local finished = false
local n = 0
local orientation = 0
local lineLength = 21
local waitForMoreBuildMaterial = true

function d()
    return turtle.detect()
end

function dd()
    return turtle.detectDown()
end

function l()
    turtle.turnLeft()
    orientation = orientation - 90
    if (orientation == -360) then
        orientation = 0
    elseif (orientation == -270) then
        orientation = 90
    end
end

function r()
    turtle.turnRight()
    orientation = orientation + 90
    if (orientation == 360) then
        orientation = 0
    elseif (orientation == 270) then
        orientation = -90
    end
end

function f()
    turtle.forward()
end

function b()
    turtle.back()
end

function u()
    turtle.up()
end

function selectBuildMaterial()
    local foundBuildMaterial = false
    local buildMaterialIndex = 1
    for i = 1, 16 do
        turtle.select(i)
        if (not turtle.refuel(0)) and (not foundBuildMaterial) and (turtle.getItemCount() > 0) then
            foundBuildMaterial = true
            buildMaterialIndex = i
        end
    end

    if not foundBuildMaterial then
        if waitForMoreBuildMaterial then
            sleep(10)
            selectBuildMaterial()
        else
            inished = true
        end
    else
        turtle.select(buildMaterialIndex)
    end
end

function refuel()
    local foundFuel = false
    for i = 1, 16 do
        turtle.select(i)
        if turtle.refuel(0) and (not foundFuel) then
            turtle.refuel(1)
            foundFuel = true
        end
    end

    if not foundFuel then
        finished = true
    end

    selectBuildMaterial()
end

while not finished do
    if (turtle.getFuelLevel() <= 0) then
        refuel()
    end

    if (turtle.getItemCount() <= 0) then
        selectBuildMaterial()
    end

    turtle.placeDown()

    n = n+1

    if (n == lineLength) then
        r()
        r()
        u()
        n = 0
    else
        f()
    end
end