charm/packages/charm-sync/src/client.luau

local Charm = require(script.Parent.Parent.Parent.charm)
local patch = require(script.Parent.patch)
local types = require(script.Parent.types)
type AtomMap = types.AtomMap
type SyncPayload = types.SyncPayload

type ClientOptions = {
	--[=[
		The atoms to synchronize with the server.
	]=]
	atoms: AtomMap,
	--[=[
		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 atoms = options.atoms
	local ignoreUnhydrated = options.ignoreUnhydrated ~= false

	local self = {} :: ClientSyncer
	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