extends Node

const INVENTORY = preload("res://Inventory.gd")
const RESOURCE_DEFINITIONS = preload("res://ResourceDefinitions.gd")
const BUILDING_DEFINITIONS = preload("res://BuildingDefinitions.gd")
const VESSEL_DEFINITIONS = preload("res://VesselDefinitions.gd")


# Autoload singleton - the one thing that survives change_scene_to_file()
# scene swaps between space (Main.tscn) and a planet's surface
# (PlanetSurface.tscn). Everything else in either scene gets torn down
# and rebuilt from scratch on each swap, so anything that needs to
# survive the trip has to live here instead.

var has_return_position: bool = false
var surviving_ship_count: int = 5
var surviving_vessel_types: PackedStringArray = PackedStringArray()
var return_world_position: Vector2 = Vector2.ZERO
var return_camera_zoom: float = 1.0

var planet_name: String = ""
var planet_id: String = ""
var planet_definition_id: String = "rocky"

# Explored-chunk history for the world map's fog-of-war reveal. Lives
# here (not on ExplorationTracker, which gets destroyed and recreated on
# every scene swap) so exploration progress isn't lost every time the
# player lands on and leaves a planet.
var explored_chunks: Dictionary = {}

# --- Resources -------------------------------------------------------------

const RESOURCE_ORE: String = RESOURCE_DEFINITIONS.ORE_ID
const RESOURCE_GAS: String = RESOURCE_DEFINITIONS.GAS_ID
const RESOURCE_ENERGY: String = RESOURCE_DEFINITIONS.ENERGY_ID
const RESOURCE_DARK_MATTER: String = RESOURCE_DEFINITIONS.DARK_MATTER_ID
const RESOURCE_TYPES: PackedStringArray = RESOURCE_DEFINITIONS.ORDER

# All resource-bearing locations use the same container. The old public
# names below are computed compatibility accessors, not separate storage.
var bank_inventory: RefCounted = INVENTORY.new({RESOURCE_ORE: 500})
var fleet_inventory: RefCounted = INVENTORY.new()

var rocks: int:
	get: return bank_inventory.amount(RESOURCE_ORE)
	set(value): bank_inventory.set_amount(RESOURCE_ORE, value)

var gas: int:
	get: return bank_inventory.amount(RESOURCE_GAS)
	set(value): bank_inventory.set_amount(RESOURCE_GAS, value)

var fleet_cargo: int:
	get: return fleet_inventory.amount(RESOURCE_ORE)
	set(value): fleet_inventory.set_amount(RESOURCE_ORE, value)

var fleet_gas_cargo: int:
	get: return fleet_inventory.amount(RESOURCE_GAS)
	set(value): fleet_inventory.set_amount(RESOURCE_GAS, value)

# Both return the amount actually accepted (#56: the fleet hold now has a
# finite total_capacity), so a collector can tell a full hold apart from a
# successful pickup instead of assuming everything offered was taken.
func collect_cargo(amount: int = 1) -> int:
	return fleet_inventory.deposit(RESOURCE_ORE, amount)

func collect_gas_cargo(amount: int = 1) -> int:
	return fleet_inventory.deposit(RESOURCE_GAS, amount)


func resource_types() -> PackedStringArray:
	return RESOURCE_DEFINITIONS.ids()


func resource_definition(resource_type: String) -> Resource:
	return RESOURCE_DEFINITIONS.get_definition(resource_type)


func resource_name(resource_type: String) -> String:
	var definition: Resource = resource_definition(resource_type)
	return String(definition.display_name) if definition != null else resource_type.capitalize()


func resource_color(resource_type: String) -> Color:
	var definition: Resource = resource_definition(resource_type)
	return definition.color if definition != null else Color.WHITE


func banked_resource(resource_type: String) -> int:
	return bank_inventory.amount(resource_type)


func fleet_resource(resource_type: String) -> int:
	return fleet_inventory.amount(resource_type)


# #56: total across every resource type in the hold, and the combined cap
# that limits it - a HUD readout wants both, not any one resource's amount.
func fleet_cargo_used() -> int:
	return fleet_inventory.total()


func fleet_cargo_total_capacity() -> int:
	return fleet_inventory.total_capacity


func _inventory_for_record(record: Dictionary) -> RefCounted:
	var inventory: RefCounted = record.get("inventory") as RefCounted
	if inventory == null:
		inventory = INVENTORY.new()
		record.inventory = inventory
	# Compatibility migration for state made before #33. Erase each legacy
	# field once absorbed so it cannot drift out of step with the inventory.
	if record.has("stock"):
		inventory.set_amount(RESOURCE_ORE, int(record.stock))
		record.erase("stock")
	if record.has("gas_stock"):
		inventory.set_amount(RESOURCE_GAS, int(record.gas_stock))
		record.erase("gas_stock")
	return inventory


func building_inventory(id: int) -> RefCounted:
	var building: Dictionary = find_building(id)
	if building.is_empty():
		return null
	if building_has_capability(building, "bank"):
		return bank_inventory
	return _inventory_for_record(building)


func building_resource(id: int, resource_type: String) -> int:
	var inventory: RefCounted = building_inventory(id)
	return 0 if inventory == null else inventory.amount(resource_type)


func transfer_resource_to_building(id: int, resource_type: String, amount: int) -> int:
	return fleet_inventory.transfer_to(building_inventory(id), resource_type, amount)


func transfer_resource_to_fleet(id: int, resource_type: String, amount: int) -> int:
	var source: RefCounted = building_inventory(id)
	return 0 if source == null else source.transfer_to(fleet_inventory, resource_type, amount)


# The batch size the transfer menu offers, next to "All". A batch rather
# than only all-or-nothing: the hold is the part that can be lost, and
# emptying the bank in one tap would strand research, which spends from it.
const CARGO_LOAD_BATCH: int = 25


# --- moving ore by hand, in either direction (#24) --------------------------
#
# One pair of primitives the transfer menu drives, rather than the two
# one-way special cases that used to live inside the skill and craft panels
# ("load ore" at the mothership, "store ore here" at a crafter).
#
# The mothership is deliberately not a special case in the UI: it is simply
# the building whose holdings ARE the bank. Depositing at one banks the ore,
# withdrawing from one draws on the bank, and every other building keeps its
# own stock (#16). That is what lets one menu serve every structure.


func building_holdings(id: int) -> int:
	return building_resource(id, RESOURCE_ORE)

func building_gas_holdings(id: int) -> int:
	return building_resource(id, RESOURCE_GAS)


func transfer_to_building(id: int, amount: int) -> int:
	# Hold -> this building. Returns how much actually moved, which is capped
	# by the hold: a caller asking for "all" passes a number too big on
	# purpose and reads the result back.
	return transfer_resource_to_building(id, RESOURCE_ORE, amount)


func transfer_to_fleet(id: int, amount: int) -> int:
	# This building -> hold. Capped by what the building actually holds, so
	# there is no overdraft in either direction.
	return transfer_resource_to_fleet(id, RESOURCE_ORE, amount)

func transfer_gas_to_building(id: int, amount: int) -> int:
	return transfer_resource_to_building(id, RESOURCE_GAS, amount)

func transfer_gas_to_fleet(id: int, amount: int) -> int:
	return transfer_resource_to_fleet(id, RESOURCE_GAS, amount)

const MOTHERSHIP_COST: int = 20
const SHIP_CRAFTER_COST: int = 12
const SHIP_COST: int = 6

