class_name PathPreview
extends Node3D
## T-1088 (Live-session feedback item 2) — mouse-over move-here marker + optimal
## path line. A Node3D placed UNDER WorldRoot by the sandbox root, so it inherits
## the single D-148 45° map rotation for free: its children live in the same
## WorldRoot-local (sim-aligned) metric space the greybox tiles do, and
## SandboxSpace.tile_to_world positions them directly.
##
## Two visuals, both children built in setup():
##   - marker: a flat PlaneMesh quad on the hovered destination subtile, lifted a
##     hair above the floor, in a distinct accent colour.
##   - line: an ImmediateMesh line strip through the tile centers of the planned
##     path, lifted slightly higher so it reads on top of the marker.
##
## The A* runs over the greybox KNOWN-tile store via the injected is_floor
## Callable (PathFinder honours the information boundary — fog is unpathable).
## Recompute is edge-triggered — on hovered-tile change, character-tile change, or
## knowledge growth — NEVER per frame (A* every frame over ~14k tiles is waste).
## Hidden whenever there is no valid path: hovering unknown/void/wall, or a
## known-floor tile with no known route.
##
## Note on knowledge_version: the root passes store.size() (monotonic — the store
## never evicts). A revealed wall REPLACING a known floor (a rekind, no size
## change) can leave the drawn line momentarily stale until the next hover/step,
## but the EXECUTED route is always safe — path_follower.gd revalidates every
## remaining tile per step and replans. Preview is advisory; the follower is
## authoritative.

## Hover-pick ray sources, injected in setup().
var _camera: Camera3D = null
var _world_root: Node3D = null

var _marker: MeshInstance3D = null
var _line: MeshInstance3D = null
var _line_mesh: ImmediateMesh = null

## Latest computed path (character tile -> hovered tile, inclusive). Empty when
## the hovered tile is unpathable. Read by the root's click handler.
var _current_path: Array[Vector3i] = []

## Edge-trigger memory — recompute only when one of these changes.
var _last_hover: Vector3i = Vector3i(2147483647, 0, 0)  # sentinel: forces first pass
var _last_char_tile: Vector3i = Vector3i(2147483647, 0, 0)
var _last_version: int = -1


## Inject the ray-pick nodes and build the two child visuals. Called by the
## sandbox root right after the preview is added under WorldRoot.
func setup(camera: Camera3D, world_root: Node3D) -> void:
	_camera = camera
	_world_root = world_root

	# Move-here marker — PlaneMesh faces +Y natively (like the floor tiles); a
	# double-sided unshaded material keeps it readable from every camera preset.
	var quad := PlaneMesh.new()
	quad.size = Vector2(SandboxConstants.SUBTILE_M, SandboxConstants.SUBTILE_M)
	_marker = MeshInstance3D.new()
	_marker.name = "MoveHereMarker"
	_marker.mesh = quad
	_marker.material_override = _flat_material(SandboxConstants.PATH_MARKER_COLOR)
	_marker.visible = false
	add_child(_marker)

	# Path line — an ImmediateMesh rebuilt on recompute.
	_line_mesh = ImmediateMesh.new()
	_line = MeshInstance3D.new()
	_line.name = "PathLine"
	_line.mesh = _line_mesh
	_line.material_override = _flat_material(SandboxConstants.PATH_LINE_COLOR)
	_line.visible = false
	add_child(_line)


## One frame of preview maintenance (called by the root while gameplay is live).
##   char_tile: the server-confirmed character tile (path origin).
##   is_floor: greybox known-floor lookup (Vector3i) -> bool.
##   knowledge_version: store.size() — bumps when new tiles are learned.
func update(char_tile: Vector3i, is_floor: Callable, knowledge_version: int) -> void:
	var hover: Variant = _hovered_tile()
	if hover == null:
		# Mouse off the ground plane (pointing at sky / degenerate ray).
		_clear_visuals()
		_last_hover = Vector3i(2147483647, 0, 0)
		return
	var hover_tile: Vector3i = hover
	if (
		hover_tile == _last_hover
		and char_tile == _last_char_tile
		and knowledge_version == _last_version
	):
		return  # nothing that affects the path changed — leave visuals as-is
	_last_hover = hover_tile
	_last_char_tile = char_tile
	_last_version = knowledge_version

	_current_path = PathFinder.find_path(char_tile, hover_tile, is_floor)
	_redraw()


## The planned path (character -> hovered), inclusive of both ends; empty when the
## hovered tile is unpathable. The root hands this to the follower on click.
func get_current_path() -> Array[Vector3i]:
	return _current_path


## Hide both visuals and forget the current path (root calls on teleport / when
## gameplay is suppressed).
func clear() -> void:
	_current_path = []
	_clear_visuals()
	_last_hover = Vector3i(2147483647, 0, 0)


# ---------------------------------------------------------------------------
# Internals
# ---------------------------------------------------------------------------


## The tile currently under the mouse, or null if the ray misses the ground. Reuses
## the facing provider's ground-plane unproject (one unproject, one place), then
## SandboxSpace.world_to_tile — WorldRoot-local metres are sim-aligned space.
func _hovered_tile() -> Variant:
	if not is_instance_valid(_camera) or not is_instance_valid(_world_root):
		return null
	if not _camera.is_inside_tree():
		return null
	var viewport := _camera.get_viewport()
	if viewport == null:
		return null
	var mouse := viewport.get_mouse_position()
	var hit_local: Variant = SandboxMouseAimProvider.ground_hit_local(
		_camera.project_ray_origin(mouse),
		_camera.project_ray_normal(mouse),
		_world_root.global_transform
	)
	if hit_local == null:
		return null
	return SandboxSpace.world_to_tile(hit_local as Vector3)


## Repaint marker + line from _current_path. Marker on the destination when a path
## exists; line only for a real (>= 2 tile) move.
func _redraw() -> void:
	if _current_path.is_empty():
		_clear_visuals()
		return
	var dest: Vector3i = _current_path[_current_path.size() - 1]
	var dest_world := SandboxSpace.tile_to_world(dest)
	_marker.position = Vector3(dest_world.x, SandboxConstants.PATH_MARKER_Y, dest_world.z)
	_marker.visible = true

	_line_mesh.clear_surfaces()
	if _current_path.size() >= 2:
		_line_mesh.surface_begin(Mesh.PRIMITIVE_LINE_STRIP)
		for tile in _current_path:
			var c := SandboxSpace.tile_to_world(tile)
			_line_mesh.surface_add_vertex(Vector3(c.x, SandboxConstants.PATH_LINE_Y, c.z))
		_line_mesh.surface_end()
		_line.visible = true
	else:
		_line.visible = false


func _clear_visuals() -> void:
	if _marker != null:
		_marker.visible = false
	if _line != null:
		_line.visible = false
		if _line_mesh != null:
			_line_mesh.clear_surfaces()


## Unshaded, double-sided, alpha-blended material — a flat overlay swatch that
## ignores scene lighting so the accent colour stays constant at any camera pitch.
func _flat_material(color: Color) -> StandardMaterial3D:
	var mat := StandardMaterial3D.new()
	mat.shading_mode = BaseMaterial3D.SHADING_MODE_UNSHADED
	mat.transparency = BaseMaterial3D.TRANSPARENCY_ALPHA
	mat.cull_mode = BaseMaterial3D.CULL_DISABLED
	mat.albedo_color = color
	mat.vertex_color_use_as_albedo = false
	return mat