-- Luanti
-- SPDX-License-Identifier: LGPL-2.1-or-later
-- Copyright (C) 2023 v-rob, Vincent Robinson <robinsonvincent89@gmail.com>

ui._elem_types = {}

function ui._new_type(base, type, type_id, id_required)
	local class = core.class(base)

	class._type = type
	class._type_id = type_id
	class._id_required = id_required
	class._handlers = setmetatable({}, {__index = base and base._handlers})

	ui._elem_types[type] = class

	return class
end

function ui.derive_elem(base, type)
	assert(core.is_subclass(base, ui.Elem))
	ui._req(type, "id")

	assert(not ui._elem_types[type],
			"Derived element name already used: '" .. type .. "'")

	return ui._new_type(base, type, base._type_id, base._id_required)
end

ui.Elem = ui._new_type(nil, "elem", 0x00, false)

function ui.Elem:new(param)
	local function make_elem(props)
		self:_init(ui._req(props, "table"))
		return self
	end

	if type(param) == "string" then
		self._id = ui._req(param, "id")
		return make_elem
	end

	self._id = ui.new_id()
	return make_elem(param)
end

function ui.Elem:_init(props)
	self._label = ui._opt(props.label, "string")

	self._groups = {}
	self._children = {}

	self._props = ui._cascade_props(props.props or props, {})
	self._styles = {}

	-- Set by parent ui.Elem
	self._parent = nil

	-- Set by ui.Window
	self._boxes = {main = true}
	self._window = nil

	if self._id_required then
		assert(not ui._is_reserved_id(self._id),
				"Element ID is required for '" .. self._type .. "'")
	end

	for _, group in ipairs(ui._opt_array(props.groups, "id", {})) do
		self._groups[group] = true
	end

	for _, child in ipairs(ui._opt_array(props.children, ui.Elem, props)) do
		if core.is_instance(child, ui.Elem) then
			assert(child._parent == nil,
					"Element '" .. child._id .. "' already has a parent")
			assert(not core.is_instance(child, ui.Root),
					"ui.Root may not be a child element")

			child._parent = self
			table.insert(self._children, child)
		end
	end

	for _, style in ipairs(ui._opt_array(props.styles, ui.Style, props)) do
		if core.is_instance(style, ui.Style) then
			table.insert(self._styles, style)
		end
	end

	for _, item in ipairs(props) do
		assert(core.is_instance(item, ui.Elem) or core.is_instance(item, ui.Style))
	end
end

function ui.Elem:_get_flat()
	local elems = {self}
	for _, child in ipairs(self._children) do
		table.insert_all(elems, child:_get_flat())
	end
	return elems
end

function ui.Elem:_encode()
	return ui._encode("Bz S", self._type_id, self._id, self:_encode_fields())
end

function ui.Elem:_encode_fields()
	local fl = ui._make_flags()

	if ui._shift_flag(fl, #self._children > 0) then
		local child_ids = {}
		for i, child in ipairs(self._children) do
			child_ids[i] = child._id
		end

		ui._encode_flag(fl, "Z", ui._encode_array("z", child_ids))
	end

	if ui._shift_flag(fl, self._label) then
		ui._encode_flag(fl, "s", self._label)
	end

	self:_encode_box(fl, self._boxes.main)

	return ui._encode_flags(fl)
end

function ui.Elem:_encode_box(fl, box)
	-- Element encoding always happens after styles are computed and boxes are
	-- populated with style indices. So, if this box has any styles applied to
	-- it, encode the relevant states.
	if not ui._shift_flag(fl, box.n > 0) then
		return
	end

	local box_fl = ui._make_flags()

	-- For each state, check if there is any styling. If there is, add it
	-- to the box's flags.
	for i = ui._STATE_NONE, ui._NUM_STATES - 1 do
		if ui._shift_flag(box_fl, box[i] ~= ui._NO_STYLE) then
			ui._encode_flag(box_fl, "I", box[i])
		end
	end

	ui._encode_flag(fl, "s", ui._encode_flags(box_fl))
end

function ui.Elem:_on_event(code, ev, data)
	-- Get the handler function for this event if we recognize it.
	local handler = self._handlers[code]
	if not handler then
		core.log("info", "Invalid event for " .. self._type_id .. ": " .. code)
		return
	end

	-- If the event handler returned a callback function for the user, call it
	-- with the event table.
	local callback = handler(self, ev, data)
	if callback then
		callback(ev)
	end
end