# --- Buildings -------------------------------------------------------------

# Player-placed structures, as [{"type": String, "position": Vector2}].
# Buildings exist only in space (Main.tscn) but are stored here so they
# survive the scene swap to a planet's surface and back.
const BUILDING_MOTHERSHIP: String = "mothership"
const BUILDING_SHIP_CRAFTER: String = "ship_crafter"
const BUILDING_COMMAND_CENTER: String = "command_center"
# Extractors are not placed in space like the others - they are built ON a
# planet's surface and tracked separately (see `extractors`).
const BUILDING_EXTRACTOR: String = "extractor"
# Hosts the transport vessels that supply other buildings (#18). Built in
# space like the rest; it is the transporters (#19) that do the moving.
const BUILDING_TRANSPORT_HUB: String = "transport_hub"
# Where vessel types are researched and new ones unlocked (#5).
const BUILDING_SHIP_LAB: String = "ship_lab"
# Converts gas into energy, both stored/moved through the building's own
# inventory exactly like every other building (#54).
const BUILDING_GAS_BURNER: String = "gas_burner"

const COMMAND_CENTER_COST: int = 15
const EXTRACTOR_COST: int = 25
const TRANSPORT_HUB_COST: int = 30
const SHIP_LAB_COST: int = 35
const GAS_BURNER_COST: int = 30

var buildings: Array = []

# --- Skill tree ------------------------------------------------------------

# Researched at the mothership. Two things hang off it: which structures the
# player is allowed to build at all, and permanent upgrades that have no
# building of their own. The mothership itself is deliberately NOT in the
# tree - it is the thing you research AT, so gating it behind research would
# be a deadlock.
#
# `x` is a horizontal position on a 0..1 grid; the vertical position is NOT
# stored, it is derived from how many prerequisites deep the node is, so the
# tree always reads root-at-the-bottom and cannot drift out of step with the
# dependencies when nodes are added. `requires` is a single prerequisite id
# ("" for a root).
const SKILL_TREE: Array = [
	{
		"id": "shipyards", "name": "Shipyards", "cost": 15, "requires": "",
		"x": 0.5, "unlocks": BUILDING_SHIP_CRAFTER,
		"desc": "Build ship crafters, and buy extra vessels at them.",
	},
	{
		"id": "logistics", "name": "Logistics", "cost": 25, "requires": "shipyards",
		"x": 0.18, "unlocks": BUILDING_EXTRACTOR,
		"desc": "Build extractors on planets. They mine ore whether or not you are nearby.",
	},
	{
		"id": "coordination", "name": "Coordination", "cost": 20, "requires": "shipyards",
		"x": 0.50, "unlocks": BUILDING_COMMAND_CENTER,
		"desc": "Build command centers, where the fleet formation is arranged.",
	},
	{
		"id": "freight", "name": "Freight Handling", "cost": 40, "requires": "logistics",
		"x": 0.18, "unlocks": BUILDING_TRANSPORT_HUB,
		"desc": "Build transport hubs. Each hub includes its own automatic transporters.",
	},
	{
		"id": "vessel_science", "name": "Vessel Science", "cost": 35, "requires": "shipyards",
		"x": 0.82, "unlocks": BUILDING_SHIP_LAB,
		"desc": "Build ship labs, where each vessel type is upgraded and new ones unlocked.",
	},
	{
		"id": "freight_yards", "name": "Freight Yards", "cost": 80, "requires": "freight",
		"x": 0.18, "hub_bonus": 1,
		"desc": "Permanent: +1 transporter stationed at every hub, including ones already built.",
	},
	{
		"id": "power_systems", "name": "Power Systems", "cost": 45, "requires": "freight",
		"x": 0.50, "unlocks": BUILDING_GAS_BURNER,
		"desc": "Build gas burners. Each converts gas into energy at its own site - hub transporters keep it stocked and collect what it makes.",
	},
	{
		"id": "wing", "name": "Wing Doctrine", "cost": 30, "requires": "coordination",
		"x": 0.82, "fleet_bonus": 1,
		"desc": "Permanent: +1 vessel in the fleet.",
	},
	{
		"id": "squadron", "name": "Squadron Doctrine", "cost": 70, "requires": "wing",
		"x": 0.50, "fleet_bonus": 1,
		"desc": "Permanent: +1 vessel in the fleet.",
	},
	{
		"id": "armada", "name": "Armada Doctrine", "cost": 150, "requires": "squadron",
		"x": 0.50, "fleet_bonus": 1,
		"desc": "Permanent: +1 vessel in the fleet.",
	},
]

const BASE_FLEET_SIZE: int = 5

var unlocked: Array = []


func skill_node(id: String) -> Dictionary:
	for node in SKILL_TREE:
		if node.id == id:
			return node
	return {}


func skill_depth(id: String) -> int:
	# How many prerequisites deep this node sits. Drives its height in the
	# tree view: roots at the bottom, everything that depends on something
	# above it.
	var depth: int = 0
	var node: Dictionary = skill_node(id)
	while not node.is_empty() and node.requires != "":
		depth += 1
		node = skill_node(node.requires)
		if depth > SKILL_TREE.size():
			break  # a cycle in the data would otherwise hang here
	return depth


func max_skill_depth() -> int:
	var deepest: int = 0
	for node in SKILL_TREE:
		deepest = maxi(deepest, skill_depth(node.id))
	return deepest


func is_unlocked(id: String) -> bool:
	return id in unlocked


func prerequisite_met(id: String) -> bool:
	var node: Dictionary = skill_node(id)
	if node.is_empty():
		return false
	return node.requires == "" or is_unlocked(node.requires)


func can_unlock(id: String) -> bool:
	return not is_unlocked(id) and prerequisite_met(id) and can_afford(int(skill_node(id).cost))


func unlock(id: String) -> bool:
	if not can_unlock(id):
		return false
	if not spend(int(skill_node(id).cost)):
		return false
	unlocked.append(id)
	if int(skill_node(id).get("hub_bonus", 0)) > 0:
		_sync_hub_transporters()
	return true


func is_building_unlocked(type: String) -> bool:
	for node in SKILL_TREE:
		if node.get("unlocks", "") == type:
			return is_unlocked(node.id)
	return true


func research_for_building(type: String) -> String:
	for node in SKILL_TREE:
		if node.get("unlocks", "") == type:
			return node.name
	return ""


func max_fleet_size() -> int:
	var n: int = BASE_FLEET_SIZE
	for id in unlocked:
		n += int(skill_node(id).get("fleet_bonus", 0))
	return mini(n, DEFAULT_FORMATION.size())


func reset_progression() -> void:
	unlocked.clear()
	vessel_levels.clear()


# Called from the main menu's Play button (#47): the autoload survives
# change_scene_to_file(), so without this a second playthrough in the same
# process would start from wherever the last one left off instead of a
# fresh game.
func reset_new_game() -> void:
	has_return_position = false
	surviving_ship_count = BASE_FLEET_SIZE
	surviving_vessel_types = PackedStringArray()
	return_world_position = Vector2.ZERO
	return_camera_zoom = 1.0
	planet_name = ""
	planet_id = ""
	planet_definition_id = "rocky"
	explored_chunks.clear()
	bank_inventory = INVENTORY.new({RESOURCE_ORE: 500})
	fleet_inventory = INVENTORY.new()
	buildings.clear()
	next_building_id = 1
	stored_vessels.clear()
	vessel_deliveries.clear()
	extractors.clear()
	transporters.clear()
	planet_capture.clear()
	reset_progression()
	reset_formation()


