spaceship/enemies/EnemyLungeComponent.gd

class_name EnemyLungeComponent
extends Node2D

# Forgejo #96. A ramming enemy that does not simply beeline the way
# EnemyPursuitComponent does: it drifts in from a distance, LOCKS a point,
# rocks back and forth on the spot while it winds up, shows the line it is
# about to fly down, and only then crosses the gap in one fast straight run.
#
# The lock is the whole point. Once WINDUP starts, nothing re-reads the
# fleet: the charge goes to where the target WAS, so the wind-up and the
# trajectory line are a real warning the player can act on, rather than
# decoration on an unavoidable hit. Same bargain as EnemyBigLaserBeam, which
# locks its aim in launch() for exactly this reason.
#
# A Node2D rather than a plain Node because the trajectory line has to be
# drawn somewhere, and top_level keeps that drawing in world space - the
# parent enemy spins to face its target, and a line that spun with it would
# not point where the charge is going.
#
# Never pair with a pursuit or standoff component: all three write the
# enemy's position every tick and would fight over it.

var capability_id: String = "lunge"

enum Phase { HUNT, WINDUP, CHARGE, RECOVER }

# Far enough that it is already on screen, and visibly waiting, before it
# commits - "starts a bit far from the target" is the behaviour, so a lancer
# that locked the instant it could see anything would not read as one.
@export var detection_range: float = 1500.0
@export var lock_range: float = 820.0
# The drift in HUNT is deliberately slower than the charge by an order of
# magnitude: the approach is a stalk, the charge is the attack.
@export var approach_speed_factor: float = 0.5
@export var windup_time: float = 1.2
# #96 to the letter: the trajectory line appears 300ms before it leaves.
@export var telegraph_time: float = 0.3
# The "small back and forth" - it recoils along the charge axis, so the
# motion reads as winding up to spring rather than as drifting.
@export var windup_sway: float = 30.0
@export var windup_cycles: float = 2.5
@export var charge_speed: float = 950.0
# It flies THROUGH the locked point rather than stopping on it. A charge
# that halted exactly where the ship used to be would look like it was
# aiming at empty space on purpose.
@export var charge_overshoot: float = 300.0
@export var recover_time: float = 1.3
@export var telegraph_color: Color = Color(1.0, 0.45, 0.15)

var phase: int = Phase.HUNT
var velocity: Vector2 = Vector2.ZERO
# Where the charge is going, and where it started - both frozen at lock.
var locked_point: Vector2 = Vector2.ZERO
var charge_direction: Vector2 = Vector2.RIGHT
var charge_anchor: Vector2 = Vector2.ZERO
var charge_distance: float = 0.0
var travelled: float = 0.0
var windup_left: float = 0.0
var recover_left: float = 0.0


func setup() -> void:
	# World space, not the enemy's: see the class comment.
	top_level = true
	position = Vector2.ZERO
	rotation = 0.0


# True while the trajectory line is up, i.e. the last telegraph_time of the
# wind-up. Public because it is the one piece of state a test can check that
# says "the warning is showing" without reaching into a _draw().
func is_telegraphing() -> bool:
	return phase == Phase.WINDUP and windup_left <= telegraph_time


func tick(delta: float) -> void:
	var enemy: Node2D = get_parent()
	match phase:
		Phase.HUNT:
			_tick_hunt(enemy, delta)
		Phase.WINDUP:
			_tick_windup(enemy, delta)
		Phase.CHARGE:
			_tick_charge(enemy, delta)
		Phase.RECOVER:
			_tick_recover(enemy, delta)
	queue_redraw()


func _tick_hunt(enemy: Node2D, delta: float) -> void:
	var target: Node2D = _nearest_ship(enemy)
	if target == null:
		return
	var to_target: Vector2 = target.global_position - enemy.global_position
	var distance: float = to_target.length()
	if distance > detection_range or distance < 0.001:
		return
	var direction: Vector2 = to_target / distance
	if distance <= lock_range:
		_lock(enemy, target)
		return
	var desired: Vector2 = direction * enemy.speed * approach_speed_factor
	velocity = velocity.move_toward(desired, enemy.acceleration * delta)
	enemy.global_position += velocity * delta
	_face(enemy, direction, delta)


