refactor: move modules to packages (#41)

* refactor: move modules to `packages`

* chore: remove .vscode

packages/charm-sync/default.project.json

@@ -0,0 +1,6 @@
+{
+	"name": "CharmSync",
+	"tree": {
+		"$path": "src"
+	}
+}

packages/charm-sync/package.json

@@ -0,0 +1,16 @@
+{
+	"name": "@rbxts/charm-sync",
+	"version": "0.1.1",
+	"description": "Sync server state with clients using Charm",
+	"repository": "littensy/charm",
+	"license": "MIT",
+	"main": "src/init.luau",
+	"types": "src/index.d.ts",
+	"scripts": {
+		"prepare": "cp ../../LICENSE.md . && cp ../../README.md .",
+		"publish:wally": "wally publish"
+	},
+	"dependencies": {
+		"@rbxts/charm": "workspace:*"
+	}
+}

packages/charm-sync/src/client.luau

@@ -0,0 +1,82 @@
+local Charm = require(script.Parent.Parent.Charm)
+local patch = require(script.Parent.patch)
+local types = require(script.Parent.types)
+type SyncPayload = types.SyncPayload
+
+type ClientOptions = {
+	--[=[
+		The atoms to synchronize with the server.
+	]=]
+	atoms: { [string | number]: Charm.Atom<any> },
+	--[=[
+		Whether to ignore patches sent before the client has been hydrated.
+		Default is `true`.
+	]=]
+	ignoreUnhydrated: boolean?,
+}
+
+type ClientSyncer = {
+	--[=[
+		Applies a patch or initializes the state of the atoms with the given
+		payload from the server.
+		
+		@param ...payloads The patches or hydration payloads to apply.
+	]=]
+	sync: (self: ClientSyncer, ...SyncPayload) -> (),
+}
+
+--[=[
+	Creates a `ClientSyncer` object that receives patches from the server and
+	applies them to the local state.
+	
+	@param options The atoms to synchronize with the server.
+	@return A `ClientSyncer` object.
+]=]
+local function client(options: ClientOptions): ClientSyncer
+	local self = {} :: ClientSyncer
+
+	local atoms = options.atoms
+	local ignoreUnhydrated = options.ignoreUnhydrated ~= false
+	local hydrated = false
+
+	local function hydrate(state: { [string | number]: any })
+		hydrated = true
+
+		for key, value in next, state do
+			local atom = atoms[key]
+			atom(value)
+		end
+	end
+
+	local function apply(data: { [string | number]: any })
+		local target = {}
+
+		for key, atom in next, atoms do
+			target[key] = atom()
+		end
+
+		target = patch.apply(target, data)
+
+		for key, atom in next, atoms do
+			atom(target[key])
+		end
+	end
+
+	function self:sync(...)
+		for index = 1, select("#", ...) do
+			local payload: SyncPayload = select(index, ...)
+
+			Charm.batch(function()
+				if payload.type == "init" then
+					hydrate(payload.data)
+				elseif not ignoreUnhydrated or hydrated then
+					apply(payload.data)
+				end
+			end)
+		end
+	end
+
+	return self
+end
+
+return client

