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src/ServerScriptService/ecs/systems/server/replication.ts

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+import { useEvent, World } from "@rbxts/matter"
+import { Players } from "@rbxts/services"
+import * as Components from "ReplicatedStorage/ecs/components"
+import { getEvent } from "ReplicatedStorage/remotes"
+
+type ComponentName = keyof typeof Components
+type ComponentConstructor = (typeof Components)[ComponentName]
+
+const REPLICATED_COMPONENT_NAMES: readonly ComponentName[] = ["Model", "Health"]
+
+const replicatedComponents: ReadonlySet<ComponentConstructor> = REPLICATED_COMPONENT_NAMES.reduce(
+	(set: Set<ComponentConstructor>, name: ComponentName) => {
+		return set.add(Components[name])
+	},
+	new Set()
+)
+
+getEvent("EcsReplication")
+
+function replication(world: World): void {
+	const replicationEvent = getEvent("EcsReplication")
+
+	let payload: Map<string, Map<ComponentName, { data?: Components.GooplerComponent }>> | undefined
+	for (const [_, player] of useEvent(Players, "PlayerAdded")) {
+		if (!payload) {
+			payload = new Map()
+
+			for (const [id, entityData] of world) {
+				const entityPayload: Map<ComponentName, { data?: Components.GooplerComponent }> =
+					new Map()
+				payload.set(tostring(id), entityPayload)
+
+				for (const [component, componentData] of entityData) {
+					if (replicatedComponents.has(component)) {
+						// Here we are certain that the component has the name of one of our
+						// components because it exists in our set of components.
+						entityPayload.set(tostring(component) as ComponentName, { data: componentData })
+					}
+				}
+			}
+		}
+
+		print("Sending initial payload to", player)
+		replicationEvent.FireClient(player, payload)
+	}
+
+	const changes: Map<
+		string,
+		Map<ComponentName, { data?: Components.GooplerComponent }>
+	> = new Map()
+	for (const component of replicatedComponents) {
+		// Here we are certain that the component has the name of one of our
+		// components since it came from our set.
+		const name = tostring(component) as ComponentName
+
+		for (const [id, record] of world.queryChanged(component)) {
+			const key = tostring(id)
+
+			if (!changes.has(key)) {
+				changes.set(key, new Map())
+			}
+
+			if (world.contains(id)) {
+				changes.get(key)?.set(name, { data: record.new })
+			}
+		}
+	}
+
+	if (!changes.isEmpty()) {
+		replicationEvent.FireAllClients(changes)
+	}
+}
+
+/**
+ * A system that replicates all replicated components to the client.
+ *
+ * This system runs after after all other systems to ensure any changes made are
+ * included.
+ */
+export = {
+	system: replication,
+	priority: math.huge
+}