app/models/agents/change_detector_agent.rb
module Agents
class ChangeDetectorAgent < Agent
cannot_be_scheduled!
description <<~MD
The Change Detector Agent receives a stream of events and emits a new event when a property of the received event changes.
`property` specifies a [Liquid](https://github.com/huginn/huginn/wiki/Formatting-Events-using-Liquid) template that expands to the property to be watched, where you can use a variable `last_property` for the last property value. If you want to detect a new lowest price, try this: `{% assign drop = last_property | minus: price %}{% if last_property == blank or drop > 0 %}{{ price | default: last_property }}{% else %}{{ last_property }}{% endif %}`
`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.
MD
event_description <<~MD
This will change based on the source event. If you were event from the ShellCommandAgent, your outbound event might look like:
{
'command' => 'pwd',
'path' => '/home/Huginn',
'exit_status' => '0',
'errors' => '',
'output' => '/home/Huginn'
}
MD
def default_options
{
'property' => '{{output}}',
'expected_update_period_in_days' => 1
}
end
def validate_options
unless options['property'].present? && options['expected_update_period_in_days'].present?
errors.add(:base, "The property 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|
interpolation_context.stack do
interpolation_context['last_property'] = last_property
handle(interpolated(event), event)
end
end
end
private
def handle(opts, event = nil)
property = opts['property']
if has_changed?(property)
created_event = create_event payload: event.payload
log("Propagating new event as property has changed to #{property} from #{last_property}",
outbound_event: created_event, inbound_event: event)
update_memory(property)
else
log("Not propagating as incoming event has not changed from #{last_property}.", inbound_event: event)
end
end
def has_changed?(property)
property != last_property
end
def last_property
self.memory['last_property']
end
def update_memory(property)
self.memory['last_property'] = property
end
end
end