packages/charm-sync/src/index.d.ts

@@ -0,0 +1,176 @@
+import { Atom, Selector } from "@rbxts/charm";
+
+export = CharmSync;
+export as namespace CharmSync;
+
+type Cleanup = () => void;
+
+declare namespace CharmSync {
+	type AtomMap = Record<string, Atom<any>>;
+
+	type SelectorMap = Record<string, Selector<any>>;
+
+	/**
+	 * @deprecated Use `SelectorMap` instead.
+	 */
+	type MoleculeMap = SelectorMap;
+
+	/**
+	 * Infers the type of the return values produced by a map of functions.
+	 */
+	type StateOfMap<T> = {
+		readonly [P in keyof T]: T[P] extends Selector<infer State> ? State : never;
+	};
+
+	/**
+	 * Represents the removal of a value from the state.
+	 */
+	interface None {
+		readonly __none: "__none";
+	}
+
+	type MaybeNone<T> = undefined extends T ? None : never;
+
+	/**
+	 * Creates a `ClientSyncer` object that receives patches from the server and
+	 * applies them to the local state.
+	 *
+	 * @client
+	 * @param options The atoms to synchronize with the server.
+	 * @returns A `ClientSyncer` object.
+	 */
+	function client<Atoms extends AtomMap>(options: ClientOptions<Atoms>): ClientSyncer<Atoms>;
+
+	/**
+	 * Creates a `ServerSyncer` object that sends patches to the client and
+	 * hydrates the client's state.
+	 *
+	 * @server
+	 * @param options The atoms to synchronize with the client.
+	 * @returns A `ServerSyncer` object.
+	 */
+	function server<Selectors extends SelectorMap>(options: ServerOptions<Selectors>): ServerSyncer<Selectors>;
+
+	/**
+	 * Checks whether a value is `None`. If `true`, the value is scheduled to be
+	 * removed from the state when the patch is applied.
+	 *
+	 * @param value The value to check.
+	 * @returns `true` if the value is `None`, otherwise `false`.
+	 */
+	function isNone(value: unknown): value is None;
+
+	type DataTypes = {
+		[P in keyof CheckableTypes as P extends keyof CheckablePrimitives ? never : P]: CheckableTypes[P];
+	};
+
+	/**
+	 * A type that should not be made partial in patches.
+	 */
+	type DataType = DataTypes[keyof DataTypes];
+
+	/**
+	 * A partial patch that can be applied to the state to update it. Represents
+	 * the difference between the current state and the next state.
+	 *
+	 * If a value was removed, it is replaced with `None`. This can be checked
+	 * using the `sync.isNone` function.
+	 */
+	type SyncPatch<State> =
+		| MaybeNone<State>
+		| (State extends ReadonlyMap<infer K, infer V> | Map<infer K, infer V>
+				? ReadonlyMap<K, SyncPatch<V> | None>
+				: State extends Set<infer T> | ReadonlySet<infer T>
+					? ReadonlyMap<T, true | None>
+					: State extends readonly (infer T)[]
+						? readonly (SyncPatch<T> | None | undefined)[]
+						: State extends DataType
+							? State
+							: State extends object
+								? { readonly [P in keyof State]?: SyncPatch<State[P]> }
+								: State);
+
+	/**
+	 * A payload that can be sent from the server to the client to synchronize
+	 * state between the two.
