Inventory With Recursion

local HTTPService = game:GetService("HttpService")

local itemInfos = { -- only here for example, this should be a module of its own
    ["RedApple"] = {
        DisplayName = "Red Apple",
        MaxQuantity = 4,
    },
    ["GreenApple"] = {
        DisplayName = "Green Apple",
        MaxQuantity = 1,
    }
}

local Inventory = {}
Inventory.__index = Inventory


function Inventory.new(player)
    local self = setmetatable({
        Player = player,
        Items = {},
        ItemCount = 0,
        MaxItems = 4,
    }, Inventory)
    return self
end

function Inventory:GetHighestOpenItem(itemName)
    local itemInfo = assert(itemInfos[itemName], "Invalid Item Name")
    local highestItem = nil
    local highestQuantity = 0

    for uuid, item in pairs(self.Items) do
        if item.ItemName == itemName and item.Quantity > highestQuantity and item.Quantity < itemInfo.MaxQuantity then
            highestItem = item
            highestQuantity = item.Quantity
        end
    end

    return highestItem
end

function Inventory:AddItem(itemName, itemQuantity)
    local itemInfo = assert(itemInfos[itemName], "Invalid Item Name")
    local highestOpenItem = self:GetHighestOpenItem(itemName)
    local atInventoryMaxItems = self.ItemCount == self.MaxItems


    local function addToItem(item) -- takes quantity from itemQuantity and gives it to the item
        local quantityToTake = math.clamp(itemQuantity, 0, itemInfo.MaxQuantity - item.Quantity)
        item.Quantity += quantityToTake
        itemQuantity -= quantityToTake
    end

    if itemQuantity > 0 then
        if highestOpenItem then -- add to existing item
            addToItem(highestOpenItem)
            self:AddItem(itemName, itemQuantity)
        elseif not atInventoryMaxItems then -- new item
            local item = {
                ItemName = itemName,
                Quantity = 0,
                UUID = HTTPService:GenerateGUID(false)
            }
            addToItem(item)
            self.ItemCount += 1
            self.Items[item.UUID] = item
            self:AddItem(itemName, itemQuantity)
        end
    end
end

return Inventory