jecs/demo/src/ReplicatedStorage/systems/receive_replication.luau

local types = require("../types")
local jecs = require(game:GetService("ReplicatedStorage").ecs)
local remotes = require("../remotes")
local collect = require("../collect")
local components = require("../components")


local client_ids: {[jecs.Entity]: jecs.Entity } = {}

local function ecs_ensure_entity(world: jecs.World, id: jecs.Entity)
	local e = 0

	local ser_id = id
	local deser_id = client_ids[ser_id]
	if deser_id then
		if deser_id == 0 then
			local new_id = world:entity()
			client_ids[ser_id] = new_id
			deser_id = new_id
		end
	else
		if not world:exists(ser_id)
			or (world:contains(ser_id) and not world:get(ser_id, jecs.Name))
		then
			deser_id = world:entity()
		else
			if world:contains(ser_id) and world:get(ser_id, jecs.Name) then
				deser_id = ser_id
			else
				deser_id = world:entity()
			end
		end
		client_ids[ser_id] = deser_id
	end

	e = deser_id

	return e
end

-- local rel_render = `e{jecs.ECS_ID(rel)}v{jecs.ECS_GENERATION(rel)}`
-- local tgt_render = `e{jecs.ECS_ID(tgt)}v{jecs.ECS_GENERATION(tgt)}`
-- local function ecs_deser_pairs_str(world, token)
-- 	local tokens = string.split(token, ",")
-- 	local rel = tonumber(tokens[1]) :: jecs.Entity
-- 	local tgt = tonumber(tokens[2]) :: jecs.Entity

-- 	rel = ecs_ensure_entity(world, rel)
-- 	tgt = ecs_ensure_entity(world, tgt)

-- 	return jecs.pair(rel, tgt)
-- end

local function ecs_deser_pairs(world, rel, tgt)
	rel = ecs_ensure_entity(world, rel)
	tgt = ecs_ensure_entity(world, tgt)

	return jecs.pair(rel, tgt)
end

local snapshots = collect(remotes.replication.OnClientEvent)

return function(world: jecs.World)
	for entity in world:each(components.Destroy) do
		client_ids[entity] = nil
	end
    for snapshot in snapshots do
        for ser_id, map in snapshot do
        	local id = (tonumber(ser_id) :: any) :: jecs.Entity
            if jecs.IS_PAIR(id) and map.pair then
            	id = ecs_deser_pairs(world, map.relation, map.target)
            elseif id then
            	id = ecs_ensure_entity(world, id)
            end
            -- if not id then
            --    	id = ecs_deser_pairs_str(world, ser_id)
            -- else
            --    	id = ecs_ensure_entity(world, id)
            -- end
            local members = world:get(id, components.NetworkedMembers)

            local set = map.set
            if set then
                if jecs.is_tag(world, id) then
                   	for _, entity in set do
                       	entity = ecs_ensure_entity(world, entity)
                  		world:add(entity, id)
                   	end
                else
	                local values = map.values :: { any }
	                for i, entity in set do
						entity = ecs_ensure_entity(world, entity)
						local value = values[i]
						if members then
							for _, member in members do
								local data = value[member] :: {jecs.Entity} | jecs.Entity -- targets
								if typeof(data) == "table" then
									for pos, tgt in data :: { jecs.Entity } do
										data[pos] = ecs_ensure_entity(world, tgt)
									end
								else
									value[member] = ecs_ensure_entity(world, data :: any)
								end
							end
						end
						world:set(entity, id, value)
                   	end
			    end
            end

            local removed = map.removed

            if removed then
                for _, entity in removed do
                    entity = ecs_ensure_entity(world, entity)
                    world:remove(entity, id)
                end
            end
        end
    end
end