placeblocks

print("Bridge build program")

print("")
print("Place turtle facing away.")
print("Turtle will build a 4x4 structure")
print("using the blocks in the corresponding")
print("square of its interface.  Put a torch")
print("in the slot the corresponds to the")
print("turtle's relative location.")
print("Turtle will keep building until the")
print("largest stack is out of blocks.")

-- find the turtle's relative location

local turtleslot = -1
local maxstack = 0

for x=1,16 do
  if turtle.getItemCount(x) > 0 then
    if(turtle.getItemDetail(x).name == "minecraft:torch") then
      turtleslot = x
    end
    if turtle.getItemCount(x) > maxstack then
      maxstack = turtle.getItemCount(x)
    end
  end
end

if turtleslot == -1 then
  error("Must have a torch in the turtle's inventory")
end

-- move turtle to the upper left

turtle.forward()
turtle.forward()
turtle.turnLeft()

turtle.select(turtleslot)

while turtle.getSelectedSlot() > 4 do
  turtle.up()
  turtle.select(turtle.getSelectedSlot() - 4)
end

while turtle.getSelectedSlot() > 1 do
  turtle.forward()
  turtle.select(turtle.getSelectedSlot() - 1)
end

turtle.turnLeft()

-- place blocks

for z=1,maxstack do

  if z ~= 1 then
    turtle.turnRight()
    turtle.turnRight()
    turtle.forward()
    turtle.turnLeft()
    turtle.turnLeft()
  end

  for x=1,4 do

    if x ~= 1 then
      turtle.turnLeft()
      turtle.forward()
      turtle.turnRight()
    end

    for y=1,4 do

      if y ~= 1 then
        turtle.down()
      end

      local blockslot = (x-1)+((y-1)*4)+1
      if blockslot ~= turtleslot then
        turtle.select(blockslot)
        turtle.place()
      end

    end

    -- return to top

    turtle.up()
    turtle.up()
    turtle.up()

  end

  -- return to left

  turtle.turnRight()
  turtle.forward()
  turtle.forward()
  turtle.forward()
  turtle.turnLeft()

end

-- move turtle back to starting spot

turtle.select(1)

while turtleslot - turtle.getSelectedSlot() >= 4 do
  turtle.down()
  turtle.select(turtle.getSelectedSlot() + 4)
end

turtle.turnLeft()

while turtleslot - turtle.getSelectedSlot() >= 1 do
  turtle.forward()
  turtle.select(turtle.getSelectedSlot() + 1)
end

turtle.turnRight()
turtle.forward()
turtle.turnRight()
turtle.turnRight()