# --- building stock and production queue (#16) -----------------------------

# Since #12, a building cannot just deduct from the bank at the moment of
# purchase: what it produces has to be paid for out of resources physically
# delivered to it. So each building carries its own `stock`, and an order it
# cannot afford yet is QUEUED rather than refused, and completes by itself
# once the stock turns up.
#
# `id` exists because a building has to be referable across the space <->
# planet-surface scene swap, when every Building NODE has been destroyed and
# rebuilt. Position would nearly work and then fail on two buildings placed
# on the same spot.
var next_building_id: int = 1

# Finished vessels waiting at the mothership for the player to collect
# (#23), as a list of VESSEL_* types - a shield vessel must not come back as
# an interceptor. They are NOT handed to the fleet automatically: the player
# picks what to crew from the hangar, so a full fleet no longer stops a
# crafter from building.
#
# Production is simulated here, in the autoload, the same way extractor
# haulers are, so a build finishes whether or not the player is in space.
var stored_vessels: Array = []
# Finished crafter orders travel to the mothership before appearing in its
# hangar. State is authoritative here so delivery continues off-screen.
# {"type", "from", "to", "progress"}
var vessel_deliveries: Array = []
const VESSEL_DELIVERY_SPEED: float = 180.0

signal order_completed(building_id: int, type: String)


func add_building(type: String, at_position: Vector2) -> int:
	var id: int = next_building_id
	next_building_id += 1
	buildings.append({
		"id": id, "type": type, "position": at_position,
		"inventory": INVENTORY.new(), "orders": [],
	})
	var building: Dictionary = buildings[-1]
	if building_has_capability(building, "transport_hub"):
		_provision_hub_transporters(building)
	return id


func find_building(id: int) -> Dictionary:
	for b in buildings:
		if b.get("id", 0) == id:
			return b
	return {}


func building_has_capability(building: Dictionary, capability: String) -> bool:
	if building.is_empty():
		return false
	var definition: Resource = BUILDING_DEFINITIONS.get_definition(String(building.type))
	return definition != null and capability in definition.capabilities


# --- vessel types and their upgrades (#5) ---------------------------------

# Combat vessels can join the player fleet. Transporter metadata lives in the
# same definition catalog so the lab can upgrade its cargo and travel stats,
# but transporters themselves belong to hubs and are never production orders.
const VESSEL_INTERCEPTOR: String = "interceptor"
const VESSEL_SHIELD: String = "shield"
const VESSEL_GAS_BOMBER: String = "gas_bomber"
const VESSEL_TRANSPORTER: String = "transporter"
const VESSEL_CARRIER: String = "carrier"

# Compatibility constants for callers and old tests. Runtime metadata is
# resolved from VesselDefinition below.
const SHIELD_COST: int = 14
const LAB_RESEARCH_TIME: float = 8.0


# Test seam. Headless tests need the timed path - queued, started, finishing
# - without sitting through a real 10-second build each, and a suite that
# slow stops being run. Left at 1.0 in the game.
var build_time_scale: float = 1.0


func build_time(product: String) -> float:
	var definition: Resource = VESSEL_DEFINITIONS.get_definition(product)
	return (definition.build_time if definition != null else 10.0) * build_time_scale


func lab_research_time() -> float:
	return LAB_RESEARCH_TIME * build_time_scale

# Compatibility constants. VesselDefinition owns the live base figures.
const SHIP_BASE_DAMAGE: int = 1
const SHIP_BASE_COOLDOWN: float = 0.5
const SHIP_BASE_RANGE: float = 320.0
const SHIP_BASE_SPEED: float = 460.0
const SHIP_BASE_ACCEL: float = 450.0
const SHIELD_BASE_CHARGES: int = 1
const SHIELD_BASE_RECHARGE: float = 6.0
var vessel_levels: Dictionary = {}

signal vessel_upgraded(upgrade_id: String)


func has_ship_lab() -> bool:
	for b in buildings:
		if building_has_capability(b, "vessel_research"):
			return true
	return false


func shield_vessel_unlocked() -> bool:
	return vessel_is_unlocked(VESSEL_SHIELD)


const UNLOCK_SHIELD_VESSEL: String = "unlock_shield"
const UNLOCK_SHIELD_COST: int = 45


func unlock_shield_vessel() -> bool:
	return unlock_vessel(VESSEL_SHIELD)


func vessel_definition(vessel: String) -> Resource:
	return VESSEL_DEFINITIONS.get_definition(vessel)


func vessel_name(vessel: String) -> String:
	var definition: Resource = vessel_definition(vessel)
	return definition.display_name if definition != null else vessel.capitalize()


func vessel_has_capability(vessel: String, capability: String) -> bool:
	var definition: Resource = vessel_definition(vessel)
	return definition != null and definition.has_capability(capability)


func vessel_is_fleet_eligible(vessel: String) -> bool:
	var definition: Resource = vessel_definition(vessel)
	return definition != null and definition.fleet_eligible


func vessel_is_unlocked(vessel: String) -> bool:
	var definition: Resource = vessel_definition(vessel)
	if definition == null:
		return false
	return definition.unlock_id == "" or int(vessel_levels.get(definition.unlock_id, 0)) > 0


func vessel_for_unlock(unlock_id: String) -> Resource:
	for definition in VESSEL_DEFINITIONS.all():
		if definition.unlock_id == unlock_id:
			return definition
	return null


func unlock_vessel(vessel: String) -> bool:
	var definition: Resource = vessel_definition(vessel)
	if definition == null or definition.unlock_id == "" or vessel_is_unlocked(vessel) or not has_ship_lab():
		return false
	var costs: Dictionary = research_costs(definition.unlock_id)
	if not can_afford_resources(costs):
		return false
	for resource_type in costs:
		bank_inventory.withdraw(String(resource_type), int(costs[resource_type]))
	vessel_levels[definition.unlock_id] = 1
	vessel_upgraded.emit(definition.unlock_id)
	return true


func upgrade_def(id: String) -> Dictionary:
	for definition in VESSEL_DEFINITIONS.all():
		for upgrade in definition.upgrades:
			if upgrade.upgrade_id == id:
				return {"id": upgrade.upgrade_id, "vessel": definition.definition_id,
					"name": upgrade.display_name, "desc": upgrade.description,
					"cost": upgrade.base_cost, "max_level": upgrade.max_level,
					"icon": upgrade.icon, "resource": upgrade}
	return {}


func upgrades_for(vessel: String) -> Array:
	var out: Array = []
	var definition: Resource = vessel_definition(vessel)
	if definition == null:
		return out
	for upgrade in definition.upgrades:
		out.append({"id": upgrade.upgrade_id, "vessel": vessel,
			"name": upgrade.display_name, "desc": upgrade.description,
			"cost": upgrade.base_cost, "max_level": upgrade.max_level,
			"icon": upgrade.icon, "resource": upgrade})
	return out


func upgrade_level(id: String) -> int:
	return int(vessel_levels.get(id, 0))


