Computer Craft Tunnel Bore Program

function getLength()
    print("How long should the tunnel be?")
    return read()
end

function mine()
    while turtle.detect() == true do
        turtle.dig()
        os.sleep(0.8)
    end
    turtle.forward()
    turtle.digUp()
    turtle.digDown()
end

local layer = 0

local items = {
    ["minecraft:cobblestone"] = true,
    ["minecraft:dirt"] = true,
    ["minecraft:gravel"] = true,
}

function dump()
    details = turtle.getItemDetail()
    if items[details.name] then
        turtle.dropDown()
    end
end

function full()
    if layer == 5 then
        for i = 1, 16 do
            turtle.select(i)
            if turtle.getItemCount() > 0 then
                dump()
            end
        end
        layer = 0
    end
end

local length = tonumber(getLength())

function goHome()
    for i = 1, 2 do
        turtle.turnRight()
    end
    for i = 1, length do
        while turtle.detect() do
            turtle.dig()
            os.sleep(0.7)
        end
        turtle.forward()
    end
    for i = 1, 16 do
    turtle.select(i)
    turtle.drop()
    end
end

function tunnel()
    for i = 1, length/2 do
        mine()
        layer = layer + 1
        full()
        turtle.turnRight()
        mine()
        mine()
        turtle.turnLeft()
        mine()
        layer = layer + 1
        full()
        turtle.turnLeft()
        mine()
        mine()
        turtle.turnRight()
    end
end

tunnel()
goHome()