CC Turtle Excavator

local modem = peripheral.find("modem")
local channel = 42

function printMessage(msg)
  print(msg)
  if modem then
    modem.transmit(channel, 0, msg)
  end
end

function printFuelInfo()
  local level = turtle.getFuelLevel()
  local limit = turtle.getFuelLimit()
  local percent = (type(level) == "number" and type(limit) == "number" and limit > 0)
    and math.floor(level / limit * 100)
    or "?"

  local msg = string.format("Fuel: %s / %s (%s%%)", level, limit, percent)
  printMessage(msg)
end

local position = { x = 0, y = 0, z = 0 }
local facing = 0
local moveHistory = {}

function forwardTrack()
  if turtle.forward() then
    if facing == 0 then position.z = position.z - 1
    elseif facing == 1 then position.x = position.x + 1
    elseif facing == 2 then position.z = position.z + 1
    elseif facing == 3 then position.x = position.x - 1 end
    table.insert(moveHistory, "forward")
    return true
  end
  return false
end

function backTrack()
  if turtle.back() then
    if facing == 0 then position.z = position.z + 1
    elseif facing == 1 then position.x = position.x - 1
    elseif facing == 2 then position.z = position.z - 1
    elseif facing == 3 then position.x = position.x + 1 end
    table.insert(moveHistory, "back")
    return true
  end
  return false
end

function upTrack()
  if turtle.up() then
    position.y = position.y + 1
    table.insert(moveHistory, "up")
    return true
  end
  return false
end

function downTrack()
  if turtle.down() then
    position.y = position.y - 1
    table.insert(moveHistory, "down")
    return true
  end
  return false
end

function turnLeftTrack()
  turtle.turnLeft()
  facing = (facing - 1) % 4
  table.insert(moveHistory, "left")
end

function turnRightTrack()
  turtle.turnRight()
  facing = (facing + 1) % 4
  table.insert(moveHistory, "right")
end

function returnHome()
  for i = #moveHistory, 1, -1 do
    local move = moveHistory[i]

    if move == "forward" then
      turtle.back()
      -- update position ...
    elseif move == "back" then
      turtle.forward()
      -- update position ...
    elseif move == "up" then
      turtle.down()
      position.y = position.y - 1
    elseif move == "down" then
      turtle.up()
      position.y = position.y + 1
    elseif move == "left" then
      turtle.turnRight()
      facing = (facing + 1) % 4
    elseif move == "right" then
      turtle.turnLeft()
      facing = (facing - 1) % 4
    end
  end

  moveHistory = {}
  print("Returned to home at:", position.x, position.y, position.z)
  return true
end

function refuelToTarget()
  local targetRatio = 0.97
  local fuelLimit = turtle.getFuelLimit()
  local targetFuel = math.floor(fuelLimit * targetRatio)

  if turtle.getFuelLevel() == "unlimited" or turtle.getFuelLevel() >= targetFuel then
    return true
  end

  turtle.turnRight()
  turtle.select(1)

  while turtle.getFuelLevel() < targetFuel do
    if not turtle.suck() then
      turtle.turnLeft()
      return false
    end
    turtle.refuel()
  end

  if turtle.getItemCount(1) > 0 then
    turtle.drop()
  end

  turtle.turnLeft()
  return true
end

function unloadAfterMining()
  turtle.turnLeft()
  for i = 1, 16 do
    turtle.select(i)
    turtle.drop()
  end
  turtle.select(1)
  turtle.turnRight()
end

function hasFreeSlot()
  for slot = 1, 16 do
    if turtle.getItemCount(slot) == 0 then return true end
  end
  return false
end

function shouldReturn()
  local level = turtle.getFuelLevel()
  local limit = turtle.getFuelLimit()
  return (type(level) == "number" and level < (limit * 0.4)) or not hasFreeSlot()
end

function mineLayer(width, depth)
  local evenRow = true
  for row = 1, depth do
    for col = 1, width - 1 do
      if turtle.detect() then turtle.dig() end
      forwardTrack()
      turtle.digUp()
      turtle.digDown()

      if shouldReturn() then
        printMessage("Fuel low or inventory full, returning to base.")
        return false -- interrupt layer, let main handle return
      end

        printFuelInfo()
    end

    if row < depth then
      if evenRow then
        turnRightTrack()
        if turtle.detect() then turtle.dig() end
        forwardTrack()
        turnRightTrack()
      else
        turnLeftTrack()
        if turtle.detect() then turtle.dig() end
        forwardTrack()
        turnLeftTrack()
      end
      evenRow = not evenRow
    end
  end
  return true
end

function descendToStart(depth)
  forwardTrack()
  for i = 1, depth do
    if turtle.detectDown() then turtle.digDown() end
    if not downTrack() then break end
  end
  turnRightTrack()
end

function mineChunkArea(width, depth, layers)
  for layer = 1, layers do
    local ok = mineLayer(width, depth)
    if not ok then
      -- Aborted mid-layer: stop mining and signal interruption
      return false, layer
    end

    -- Finished layer: descend 3 blocks
    if layer < layers then
      for i = 1, 3 do
        if turtle.detectDown() then turtle.digDown() end
        downTrack()
      end
    end
  end

  return true
end

while true do
  if not refuelToTarget() then
    printMessage("Refuel failed — aborting.")
    break
  end

  printMessage("Turtle starting mining task...")

  descendToStart(30)

  local success, stoppedAtLayer = mineChunkArea(50, 50, 60)

  if not success then
    printMessage("Mining stopped early at layer: " .. stoppedAtLayer)
  else
    printMessage("Finished mining all layers.")
  end

  returnHome()
  unloadAfterMining()
end

printMessage("Turtle script ended.")