add gs

RCCService2018/content/LuaPackages/PurchasePrompt/Thunk.lua

@@ -0,0 +1,85 @@
+--[[
+	An upgraded version of Rodux's thunk middleware that describes a table
+	format for thunks. This allows them to be named (via the `type` field)
+	and gives us cleaner methods for dependency injection via providing
+	services to our middleware that can be threaded into any thunks that
+	might request them
+]]
+local Symbol = require(script.Parent.Symbol)
+
+local Thunk = {}
+
+local ThunkTag = Symbol.named("ThunkTag")
+
+function Thunk.middleware(services)
+	services = services or {}
+
+	return function(nextDispatch, store)
+		--[[
+			This middleware doesn't need to do anything during initialization
+			so we go straight to returning the wrapped dispatch function
+		]]
+		return function(action)
+			if action[ThunkTag] == true then
+				local injectedServices = {}
+
+				for _, service in pairs(action.requiredServices) do
+					local providedService = services[service]
+
+					if providedService == nil then
+						error((
+							"Service with key %s is a dependency but was not provided"
+						):format(service))
+					end
+
+					injectedServices[service] = providedService
+				end
+
+				--[[
+					By convention, we return the result of our thunk operation.
+					This value is not guaranteed to have any particular form or
+					meaning, but it prevents our middleware from conditionally returning,
+					which is a dangerous pattern in Lua.
+				]]
+				return action(store, injectedServices)
+			else
+				return nextDispatch(action)
+			end
+		end
+	end
+end
+
+function Thunk.new(name, requiredServices, onInvoke)
+	assert(typeof(name) == "string", "Bad arg #1: name must be a string")
+	assert(requiredServices == nil or typeof(requiredServices) == "table",
+		"Bad arg #2: requiredServices must be a table or nil")
+	assert(typeof(onInvoke) == "function", "Bad arg #3: onInvoke must be a function")
+
+	requiredServices = requiredServices or {}
+
+	return setmetatable({
+		[ThunkTag] = true,
+		type = name,
+		requiredServices = requiredServices,
+	}, {
+		__call = function(self, ...)
+			onInvoke(...)
+		end,
+	})
+end
+
+function Thunk.test(thunk, store, providedServices)
+	assert(typeof(thunk) == "table" and thunk[ThunkTag] == true,
+		"Test Error - Bad arg #1: Must provide a valid thunk")
+
+	if #thunk.requiredServices > 0 then
+		for _, service in ipairs(thunk.requiredServices) do
+			assert(providedServices[service] ~= nil,
+				"Test Error - Bad arg #3: Missing required service "..tostring(service))
+		end
+	end
+
+	return thunk(store, providedServices)
+end
+
+return Thunk