extends Node
## HUD layer manager (D-170).
##
## Controls z-ordering and layout mode for HUD elements. Nothing gets hidden —
## fullscreen apps render on top of gameplay, insert-mode apps share the screen.
##
## Modes:
##   MODE_GAMEPLAY  — default z-level, normal layout
##   MODE_INSERT    — small overlay alongside gameplay (e.g. minimap-sized star map)
##   MODE_FULLSCREEN — takes over the screen, gameplay renders behind
##
## Groups use hierarchical paths:
##   "gameplay"                 — HUD status, minimap, prompts, stance
##   "implant/map"             — unified atlas (reach map → system → planet → regional, D-191)
##   "implant/wiki/gttr"       — Drifter's Guide reader
##   "implant/journal"         — knowledge journal
##   "implant/economics"       — economics monitor (D-181, #824)
##
## Usage:
##   HudGroups.register(self, "implant/map")
##   HudGroups.open_app("implant/map")     # fullscreen by default
##   HudGroups.open_app("implant/map", HudGroups.MODE_INSERT)
##   HudGroups.close_app()
##   HudGroups.toggle_app("implant/map")

## Emitted when an app opens, closes, or changes mode.
## mode is a HudGroups.Mode enum value.
signal app_changed(app_path: String, mode: int)

## Emitted when gameplay rendering should pause or resume.
## Fullscreen implant apps occlude gameplay — expensive renderers (world,
## fog, entities) should skip draw calls while this is true.
signal gameplay_occluded(occluded: bool)

enum Mode { GAMEPLAY, INSERT, FULLSCREEN }

## Z-index values for each mode. Gameplay is the base layer.
const Z_GAMEPLAY: int = 0
const Z_INSERT: int = 10
const Z_FULLSCREEN: int = 20
const Z_MODAL: int = 30

var _groups: Dictionary = {}  # group_path -> Array[CanvasItem]
var _active_app: String = ""  # currently focused implant app ("" = none)
var _active_mode: Mode = Mode.GAMEPLAY


func register(node: CanvasItem, group: String) -> void:
	if not _groups.has(group):
		_groups[group] = []
	if node not in _groups[group]:
		_groups[group].append(node)
	# Apply current z-level
	_apply_z(node, group)


func unregister(node: CanvasItem, group: String) -> void:
	if _groups.has(group):
		_groups[group].erase(node)


## Open an implant app in fullscreen (default) or insert mode.
func open_app(app: String, mode: Mode = Mode.FULLSCREEN) -> void:
	# Capture occlusion state BEFORE mutating — used for change detection below
	var was_occluded := _active_mode == Mode.FULLSCREEN and not _active_app.is_empty()

	# Close previous app if different
	if not _active_app.is_empty() and _active_app != app:
		_set_group_z(_active_app, Z_GAMEPLAY)
		app_changed.emit(_active_app, Mode.GAMEPLAY)

	_active_app = app
	_active_mode = mode

	# Set z-levels based on mode
	if mode == Mode.FULLSCREEN:
		_set_group_z("gameplay", Z_GAMEPLAY)
		_set_group_z(app, Z_FULLSCREEN)
	elif mode == Mode.INSERT:
		_set_group_z("gameplay", Z_GAMEPLAY)
		_set_group_z(app, Z_INSERT)

	app_changed.emit(app, mode)

	# Notify renderers about occlusion state change
	var now_occluded := mode == Mode.FULLSCREEN
	if now_occluded != was_occluded:
		gameplay_occluded.emit(now_occluded)


## Close the current app. Returns everything to gameplay z-level.
func close_app() -> void:
	var was_fullscreen := _active_mode == Mode.FULLSCREEN and not _active_app.is_empty()
	if not _active_app.is_empty():
		_set_group_z(_active_app, Z_GAMEPLAY)
		app_changed.emit(_active_app, Mode.GAMEPLAY)
	_active_app = ""
	_active_mode = Mode.GAMEPLAY
	_set_group_z("gameplay", Z_GAMEPLAY)
	if was_fullscreen:
		gameplay_occluded.emit(false)


## Toggle an app. If open, close it. If closed or different app, open it.
func toggle_app(app: String, mode: Mode = Mode.FULLSCREEN) -> void:
	if _active_app == app:
		close_app()
	else:
		open_app(app, mode)


## Check if a specific app is currently open.
func is_app_active(app: String) -> bool:
	return _active_app == app


## Check if any implant app is open.
func is_implant_active() -> bool:
	return not _active_app.is_empty()


## Get the currently active app path, or "" if none.
func get_active_app() -> String:
	return _active_app


## Get the current mode of the active app.
func get_active_mode() -> Mode:
	return _active_mode


func _apply_z(node: CanvasItem, group: String) -> void:
	if group == "gameplay":
		node.z_index = Z_GAMEPLAY
	elif group.begins_with("implant/"):
		if group == _active_app:
			node.z_index = Z_FULLSCREEN if _active_mode == Mode.FULLSCREEN else Z_INSERT
		else:
			node.z_index = Z_GAMEPLAY
	elif group == "modal":
		node.z_index = Z_MODAL


func _set_group_z(group: String, z: int) -> void:
	if not _groups.has(group):
		return
	for node: CanvasItem in _groups[group]:
		if is_instance_valid(node):
			node.z_index = z