func upgrade_maxed(id: String) -> bool:
	var d: Dictionary = upgrade_def(id)
	return d.is_empty() or upgrade_level(id) >= int(d.max_level)


func upgrade_cost(id: String) -> int:
	var d: Dictionary = upgrade_def(id)
	if d.is_empty():
		return 0
	return int(d.cost) * (upgrade_level(id) + 1)


func can_buy_upgrade(id: String) -> bool:
	return has_ship_lab() and not upgrade_maxed(id) and can_afford(upgrade_cost(id))


func buy_upgrade(id: String) -> bool:
	if not can_buy_upgrade(id):
		return false
	if not spend(upgrade_cost(id)):
		return false
	vessel_levels[id] = upgrade_level(id) + 1
	vessel_upgraded.emit(id)
	return true


func vessel_stat(vessel: String, stat: String) -> float:
	var definition: Resource = vessel_definition(vessel)
	if definition == null:
		return 0.0
	var value: float = float(definition.base_stats.get(stat, 0.0))
	for upgrade in definition.upgrades:
		var level: int = upgrade_level(upgrade.upgrade_id)
		value += float(upgrade.additive_modifiers.get(stat, 0.0)) * level
		if upgrade.multiplicative_modifiers.has(stat):
			value *= pow(float(upgrade.multiplicative_modifiers[stat]), level)
	if definition.minimum_stats.has(stat):
		value = maxf(value, float(definition.minimum_stats[stat]))
	return value


func ship_damage(vessel: String) -> int: return int(vessel_stat(vessel, "damage"))
func ship_fire_cooldown(vessel: String) -> float: return vessel_stat(vessel, "fire_cooldown")
func ship_fire_range(vessel: String) -> float: return vessel_stat(vessel, "fire_range")
func ship_max_speed(vessel: String) -> float: return vessel_stat(vessel, "max_speed")
func ship_acceleration(vessel: String) -> float: return vessel_stat(vessel, "acceleration")

func shield_max_charges() -> int:
	var definition: Resource = VESSEL_DEFINITIONS.with_capability("shield")
	return int(vessel_stat(definition.definition_id, "shield_charges"))

func shield_recharge_time() -> float:
	var definition: Resource = VESSEL_DEFINITIONS.with_capability("shield")
	return vessel_stat(definition.definition_id, "shield_recharge")

# #56: sums cargo_capacity over ships that actually declare the "cargo"
# capability, so combat specialists (no capability, whatever their stat
# dict says) contribute nothing - data-driven rather than a vessel-id list.
# Takes the composition as an argument rather than reading it off a live
# Fleet node: GameState has no fixed reference to "the" Fleet (space and a
# planet surface each own a separate one), so the caller passes its own
# Fleet.vessel_types().
func fleet_cargo_capacity(vessel_types: PackedStringArray) -> int:
	var total: int = 0
	for vessel_type in vessel_types:
		if vessel_has_capability(vessel_type, "cargo"):
			total += int(vessel_stat(vessel_type, "cargo_capacity"))
	return total


func sync_fleet_cargo_capacity(vessel_types: PackedStringArray) -> void:
	fleet_inventory.total_capacity = fleet_cargo_capacity(vessel_types)


func transporter_load_limit() -> int:
	var definition: Resource = VESSEL_DEFINITIONS.with_capability("transport")
	return int(vessel_stat(definition.definition_id, "cargo_capacity"))

func transporter_speed() -> float:
	var definition: Resource = VESSEL_DEFINITIONS.with_capability("transport")
	return vessel_stat(definition.definition_id, "transport_speed")


const PRODUCT_SHIP: String = "interceptor"


func product_cost(product: String) -> int:
	return int(product_costs(product).get(RESOURCE_ORE, 0))


func product_costs(product: String) -> Dictionary:
	var definition: Resource = vessel_definition(product)
	if definition == null:
		return {}
	if not definition.build_resource_costs.is_empty():
		return definition.build_resource_costs.duplicate()
	return {RESOURCE_ORE: definition.build_cost} if definition.build_cost > 0 else {}


func can_produce(type: String) -> bool:
	var definition: Resource = BUILDING_DEFINITIONS.get_definition(type)
	return definition != null and "production" in definition.capabilities


func building_stock(id: int) -> int:
	return building_resource(id, RESOURCE_ORE)


func pending_orders(id: int) -> int:
	var b: Dictionary = find_building(id)
	return 0 if b.is_empty() else (b.get("orders", []) as Array).size()


func pending_orders_of(id: int, product: String) -> int:
	var b: Dictionary = find_building(id)
	if b.is_empty():
		return 0
	var n: int = 0
	for o in b.get("orders", []):
		if String(o.product) == product:
			n += 1
	return n


func order_list(id: int) -> Array:
	# What the queue panel draws: product, and how far along the one being
	# built is. Everything behind it reads as simply waiting.
	var out: Array = []
	var b: Dictionary = find_building(id)
	if b.is_empty():
		return out
	for o in b.get("orders", []):
		var product: String = String(o.product)
		out.append({
			"product": product,
			"started": bool(o.started),
			"progress": clampf(float(o.elapsed) / maxf(build_time(product), 0.001), 0.0, 1.0),
		})
	return out


func cancel_order(id: int, index: int) -> bool:
	# Refunds whatever was actually taken: a build that has started has its
	# ore in the building already, one still waiting never paid.
	var b: Dictionary = find_building(id)
	if b.is_empty():
		return false
	var orders: Array = b.get("orders", [])
	if index < 0 or index >= orders.size():
		return false
	var order: Dictionary = orders[index]
	if bool(order.started):
		var inventory: RefCounted = _inventory_for_record(b)
		var costs: Dictionary = product_costs(String(order.product))
		for resource_type in costs:
			inventory.deposit(String(resource_type), int(costs[resource_type]))
	orders.remove_at(index)
	return true


func outstanding_cost(id: int) -> int:
	return outstanding_resource_cost(id, RESOURCE_ORE)


func outstanding_costs(id: int) -> Dictionary:
	var result: Dictionary = {}
	for resource_type in resource_types():
		var need: int = outstanding_resource_cost(id, resource_type)
		if need > 0:
			result[resource_type] = need
	return result


func outstanding_resource_cost(id: int, resource_type: String) -> int:
	# What this building still needs delivered to clear everything queued.
	var b: Dictionary = find_building(id)
	if b.is_empty():
		return 0
	var need: int = 0
	for o in b.get("orders", []):
		if not bool(o.started):
			need += int(product_costs(String(o.product)).get(resource_type, 0))
	for order in b.get("research_orders", []):
		if not bool(order.started):
			need += int(research_costs(String(order.id)).get(resource_type, 0))
	return maxi(need - _inventory_for_record(b).amount(resource_type), 0)


func deposit_to_building(id: int, amount: int) -> int:
	return deposit_resource_to_building(id, RESOURCE_ORE, amount)


func deposit_resource_to_building(id: int, resource_type: String, amount: int) -> int:
	if amount <= 0:
		return 0
	var b: Dictionary = find_building(id)
	if b.is_empty():
		return 0
	return _inventory_for_record(b).deposit(resource_type, amount)


func queue_order(id: int, product: String = PRODUCT_SHIP) -> bool:
	var b: Dictionary = find_building(id)
	if b.is_empty() or not can_produce(b.type):
		return false
	var definition: Resource = vessel_definition(product)
	if definition == null or not definition.fleet_eligible \
			or not vessel_is_unlocked(product):
		return false
	(b.orders as Array).append({"product": product, "elapsed": 0.0, "started": false})
	return true


func _advance_production(delta: float) -> void:
	for b in buildings:
		if not can_produce(b.type):
			continue
		var orders: Array = b.get("orders", [])
		if orders.is_empty():
			continue

