-- ================
-- Private helpers
-- ================
local setmetatable = setmetatable

-- Internal class constructor
local class = function(...)
  local klass = {}
  klass.__index = klass
  klass.__call = function(_,...) return klass:new(...) end
  function klass:new(...)
    local instance = setmetatable({}, klass)
    klass.__init(instance, ...)
    return instance
  end
  return setmetatable(klass,{__call = klass.__call})
end

local Node = class()
Node.__tostring = function(n)
	local res = 'Node %d (%d neighbours)'
	res = res:format(n.id, #n.neighbours)
	for _,nn in pairs(n.neighbours) do
		res = res..('\n=> %d'):format(nn.id)
	end
	return res
end

function Node:__init( id )
	self.id = id
	self.neighbours = {}
end

function Node:link( node )
	table.insert(self.neighbours, node)
end

return Node