opus/sys/etc/scripts/follow

local function follow(id)

  require = requireInjector(getfenv(1))
  local GPS = require('gps')
  local Socket = require('socket')
  local Point = require('point')
  local process = require('process')

  turtle.status = 'follow ' .. id

  local pt = GPS.getPointAndHeading()
  if not pt or not pt.heading then
    error('turtle: No GPS found')
  end

  turtle.setPoint(pt)

  local socket = Socket.connect(id, 161)
  if not socket then
    error('turtle: Unable to connect to ' .. id)
    return
  end

  local lastPoint
  local following = false

  local followThread = process:newThread('follower', function()
    while true do

      local function getRemotePoint()
        if not turtle.abort then
          if socket:write({ type = 'gps' }) then
            return socket:read(3)
          end
        end
      end

      -- sometimes gps will fail if moving
      local pt, d

      for i = 1, 3 do
        pt, d = getRemotePoint()
        if pt then
          break
        end
        os.sleep(.5)
      end

      if not pt or turtle.abort then
        error('Did not receive GPS location')
      end

      if not lastPoint or (lastPoint.x ~= pt.x or lastPoint.y ~= pt.y or lastPoint.z ~= pt.z) then

        if following then
          turtle.abort = true
          while following do
            os.sleep(.1)
          end
          turtle.abort = false
        end

        -- check if gps is inaccurate (player moving too fast)
        if d < Point.pythagoreanDistance(turtle.point, pt) + 10 then
          lastPoint = Point.copy(pt)
          following = true
          process:newThread('turtle_follow', function()

            local pts = {
              { x = pt.x + 2, z = pt.z,     y = pt.y },
              { x = pt.x - 2, z = pt.z,     y = pt.y },
              { x = pt.x,     z = pt.z + 2, y = pt.y },
              { x = pt.x,     z = pt.z - 2, y = pt.y },
            }

            local cpt = Point.closest(turtle.point, pts)

            local blocks = { }

            local function addBlocks(tpt)
              table.insert(blocks, tpt)
              local apts = Point.adjacentPoints(tpt)
              for _,apt in pairs(apts) do
                table.insert(blocks, apt)
              end
            end

            -- don't run into player
            addBlocks(pt)
            addBlocks({ x = pt.x, z = pt.z, y = pt.y + 1 })

            if turtle.pathfind(cpt, blocks) then
              turtle.headTowards(pt)
            end
            following = false
          end)
        end
      end

      os.sleep(.5)
    end
  end)

  while true do
    local e = process:pullEvent()
    if e == 'terminate' or followThread:isDead() or e =='turtle_abort' then
      process:threadEvent('terminate')
      break
    end
  end

  socket:close()

  return true
end

local s, m = turtle.run(function() follow({COMPUTER_ID}) end)
if not s and m then
  error(m)
end