		# ONE at a time, in order. A queue the player can watch and cancel
		# has to have a thing being built and things waiting behind it -
		# clearing the whole queue the instant the ore lands (which is what
		# this did before #23) leaves nothing to see or cancel.
		var order: Dictionary = orders[0]
		var product: String = String(order.product)
		var costs: Dictionary = product_costs(product)
		var inventory: RefCounted = _inventory_for_record(b)
		var definition: Resource = vessel_definition(product)

		if not bool(order.started):
			var affordable := true
			for resource_type in costs:
				if inventory.amount(String(resource_type)) < int(costs[resource_type]):
					affordable = false
					break
			if not affordable:
				continue
			for resource_type in costs:
				inventory.withdraw(String(resource_type), int(costs[resource_type]))
			order.started = true

		order.elapsed = float(order.elapsed) + delta
		if float(order.elapsed) < build_time(product):
			continue

		orders.pop_front()
		# A finished combat hull launches from the crafter and physically flies
		# to the mothership hangar. Hub transporters are provisioned by hubs and
		# never enter this production path.
		var mothership: Variant = get_mothership_position()
		if mothership == null:
			stored_vessels.append(product)
		else:
			vessel_deliveries.append({"type": product, "from": b.position,
				"to": mothership, "progress": 0.0})
		order_completed.emit(int(b.id), product)


func queue_lab_research(lab_id: int, upgrade_id: String) -> bool:
	var lab: Dictionary = find_building(lab_id)
	if not building_has_capability(lab, "vessel_research") or upgrade_id == "":
		return false
	var orders: Array = lab.get("research_orders", [])
	var unlock_definition: Resource = vessel_for_unlock(upgrade_id)
	if not orders.is_empty() or (unlock_definition == null and upgrade_maxed(upgrade_id)):
		return false
	orders.append({"id": upgrade_id, "elapsed": 0.0, "started": false})
	lab.research_orders = orders
	return true


func lab_research_order(lab_id: int) -> Dictionary:
	var lab: Dictionary = find_building(lab_id)
	var orders: Array = lab.get("research_orders", [])
	return {} if orders.is_empty() else orders[0]


func research_cost(id: String) -> int:
	return int(research_costs(id).get(RESOURCE_ORE, 0))


func research_costs(id: String) -> Dictionary:
	var unlock_definition: Resource = vessel_for_unlock(id)
	if unlock_definition != null:
		if not unlock_definition.unlock_resource_costs.is_empty():
			return unlock_definition.unlock_resource_costs.duplicate()
		return {RESOURCE_ORE: unlock_definition.unlock_cost} if unlock_definition.unlock_cost > 0 else {}
	var cost: int = upgrade_cost(id)
	return {RESOURCE_ORE: cost} if cost > 0 else {}


func _advance_lab_research(delta: float) -> void:
	for lab in buildings:
		if not building_has_capability(lab, "vessel_research"):
			continue
		var orders: Array = lab.get("research_orders", [])
		if orders.is_empty():
			continue
		var order: Dictionary = orders[0]
		var id: String = String(order.id)
		var unlock_definition: Resource = vessel_for_unlock(id)
		var costs: Dictionary = research_costs(id)
		var inventory: RefCounted = _inventory_for_record(lab)
		if not bool(order.started):
			var affordable := true
			for resource_type in costs:
				if inventory.amount(String(resource_type)) < int(costs[resource_type]):
					affordable = false
					break
			if not affordable:
				continue
			for resource_type in costs:
				inventory.withdraw(String(resource_type), int(costs[resource_type]))
			order.started = true
		order.elapsed = float(order.elapsed) + delta
		if float(order.elapsed) < lab_research_time():
			continue
		if unlock_definition != null:
			vessel_levels[id] = 1
		else:
			vessel_levels[id] = upgrade_level(id) + 1
		vessel_upgraded.emit(id)
		orders.pop_front()


func claim_stored_vessel(index: int) -> String:
	# Hands one finished vessel over to be crewed. Returns its type, or ""
	# when there is nothing there - the caller decides whether the fleet
	# actually has room.
	if index < 0 or index >= stored_vessels.size():
		return ""
	return String(stored_vessels[index])


func take_stored_vessel(index: int) -> String:
	var product: String = claim_stored_vessel(index)
	if product == "":
		return ""
	stored_vessels.remove_at(index)
	return product


func has_mothership() -> bool:
	return get_mothership_position() != null


func has_building_of_type(type: String) -> bool:
	for building in buildings:
		if building.type == type:
			return true
	return false


func remove_buildings_of_type(type: String) -> int:
	var kept: Array = []
	var removed_ids: Array = []
	var removed: int = 0
	for b in buildings:
		if b.type == type:
			removed += 1
			removed_ids.append(int(b.id))
		else:
			kept.append(b)
	buildings = kept
	if type == BUILDING_TRANSPORT_HUB and not removed_ids.is_empty():
		var kept_transporters: Array = []
		for transporter in transporters:
			if int(transporter.get("hub_id", 0)) not in removed_ids:
				kept_transporters.append(transporter)
		transporters = kept_transporters
	return removed


func get_mothership_position() -> Variant:
	# Where a wiped-out fleet gets rebuilt. Returns null when no mothership
	# has been built yet, so the caller can fall back to the world origin.
	for b in buildings:
		if building_has_capability(b, "bank"):
			return b.position
	return null


# --- Fleet formation -------------------------------------------------------

# Where each vessel sits relative to the fleet centre, editable at a command
# centre. Lives here (not as a const on Fleet) so a layout the player has
# arranged survives the trip to a planet's surface and back, and so a
# rebuilt fleet keeps their arrangement.
# Slots beyond BASE_FLEET_SIZE only become usable once the matching fleet
# capacity upgrade is researched, but they are defined up front so the wedge
# keeps a deliberate shape as it grows rather than having positions invented
# at unlock time.
const DEFAULT_FORMATION: Array = [
	Vector2(0, -48), Vector2(-30, -8), Vector2(30, -8), Vector2(-60, 32), Vector2(60, 32),
	Vector2(-90, 72), Vector2(90, 72), Vector2(0, 56),
]

var formation: Array = DEFAULT_FORMATION.duplicate()


func reset_formation() -> void:
	formation = DEFAULT_FORMATION.duplicate()


func rotate_formation(radians: float) -> void:
	# Pivots every slot about the fleet centre, keeping the shape intact
	# and only changing which way it faces.
	for i in range(formation.size()):
		formation[i] = formation[i].rotated(radians)


