Concord/fluid/eventManager.lua

local EventManager = {}
EventManager.__index = EventManager

function EventManager.new()
   local eventManager = setmetatable({
      listeners = {},
   }, EventManager)

   return eventManager
end

function EventManager:emit(name, ...)
   local listeners = self.listeners[name]

   if listeners then
      for i = 1, #listeners do
         local listener = listeners[i]
         listener[1][listener[2]](listener[1], ...)
      end
   end

   return self
end

function EventManager:register(name, listener, callback)
   local listeners = self.listeners[name]

   if not listeners then
      listeners = {count = 0}
      self.listeners[name] = listeners
   end

   listeners.count = listeners.count + 1
   listeners[listeners.count] = {listener, callback or name}

   return self
end

function EventManager:deregister(name, listener, callback)
   local listeners = self.listeners[name]

   if listeners then
      for index, other in ipairs(listeners) do
         if listener[1] == other and listener[2] == (callback or name) then
            table.remove(listeners, index)
            listeners.count = listeners.count - 1

            if callback then
               break
            end
         end
      end
   end

   return self
end

return setmetatable(EventManager, {
   __call = function(_, ...) return EventManager.new(...) end,
})