload[opts['output']] = change
+
+      elsif opts['method'] == 'decimal_difference'
+        difference = calculate_decimal_difference(attribute_value, opts['decimal_precision'])
+        payload[opts['output']] = difference
+
+      elsif opts['method'] == 'integer_difference'
+        difference = calculate_integer_difference(attribute_value)
+        payload[opts['output']] = difference
+      end
+
+      created_event = create_event(payload: payload)
+      log('Propagating new event', outbound_event: created_event, inbound_event: event)
+      update_memory(attribute_value)
+    end
+
+    def calculate_integer_difference(new_value)
+      return 0 if last_value.nil?
+      (new_value.to_i - last_value.to_i)
+    end
+
+    def calculate_decimal_difference(new_value, dec_pre)
+      return 0.0 if last_value.nil?
+      (new_value.to_f - last_value.to_f).round(dec_pre.to_i)
+    end
+
+    def calculate_percentage_change(new_value, dec_pre)
+      return 0.0 if last_value.nil?
+      (((new_value.to_f / last_value.to_f) * 100) - 100).round(dec_pre.to_i)
+    end
+
+    def last_value
+      memory['last_value']
+    end
+
+    def update_memory(new_value)
+      memory['last_value'] = new_value
+    end
+  end
+end

spec/models/agents/attribute_difference_agent_spec.rb

@@ -0,0 +1,131 @@
+require 'rails_helper'
+
+describe Agents::AttributeDifferenceAgent do
+  def create_event(value=nil)
+    event = Event.new
+    event.agent = agents(:jane_weather_agent)
+    event.payload = {
+      rate: value
+    }
+    event.save!
+
+    event
+  end
+
+  before do
+    @valid_params = {
+      path: 'rate',
+      output: 'rate_diff',
+      method: 'integer_difference',
+      expected_update_period_in_days: '1'
+    }
+
+    @checker = Agents::AttributeDifferenceAgent.new(name: 'somename', options: @valid_params)
+    @checker.user = users(:jane)
+    @checker.save!
+  end
+
+  describe 'validation' do
+    before do
+      expect(@checker).to be_valid
+    end
+
+    it 'should validate presence of output' do
+      @checker.options[:output] = nil
+      expect(@checker).not_to be_valid
+    end
+
+    it 'should validate presence of path' do
+      @checker.options[:path] = nil
+      expect(@checker).not_to be_valid
+    end
+
+    it 'should validate presence of method' do
+      @checker.options[:method] = nil
+      expect(@checker).not_to be_valid
+    end
+
+    it 'should validate presence of expected_update_period_in_days' do
+      @checker.options[:expected_update_period_in_days] = nil
+      expect(@checker).not_to be_valid
+    end
+  end
+
+  describe '#working?' do
+    before :each do
+      # Need to create an event otherwise event_created_within? returns nil
+      event = create_event
+      @checker.receive([event])
+    end
+
+    it 'is when event created within :expected_update_period_in_days' do
+      @checker.options[:expected_update_period_in_days] = 2
+      expect(@checker).to be_working
+    end
+
+    it 'isnt when event created outside :expected_update_period_in_days' do
+      @checker.options[:expected_update_period_in_days] = 2
+
+      time_travel_to 2.days.from_now do
+        expect(@checker).not_to be_working
+      end
+    end
+  end
+
+  describe '#receive' do
+    before :each do
+      @event = create_event('5.5')
+    end
+
+    it 'creates events when memory is empty' do
+      expect {
+        @checker.receive([@event])
+      }.to change(Event, :count).by(1)
+      expect(Event.last.payload[:rate_diff]).to eq(0)
+    end
+
+    it 'creates event with extra attribute for integer_difference' do
+      @checker.receive([@event])
+      event = create_event('6.5')
+
+      expect {
+        @checker.receive([event])
+      }.to change(Event, :count).by(1)
+      expect(Event.last.payload[:rate_diff]).to eq(1)
+    end
+
+    it 'creates event with extra attribute for decimal_difference' do
+      @checker.options[:method] = 'decimal_difference'
+      @checker.receive([@event])
+      event = create_event('6.4')
+
+      expect {
+        @checker.receive([event])
+      }.to change(Event, :count).by(1)
+      expect(Event.last.payload[:rate_diff]).to eq(0.9)
+    end
+
+    it 'creates event with extra attribute for percentage_change' do
+      @checker.options[:method] = 'percentage_change'
+      @checker.receive([@event])
+      event = create_event('9')
+
+      expect {
+        @checker.receive([event])
+      }.to change(Event, :count).by(1)
+      expect(Event.last.payload[:rate_diff]).to eq(63.636)
+    end
+
+    it 'creates event with extra attribute for percentage_change with the correct rounding' do
+      @checker.options[:method] = 'percentage_change'
+      @checker.options[:decimal_precision] = 5
+      @checker.receive([@event])
+      event = create_event('9')
+
+      expect {
+        @checker.receive([event])
+      }.to change(Event, :count).by(1)
+      expect(Event.last.payload[:rate_diff]).to eq(63.63636)
+    end
+  end
+end