func _lock(enemy: Node2D, target: Node2D) -> void:
	locked_point = target.global_position
	charge_anchor = enemy.global_position
	var to_target: Vector2 = locked_point - charge_anchor
	charge_distance = to_target.length()
	charge_direction = to_target.normalized() if charge_distance > 0.001 else Vector2.RIGHT
	windup_left = windup_time
	travelled = 0.0
	velocity = Vector2.ZERO
	phase = Phase.WINDUP


func _tick_windup(enemy: Node2D, delta: float) -> void:
	windup_left -= delta
	# Snap to the locked heading rather than easing into it: the nose is part
	# of the warning, and a lancer still turning when the line appears would
	# be lying about where it is going.
	enemy.rotation = charge_direction.angle() + PI / 2.0
	if windup_left <= 0.0:
		phase = Phase.CHARGE
		enemy.global_position = charge_anchor
		return
	# One full back-and-forth per cycle, starting and ending at the anchor,
	# leaning BACKWARDS first (-sin) so the recoil comes before the spring.
	var progress: float = 1.0 - windup_left / maxf(windup_time, 0.001)
	var sway: float = -sin(progress * TAU * windup_cycles) * windup_sway
	enemy.global_position = charge_anchor + charge_direction * sway


func _tick_charge(enemy: Node2D, delta: float) -> void:
	var step: float = charge_speed * delta
	travelled += step
	enemy.global_position += charge_direction * step
	enemy.rotation = charge_direction.angle() + PI / 2.0
	if travelled >= charge_distance + charge_overshoot:
		phase = Phase.RECOVER
		recover_left = recover_time
		velocity = charge_direction * charge_speed


func _tick_recover(enemy: Node2D, delta: float) -> void:
	# Coasts to a stop instead of stopping dead, then hunts again. Without
	# this it would re-lock the frame it finished and the wind-up would stop
	# being a rhythm the player can read.
	recover_left -= delta
	velocity = velocity.move_toward(Vector2.ZERO, enemy.acceleration * delta)
	enemy.global_position += velocity * delta
	if recover_left <= 0.0:
		phase = Phase.HUNT
		velocity = Vector2.ZERO


func _face(enemy: Node2D, direction: Vector2, delta: float) -> void:
	var target_angle: float = direction.angle() + PI / 2.0
	enemy.rotation = lerp_angle(enemy.rotation, target_angle, enemy.rotation_speed * delta)


# #101: a lancer will lock a structure exactly as it locks a vessel - the
# wind-up, the line and the charge are the same, and so is what happens when
# it arrives.
func _nearest_ship(enemy: Node2D) -> Node2D:
	return EnemyTargets.nearest_target(self, enemy.global_position)


func _draw() -> void:
	if not is_telegraphing():
		return
	var enemy: Node2D = get_parent()
	if enemy == null:
		return
	# Thin, and brightening as the launch approaches, so it reads as a sight
	# line being drawn rather than as a beam already firing.
	var urgency: float = clampf(1.0 - windup_left / maxf(telegraph_time, 0.001), 0.0, 1.0)
	var from: Vector2 = enemy.global_position
	var to: Vector2 = locked_point + charge_direction * charge_overshoot
	draw_line(from, to, Color(telegraph_color, 0.18 + 0.30 * urgency), 2.0, true)
	draw_line(from, to, Color(1.0, 0.92, 0.82, 0.25 + 0.45 * urgency), 1.0, true)
	# A tick across the locked point: the line says WHERE, this says how far.
	var across: Vector2 = Vector2(-charge_direction.y, charge_direction.x) * 14.0
	draw_line(locked_point - across, locked_point + across,
		Color(telegraph_color, 0.35 + 0.5 * urgency), 2.0, true)