OpenComputers script to show various statistics about the number of items in an ME network

items.lua

-- Total number of bits that can be stored in the system
local TOTAL_BITS = 1174405120
-- Approximate number of seconds between average rate resets
local AVG_INTERVAL = 3600 -- 1 hour

local component = require "component"
local event = require "event"
local term = require "term"

local interface = component.me_interface

-- Calculate the current number of bits used in the system
local function getUsedBits()
    local items = interface.getItemsInNetwork()
    local total = 0
    for _, item in ipairs(items) do
        total = total + 8 + item.size
    end
    return total
end

-- Write a vertically centered message on the screen
local function writeCentered(message, row, color)
    local width = term.getViewport()
    term.setCursor(math.max(0, (width - message:len()) / 2 + 1), row)
    term.gpu().setForeground(color)
    term.write(message, false)
end


-- Previous count value, used for rate calculation
local lastCount = nil
-- Numerator and denominator, used for calculating average rate
local avgNum = 0
local avgDen = 0

while true do
    -- Get the current number of bits used in the system
    local count = getUsedBits()
    -- Format the first line without rate
    local line1 = string.format("%d bits used", count)
    -- If the previous count is available, calculate and append rate
    if lastCount then
        local diff = count - lastCount
        line1 = line1..string.format(" (%+d bits/s)", diff)
    end
    -- Format the second line without time estimate
    local line2 = string.format("~%d%% used",
                                math.floor(count / TOTAL_BITS * 100))
    -- If the rate is available, update the average and append time estimate
    if lastCount then
        avgNum = avgNum + (count - lastCount)
        avgDen = avgDen + 1
        -- Calculate estimate and average
        if avgNum > 0 and count < TOTAL_BITS then
            local secsUntilFull = (TOTAL_BITS - count) / (avgNum / avgDen)
            line2 = line2..string.format(" (~%d days until full)",
                                         math.floor(secsUntilFull / 86400))
        elseif avgNum < 0 and count > 0 then
            local secsUntilEmpty = count / -(avgNum / avgDen)
            line2 = line2..string.format(" (~%d days until empty)",
                                         math.floor(secsUntilEmpty / 86400))
        end
        -- Reset average if AVG_INTERVAL has elapsed
        if avgDen >= AVG_INTERVAL then
            avgNum = 0
            avgDen = 0
        end
    end
    -- Clear the screen and write both lines
    term.clear()
    writeCentered(line1, 1, 0xFFFFFF) -- White
    writeCentered(line2, 2, 0x686868) -- Gray
    -- Update lastCount
    lastCount = count
    -- Wait one second between updates
    if event.pull(1, "interrupted") then
        -- Break on <C-c>
        break
    end
end