+	 */
+	type SyncPayload<Selectors extends SelectorMap> =
+		| { readonly type: "init"; readonly data: StateOfMap<Selectors> }
+		| { readonly type: "patch"; readonly data: SyncPatch<StateOfMap<Selectors>> };
+
+	interface ClientOptions<Atoms extends AtomMap> {
+		/**
+		 * The atoms to synchronize with the server.
+		 */
+		atoms: Atoms;
+		/**
+		 * Whether to ignore patches sent before the client has been hydrated.
+		 * Defaults to `true`.
+		 */
+		ignoreUnhydrated?: boolean;
+	}
+
+	interface ServerOptions<Selectors extends SelectorMap> {
+		/**
+		 * The atoms to synchronize with the client.
+		 */
+		atoms: Selectors;
+		/**
+		 * The interval at which to send patches to the client, in seconds.
+		 * Defaults to `0` (patches are sent up to once per frame). Set to a
+		 * negative value to disable automatic syncing.
+		 */
+		interval?: number;
+		/**
+		 * Whether the history of state changes since the client's last update
+		 * should be preserved. This is useful for values that change multiple times
+		 * per frame, where each individual change is important. Defaults to `false`.
+		 *
+		 * If `true`, the broadcaster will send a list of payloads to the client
+		 * instead of a single payload. The client will apply each payload in order
+		 * to reconstruct the state's changes over time.
+		 */
+		preserveHistory?: boolean;
+		/**
+		 * When `true`, convert problematic sparse arrays into dictionaries
+		 * with string keys. Defaults to `true`.
+		 *
+		 * While this is mandatory for safely syncing arrays over vanilla Roblox
+		 * remotes, it can be disabled if your network library uses a custom
+		 * serialization method (i.e. Zap, ByteNet).
+		 */
+		serializeArrays?: boolean;
+	}
+
+	interface ClientSyncer<Atoms extends AtomMap> {
+		/**
+		 * Applies a patch or initializes the state of the atoms with the given
+		 * payload from the server.
+		 *
+		 * @param payloads The patches or hydration payloads to apply.
+		 */
+		sync(...payloads: SyncPayload<Atoms>[]): void;
+	}
+
+	interface ServerSyncer<Selectors extends SelectorMap> {
+		/**
+		 * Sets up a subscription to each atom that schedules a patch to be sent to
+		 * the client whenever the state changes. When a change occurs, the `callback`
+		 * is called with the player and the payloads to send.
+		 *
+		 * Note that a `payload` object should not be mutated. If you need to modify
+		 * a payload, apply the changes to a copy of the object.
+		 *
+		 * @param callback The function to call when the state changes.
+		 * @returns A cleanup function that unsubscribes all listeners.
+		 */
+		connect(callback: (player: Player, ...payloads: SyncPayload<Selectors>[]) => void): Cleanup;
+		/**
+		 * Hydrates the client's state with the server's state. This should be
+		 * called when a player joins the game and requires the server's state.
+		 *
+		 * @param player The player to hydrate.
+		 */
+		hydrate(player: Player): void;
+	}
+}

