extends Area2D

# #101 (#97c): the part of a structure a wave can actually hit.
#
# A Building is a plain Node2D, so nothing could collide with it - enemies
# flew through the mothership without noticing. This gives it a body in the
# same shape the rest of the game already understands: an Area2D in a group,
# exactly like a Ship or an asteroid, so EnemyProjectile needed one extra
# branch rather than a new concept.
#
# Damage is applied on a TICK rather than on area_entered. Entry fires once,
# which is right for a rammer - it dies on the first strike - but would let
# a sniper that drifted inside sit there scratch-free for ever. On a tick,
# an enemy parked on a structure is besieging it, which is what #97 asks
# for.

const STRIKE_INTERVAL: float = 0.7
# #165: how fast a friendly vessel has to be going before touching a structure
# counts as hitting it. Comfortably above the speed a fleet drifts onto its own
# mothership to unload at, and below cruise - so ordinary docking is free and
# flying INTO a building is not.
const RAM_SPEED: float = 420.0
const RAM_DAMAGE: int = 4
const RAM_DAMAGE_MAX: int = 12

var _strike_timer: float = 0.0


func _ready() -> void:
	add_to_group("player_buildings")
	area_entered.connect(_on_area_entered)


# #165: a vessel of the player's own, arriving fast enough, damages what it
# hits.
#
# On ENTRY, not on the strike tick above. The tick is right for a siege - an
# enemy parked on a structure is besieging it - but wrong for a collision: a
# vessel is only moving fast for the instant it arrives, and by the time a
# 0.7s tick came round it had already braked to nothing. Measured: a ship sent
# in at 900 did no damage at all until this moved to entry.
#
# Below the threshold it is docking, not a collision. The fleet sits on its own
# mothership constantly to bank ore, and if resting there hurt, the economy
# loop would grind the player's own buildings down.
func _on_area_entered(area: Area2D) -> void:
	if not is_instance_valid(area) or not area.is_in_group("player_ships"):
		return
	# A vessel stationed at an outpost is not ramming it. It launches from
	# there, patrols, and comes back - repeatedly, and at speed. Only the
	# fleet can collide with a structure.
	if area.is_in_group("garrison_ships"):
		return
	var speed: float = float(area.velocity.length()) if "velocity" in area else 0.0
	if speed < RAM_SPEED:
		return
	var id: int = building_id()
	if id == 0:
		return
	# Scaled by how much faster than the threshold it was going, so a glancing
	# touch above the line is not a full-speed charge, and capped so no engine
	# upgrade turns a vessel into a wrecking ball.
	var impact: int = mini(int(round(RAM_DAMAGE * speed / RAM_SPEED)), RAM_DAMAGE_MAX)
	GameState.damage_building(id, impact)
	area.take_damage(1)


func building_id() -> int:
	var building: Node = get_parent()
	return 0 if building == null else int(building.building_id)


# Called by EnemyProjectile, which knows nothing about buildings beyond this
# name - the same call it makes on a Ship.
func take_damage(amount: int) -> void:
	GameState.damage_building(building_id(), amount)


func _physics_process(delta: float) -> void:
	_strike_timer -= delta
	if _strike_timer > 0.0:
		return
	_strike_timer = STRIKE_INTERVAL
	var id: int = building_id()
	if id == 0:
		return
	for area in get_overlapping_areas():
		if not is_instance_valid(area) or not area.is_in_group("enemies"):
			continue
		var damage: int = area.contact_damage() if area.has_method("contact_damage") else 6
		# The structure is told first, for the same reason Ship tells the
		# enemy first: resolving the enemy's own death can free it, and a
		# rammer must still land its hit on the way out.
		GameState.damage_building(id, damage)
		if area.has_method("collide_with_player_building"):
			area.collide_with_player_building()