Luau AI generator for Roblox Studio

--!strict
-- ServerScriptService/SaveService.server.lua

local DataStoreService = game:GetService("DataStoreService")
local Players = game:GetService("Players")
local RunService = game:GetService("RunService")

-- GetDataStore throws in a place that was never published (and can in Studio
-- without API access). Bare up here, that error would stop this whole script
-- before anyone joins; inside pcall a failure only leaves the store nil.
local storeOk, storeResult = pcall(function()
    return DataStoreService:GetDataStore("PlayerData_v1")
end)
local store: DataStore? = if storeOk then storeResult else nil

type Profile = {
    coins: number,
    level: number,
}

local DEFAULT: Profile = { coins = 0, level = 1 }
local RETRIES = 4
local cache: { [Player]: Profile } = {}

local function keyFor(player: Player): string
    -- A numeric UserId, never a name. Names change; keys built from them orphan the save.
    return "u_" .. tostring(player.UserId)
end

local function withRetry<T>(work: () -> T): (boolean, T?)
    local backoff = 0.5
    for attempt = 1, RETRIES do
        local ok, result = pcall(work)
        if ok then
            return true, result
        end
        if attempt < RETRIES then
            task.wait(backoff)
            backoff *= 2
        end
    end
    return false, nil
end

local function load(player: Player)
    local s = store
    if not s then
        -- No store: the read fails at once, with no retries. A Studio play test
        -- goes on in memory and saves nothing; a live server kicks, as below.
        if RunService:IsStudio() then
            warn("[Save] DataStore unavailable in Studio (publish the place and turn on Game Settings > Security > Enable Studio Access to API Services to test saving); this play test will not be saved")
            cache[player] = table.clone(DEFAULT)
            return
        end
        player:Kick("Could not reach the data store. Rejoin in a moment.")
        return
    end
    local ok, data = withRetry(function()
        return s:GetAsync(keyFor(player))
    end)
    -- A failed read must not look like a fresh account, or the save that
    -- follows overwrites real progress with defaults.
    if not ok then
        player:Kick("Could not reach the data store. Rejoin in a moment.")
        return
    end
    cache[player] = (data :: Profile?) or table.clone(DEFAULT)
end

local function save(player: Player)
    local profile = cache[player]
    local s = store
    if not profile or not s then
        return -- no profile (its read failed), or no store (a Studio play test): nothing is saved
    end
    withRetry(function()
        return s:UpdateAsync(keyFor(player), function()
            return profile
        end)
    end)
end

Players.PlayerAdded:Connect(load)

Players.PlayerRemoving:Connect(function(player: Player)
    save(player)
    cache[player] = nil
end)

game:BindToClose(function()
    if RunService:IsStudio() then
        return
    end
    for _, player in Players:GetPlayers() do
        save(player)
    end
end)