spaceship/vessels/VesselGarrisonComponent.gd

class_name VesselGarrisonComponent
extends Node

# #105 (#97g): "When a vessel is assigned to an outpost, it navigates around
# the outpost by itself, attacking nearby ennemies if any are detected."
#
# Attached to a Ship at spawn by GarrisonField rather than declared on the
# vessel definition: garrisoning is a ROLE a hull is put into, not a property
# of the hull. The same interceptor is a fleet vessel one minute and a
# garrison the next, and nothing about it changes but who is steering.
#
# It steers by writing move_target and lets Ship's own steering do the
# flying, so a garrison vessel accelerates, banks and brakes exactly like one
# in the formation. It is not in Fleet.ships, so it does not follow the
# formation, does not count against max_fleet_size(), and does not move when
# the player flies away - which is the whole point of stationing it.

var capability_id: String = "garrison"

# Which outpost this belongs to, and where that outpost is. The position is
# copied rather than looked up every tick: the record is the truth, and if
# the outpost is levelled the vessel should hold the ground it was left on
# rather than snap to the origin.
var outpost_id: int = 0
var station: Vector2 = Vector2.ZERO

@export var orbit_radius: float = 170.0
@export var orbit_speed: float = 0.85
@export var detection_range: float = 950.0
# How far from its post it will go. Without a leash a garrison would be
# drawn off by anything that flew past, which is exactly what stationing it
# was meant to stop - and the outpost would be left open behind it.
@export var leash_range: float = 620.0
# Held off the target rather than ramming it: these are gunships, and a
# vessel that closed to zero would trade itself for a chaser every time.
@export var engage_distance: float = 300.0

var _angle: float = 0.0
var _engaging: bool = false


func setup() -> void:
	# Start the orbit from where the vessel actually IS, not from a random
	# bearing. A random one makes the first move_target a point on the far
	# side of the circle, and the vessel flies straight across the middle to
	# reach it - through the outpost it is supposed to be guarding.
	var ship: Node2D = get_parent()
	var offset: Vector2 = ship.global_position - station
	_angle = offset.angle() if offset.length() > 1.0 else randf() * TAU


func is_engaging() -> bool:
	return _engaging


func tick(delta: float) -> void:
	var ship: Node2D = get_parent()
	var target: Node2D = _nearest_enemy(ship)
	_engaging = target != null
	if target == null:
		_patrol(ship, delta)
		_hold_fire(ship)
		return
	_engage(ship, target, delta)


func _patrol(ship: Node2D, delta: float) -> void:
	_angle += orbit_speed * delta
	ship.move_target = station + Vector2(cos(_angle), sin(_angle)) * orbit_radius


func _engage(ship: Node2D, target: Node2D, delta: float) -> void:
	# Keep station off the target, but never further from the post than the
	# leash allows - the approach is clamped to a circle around the outpost
	# rather than to a straight line, so it still manoeuvres while pinned.
	var to_target: Vector2 = target.global_position - ship.global_position
	var distance: float = to_target.length()
	var wanted: Vector2 = target.global_position
	if distance > 0.001:
		wanted = target.global_position - to_target.normalized() * engage_distance
	var from_station: Vector2 = wanted - station
	if from_station.length() > leash_range:
		wanted = station + from_station.normalized() * leash_range
	ship.move_target = wanted
	# The orbit angle keeps advancing while engaged, so breaking off does not
	# snap the vessel back to whatever bearing it left on.
	_angle += orbit_speed * delta

	_shoot(ship, target, distance, to_target)


# Two kinds of armament, one rule: point the gun, or fire the ability. Which
# one this vessel has is a question about its components, not about its type,
# so a third armed vessel needs nothing here.
func _shoot(ship: Node2D, target: Node2D, distance: float, to_target: Vector2) -> void:
	var weapon: Node = _component(ship, "weapon")
	if weapon != null:
		# The gun is a held trigger: it is aimed every tick and stops the
		# moment the direction is cleared.
		weapon.set_fire_direction(to_target if distance <= weapon.fire_range else Vector2.ZERO)
	for component in ship.get_children():
		if not component.has_method("fire_ability") or not component.has_ability():
			continue
		if not component.is_ready() or distance > component.ability_range():
			continue
		# The magazine is the OUTPOST's, not the fleet's hold. A garrison
		# spends what was flown out to it, which is the whole point of the
		# outpost holding a store at all - and if the store is empty the
		# vessel holds its fire rather than firing free shots.
		var resource_type: String = component.ability_ammo_resource()
		var cost: int = component.ability_ammo_cost()
		if not GameState.spend_garrison_ammo(outpost_id, resource_type, cost):
			continue
		if not component.fire_ability(get_tree().root, ship.global_position,
				target.global_position):
			# It refused after being paid - put the ammunition back rather
			# than burning it on a shot that never happened.
			GameState.building_inventory(outpost_id).deposit(resource_type, cost)


func _component(ship: Node2D, capability: String) -> Node:
	return ship.get_component(capability) if ship.has_method("get_component") else null


func _hold_fire(ship: Node2D) -> void:
	var weapon: Node = _component(ship, "weapon")
	if weapon != null:
		weapon.set_fire_direction(Vector2.ZERO)


func _nearest_enemy(ship: Node2D) -> Node2D:
	var nearest: Node2D = null
	var best: float = detection_range
	for enemy in get_tree().get_nodes_in_group("enemies"):
		if not is_instance_valid(enemy) or enemy.is_queued_for_deletion():
			continue
		var at: Vector2 = (enemy as Node2D).global_position
		# Judged from the POST, not from the vessel: otherwise a garrison
		# that had drifted out to its leash would see further still, and
		# could be walked away from its outpost one enemy at a time.
		if station.distance_to(at) > leash_range + engage_distance:
			continue
		var d: float = ship.global_position.distance_to(at)
		if d < best:
			best = d
			nearest = enemy
	return nearest