WIP: Introduce StoreUpdateGate, for temporarily blocking store updates for its descendants

lib/GatedSignal.lua

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+--[[
+	A limited, simple implementation of a GatedSignal with the addition of a
+	gated condition.
+
+	If the signal has 'isBlocking' set, changes will be witheld until
+	'isBlocking' is reset to false..
+
+	Handlers are fired in order, and (dis)connections are properly handled when
+	executing an event.
+]]
+
+local function immutableAppend(list, ...)
+	local new = {}
+	local len = #list
+
+	for key = 1, len do
+		new[key] = list[key]
+	end
+
+	for i = 1, select("#", ...) do
+		new[len + i] = select(i, ...)
+	end
+
+	return new
+end
+
+local function immutableRemoveValue(list, removeValue)
+	local new = {}
+
+	for i = 1, #list do
+		if list[i] ~= removeValue then
+			table.insert(new, list[i])
+		end
+	end
+
+	return new
+end
+
+local GatedSignal = {}
+
+GatedSignal.__index = GatedSignal
+
+function GatedSignal.new()
+	local self = {
+		_listeners = {},
+		_isBlocking = false,
+		_shouldFireWhenUnblocked = false,
+	}
+
+	setmetatable(self, GatedSignal)
+
+	return self
+end
+
+function GatedSignal:connect(callback)
+	local listener = {
+		callback = callback,
+		disconnected = false,
+	}
+
+	self._listeners = immutableAppend(self._listeners, listener)
+
+	local function disconnect()
+		listener.disconnected = true
+		self._listeners = immutableRemoveValue(self._listeners, listener)
+	end
+
+	return {
+		disconnect = disconnect
+	}
+end
+
+function GatedSignal:fire(...)
+	if self._isBlocking then
+		self._shouldFireWhenUnblocked = true
+		return
+	end
+
+	for _, listener in ipairs(self._listeners) do
+		if not listener.disconnected then
+			listener.callback(...)
+		end
+	end
+end
+
+function GatedSignal:block()
+	if self._isBlocking then
+		return
+	end
+
+	self._isBlocking = true
+end
+
+function GatedSignal:unblock(...)
+	if not self._isBlocking then
+		return
+	end
+
+	self._isBlocking = false
+
+	if self._shouldFireWhenUnblocked then
+		self._shouldFireWhenUnblocked = false
+		self:fire(...)
+	end
+end
+
+return GatedSignal

lib/StoreUpdateGate.lua

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+local Roact = require(script.Parent.Parent.Roact)
+
+local storeKey = require(script.Parent.storeKey)
+local GatedSignal = require(script.Parent.GatedSignal)
+
+local StoreUpdateGate = Roact.Component:extend("StoreUpdateGate")
+
+function StoreUpdateGate:init()
+	local realStore = self._context[storeKey]
+
+	if not realStore then
+		error("StoreUpdateGate must be placed below a StoreProvider in the tree!")
+	end
+
+	-- The 'mock store' only exposes a subset of the real store's methods!
+	local mockStore = {}
+	mockStore.changed = GatedSignal.new()
+
+	mockStore.getState = function()
+		if self.props.shouldBlockUpdates then
+			return self.stateAtLastBlock
+		else
+			return realStore:getState()
+		end
+	end
+
+	mockStore.dispatch = function(self, action)
+		return realStore:dispatch(action)
+	end
+
+	self.changedConnection = realStore.changed:connect(function(...)
+		mockStore.changed:fire(...)
+	end)
+
+	self.mockStore = mockStore
+	self._context[storeKey] = mockStore
+
+	self.stateAtLastBlock = nil
+
+	if self.props.shouldBlockUpdates then
+		self:blockChanges()
+	end
+end
+
+function StoreUpdateGate:blockChanges()
+	self.stateAtLastBlock = self.mockStore:getState()
+	self.mockStore:block()
+end
+
+function StoreUpdateGate:unblockChanges()
+	local oldState = self.stateAtLastBlock
+	local newState = self.mockStore:getState()
+
+	self.stateAtLastBlock = nil
+	self.mockStore:unblock(oldState, newState)
+end
+
+function StoreUpdateGate:didUpdate(oldProps)
+	if self.props.shouldBlockUpdates ~= oldProps.shouldBlockUpdates then
+		if self.props.shouldBlockUpdates then
+			self:blockChanges()
+		else
+			self:unblockChanges()
+		end
+	end
+end
+
+function StoreUpdateGate:willUnmount()
+	self.changedConnection:disconnect()
+end
+
+function StoreUpdateGate:render()
+	return Roact.oneChild(self.props[Roact.Children])
+end
+
+return StoreUpdateGate

lib/StoreUpdateGate.spec.lua

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+return function()
+	local Roact = require(script.Parent.Parent.Roact)
+	local StoreProvider = require(script.Parent.StoreProvider)
+
+	local StoreUpdateGate = require(script.Parent.StoreUpdateGate)
+end