# --- Extractors ------------------------------------------------------------

# Extractors mine into their OWN local stock. They do not own a magical
# hauler: ore becomes spendable only when a hub-stationed transporter picks
# up a full load and physically delivers it to the mothership. Entries are
# {"position", "planet_id", "planet_name", "resource_type", "inventory", "mining_progress"}.
const EXTRACTOR_RATE: float = 2.0  # ore per second

var extractors: Array = []


func has_extractor_at(planet_key: String) -> bool:
	for e in extractors:
		# Old saves have no planet_id; their name remains a migration fallback.
		if String(e.get("planet_id", e.get("planet_name", ""))) == planet_key:
			return true
	return false


func extractor_index_at(planet_key: String) -> int:
	for i in range(extractors.size()):
		var extractor: Dictionary = extractors[i]
		if String(extractor.get("planet_id", extractor.get("planet_name", ""))) == planet_key:
			return i
	return -1


signal extractor_added(planet_name: String)


func add_extractor(planet_name: String, at_position: Vector2, resource_type: String = "ore",
		planet_key: String = "") -> void:
	var stable_id: String = planet_key if planet_key != "" else planet_name
	extractors.append({
		"position": at_position,
		"planet_id": stable_id,
		"planet_name": planet_name,
		"resource_type": resource_type,
		"inventory": INVENTORY.new(),
		"mining_progress": 0.0,
	})
	# An extractor is built from SPACE, with the fleet parked on the planet -
	# so the Planet node is already in the tree with its _ready() long since
	# run. Without this it kept showing no derrick until it happened to
	# despawn and respawn, which reads as the build having done nothing.
	extractor_added.emit(stable_id)


func extractor_stock(index: int) -> int:
	if index < 0 or index >= extractors.size():
		return 0
	var extractor: Dictionary = extractors[index]
	return _extractor_inventory(extractor).amount(String(extractor.get("resource_type", RESOURCE_ORE)))


func extractor_resource(index: int, resource_type: String) -> int:
	if index < 0 or index >= extractors.size():
		return 0
	return _extractor_inventory(extractors[index]).amount(resource_type)


func transfer_resource_to_extractor(index: int, resource_type: String, amount: int) -> int:
	if index < 0 or index >= extractors.size():
		return 0
	return fleet_inventory.transfer_to(_extractor_inventory(extractors[index]), resource_type, amount)


func transfer_resource_from_extractor(index: int, resource_type: String, amount: int) -> int:
	if index < 0 or index >= extractors.size():
		return 0
	return _extractor_inventory(extractors[index]).transfer_to(fleet_inventory, resource_type, amount)


func _extractor_inventory(extractor: Dictionary) -> RefCounted:
	var inventory: RefCounted = extractor.get("inventory") as RefCounted
	if inventory == null:
		inventory = INVENTORY.new()
		extractor.inventory = inventory
	# Old extractor state had one stock field whose material was described by
	# resource_type. Absorb it into that key on first access.
	if extractor.has("stock"):
		inventory.set_amount(String(extractor.get("resource_type", RESOURCE_ORE)), int(extractor.stock))
		extractor.erase("stock")
	return inventory


# --- gas burners (#54) -----------------------------------------------------
#
# Converts gas into energy at the building's own site, simulated here
# alongside extractor mining and production so it keeps running whether or
# not the player is nearby. Deliberately withdraws only from the building's
# OWN inventory, never the bank - a burner with no local gas simply stalls,
# exactly like a lab or crafter waiting on materials, rather than conjuring
# energy for free.

const GAS_BURN_RATE: float = 1.0  # gas/second
const ENERGY_PER_GAS: int = 2
# Local gas reserve a burner tries to keep topped up. Transporters treat
# falling short of this the same way they treat a queued production/research
# order (see _dispatch_transporters()'s gas_burner_gas_deficit() use).
const GAS_BURNER_BUFFER: int = 40


func gas_burner_gas_deficit(id: int) -> int:
	var b: Dictionary = find_building(id)
	if not building_has_capability(b, "gas_burner"):
		return 0
	return maxi(0, GAS_BURNER_BUFFER - building_resource(id, RESOURCE_GAS))


func _advance_gas_burners(delta: float) -> void:
	for b in buildings:
		if not building_has_capability(b, "gas_burner"):
			continue
		var inventory: RefCounted = _inventory_for_record(b)
		if inventory.amount(RESOURCE_GAS) <= 0:
			continue  # stalled - no local gas to burn
		var progress: float = float(b.get("gas_burn_progress", 0.0)) + delta * GAS_BURN_RATE
		var whole: int = mini(int(floor(progress)), inventory.amount(RESOURCE_GAS))
		if whole > 0:
			inventory.withdraw(RESOURCE_GAS, whole)
			inventory.deposit(RESOURCE_ENERGY, whole * ENERGY_PER_GAS)
			progress -= whole
		b.gas_burn_progress = progress


# Planet conquest: a planet must have every one of its capture points held
# before an extractor can be built there (see BuildController's placement
# gates). Keyed by the same stable planet_id as `extractors`, entirely
# separate from it - a planet can be conquered long before anyone builds an
# extractor on it, or never get one at all.
var planet_capture: Dictionary = {}

signal planet_conquered(planet_id: String)


func register_capture_points(planet_key: String, total: int) -> void:
	# Idempotent: landing again on a planet must not wipe points already
	# captured on a previous visit.
	if planet_capture.has(planet_key):
		return
	var captured: Array = []
	captured.resize(total)
	captured.fill(false)
	# A planet demanding zero points is vacuously already held (#55: a
	# black hole's "void" profile has no authored PlanetSetup at all, so
	# this is the only registration it ever gets) - every planet WITH real
	# points still starts unconquered, exactly as before.
	planet_capture[planet_key] = {"captured": captured, "conquered": total <= 0}


func capture_state(planet_key: String) -> Dictionary:
	return planet_capture.get(planet_key, {"captured": [], "conquered": false})


func is_point_captured(planet_key: String, index: int) -> bool:
	var captured: Array = capture_state(planet_key).get("captured", [])
	if index < 0 or index >= captured.size():
		return false
	return bool(captured[index])


func mark_point_captured(planet_key: String, index: int) -> void:
	if not planet_capture.has(planet_key):
		return
	var state: Dictionary = planet_capture[planet_key]
	var captured: Array = state.captured
	if index < 0 or index >= captured.size():
		return
	captured[index] = true
	if state.conquered:
		return
	if captured.all(func(c): return bool(c)):
		state.conquered = true
		planet_conquered.emit(planet_key)


func is_planet_conquered(planet_key: String) -> bool:
	return bool(capture_state(planet_key).get("conquered", false))


func captured_point_count(planet_key: String) -> int:
	var captured: Array = capture_state(planet_key).get("captured", [])
	var count: int = 0
	for c in captured:
		if c:
			count += 1
	return count


func total_capture_points(planet_key: String) -> int:
	return capture_state(planet_key).get("captured", []).size()


func _process(delta: float) -> void:
	# Runs in the autoload, so mining and transport continue while the player
	# is on a planet's surface or nowhere near either.
	_advance_production(delta)
	_advance_lab_research(delta)
	_advance_vessel_deliveries(delta)
	_advance_gas_burners(delta)
	for e in extractors:
		e.mining_progress = float(e.get("mining_progress", 0.0)) + delta * EXTRACTOR_RATE
		var whole: int = int(floor(float(e.mining_progress)))
		if whole > 0:
			_extractor_inventory(e).deposit(String(e.get("resource_type", RESOURCE_ORE)), whole)
			e.mining_progress = float(e.mining_progress) - whole
	_advance_transporters(delta)


func vessel_delivery_position(delivery: Dictionary) -> Vector2:
	return (delivery.from as Vector2).lerp(delivery.to as Vector2,
		clampf(float(delivery.progress), 0.0, 1.0))


func _advance_vessel_deliveries(delta: float) -> void:
	for i in range(vessel_deliveries.size() - 1, -1, -1):
		var delivery: Dictionary = vessel_deliveries[i]
		var distance: float = (delivery.from as Vector2).distance_to(delivery.to as Vector2)
		var delivery_speed: float = vessel_stat(String(delivery.type), "delivery_speed")
		if delivery_speed <= 0.0:
			delivery_speed = VESSEL_DELIVERY_SPEED
		delivery.progress = float(delivery.progress) + delta / maxf(distance / delivery_speed, 0.001)
		if float(delivery.progress) >= 1.0:
			stored_vessels.append(String(delivery.type))
			vessel_deliveries.remove_at(i)