packages/charm-sync/src/init.luau

@@ -0,0 +1,16 @@
+local client = require(script.client)
+local patch = require(script.patch)
+local server = require(script.server)
+local types = require(script.types)
+
+export type SyncPayload = types.SyncPayload
+
+--[=[
+	Synchronizes state between the client and server. The server sends patches
+	to the client, which applies them to its local state.
+]=]
+return {
+	client = client,
+	server = server,
+	isNone = patch.isNone,
+}

packages/charm-sync/src/interval.luau

@@ -0,0 +1,30 @@
+local RunService = game:GetService("RunService")
+
+--[=[
+	Schedules a function to be called at a fixed interval of `seconds`.
+	
+	@param callback The function to call.
+	@param seconds The interval in seconds.
+	@return A function that cancels the interval.
+]=]
+local function interval(callback: () -> (), seconds: number): () -> ()
+	if seconds < 0 then
+		return function() end
+	end
+
+	local clock = 0
+
+	local connection = RunService.Heartbeat:Connect(function(delta)
+		clock += delta
+		if clock >= seconds then
+			clock = 0
+			callback()
+		end
+	end)
+
+	return function()
+		connection:Disconnect()
+	end
+end
+
+return interval

packages/charm-sync/src/patch.luau

@@ -0,0 +1,121 @@
+local validate = require(script.Parent.validate)
+
+local __DEV__ = _G.__DEV__
+
+--[=[
+	A special symbol that denotes the absence of a value. Used to represent
+	deleted values in patches.
+]=]
+local None = { __none = "__none" }
+
+local function isNone(value: any): boolean
+	return type(value) == "table" and value.__none == "__none"
+end
+
+--[=[
+	JSON serialization can drop the last values of a sparse array. For example,
+	`{ [1] = 1, [3] = 3 }` becomes `[1]` in some cases. Ambiguity in the
+	serialization of sparse arrays can be resolved by converting them to
+	dictionaries with string keys.
+
+	The `apply` function will convert these dictionaries back into arrays as
+	long as the target array is not sparse. This function ensures that the diff
+	function produces a patch that can be correctly applied.
+]=]
+local function stringifySparseArray(object: { any }): { [string | number]: any }
+	local maxn = table.maxn(object)
+
+	if maxn == 0 or maxn == #object then
+		-- The object is either not an array or a dense array
+		return object
+	end
+
+	local dictionary = {}
+
+	for index, value in next, object do
+		dictionary[tostring(index)] = value
+	end
+
+	return dictionary
+end
+
+--[=[
+	Compares two states and returns a patch that can be applied to the previous
+	state to produce the next state.
+
+	@param prevState The previous state.
+	@param nextState The next state.
+	@param serializeArrays Whether to convert sparse arrays into dictionaries. Defaults to `true`.
+	@returns A patch that can be applied to the previous state.
+]=]
+local function diff(prevState: { [any]: any }, nextState: { [any]: any }, serializeArrays: boolean?)
+	local patches = table.clone(nextState)
+
+	for key, previous in next, prevState do
+		local current = nextState[key]
+
+		if previous == current then
+			patches[key] = nil
+		elseif current == nil then
+			patches[key] = None
+		elseif type(previous) == "table" and type(current) == "table" then
+			patches[key] = diff(previous, current, serializeArrays)
+		end
+	end
+
+	-- Coerce sparse array patches into dictionaries
+	if serializeArrays ~= false and (prevState[1] ~= nil or nextState[1] ~= nil) then
+		patches = stringifySparseArray(patches)
+	end
+
+	if __DEV__ then
+		for key, value in next, prevState do
+			validate(value, key)
+		end
+
+		for key, value in nextState do
+			if prevState[key] ~= value then
+				validate(value, key)
+			end
+		end
+	end
+
+	return patches
+end
+
+--[=[
+	Applies a patch to a state and returns the next state.
+
+	@param state The current state.
+	@param patches The patches to apply.
+	@returns The next state.
+]=]
+local function apply(state: any, patches: any): any
+	if type(patches) == "table" and patches.__none == "__none" then
+		return nil
+	elseif type(state) ~= "table" or type(patches) ~= "table" then
+		return patches
+	end
+
+	local nextState = table.clone(state)
+	local stateIsArray = state[1] ~= nil
+
+	for key, patch in next, patches do
+		-- Diff-checking an array produces a sparse array, which will not be
+		-- preserved when converted to JSON. To prevent this, we turn string
+		-- keys back into numeric keys.
+		if stateIsArray and type(key) == "string" then
+			key = tonumber(key) or key
+		end
+
+		nextState[key] = apply(nextState[key], patch)
+	end
+
+	return nextState
+end
+
+return {
+	isNone = isNone,
+	diff = diff,
+	apply = apply,
+}

