Item upgrade/exchange script

local T = {}
T.Items =
{
--  {GivenItem, ReqItem1, ReqItem2, ... ReqItemN}
    {25, 35},
    {25, 36},
    {25, 37},
    {25, 38},
    {25, 39},
    {25, 40}, -- Testing paging with item entry 40
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {25, 40},
    {35, 40}, -- Testing vendor with item entry 35
}

T.Page = {}
T.Options = 20
local X = 10

function T.Count(Page)
    if(not Page or Page < 1) then
        return 1
    else
        return (Page*T.Options)
    end
end

function T.Max(Count, LData)
    if(LData - Count >= T.Options) then
        return Count+T.Options-1, true
    else
        return LData, false
    end
end

function T.Hello(pUnit, event, pPlayer)
    local Items = {}
    for k,v in ipairs(T.Items) do
        local Add = true
        for i = 2, #v do
            if(not pPlayer:HasItem(v[i])) then
                Add = false
                break
            end
        end
        if(Add) then
            Items[#Items+1] = {k,v[1]}
        end
    end
    local str = tostring(pPlayer)
    if(not T.Page[str] or T.Page[str] < 0) then
        T.Page[str] = 0
    end
    local Page = T.Page[str]
    local Count = T.Count(Page)
    local Max, Next = T.Max(Count, #Items)
    pUnit:GossipCreateMenu(100, pPlayer, 0)
    if(Next) then
        pUnit:GossipMenuAddItem(7, "Next page", 3, 0, '', 0)
    end
    if(Page > 0) then
        pUnit:GossipMenuAddItem(7, "Previous page", 4, 0, '', 0)
    end
    pUnit:GossipMenuAddItem(4, "Refresh", 1, 0, '', 0)
    pUnit:GossipMenuAddItem(6, "Preview page's items", X, 0, '', 0)
    for k = Count, Max do
        local Name = WorldDBQuery("SELECT Name1 FROM items WHERE entry = "..Items[k][2]):GetColumn(0):GetString()
        pUnit:GossipMenuAddItem(0, Name, X+Items[k][1], 0, 'NOTE! You will lose the items required to buy this item.', 0)
    end
    pUnit:GossipSendMenu(pPlayer)
end

function T.Select(pUnit, event, pPlayer, id, intid, code)
    local str = tostring(pPlayer)
    if(intid == 3) then
        T.Page[str] = T.Page[str] + 1
    elseif(intid == 4) then
        T.Page[str] = T.Page[str] - 1
    elseif(intid == X) then
        pPlayer:GossipComplete()
        pUnit:VendorRemoveAllItems()
        local Items = {}
        for k,v in ipairs(T.Items) do
            local Add = true
            for i = 2, #v do
                if(not pPlayer:HasItem(v[i])) then
                    Add = false
                    break
                end
            end
            if(Add) then
                Items[#Items+1] = v[1]
            end
        end
        local Page = T.Page[str]
        local Count = T.Count(Page)
        local Max, Next = T.Max(Count, #Items)
        for k = Count, Max do
            pUnit:VendorAddItem(Items[k], -1, 0)
        end
        pPlayer:SendVendorWindow(pUnit)
        return
    elseif(T.Items[intid-X]) then
        local intid = intid-X
        local Add = true
        for i = 2, #T.Items[intid] do
            if(not pPlayer:HasItem(T.Items[intid][i])) then
                Add = false
                break
            end
        end
        if(Add) then
            if(pPlayer:AddItem(T.Items[intid][1], 1)) then
                for i = 2, #T.Items[intid] do
                    pPlayer:RemoveItem(T.Items[intid][i], 1)
                end
            else
                pPlayer:SendAreaTriggerMessage("Your inventory is full")
            end
        else
            pPlayer:SendAreaTriggerMessage("You do not have the required items")
        end
    end
    T.Hello(pUnit, event, pPlayer)
end

local ID = 180001 -- NPC entry
RegisterUnitGossipEvent(ID, 1, T.Hello)
RegisterUnitGossipEvent(ID, 2, T.Select)