extends Control
class_name OptionSetList

const POINTER_VELOCITY_DECAYING_FACTOR: float = PI
const POINTER_VELOCITY_BOOST_FACTOR: float = 1.25
const EXACT_SELECTION: bool = false

signal item_selected		# (idx: int, text: String)
signal nothing_selected		# ()

export var autowrap			:= true

var v_scroll_bar			: VScrollBar
var sensor					: PointerInputSensor
var is_pointer_dragging		:= false
var pointer_drag_velocity	:= 0.0
var when_last_dragged		:= 0

var labels					: Control
var labels_end_positions:	Array
var labels_sizes			: Array

var items					: Array
var selected_idx			:= -1
var is_dirty				:= true

var normal_style			: StyleBoxFlat
var selected_style			: StyleBoxFlat
var border_size				:= 5

onready var font			: Font = get_font("font")
onready var screen_dpcm		: float = float(OS.get_screen_dpi()) / 2.54

func _init():
	self.anchor_right			= 1.0
	self.anchor_bottom			= 1.0
	self.rect_clip_content		= true
	
	labels						= Control.new()
	labels.anchor_right			= 1.0
	labels.anchor_bottom		= 1.0
	labels.mouse_filter			= Control.MOUSE_FILTER_IGNORE
	labels.name					= "labels"
	add_child(labels)
	
	v_scroll_bar					= VScrollBar.new()
	v_scroll_bar.anchor_left		= 1.0
	v_scroll_bar.anchor_bottom		= 1.0
	v_scroll_bar.grow_horizontal	= Control.GROW_DIRECTION_BEGIN
	v_scroll_bar.name				= "v_scroll_bar"
	add_child(v_scroll_bar)
	
	sensor						= PointerInputSensor.new()
	sensor.anchor_right			= 1.0
	sensor.anchor_bottom		= 1.0
	sensor.name					= "sensor"
	add_child(sensor)
	
	normal_style = StyleBoxFlat.new()
	normal_style.border_width_bottom = border_size
	normal_style.border_color = Color.white * 0.333
	normal_style.bg_color = Color.transparent
	
	selected_style = StyleBoxFlat.new()
	selected_style.border_width_bottom = border_size
	selected_style.border_color = Color.white * 0.333
	selected_style.bg_color = Color.dimgray
	
	connect("resized", self, "mark_as_dirty")
	
	sensor.connect("on_press", self, "pointer_input_on_press_handler")
	sensor.connect("on_drag", self, "pointer_input_on_drag_handler")
	sensor.connect("on_end_drag", self, "pointer_input_on_end_drag_handler")
	sensor.connect("on_click", self, "pointer_input_on_click_handler")
	sensor.connect("on_scroll", self, "pointer_input_on_scroll_handler")


func mark_as_dirty():
	is_dirty = true


func add_item(text: String):
	items.append(text)
	is_dirty = true


func add_items(texts: Array):
	items.append_array(texts)
	is_dirty = true


func set_item(index: int, text: String):
	items[index] = text
	is_dirty = true


func set_items(indices: Array, texts: Array):
	for idx in indices.size():
		items[indices[idx]] = texts[idx]
	is_dirty = true


func remove_item(index: int):
	items.remove(index)
	is_dirty = true


func remove_items(indices: Array):
	indices.sort()
	var idx := indices.size()-1
	while idx >= 0:
		items.remove(indices[idx])
		idx -= 1
	is_dirty = true


func clear_items():
	items.clear()
	v_scroll_bar.value = 0.0
	is_dirty = true


func build_labels():
	
	var num_of_labels := int(min(
		items.size(),
		ceil(labels.rect_size.y / (font.get_height() + border_size)) + 1
	))
	
	var delta := num_of_labels - labels.get_child_count()
	
	while delta > 0:
		var label := Label.new()
		label.autowrap = autowrap
		label.anchor_right = 1.0
		label.valign = Label.VALIGN_TOP
		labels.add_child(label)
		delta -= 1
	
	while delta < 0:
		var label := labels.get_child(0) as Label
		labels.remove_child(label)
		label.free()
		delta += 1
	
	labels_end_positions.clear()
	labels_sizes.clear()
	
