bridge

-- bridge <distance>
-- needs building material in the first slot (eg. cobblestone)
-- more building material can be supplied in other slots too if needed

local WALL_SLOT = 1
local args = { ... }
local distance = 0
if #args ~= 1 then
    print("Usage: bridge<distance>")
    error()
end
distance = args[1]
if turtle.getFuelLevel() < 1*distance then
    print("Not enough fuel to build the specified distance")
    error()
end
-- ---------------------------------------------------------------------
function reorderWalls()
    for i = 1,16 do
        if i~=WALL_SLOT then
            turtle.select(i)
            -- os.sleep(0.1)
            if turtle.compareTo(WALL_SLOT) and (turtle.getItemCount(i)>0) then
                while (turtle.getItemCount(i)>0) and (turtle.getItemCount(WALL_SLOT)<64) and (turtle.transferTo(WALL_SLOT,1)) do
                    -- os.sleep(0.01)
                end
            end
        end
    end
    turtle.select(WALL_SLOT)
end

function suckAll()
    local i = 1
    while i <= 16 and (i==WALL_SLOT or turtle.getItemSpace(i)==0) do
        i = i + 1
    end
    if i <= 16 then
        turtle.select(i)
        turtle.suck()
        turtle.suckUp()
        turtle.suckDown()
        reorderWalls()
    end
    turtle.select(WALL_SLOT)
end

function wall()
    turtle.select(WALL_SLOT)
    while turtle.detect() and not turtle.compare() do
        turtle.dig()
        -- suckAll()
    end
    turtle.select(WALL_SLOT)
    if not turtle.compare() then
        while not turtle.place() do
            turtle.dig()
        end
    end
end
function wallDown()
    turtle.select(WALL_SLOT)
    while turtle.detectDown() and not turtle.compareDown() do
        turtle.digDown()
        -- suckAll()
    end
    turtle.select(WALL_SLOT)
    if not turtle.compareDown() then
        while not turtle.placeDown() do
            turtle.digDown()
        end
    end
end

-- ---------------------------------------------------------------------
local stepsSinceReorder = 21

for i=1,distance do
    if stepsSinceReorder>20 then
        reorderWalls()
        stepsSinceReorder = 0
        turtle.select(WALL_SLOT)
        if turtle.getItemCount() < 3 then
            print("not enough building blocks")
            error()
        end
    end
    while not turtle.forward() do
        turtle.dig()
        -- suckAll()
    end
    wallDown()
    while turtle.detectUp() do
        turtle.digUp()
        -- suckAll()
    end
    turtle.turnLeft()
    wall()
    turtle.turnRight()
    turtle.turnRight()
    wall()
    turtle.turnLeft()
    stepsSinceReorder = stepsSinceReorder+1
end
print("bridge built")