# Calculates acceleration to take an agent to its target's location. The
# calculation attempts to arrive with zero remaining velocity.
# @category - Individual behaviors
class_name GSAIArrive
extends GSAISteeringBehavior

# Target agent to arrive to.
var target : GSAIAgentLocation
# Distance from the target for the agent to be considered successfully
# arrived.
var arrival_tolerance : float = 0.0
# Distance from the target for the agent to begin slowing down.
var deceleration_radius : float = 0.0
# Represents the time it takes to change acceleration.
var time_to_reach : float = 0.1


func _init(agent : GSAISteeringAgent, _target : GSAIAgentLocation).(agent) -> void:
	self.target = _target


func _arrive(acceleration : GSAITargetAcceleration, target_position : Vector3) -> void:
	var to_target : Vector3 = target_position - agent.position
	var distance : float = to_target.length()

	if distance <= arrival_tolerance:
		acceleration.set_zero()
	else:
		var desired_speed : float = agent.linear_speed_max

		if distance <= deceleration_radius:
			desired_speed *= distance / deceleration_radius

		var desired_velocity : Vector3 = to_target * desired_speed / distance

		desired_velocity = ((desired_velocity - agent.linear_velocity) * 1.0 / time_to_reach)

		acceleration.linear = GSAIUtils.clampedv3(desired_velocity, agent.linear_acceleration_max)
		acceleration.angular = 0


func _calculate_steering(acceleration: GSAITargetAcceleration) -> void:
	_arrive(acceleration, target.position)