opus/sys/etc/scripts/follow

local function follow(id)

  requireInjector(getfenv(1))

  local Event  = require('event')
  local Point  = require('point')
  local Socket = require('socket')

  turtle.status = 'follow ' .. id

  if not turtle.enableGPS() then
    error('turtle: No GPS found')
  end

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

  local lastPoint
  local following = false

  Event.on('turtle_follow', function(_, pt)

    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)

  Event.onInterval(.5, function()

    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
        os.queueEvent('turtle_follow', pt)
      end
    end
  end)

  Event.on('turtle_abort', function()
    Event.exitPullEvents()
  end)

  Event.pullEvents()

  socket:close()

  return true
end

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