packages/charm-sync/src/server.luau

@@ -0,0 +1,262 @@
+local Players = game:GetService("Players")
+
+local Charm = require(script.Parent.Parent.Charm)
+local interval = require(script.Parent.interval)
+local patch = require(script.Parent.patch)
+local types = require(script.Parent.types)
+type SyncPayload = types.SyncPayload
+
+type ServerOptions = {
+	--[=[
+		The atoms to synchronize with the client.
+	]=]
+	atoms: { [string | number]: Charm.Atom<any> },
+	--[=[
+		The interval at which to send patches to the client, in seconds.
+		Defaults to `0` (patches are sent up to once per frame). Set to a
+		negative value to disable automatic syncing.
+	]=]
+	interval: number?,
+	--[=[
+		Whether the history of state changes since the client's last update
+		should be preserved. This is useful for values that change multiple times
+		per frame, where each individual change is important. Defaults to `false`.
+	]=]
+	preserveHistory: boolean?,
+	--[=[
+		Whether to convert problematic sparse arrays into dictionaries with
+		string keys. Defaults to `true`.
+
+		While this is mandatory for safely syncing arrays over vanilla Roblox
+		remotes, it can be disabled if your network library uses a custom
+		serialization method (i.e. Zap, ByteNet).
+	]=]
+	serializeArrays: boolean?,
+}
+
+type ServerSyncer = {
+	--[=[
+		Sets up a subscription to each atom that schedules a patch to be sent to
+		the client whenever the state changes. When a change occurs, the `callback`
+		is called with the player and the payload to send.
+
+		Note that the `payload` object should not be mutated. If you need to
+		modify the payload, apply the changes to a copy of the object.
+
+		@param callback The function to call when the state changes.
+		@return A cleanup function that unsubscribes all listeners.
+	]=]
+	connect: (self: ServerSyncer, callback: (player: Player, ...SyncPayload) -> ()) -> () -> (),
+	--[=[
+		Hydrates the client's state with the server's state. This should be
+		called when a player joins the game and requires the server's state.
+
+		@param player The player to hydrate.
+	]=]
+	hydrate: (self: ServerSyncer, player: Player) -> (),
+	--[=[
+		@deprecated For internal use only.
+	]=]
+	_sendPatch: (self: ServerSyncer, player: Player) -> (),
+}
+
+--[=[
+	Creates a `ServerSyncer` object that sends patches to the client and
+	hydrates the client's state.
+	
+	@param options The atoms to synchronize with the client.
+	@return A `ServerSyncer` object.
+]=]
+local function server(options: ServerOptions): ServerSyncer
+	local self = {} :: ServerSyncer
+	local sync: (player: Player, payload: SyncPayload) -> ()
+
+	local function createSnapshot()
+		local snapshot = {}
+
+		for key, atom in next, options.atoms do
+			snapshot[key] = atom()
+		end
+
+		return snapshot
+	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
+
+	-- If the history of state changes should be preserved, keep a list of
+	-- previous snapshots and diff-check each one from the last.
+	if options.preserveHistory then
+		local snapshots = { createSnapshot() }
+		local changed = false
+
+		function self:connect(callback)
+			local subscriptions = {}
+
+			sync = callback
+
+			local function pushSnapshot(key: string | number, current: any, previous: any)
+				local lastSnapshot = snapshots[#snapshots]
+				local previousSnapshot = snapshots[#snapshots - 1]
+
+				-- Optimize snapshots by updating the most recent snapshot if the
+				-- previous and current values are the same, since this allows us
+				-- to group multiple changes into a single snapshot.
+				if previousSnapshot and previousSnapshot[key] == previous and lastSnapshot[key] == previous then
+					lastSnapshot[key] = current
+				else
+					local nextSnapshot = table.clone(lastSnapshot)
+					nextSnapshot[key] = current
+					table.insert(snapshots, nextSnapshot)
+				end
+			end
+
+			-- 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
+				subscriptions[key] = Charm.subscribe(atom, function(current, previous)
+					pushSnapshot(key, current, previous)
+					changed = true
+				end)
+			end
+
+			local disconnect = interval(function()
+				if not changed then
+					return
+				end
+
+				local payloads: { SyncPayload } = {}
+				local lastSnapshot
+
+				for index, snapshot in next, snapshots do
+					lastSnapshot = snapshot
+
+					if index == 1 then
+						continue
+					end
+
+					table.insert(payloads, {
+						type = "patch",
+						data = patch.diff(snapshots[index - 1], snapshot, options.serializeArrays),
+					})
+				end
+
+				snapshots = { lastSnapshot }
+				changed = false
+
+				for _, player in next, Players:GetPlayers() do
+					callback(player, unpack(payloads))
+				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 payloads: { SyncPayload } = {}
+
+			for index, snapshot in next, snapshots do
+				if index == 1 then
+					continue
+				end
+
+				table.insert(payloads, {
+					type = "patch",
+					data = patch.diff(snapshots[index - 1], snapshot, options.serializeArrays),
+				})
+			end
+
+			snapshots = { snapshots[#snapshots] }
+			changed = false
+
+			sync(player, unpack(payloads))
+		end
+
+		return self
+	end
+
+	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] = Charm.subscribe(atom, function(state)
+				currentSnapshot[key] = state
+				changed = true
+			end)
+		end
+
+		local disconnect = interval(function()
+			if not changed then
+				return
+			end
+
+			local payload: SyncPayload = {
+				type = "patch",
+				data = patch.diff(previousSnapshot, currentSnapshot, options.serializeArrays),
+			}
+
+			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)
+		assert(sync, "connect() must be called before _sendPatch()")
+
+		if not changed then
+			return
+		end
+
+		local payload: SyncPayload = {
+			type = "patch",
+			data = patch.diff(previousSnapshot, currentSnapshot, options.serializeArrays),
+		}
+
+		previousSnapshot = table.clone(currentSnapshot)
+		changed = false
+
+		sync(player, payload)
+	end
+
+	return self
+end
+
+return server

