Chest = {name = "", itemList = {}, wrap = nil}

function Chest:new(o, name)
   o = o or {}
   setmetatable(o, self)
   self.__index = self
   self.name = name or ""
   return o
end

function Chest:init(x)
    for slot, item in pairs(self.wrap.list()) do
        --print(("%s:%d in slot %d"):format(item.name, item.count, slot))
        if self.itemList[item.name] == nil then
            self.itemList[item.name] = { slot = { slot } }
        else
            table.insert(self.itemList[item.name]["slot"], slot)
        end
    end
end

function Chest:connect(x)
    self.wrap = peripheral.wrap(self.name)
end

function Chest:print(x)
    for item, slot in pairs(self.itemList) do
        textutils.pagedPrint(("%s in %s"):format(item, textutils.serialise(slot)))
    end
end

chest = Chest:new{name = "expandedstorage:chest_1"}

chest:connect()
chest:init()
chest:print()