stair

-- data entry --
local Args = {...}

if #Args ~= 1 then
    print("Usage: stair <distance>")
    return
end

-- check fuel level --
function checkfuel()
    if turtle.getFuelLevel() < 80 then
        print("Add coal on inventory!")
        for n=1,16 do
            local nCount = turtle.getItemCount(n)
            if nCount > 0 then
                turtle.select( n )
                if turtle.refuel(1) then
                    print( "New Fuel level is "..turtle.getFuelLevel() )
                end
            end
        end
    end
end

-- vars --
dist = tonumber ( Args[1] )
posI = tonumber ( Args[1] )

-- Checks --
if dist < 1 then
    print ("Please enter a positive number!")
    return
end

-- funcs --

-- part 1 --
function func1()
    checkfuel()
    if turtle.detect() then
        turtle.dig()
        if turtle.detectDown() then
            turtle.digDown()
            turtle.forward()
            func2()
        end
    else
        if turtle.detectDown() then
            turtle.digDown()
            turtle.down()
            dist = dist - 1
            if turtle.detect() then
                turtle.dig()
                turtle.forward()
            end
            func2()
        else
            turtle.down()
            dist = dist -1
            fBuild()
        end
    end
end

function func2()
    if turtle.detect() then
        turtle.dig()
        if turtle.detectDown() then
            turtle.digDown()
            turtle.down()
            dist = dist - 1
        end
    end
end

-- build down--
function fBuild()
    for n=1,16 do
        local nCount = turtle.getItemCount(n)
        if nCount > 0 then
            turtle.select( n )
            if turtle.placeDown() then
                turtle.forward()
            end
        end
    end
end

function fReturn()
    turtle.turnRight()
    turtle.turnRight()

    while posI > 0 do
        turtle.up()
        turtle.forward()
        posI = posI - 1
    end

    if posI == 0 then
        for n=1,16 do
            local nCount = turtle.getItemCount(n)
            if nCount > 0 then
                turtle.select( n )
                turtle.drop(nCount)
            end
        end
    end
end

-- program --

term.clear()
print ("========= starting excavation ========")
print( "Fuel level is "..turtle.getFuelLevel() )

while dist > 0 do
    func1()
end

if dist == 0 then
    fReturn()
end