packages/charm-sync/src/types.luau

@@ -0,0 +1,13 @@
+--[=[
+	A payload that can be sent from the server to the client to synchronize
+	state between the two.
+]=]
+export type SyncPayload = {
+	type: "init",
+	data: { [string | number]: any },
+} | {
+	type: "patch",
+	data: { [string | number]: any },
+}
+
+return nil

packages/charm-sync/src/validate.luau

@@ -0,0 +1,74 @@
+local SAFE_KEYS = { string = true, number = true }
+local SAFE_VALUES = { string = true, number = true, boolean = true, table = true, userdata = true, vector = true }
+
+local function isTableUnsafe(object: { [any]: any })
+	local keyType = nil
+	local objectSize = 0
+
+	-- All keys must have the same type
+	for key in next, object do
+		local currentType = type(key)
+
+		if not keyType and SAFE_KEYS[currentType] then
+			keyType = currentType
+		elseif keyType ~= currentType then
+			return true
+		end
+
+		objectSize += 1
+	end
+
+	-- If there are more keys than the length of the array, it's an array with
+	-- non-sequential keys.
+	if objectSize > #object and keyType == "number" then
+		return true
+	end
+
+	return false
+end
+
+--[=[
+	Validates a value to ensure it can be synced over a remote event.
+
+	@param value The value to validate.
+	@param key The key of the value in the table.
+	@error Throws an error if the value cannot be synced.
+]=]
+local function validate(value: any, key: any)
+	local typeOfKey = type(key)
+	local typeOfValue = type(value)
+
+	if not SAFE_KEYS[typeOfKey] then
+		error(`Invalid key type '{typeOfKey}' at key '{key}'`)
+	elseif not SAFE_VALUES[typeOfValue] then
+		error(`Invalid value type '{typeOfValue}' at key '{key}'`)
+	elseif typeOfValue == "table" then
+		if getmetatable(value) ~= nil then
+			error(`Cannot sync tables with metatables! Got {value} at key '{key}'`)
+		elseif isTableUnsafe(value) then
+			error(
+				`Cannot sync tables unsupported by remote events! The value has the key '{key}'.\n\n`
+					.. "This can be for the following reasons:\n"
+					.. "1. The object is an array with non-sequential keys\n"
+					.. "2. The object is a dictionary with mixed key types (e.g. string and number)\n\n"
+					.. "Read more: https://create.roblox.com/docs/scripting/events/remote#argument-limitations"
+			)
+		end
+	end
+
+	if typeOfValue == "number" then
+		if value ~= value then
+			error(`Cannot sync NaN at key '{key}'`)
+		elseif value == math.huge or value == -math.huge then
+			error(`Cannot sync infinity at key '{key}'`)
+		end
+	elseif typeOfKey == "number" then
+		if key == math.huge or key == -math.huge then
+			error("Cannot sync infinity as key")
+		elseif key ~= math.floor(key) then
+			error("Cannot sync non-integer number as key")
+		end
+	end
+end
+
+return validate

packages/charm-sync/wally.toml

@@ -0,0 +1,8 @@
+[package]
+name = "littensy/charm-sync"
+version = "0.1.1"
+registry = "https://github.com/UpliftGames/wally-index"
+realm = "shared"
+
+[dependencies]
+Charm = "littensy/charm@^0.8"