# --- transporters (#19) ---------------------------------------------------

# Vessels stationed at a transport hub that fetch ore from the mothership and
# deliver it to whichever building is waiting on it.
#
# Simulated HERE rather than by any node, exactly like the extractor haulers
# above and for the same reason: a route the player is nowhere near still has
# to run. `progress` drives both the drawn position and the moment the ore
# actually moves, so what you see and what happens cannot drift apart.
#
# Entries are {"hub_id", "state", "target_id", "carrying", "progress",
# "from", "to"}.
# How many transporters each hub owns. Raised for EVERY hub - built already
# or not - by research, and provisioned automatically rather than crafted.
const BASE_HUB_CAPACITY: int = 2

const TRANSPORTER_IDLE: String = "idle"
const TRANSPORTER_TO_MOTHERSHIP: String = "to_mothership"
const TRANSPORTER_TO_BUILDING: String = "to_building"
const TRANSPORTER_RETURNING: String = "returning"
const TRANSPORTER_TO_EXTRACTOR: String = "to_extractor"
const TRANSPORTER_TO_MOTHERSHIP_FROM_EXTRACTOR: String = "extractor_to_mothership"
# Collecting an output resource (energy) directly from a regular building's
# own inventory - a gas burner, not an extractor - and banking it. Reuses
# `target_id` exactly like the ordinary supply path does, rather than
# `extractor_index`: the source is a building, already addressable that way.
const TRANSPORTER_TO_BUILDING_PICKUP: String = "to_building_pickup"
const TRANSPORTER_TO_MOTHERSHIP_FROM_BUILDING: String = "building_to_mothership"

var transporters: Array = []


func hub_capacity() -> int:
	# Per hub.
	var n: int = BASE_HUB_CAPACITY
	for id in unlocked:
		n += int(skill_node(id).get("hub_bonus", 0))
	return n


func hub_count() -> int:
	var n: int = 0
	for b in buildings:
		if building_has_capability(b, "transport_hub"):
			n += 1
	return n


func _add_hub_transporter(hub: Dictionary) -> void:
	transporters.append({
		"hub_id": int(hub.id), "state": TRANSPORTER_IDLE, "target_id": 0,
		"extractor_index": -1, "carrying": 0, "resource_type": RESOURCE_ORE,
		"progress": 1.0, "from": hub.position, "to": hub.position,
	})


func _provision_hub_transporters(hub: Dictionary) -> void:
	var stationed: int = 0
	for transporter in transporters:
		if int(transporter.get("hub_id", 0)) == int(hub.id):
			stationed += 1
	while stationed < hub_capacity():
		_add_hub_transporter(hub)
		stationed += 1


func _sync_hub_transporters() -> void:
	for hub in buildings:
		if building_has_capability(hub, "transport_hub"):
			_provision_hub_transporters(hub)


func transporter_position(t: Dictionary) -> Vector2:
	return (t.from as Vector2).lerp(t.to as Vector2, clampf(t.progress, 0.0, 1.0))


func _hub_position(hub_id: int) -> Variant:
	var hub: Dictionary = find_building(hub_id)
	return null if hub.is_empty() else hub.position


func _begin_leg(t: Dictionary, from: Vector2, to: Vector2, state: String) -> void:
	t.from = from
	t.to = to
	t.state = state
	t.progress = 0.0


func _transporter_inbound_to(building_id: int) -> bool:
	# Delivery-purpose states only (#54): a building can have BOTH a
	# transporter delivering it something (gas, for a burner) and a
	# separate one collecting something from it (energy) at once, since
	# they are two different transporters and two different legs. Matching
	# on target_id alone, regardless of state, would make either purpose
	# block the other from ever being dispatched to the same building.
	for t in transporters:
		if (t.state == TRANSPORTER_TO_MOTHERSHIP or t.state == TRANSPORTER_TO_BUILDING) \
				and int(t.target_id) == building_id:
			return true
	return false


func _transporter_inbound_for_pickup(building_id: int) -> bool:
	for t in transporters:
		if (t.state == TRANSPORTER_TO_BUILDING_PICKUP or t.state == TRANSPORTER_TO_MOTHERSHIP_FROM_BUILDING) \
				and int(t.target_id) == building_id:
			return true
	return false


func _transporter_inbound_to_extractor(index: int) -> bool:
	for t in transporters:
		if t.state == TRANSPORTER_TO_EXTRACTOR \
				or t.state == TRANSPORTER_TO_MOTHERSHIP_FROM_EXTRACTOR:
			if int(t.get("extractor_index", -1)) == index:
				return true
	return false


func _dispatch_transporters() -> void:
	var mothership: Variant = get_mothership_position()
	if mothership == null:
		return  # nowhere to load from
	# Supply already-queued production and research before collecting passive
	# extractor output. Extractors can refill forever, so servicing them first
	# can otherwise consume every transporter each time one becomes idle and
	# permanently starve a partly supplied order.
	for b in buildings:
		var needed_resource := ""
		for resource_type in resource_types():
			# A gas burner's ongoing gas deficit is folded in alongside
			# queued production/research costs (#54) - both are just "this
			# building wants more of resource_type", so the one dispatch
			# path already below serves both without any new transporter
			# state.
			var need: int = maxi(outstanding_resource_cost(int(b.id), resource_type),
				gas_burner_gas_deficit(int(b.id)) if resource_type == RESOURCE_GAS else 0)
			if need > 0 and bank_inventory.amount(resource_type) > 0:
				needed_resource = resource_type
				break
		if needed_resource == "":
			continue
		# One at a time per building: without this every idle transporter
		# would be sent after the same shortfall and they would all arrive
		# carrying resources nobody needs any more.
		if _transporter_inbound_to(int(b.id)):
			continue
		var chosen: Dictionary = {}
		var best_d: float = INF
		for t in transporters:
			if t.state != TRANSPORTER_IDLE:
				continue
			var here: Vector2 = transporter_position(t)
			var d: float = here.distance_squared_to(b.position)
			if d < best_d:
				best_d = d
				chosen = t
		if chosen.is_empty():
			return  # every transporter is busy
		chosen.target_id = int(b.id)
		chosen.resource_type = needed_resource
		_begin_leg(chosen, transporter_position(chosen), mothership, TRANSPORTER_TO_MOTHERSHIP)

