--[[**
	<description>
	Run this once to combine all keys provided into one "main key".
	Internally, this means that data will be stored in a table with the key mainKey.
	This is used to get around the 2-DataStore2 reliability caveat.
	</description>

	<parameter name = "mainKey">
	The key that will be used to house the table.
	</parameter>

	<parameter name = "...">
	All the keys to combine under one table.
	</parameter>
**--]]
function DataStore2.Combine(mainKey, ...)
	for _, name in ipairs({...}) do
		combinedDataStoreInfo[name] = mainKey
	end
end

function DataStore2.ClearCache()
	DataStoreCache = {}
end

function DataStore2.SaveAll(player)
	if DataStoreCache[player] then
		for _, dataStore in pairs(DataStoreCache[player]) do
			if dataStore.combinedStore == nil then
				dataStore:Save()
			end
		end
	end
end

DataStore2.SaveAllAsync = Promise.promisify(DataStore2.SaveAll)

function DataStore2.PatchGlobalSettings(patch)
	for key, value in pairs(patch) do
		assert(Settings[key] ~= nil, "No such key exists: " .. key)
		-- TODO: Implement type checking with this when osyris' t is in
		Settings[key] = value
	end
end

function DataStore2.__call(_, dataStoreName, player)
	assert(
		typeof(dataStoreName) == "string" and IsPlayer.Check(player),
		("DataStore2() API call expected {string dataStoreName, Player player}, got {%s, %s}")
		:format(
			typeof(dataStoreName),
			typeof(player)
		)
	)

	if DataStoreCache[player] and DataStoreCache[player][dataStoreName] then
		return DataStoreCache[player][dataStoreName]
	elseif combinedDataStoreInfo[dataStoreName] then
		local dataStore = DataStore2(combinedDataStoreInfo[dataStoreName], player)

		dataStore:BeforeSave(function(combinedData)
			for key in pairs(combinedData) do
				if combinedDataStoreInfo[key] then
					local combinedStore = DataStore2(key, player)
					local value = combinedStore:Get(nil, true)
					if value ~= nil then
						if combinedStore.combinedBeforeSave then
							value = combinedStore.combinedBeforeSave(clone(value))
						end
						combinedData[key] = value
					end
				end
			end

			return combinedData
		end)

		local combinedStore = setmetatable({
			combinedName = dataStoreName,
			combinedStore = dataStore,
		}, {
			__index = function(_, key)
				return CombinedDataStore[key] or dataStore[key]
			end,
		})

		if not DataStoreCache[player] then
			DataStoreCache[player] = {}
		end

		DataStoreCache[player][dataStoreName] = combinedStore
		return combinedStore
	end

	local dataStore = {
		Name = dataStoreName,
		UserId = player.UserId,
		callbacks = {},
		beforeInitialGet = {},
		afterSave = {},
		bindToClose = {},
	}

	dataStore.savingMethod = SavingMethods[Settings.SavingMethod].new(dataStore)

	setmetatable(dataStore, DataStoreMetatable)

	local saveFinishedEvent, isSaveFinished = Instance.new("BindableEvent"), false
	local bindToCloseEvent = Instance.new("BindableEvent")

	local bindToCloseCallback = function()
		if not isSaveFinished then
			-- Defer to avoid a race between connecting and firing "saveFinishedEvent"
			Promise.defer(function()
				bindToCloseEvent:Fire() -- Resolves the Promise.race to save the data
			end)

			saveFinishedEvent.Event:Wait()
		end

		local value = dataStore:Get(nil, true)

		for _, bindToClose in ipairs(dataStore.bindToClose) do
			bindToClose(player, value)
		end
	end

	local success, errorMessage = pcall(function()
		game:BindToClose(function()
			if bindToCloseCallback == nil then
				return
			end
	
			bindToCloseCallback()
		end)
	end)
	if not success then
		warn("DataStore2 could not BindToClose", errorMessage)
	end

	Promise.race({
		Promise.fromEvent(bindToCloseEvent.Event),
		Promise.fromEvent(player.AncestryChanged, function()
			return not player:IsDescendantOf(game)
		end),
	}):andThen(function()
		dataStore:SaveAsync():andThen(function()
			--print("player left, saved", dataStoreName)
		end):catch(function(error)
			-- TODO: Something more elegant
			warn("error when player left!", error)
		end):finally(function()
			isSaveFinished = true
			saveFinishedEvent:Fire()
		end)

		--Give a long delay for people who haven't figured out the cache :^(
		return Promise.delay(40):andThen(function() 
			DataStoreCache[player] = nil
			bindToCloseCallback = nil
		end)
	end)

	if not DataStoreCache[player] then
		DataStoreCache[player] = {}
	end

	DataStoreCache[player][dataStoreName] = dataStore

	return dataStore
end

DataStore2.Constants = Constants

return setmetatable(DataStore2, DataStore2)