Follower

rednet.open("right")

function left()
  turtle.turnLeft()
  fDir = fDir - 1
  if fDir < 0 then fDir = 3 end
end

function up()
  turtle.up()
  yPos = yPos + 1
end

function down()
  turtle.down()
  yPos = yPos - 1
end

function forward()
  turtle.forward()
  if fDir == 0 then zPos = zPos + 1 end
  if fDir == 2 then zPos = zPos - 1 end
  if fDir == 1 then xPos = xPos - 1 end
  if fDir == 3 then xPos = xPos + 1 end
end

fDir = nil
xPos = nil
yPos = nil
zPos = nil
function initDir()
  xPos, yPos, zPos = gps.locate()
  if not xPos or not yPos or not zPos then
    print("ERROR: GPS API REQUIRED")
    os.exit(goTo)
  end
  turtle.forward()
  xPos2, yPos2, zPos2 = gps.locate()
  turtle.back()
  if xPos ~= xPos2 then
    if xPos > xPos2 then
      fDir = 1
    else
      fDir = 3
    end
  else
    if zPos > zPos2 then
      fDir = 2
    else
      fDir = 0
    end
  end
end

initDir()
while true do
  id = nil
  id, location = rednet.receive(.01)
  if id then
    xDest = location[1]
    yDest = location[2]
    zDest = location[3]
  end
  if xDest < xPos then
    while fDir ~= 1 do
      left()
    end
    turtle.dig()
    forward()
  elseif xDest > xPos then
    while fDir ~= 3 do
      left()
    end
    turtle.dig()
    forward()
  elseif zDest < zPos then
    while fDir ~= 2 do
      left()
    end
    turtle.dig()
    forward()
  elseif zDest > zPos then
    while fDir ~= 0 do
      left()
    end
    turtle.dig()
    forward()
  elseif yDest < yPos then
    turtle.digDown()
    down()
  elseif yDest > yPos then
    turtle.digUp()
    up()
  end
end