How to make a Roblox trading system (with AI)

Example output from a build like this

8 files in this example. Picoo writes this code for your prompt, so file names and sizes vary.

Sample output: ServerScriptService/TradeManager.lua

--!strict
-- ServerScriptService/TradeManager.lua  (example)
local Players = game:GetService("Players")
local DataStoreService = game:GetService("DataStoreService")
-- GetDataStore throws in a place that was never published. Bare up here, that
-- error would stop this whole script before anyone joins; in pcall it leaves nil.
local storeOk, storeResult = pcall(function()
    return DataStoreService:GetDataStore("Inventory_v1")
end)
local InventoryStore: DataStore? = if storeOk then storeResult else nil

type TradeSlot = { itemId: string, count: number }
type TradeState = {
    a: Player, b: Player,
    aSlots: { TradeSlot }, bSlots: { TradeSlot },
    aReady: boolean, bReady: boolean,
    aConfirmed: boolean, bConfirmed: boolean,
}

local active: { [Player]: TradeState } = {}

local function resetReady(t: TradeState)
    t.aReady, t.bReady, t.aConfirmed, t.bConfirmed = false, false, false, false
end

local function atomicSwap(t: TradeState): boolean
    local store = InventoryStore
    if not store then return false end -- no store: no swap, and nothing is written
    local aOK, bOK = false, false
    local ok, err = pcall(function()
        store:UpdateAsync(tostring(t.a.UserId), function(data)
            if not data then return data end
            for _, s in ipairs(t.aSlots) do data[s.itemId] = (data[s.itemId] or 0) - s.count end
            for _, s in ipairs(t.bSlots) do data[s.itemId] = (data[s.itemId] or 0) + s.count end
            aOK = true; return data
        end)
        store:UpdateAsync(tostring(t.b.UserId), function(data)
            if not data then return data end
            for _, s in ipairs(t.bSlots) do data[s.itemId] = (data[s.itemId] or 0) - s.count end
            for _, s in ipairs(t.aSlots) do data[s.itemId] = (data[s.itemId] or 0) + s.count end
            bOK = true; return data
        end)
    end)
    return ok and aOK and bOK
end