ManageIQ/manageiq-providers-azure

class ManageIQ::Providers::Azure::CloudManager::EventCatcher::Stream
  EVENT_TIMESTAMP_BUFFER = 2.minutes

  SELECT_FIELDS = %w[
    authorization
    correlationId
    description
    eventDataId
    eventName
    eventTimestamp
    operationName
    resourceGroupName
    resourceProviderName
    resourceId
    resourceType
  ].join(',').freeze

  attr_reader :ems
  attr_accessor :since

  # Creates an event monitor. Used internally by the Runner.
  #
  def initialize(ems)
    @ems = ems
    @collecting_events = false
    @since = nil
    @connection = nil
  end

  # Sets a boolean used by the +each_batch+ method that indicates
  # that events should start/keep being captured.
  #
  def start
    @collecting_events = true
  end

  # Sets a boolean used by the +each_batch+ method that indicates
  # that events should stop being captured.
  #
  def stop
    @collecting_events = false
  end

  # Used internally by the Runner#monitor_events method.
  #
  def each_batch
    while @collecting_events
      yield get_events.collect(&:to_hash)
    end
  end

  private

  # Get a list of events that have happened since the most recent event time.
  #
  # Because Azure event timestamps are not necessarily stamped in order, an
  # issue occurs where we could accidentally skip over events that happen
  # in quick succession. We must therefore begin our query a couple minutes
  # back from our most recent timestamp, and filter out any duplicates.
  #
  # See https://bugzilla.redhat.com/show_bug.cgi?id=1724312 for details.
  #
  def get_events
    filter = "eventTimestamp ge #{most_recent_time}"
    events = connection.list(:filter => filter, :select => SELECT_FIELDS, :all => true)

    event_timestamp = events.max_by(&:event_timestamp)&.event_timestamp
    self.since      = DateTime.strptime(event_timestamp, "%Y-%m-%dT%H:%M:%S.%L") if event_timestamp

    events
  end

  # Retrieve the most recent Azure event minus the timestamp buffer, or the
  # startup interval (2 minutes) if no records are found.
  #
  def most_recent_time
    if since
      format_timestamp(since - EVENT_TIMESTAMP_BUFFER)
    else
      format_timestamp(2.minutes.ago)
    end
  end

  # Given a Time object, return a string suitable for the Azure REST API query.
  #
  def format_timestamp(time)
    time.strftime('%Y-%m-%dT%H:%M:%S.%L')
  end

  # A cached connection to the event service, which is used to query for events.
  #
  def connection
    @connection ||= create_event_service
  end

  # Create an event service object using the provider connection credentials.
  # This will be used by the +connection+ method to query for events.
  #
  def create_event_service
    ems.with_provider_connection do |conf|
      Azure::Armrest::Insights::EventService.new(conf)
    end
  end
end