Script for ScriptingHelpers

local marketplaceService = game:GetService("MarketplaceService")
local Players = game:GetService("Players")

local replicatedStorage = game:GetService("ReplicatedStorage")
local eventsFolder = replicatedStorage:WaitForChild("EventsFolder")
local purchaseEvent = eventsFolder:WaitForChild("PurchaseEvent")
local savePlayerProfile = eventsFolder:WaitForChild("SavePlayerProfile") -- TODO make this a BindableFunction. Make sure that in your Datastore script, you save when this is called. It will be given the 'player' whose data to save.

local products = {} --keys: name and IDs; value has .Name, .Offers, .ApplyOffer
local idToProduct = {}
local idToAmount = {}
function CreateProduct(name, offers, applyOffer)
    --  offers: dictionary between amount offered (the key) and cost to user (the value)
    --  applyOffer: function(player, amount)
    if products[name] then error("Already have a product with name " .. name .."!") end -- Make sure we don't make a mistake (ex having 2 "Gold" products, which would break this algorithm)
    -- We need to be able to look up each offer by Amount, so turn 'offers' into a dictionary
    local offerDict = {}
    for i = 1, #offers do
        offerDict[offers[i].Amount] = offers[i]
    end
    local product = {Name = name, Offers = offerDict, ApplyOffer = applyOffer}
    products[name] = product
    for i = 1, #offers do
        idToProduct[offers[i].ID] = product
        idToAmount[offers[i].ID] = offers[i].Amount
    end
end
CreateProduct("Gold", {
    {ID = 100122331, Amount = 50, Price = 50},
    {ID = 111111111, Amount = 100, Price = 100},
    --etc
}, _G.awardGold)

-- ALTERNATIVE to above (starting at CreateProduct):

function CreateProduct(name, offers, applyOffer)
    --  offers: dictionary between amount offered (the key) and cost to user (the value)
    --  applyOffer: function(player, amount)
    if products[name] then error("Already have a product with name " .. name .."!") end -- Make sure we don't make a mistake (ex having 2 "Gold" products, which would break this algorithm)
    local product = {Name = name, Offers = offers, ApplyOffer = applyOffer}
    products[name] = product
    for i = amount, offer in pairs(offers) do
        idToProduct[offer.ID] = product
        idToAmount[offer.ID] = amount
    end
end
CreateProduct("Gold", {
    [50] = {ID = 100122331, Price = 50},
    [100] = {ID = 111111111, Price = 100},
    --etc
}, _G.awardGold)

-- END OF ALTERNATIVE. The alternative is simpler, but the "[50]" is not as descriptive as Amount=50.

purchaseEvent.OnServerEvent:connect(function(player, name, amount)
    local product = products[name]
    if not product then error(string.format("Player %s attempted to purchase amount %s of non-existent %s", player.Name, amount, name)) end
    local offer = product.Offers[amount]
    if not offer then error(string.format("Player %s attempted to purchase non-existent amount %s of %s", player.Name, amount, name)) end
    marketplaceService:PromptPurchase(player, offer.ID, false)
end)

--System to record purchases temporarily (in case datastores aren't working or have slown down)
local recentPurchases = {} -- Dictionary<player, Dictionary<PurchaseId, value>>. values:
local IN_PROGRESS = 0 -- Player purchased it and was given reward, but it wasn't saved yet
local COMPLETE = 1 -- Purchase complete and fully saved
Players.PlayerAdded:Connect(function(player)
    recentPurchases[player] = {}
end)
Players.PlayerRemoving:Connect(function(player)
    recentPurchases[player] = nil
end)
function PlayerMadePurchase(player, purchaseID) -- True if the player at least started a purchase
    return recentPurchases[player][purchaseID]
end
function PlayerPurchaseComplete(player, purchaseID) -- True if the player finished the purchase
    return recentPurchases[player][purchaseID] == COMPLETE
end
function RecordPlayerPurchaseInProgress(player, purchaseID)
    recentPurchases[player][purchaseID] = IN_PROGRESS
end
function RecordPlayerPurchaseComplete(player, purchaseID)
    recentPurchases[player][purchaseID] = COMPLETE
    delay(300, function() -- Release memory after a while (but give enough time for Roblox to fire ProcessReceipt incorrectly, as suggested might happen by wiki)
        if recentPurchases[player] then -- if player is still around
            recentPurchases[player][purchaseID] = nil -- release memory
        end
    end)
end

--ProcessReceipt
function marketplaceService.ProcessReceipt(receiptInfo)
    -- find the player based on the PlayerId in receiptInfo
    local player = Players:GetPlayerByUserId(receiptInfo.PlayerId)
    -- player left? don't process it:
    if not player then return Enum.ProductPurchaseDecision.NotProcessedYet end
    local purchaseID = receiptInfo.PurchaseId
    if PlayerMadePurchase(player, purchaseID) then
        if PlayerPurchaseComplete(player, purchaseID) then
            return Enum.ProductPurchaseDecision.PurchaseGranted --We already granted it.
        end
        --Attempt to save profile again
        return AttemptToFinishPurchase(player, purchaseID)
    end

    -- Get information required to give the player what they purchased

    local product = idToProduct[receiptInfo.ProductId]
    local amount = idToAmount[receiptInfo.ProductId]

    -- call ApplyOffer safely with pcall to catch any error
    local suc, err = pcall(product.ApplyOffer, player, amount)
    if not suc then -- log it to the output
        warn("An error occured while processing a product purchase")
        print("\tProduct name:", product.Name)
        print("\tProduct amount:", amount)
        print("\tProductId:",receiptInfo.ProductId)
        print("\tPlayer:",player)
        print("\tError message:",err)
        return Enum.ProductPurchaseDecision.NotProcessedYet
    end

    -- if the function didn't error, 'err' will be whatever the function returned
    -- if our handler didn't return anything (or it returned false/nil), it means
    -- that the purchase failed for some reason, so we have to cancel it
    if not err then
        return Enum.ProductPurchaseDecision.NotProcessedYet
    end
    RecordPlayerPurchaseInProgress(player, receiptInfo.PurchaseId)
    return AttemptToFinishPurchase(player, purchaseID)
end
function AttemptToFinishPurchase()
    -- Ask for the player's profile to be saved
    if not savePlayerProfile:Invoke(player) then
        -- Save failed, try again later
        return Enum.ProductPurchaseDecision.NotProcessedYet
    end
    RecordPlayerPurchaseComplete(player, receiptInfo.PurchaseId)
    -- tell ROBLOX that we have successfully handled the transaction (required)
    return Enum.ProductPurchaseDecision.PurchaseGranted
end