class_name Inventory
extends RefCounted
## Slot-based inventory with stacking. Backs the player, chests and (later)
## grave bags, so moving items is the same operation everywhere.
##
## Pure data: no nodes, no UI. Each slot is either null or {"id": String,
## "count": int}. UI widgets render it and listen to `changed`; mutations from
## gameplay go through Actions (see docs/SURVIVAL_DESIGN.md §3).

signal changed

var slots: Array = []

func _init(size: int = 40) -> void:
	slots.resize(size)

func size() -> int:
	return slots.size()

func get_slot(i: int):
	return slots[i]

func set_slot(i: int, stack) -> void:
	slots[i] = _norm(stack)
	changed.emit()

## Looked up at runtime rather than via the ItemDB global, so this plain data
## class also compiles in contexts that load it before autoloads exist (tests,
## a future headless server tool).
static func _stack_max(id: String) -> int:
	var db := (Engine.get_main_loop() as SceneTree).root.get_node_or_null("ItemDB")
	return db.stack_size(id) if db != null else 50

static func _norm(stack):
	if stack == null or int(stack.count) <= 0:
		return null
	return {"id": String(stack.id), "count": int(stack.count)}

func count(id: String) -> int:
	var n := 0
	for s in slots:
		if s != null and s.id == id:
			n += s.count
	return n

## How many of `id` would fit right now.
func space_for(id: String) -> int:
	var cap := _stack_max(id)
	var room := 0
	for s in slots:
		if s == null:
			room += cap
		elif s.id == id:
			room += cap - s.count
	return room

## Adds up to `n` of `id`, topping up existing stacks first. Returns the
## leftover that didn't fit (0 = everything fitted).
func add(id: String, n: int) -> int:
	var cap := _stack_max(id)
	for s in slots:
		if n <= 0:
			break
		if s != null and s.id == id and s.count < cap:
			var take := mini(cap - s.count, n)
			s.count += take
			n -= take
	for i in range(slots.size()):
		if n <= 0:
			break
		if slots[i] == null:
			var take := mini(cap, n)
			slots[i] = {"id": id, "count": take}
			n -= take
	changed.emit()
	return n

## Removes `n` of `id` (from the last stacks first, so the hotbar keeps its
## items longest). Returns false and changes nothing if there aren't enough.
func remove(id: String, n: int) -> bool:
	if count(id) < n:
		return false
	for i in range(slots.size() - 1, -1, -1):
		if n <= 0:
			break
		var s = slots[i]
		if s != null and s.id == id:
			var take := mini(s.count, n)
			s.count -= take
			n -= take
			if s.count <= 0:
				slots[i] = null
	changed.emit()
	return true

## Removes `n` from a specific slot. Returns how many were removed.
func take_from(i: int, n: int) -> int:
	var s = slots[i]
	if s == null:
		return 0
	var take := mini(s.count, n)
	s.count -= take
	if s.count <= 0:
		slots[i] = null
	changed.emit()
	return take

func has_all(inputs: Dictionary) -> bool:
	for id in inputs:
		if count(id) < int(inputs[id]):
			return false
	return true

## Moves the stack in slot `i` into `other` (stacking where possible). Whatever
## doesn't fit stays put. Used for shift-click quick-move.
func quick_move(i: int, other: Inventory) -> void:
	var s = slots[i]
	if s == null:
		return
	var left := other.add(s.id, s.count)
	slots[i] = null if left <= 0 else {"id": s.id, "count": left}
	changed.emit()

## Clicking slot `i` while holding `cursor` (a stack or null). Returns the new
## cursor stack. Left click: pick up / put down / merge / swap. Right click:
## pick up half, or put down one.
func click(i: int, cursor, right: bool):
	var s = slots[i]
	var result = cursor
	if cursor == null:
		if s == null:
			return null
		if right and s.count > 1:
			var half := int(ceil(s.count / 2.0))
			s.count -= half
			result = {"id": s.id, "count": half}
		else:
			result = s
			slots[i] = null
	elif s == null:
		if right:
			slots[i] = {"id": cursor.id, "count": 1}
			result = _norm({"id": cursor.id, "count": cursor.count - 1})
		else:
			slots[i] = cursor
			result = null
	elif s.id == cursor.id:
		var cap := _stack_max(s.id)
		var move: int = 1 if right else cursor.count
		move = mini(move, cap - s.count)
		s.count += move
		result = _norm({"id": cursor.id, "count": cursor.count - move})
	else:
		slots[i] = cursor
		result = s
	changed.emit()
	return result

## Serialisable snapshot (for saves and, later, network replication).
func to_data() -> Array:
	return slots.duplicate(true)

func load_data(data: Array) -> void:
	slots.resize(data.size())
	for i in range(data.size()):
		slots[i] = _norm(data[i]) if data[i] != null else null
	changed.emit()