	if num_of_labels == 0:
		return
	
	var position		:= 0.0
	var proto_label		:= labels.get_child(0) as Label
	var line_spacing	:= proto_label.get_constant("line_spacing")
	var line_height		:= proto_label.get_line_height()
	for it in items:
		proto_label.text = it
		var line_count := proto_label.get_line_count()
		var height := line_count * line_height + (line_count - 1) * line_spacing + border_size
		
		position += height
		labels_end_positions.append(position)
		labels_sizes.append(height)


func _process(delta):
	
	if is_dirty:
		build_labels()
		is_dirty = false
	
	var viewable_ratio := 1.0
	var viewable_height := labels.rect_size.y
	if items.size() > 0:
		viewable_ratio = viewable_height / float(labels_end_positions.back())
	
	v_scroll_bar.min_value = 0
	v_scroll_bar.max_value = viewable_height / viewable_ratio
	v_scroll_bar.visible = viewable_ratio < 1.0
	v_scroll_bar.page = viewable_height
	
	var labels_offset := v_scroll_bar.value
	var idx_offset := labels_end_positions.bsearch(labels_offset)
	
	var idx := idx_offset
	for label in labels.get_children():
		
		if idx >= items.size():
			label.visible = false
			continue
		
		label.visible = true
		label.text = items[idx]
		label.rect_size.y = labels_sizes[idx]
		label.rect_position.y = labels_end_positions[idx] - labels_sizes[idx] - labels_offset
		
		if idx == selected_idx:
			label.add_stylebox_override("normal", selected_style)
		else:
			label.add_stylebox_override("normal", normal_style)
		
		idx += 1
	
	var right_margin = - v_scroll_bar.rect_size.x if v_scroll_bar.visible else 0.0
	labels.margin_right = right_margin
	sensor.margin_right = right_margin
	
	# Apply drag movement inertia.
	if is_pointer_dragging == false && abs(pointer_drag_velocity) > 0.5:
		pointer_drag_velocity *= clamp((1.0 - POINTER_VELOCITY_DECAYING_FACTOR * delta), 0.0, 1.0)
		v_scroll_bar.value -= pointer_drag_velocity * delta


func get_item_at_position(mouse_position: Vector2) -> int:
	if items.size() == 0:
		return -1
	
	var labels_offset		:= v_scroll_bar.value
	var position			:= mouse_position.y + labels_offset
	var item_idx			:= labels_end_positions.bsearch(position)
	
	return int(min(item_idx, items.size()-1)) # Return last item when position is below it.


func select(index: int):
	selected_idx = index
	emit_signal("item_selected", selected_idx, items[selected_idx])


func unselect():
	selected_idx = -1
	emit_signal("nothing_selected")


func pointer_input_on_press_handler(pointer: PointerInputSensor.PointerInputData):
	is_pointer_dragging = true
	grab_focus()


func pointer_input_on_drag_handler(pointer: PointerInputSensor.PointerInputData):
	is_pointer_dragging = true
	var reported_velocity_abs := abs(pointer.velocity.y)
	var relative_velocity := pointer.relative_position.y * Engine.get_frames_per_second()
	var relative_velocity_abs := abs(relative_velocity)
	pointer_drag_velocity = pointer.velocity.y if reported_velocity_abs > relative_velocity_abs else relative_velocity
	v_scroll_bar.value -= pointer.relative_position.y
	when_last_dragged = OS.get_ticks_msec()


func pointer_input_on_end_drag_handler(pointer: PointerInputSensor.PointerInputData):
	is_pointer_dragging = false
	if OS.get_ticks_msec() - when_last_dragged > 20:
		pointer_drag_velocity = 0.0
	else:
		pointer_drag_velocity *= POINTER_VELOCITY_BOOST_FACTOR


func pointer_input_on_click_handler(pointer: PointerInputSensor.PointerInputData):
	var selected_idx := get_item_at_position(pointer.current_position - rect_global_position)
	if selected_idx >= 0:
		select(selected_idx)
		emit_signal("item_selected", selected_idx)
	else:
		unselect()
		emit_signal("nothing_selected")


func pointer_input_on_scroll_handler(pointer: PointerInputSensor.PointerInputData):
	pointer_drag_velocity -= pointer.scroll * POINTER_VELOCITY_BOOST_FACTOR * screen_dpcm