	# A distant extractor is worth visiting only once it has a full hold ready.
	# This keeps the transporter system meaningful: mining is local until a
	# vessel physically carries a researched-sized load home.
	var load: int = transporter_load_limit()
	for i in range(extractors.size()):
		var extractor: Dictionary = extractors[i]
		var resource_id: String = String(extractor.get("resource_type", RESOURCE_ORE))
		if _extractor_inventory(extractor).amount(resource_id) < load or _transporter_inbound_to_extractor(i):
			continue
		var chosen_extractor: Dictionary = {}
		var best_extractor_distance: float = INF
		for t in transporters:
			if t.state != TRANSPORTER_IDLE:
				continue
			var d: float = transporter_position(t).distance_squared_to(extractor.position)
			if d < best_extractor_distance:
				best_extractor_distance = d
				chosen_extractor = t
		if chosen_extractor.is_empty():
			return
		chosen_extractor.extractor_index = i
		chosen_extractor.resource_type = resource_id
		chosen_extractor.target_id = 0
		_begin_leg(chosen_extractor, transporter_position(chosen_extractor), extractor.position,
			TRANSPORTER_TO_EXTRACTOR)

	# Collecting a gas burner's energy output, last: queued deliveries and
	# extractor collection both outrank it, same "supply what's needed
	# before what's merely ready" ordering _dispatch_transporters() already
	# holds for extractors over queued orders (f5c60f8).
	for b in buildings:
		if not building_has_capability(b, "gas_burner"):
			continue
		if building_resource(int(b.id), RESOURCE_ENERGY) < load or _transporter_inbound_for_pickup(int(b.id)):
			continue
		var chosen_pickup: Dictionary = {}
		var best_pickup_distance: float = INF
		for t in transporters:
			if t.state != TRANSPORTER_IDLE:
				continue
			var d: float = transporter_position(t).distance_squared_to(b.position)
			if d < best_pickup_distance:
				best_pickup_distance = d
				chosen_pickup = t
		if chosen_pickup.is_empty():
			return
		chosen_pickup.target_id = int(b.id)
		chosen_pickup.resource_type = RESOURCE_ENERGY
		chosen_pickup.extractor_index = -1
		_begin_leg(chosen_pickup, transporter_position(chosen_pickup), b.position,
			TRANSPORTER_TO_BUILDING_PICKUP)


func _advance_transporters(delta: float) -> void:
	_sync_hub_transporters()
	if transporters.is_empty():
		return
	_dispatch_transporters()
	for t in transporters:
		if t.state == TRANSPORTER_IDLE:
			continue
		var distance: float = (t.from as Vector2).distance_to(t.to as Vector2)
		var leg: float = maxf(distance / transporter_speed(), 0.0001)
		t.progress += delta / leg
		if t.progress < 1.0:
			continue
		t.progress = 1.0
		_arrive(t)


func _arrive(t: Dictionary) -> void:
	var here: Vector2 = t.to
	var hub_pos: Variant = _hub_position(int(t.hub_id))
	match t.state:
		TRANSPORTER_TO_MOTHERSHIP:
			var target: Dictionary = find_building(int(t.target_id))
			var resource_type: String = String(t.get("resource_type", RESOURCE_ORE))
			var want: int = maxi(outstanding_resource_cost(int(t.target_id), resource_type),
				gas_burner_gas_deficit(int(t.target_id)) if resource_type == RESOURCE_GAS else 0)
			var take: int = mini(mini(want, bank_inventory.amount(resource_type)), transporter_load_limit())
			if take <= 0 or target.is_empty():
				# Nothing to carry, or the building is gone. Go home empty.
				t.target_id = 0
				_begin_leg(t, here, hub_pos if hub_pos != null else here, TRANSPORTER_RETURNING)
				return
			bank_inventory.withdraw(resource_type, take)
			t.carrying = take
			_begin_leg(t, here, target.position, TRANSPORTER_TO_BUILDING)
		TRANSPORTER_TO_BUILDING:
			# The cargo moves at exactly the moment the vessel arrives.
			var resource_type: String = String(t.get("resource_type", RESOURCE_ORE))
			if deposit_resource_to_building(int(t.target_id), resource_type, int(t.carrying)) <= 0:
				# Building demolished in transit - put the cargo back rather
				# than quietly destroying it.
				bank_inventory.deposit(resource_type, int(t.carrying))
			t.carrying = 0
			t.target_id = 0
			_begin_leg(t, here, hub_pos if hub_pos != null else here, TRANSPORTER_RETURNING)
		TRANSPORTER_TO_EXTRACTOR:
			var extractor_index: int = int(t.get("extractor_index", -1))
			if extractor_index < 0 or extractor_index >= extractors.size():
				_begin_leg(t, here, hub_pos if hub_pos != null else here, TRANSPORTER_RETURNING)
				return
			var extractor: Dictionary = extractors[extractor_index]
			var load: int = transporter_load_limit()
			var resource_id: String = String(extractor.get("resource_type", RESOURCE_ORE))
			var extractor_inventory: RefCounted = _extractor_inventory(extractor)
			if extractor_inventory.amount(resource_id) < load:
				t.extractor_index = -1
				_begin_leg(t, here, hub_pos if hub_pos != null else here, TRANSPORTER_RETURNING)
				return
			extractor_inventory.withdraw(resource_id, load)
			t.carrying = load
			t.resource_type = resource_id
			_begin_leg(t, here, get_mothership_position(), TRANSPORTER_TO_MOTHERSHIP_FROM_EXTRACTOR)
		TRANSPORTER_TO_MOTHERSHIP_FROM_EXTRACTOR:
			# Bank only on arrival; cargo retains the extractor's resource type.
			bank_inventory.deposit(String(t.get("resource_type", RESOURCE_ORE)), int(t.carrying))
			t.carrying = 0
			t.extractor_index = -1
			_begin_leg(t, here, hub_pos if hub_pos != null else here, TRANSPORTER_RETURNING)
		TRANSPORTER_TO_BUILDING_PICKUP:
			var source: Dictionary = find_building(int(t.target_id))
			var resource_type: String = String(t.get("resource_type", RESOURCE_ENERGY))
			var take: int = 0 if source.is_empty() \
				else mini(building_resource(int(t.target_id), resource_type), transporter_load_limit())
			if take <= 0 or source.is_empty():
				t.target_id = 0
				_begin_leg(t, here, hub_pos if hub_pos != null else here, TRANSPORTER_RETURNING)
				return
			_inventory_for_record(source).withdraw(resource_type, take)
			t.carrying = take
			_begin_leg(t, here, get_mothership_position(), TRANSPORTER_TO_MOTHERSHIP_FROM_BUILDING)
		TRANSPORTER_TO_MOTHERSHIP_FROM_BUILDING:
			bank_inventory.deposit(String(t.get("resource_type", RESOURCE_ENERGY)), int(t.carrying))
			t.carrying = 0
			t.target_id = 0
			_begin_leg(t, here, hub_pos if hub_pos != null else here, TRANSPORTER_RETURNING)
		TRANSPORTER_RETURNING:
			t.state = TRANSPORTER_IDLE
			t.progress = 1.0


func can_afford(cost: int) -> bool:
	return bank_inventory.amount(RESOURCE_ORE) >= cost


func can_afford_resources(costs: Dictionary) -> bool:
	for resource_type in costs:
		if bank_inventory.amount(String(resource_type)) < int(costs[resource_type]):
			return false
	return true


func spend(cost: int) -> bool:
	if not can_afford(cost):
		return false
	bank_inventory.withdraw(RESOURCE_ORE, cost)
	return true