Fixation events sending
=======================

Observers are attached to pipeline steps to be notified when a method is called.

## observers.py

For this use case we need to enable [Ivy bus communication](https://gitlab.com/ivybus/ivy-python/) to log ArUco detection results (on *ArUcoCamera.on_watch* call) and fixation identification with AOI matching (on *ArUcoCamera.on_look* call).

```python
import logging

from argaze import DataFeatures, GazeFeatures

from ivy.std_api import *
from ivy.ivy import IvyIllegalStateError


class IvyBus(DataFeatures.PipelineStepObject):
	"""Handle Ivy bus."""

	@DataFeatures.PipelineStepInit
	def __init__(self, **kwargs):

		self.__bus = None

	@property
	def bus(self) -> str:
		return self.__bus

	@bus.setter
	def bus(self, bus: str):
		self.__bus = bus

	@DataFeatures.PipelineStepEnter
	def __enter__(self, parent = None):

		# Enable Ivy bus
		IvyInit(self.name)
		IvyStart(self.__bus)

		return self

	@DataFeatures.PipelineStepExit
	def __exit__(self, exception_type, exception_value, exception_traceback):

		# Stop Ivy bus
		IvyStop()


class ArUcoCameraLogger(DataFeatures.PipelineStepObject):
	"""Log ArUcoCamera activity."""

	@DataFeatures.PipelineStepInit
	def __init__(self, **kwargs):

		self._last_markers_number = None

	def on_watch(self, timestamp, aruco_camera, exception):
		"""Report ArUco markers detection info on Ivy bus."""

		# Wait for number of detected marker changes
		if aruco_camera.aruco_detector.detected_markers_number() != self._last_markers_number:

			self._last_markers_number = aruco_camera.aruco_detector.detected_markers_number()

			output = f'ArUcoDetection MarkersNumber={self._last_markers_number}'

			# Send Ivy message
			IvySendMsg(output)

			logging.debug('%i %s', timestamp, output)

	def on_look(self, timestamp, aruco_camera, exception):
		"""Report fixation and metrics on Ivy bus."""

		# Select 'Main' layer
		main_layer = aruco_camera.layers['Main']

		if GazeFeatures.is_fixation(aruco_camera.last_gaze_movement()):

			fixation = aruco_camera.last_gaze_movement()

			# Output in progress fixation data
			if not fixation.is_finished():

				output = f'FixationInProgress Start={fixation[0].timestamp} Duration={fixation.duration} AOI={main_layer.last_looked_aoi_name()} Probabilities={main_layer.aoi_matcher.looked_probabilities()}'

				# Send Ivy message
				IvySendMsg(output)
				
				logging.debug('%i %s %s %s', timestamp, aruco_camera.last_gaze_position().value, aruco_camera.name, output)
						
			# Output finished fixation data
			else:

				output = f'FixationEnd Start={fixation[0].timestamp} Duration={fixation.duration} AOI={main_layer.aoi_matcher.looked_aoi_name()} Probabilities={main_layer.aoi_matcher.looked_probabilities()}'

				# Send Ivy message
				IvySendMsg(output)
				
				logging.debug('%i %s %s %s', timestamp, aruco_camera.last_gaze_position().value, aruco_camera.name, output)
```