refactor: separate code for preserving history

src/sync/server.luau

@@ -62,32 +62,29 @@ type ServerSyncer = {
 local function server(options: ServerOptions): ServerSyncer
 	local self = {} :: ServerSyncer
 	local sync: (player: Player, payload: SyncPayload) -> ()
-	local snapshots: { { [string]: any } } = {}
-	local changed = false
 
-	-- Start the interval to send state patches over the network.
-	function self:connect(callback)
-		local cleanups = {}
-		sync = callback
-
-		local function getSnapshot()
+	local function createSnapshot()
 		local snapshot: { [string]: any } = {}
+
 		for key, atom in next, options.atoms do
 			snapshot[key] = atom()
 		end
+
 		return snapshot
 	end
 
-		local function pushSnapshot(key: string, current: any, previous: any)
-			if not options.preserveHistory then
-				if snapshots[2] then
-					snapshots[2][key] = current
-				else
-					snapshots[2] = getSnapshot()
-				end
-				return
-			end
+	if options.preserveHistory then
+		-- Preserve a history of every state change to allow for more granular
+		-- syncing with the client.
+		local snapshots: { { [string]: any } } = {}
+		local changed = false
 
+		function self:connect(callback)
+			local subscriptions = {}
+
+			sync = callback
+
+			local function pushSnapshot(key: string, current: any, previous: any)
 				local lastSnapshot = snapshots[#snapshots]
 				local previousSnapshot = snapshots[#snapshots - 1]
 
@@ -103,16 +100,16 @@ local function server(options: ServerOptions): ServerSyncer
 				end
 			end
 
-		-- Populate the initial state and snapshot for each atom.
+			-- Populate the snapshot with the initial state of each atom.
 			-- Subscribe to each atom and update the state when it changes.
 			for key, atom in next, options.atoms do
-			cleanups[key] = subscribe(atom, function(current, previous)
+				subscriptions[key] = subscribe(atom, function(current, previous)
 					pushSnapshot(key, current, previous)
 					changed = true
 				end)
 			end
 
-		snapshots[1] = getSnapshot()
+			snapshots[1] = createSnapshot()
 
 			local disconnect = setInterval(function()
 				if not changed then
@@ -145,20 +142,11 @@ local function server(options: ServerOptions): ServerSyncer
 
 			return function()
 				disconnect()
-			for _, cleanup in next, cleanups do
-				cleanup()
-			end
-		end
-	end
 
-	-- Send the initial state to a player when they join the server.
-	function self:hydrate(player)
-		assert(sync, "connect() must be called before hydrate()")
-
-		sync(player, {
-			type = "init",
-			data = snapshots[#snapshots],
-		})
+				for _, unsubscribe in next, subscriptions do
+					unsubscribe()
+				end
+			end
 		end
 
 		function self:_sendPatch(player: Player)
@@ -186,6 +174,80 @@ local function server(options: ServerOptions): ServerSyncer
 
 			sync(player, unpack(payloads))
 		end
+	else
+		-- Only send the most recent state to the client.
+		local previousSnapshot = createSnapshot()
+		local currentSnapshot = table.clone(previousSnapshot)
+		local changed = false
+
+		function self:connect(callback)
+			local subscriptions = {}
+
+			sync = callback
+
+			-- Subscribe to each atom and update the state when one changes.
+			for key, atom in next, options.atoms do
+				subscriptions[key] = subscribe(atom, function(state)
+					currentSnapshot[key] = state
+					changed = true
+				end)
+			end
+
+			local disconnect = setInterval(function()
+				if not changed then
+					return
+				end
+
+				local payload: SyncPayload = {
+					type = "patch",
+					data = patch.diff(previousSnapshot, currentSnapshot),
+				}
+
+				previousSnapshot = table.clone(currentSnapshot)
+				changed = false
+
+				for _, player in next, Players:GetPlayers() do
+					callback(player, payload)
+				end
+			end, options.interval or 0)
+
+			return function()
+				disconnect()
+
+				for _, unsubscribe in next, subscriptions do
+					unsubscribe()
+				end
+			end
+		end
+
+		function self:_sendPatch(player: Player)
+			assert(sync, "connect() must be called before _sendPatch()")
+
+			if not changed then
+				return
+			end
+
+			local payload: SyncPayload = {
+				type = "patch",
+				data = patch.diff(previousSnapshot, currentSnapshot),
+			}
+
+			previousSnapshot = table.clone(currentSnapshot)
+			changed = false
+
+			sync(player, payload)
+		end
+	end
+
+	-- Send the initial state to a player when they join the server.
+	function self:hydrate(player)
+		assert(sync, "connect() must be called before hydrate()")
+
+		sync(player, {
+			type = "init",
+			data = createSnapshot(),
+		})
+	end
 
 	return self
 end