jecs/test/examples/luau/entities/hierarchy.luau

local jecs = require("@jecs")
local pair = jecs.pair
local ChildOf = jecs.ChildOf
local world = jecs.World.new()

local Name = world:component()
local Position = world:component()
local Star = world:component()
local Planet = world:component()
local Moon = world:component()

local Vector3
do
	Vector3 = {}
	Vector3.__index = Vector3

	function Vector3.new(x, y, z)
		x = x or 0
		y = y or 0
		z = z or 0
		return setmetatable({ X = x, Y = y, Z = z }, Vector3)
	end

	function Vector3.__add(left, right)
		return Vector3.new(left.X + right.X, left.Y + right.Y, left.Z + right.Z)
	end

	function Vector3.__mul(left, right)
		if typeof(right) == "number" then
			return Vector3.new(left.X * right, left.Y * right, left.Z * right)
		end
		return Vector3.new(left.X * right.X, left.Y * right.Y, left.Z * right.Z)
	end

	Vector3.one = Vector3.new(1, 1, 1)
	Vector3.zero = Vector3.new()
end

local function path(entity)
	local str = world:get(entity, Name)
	local parent
	while true do
		parent = world:parent(entity)
		if not parent then
			break
		end
		entity = parent
		str = world:get(parent, Name) .. "/" .. str
	end
	return str
end

local function iterate(entity, parent)
	local p = world:get(entity, Position)
	local actual = p + parent
	print(path(entity))
	print(`\{{actual.X}, {actual.Y}, {actual.Z}}`)

	for child in world:query(pair(ChildOf, entity)) do
		--print(world:get(child, Name))
		iterate(child, actual)
	end
end

local sun = world:entity()
world:add(sun, Star)
world:set(sun, Position, Vector3.one)
world:set(sun, Name, "Sun")
do
	local earth = world:entity()
	world:set(earth, Name, "Earth")
	world:add(earth, pair(ChildOf, sun))
	world:add(earth, Planet)
	world:set(earth, Position, Vector3.one * 3)

	do
		local moon = world:entity()
		world:set(moon, Name, "Moon")
		world:add(moon, pair(ChildOf, earth))
		world:add(moon, Moon)
		world:set(moon, Position, Vector3.one * 0.1)

		print(`Child of Earth? {world:has(moon, pair(ChildOf, earth))}`)
	end

	local venus = world:entity()
	world:set(venus, Name, "Venus")
	world:add(venus, pair(ChildOf, sun))
	world:add(venus, Planet)
	world:set(venus, Position, Vector3.one * 2)

	local mercury = world:entity()
	world:set(mercury, Name, "Mercury")
	world:add(mercury, pair(ChildOf, sun))
	world:add(mercury, Planet)
	world:set(mercury, Position, Vector3.one)

	iterate(sun, Vector3.zero)
end

-- Output:
--  Child of Earth? true
--  Sun
--  {1, 1, 1}
--  Sun/Mercury
--  {2, 2, 2}
--  Sun/Venus
--  {3, 3, 3}
--  Sun/Earth
--  {4, 4, 4}
--  Sun/Earth/Moon
--  {4.1, 4.1, 4.1}