stairup

-- stairup
-- builds covered stairs up until it runs out of material or hits an obstacle
-- stair (bottom) material in slots 1-2 (eg. cobblestone steps/stairs)
-- WARNING! Don't use the stairs block in computercraft prior 1.5.1, placing stairs does not work there properly!
-- walls and ceiling in slots 3-16 (eg. cobblestone)


local posX = 0
local height = 0
local stepCount = 0
local orient = 1 -- 1 forward, -1 back
function selectFromTo(fromSlot,toSlot)
    local slotIndex = fromSlot
    local result = false
    turtle.select(slotIndex)
    while (turtle.getItemCount(slotIndex)==0) and (slotIndex < toSlot) do
        slotIndex = slotIndex + 1
        turtle.select(slotIndex)
    end
    if turtle.getItemCount(slotIndex)>0 then
        result = true
    end
    if not result then print("select from "..fromSlot.." failed") end
    return result
end
function selectStair()
    return selectFromTo(1,2)
end

function selectWall()
    return selectFromTo(3,16)
end

function forward()
    local result = false
    if turtle.forward() then
        result = true
        posX = posX + orient
    end
    if not result then print("forward failed") end
    return result
end
function back()
    local result = false
    if turtle.back() then
        result = true
        posX = posX - orient
    end
    if not result then print("back failed") end
    return result
end
function up()
    local result = false
    if turtle.up() then
        result = true
        height = height + 1
    end
    if not result then print("up failed") end
    return result
end
function down()
    local result = false
    if turtle.down() then
        result = true
        height = height - 1
    end
    if not result then print("down failed") end
    return result
end

function stepUp()
    local result = true
    result = selectStair()
    if result then
        result = turtle.place()
        selectWall()
        turtle.turnLeft()
        turtle.place()
        turtle.turnRight()
        turtle.turnRight()
        turtle.place()
        if result then
            result = up()
            if turtle.detectUp() then result = false end
            if result then
                turtle.place()
                turtle.turnLeft()
                turtle.turnLeft()
                turtle.place()
                turtle.turnRight()
                if result then result = forward() end
            else
                turtle.turnLeft()
            end
        else
            turtle.turnLeft()
        end
    end
    return result
end

function isAlignedDown()
    local result = false
    if height == (posX + 2) then
        result = true
    end
    return result
end
function compensateOffset()
    while (not isAlignedDown()) and (posX>0) and (height>1) do
        if not isAlignedDown() then forward() end
        if not isAlignedDown() then forward() end
        if not isAlignedDown() then down() end
        if not isAlignedDown() then forward() end
        if not isAlignedDown() then forward() end
        while (not isAlignedDown()) and (posX+2 < height) and (posX>0) and (height>1) and back() do end
    end
    if not isAlignedDown() then return false end
    return true
end

function stepDown()
    selectWall()
    turtle.placeUp()
    turtle.turnLeft()
    turtle.place()
    turtle.turnRight()
    turtle.turnRight()
    turtle.place()
    turtle.turnLeft()
    down()
    forward()
end


local buildUp = true
while buildUp do
    buildUp = stepUp()
    os.sleep(0.3)
    stepCount = stepCount + 1
    if turtle.detectUp() or turtle.detect() then
        buildUp = false
    end
end
turtle.turnLeft()
turtle.turnLeft()
orient = -1
if not compensateOffset() then
    print("can't compensate offset, something's wrong, exiting")
    return false
end
-- build ceiling on the way back
for i = 2,height do
    stepDown()
end
print("built "..stepCount.." steps")