Code

local maxX,maxY = ...
maxX= tonumber(maxX)
maxY= tonumber(maxY)
f=fs.open("log","a")
f.writeLine("--------------------")
f.write("maxX= ")
f.write(maxX)
f.write(" maxY= ")
f.writeLine(maxY)
noCoal=false

refuel=function()
  success=false
  c=1
  while (not success) and c<16 do
    turtle.select(c)
    success=turtle.refuel()
  end
  if success then
    f.writeLine("Refueled")
  end
  return success
end

clearInventory = function()
  for c=1, 16 do
    turtle.select(c)
    item=turtle.getItemDetail()
    if item then
      if not check(item.name) then
        turtle.drop()
      end
    end
  end
end

check=function (item)
  if item=="minecraft:chest" or item:match "minecraft:.*stone.*" or item:match "minecraft:dirt.*" or item=="minecraft:gravel" or item:match "chisel:.*" or item=="minecraft:torch" then
    return false
    else
      return true
  end
end

find = function ()
  local success, item=turtle.inspectUp()
  if success then
    if check(item.name) then
      turtle.select(1)
      turtle.digUp()
      f.write("Found up: ")
      f.writeLine(item.name)
    end
  end
  success, item=turtle.inspectDown()
  if success then
    if check(item.name) then
      turtle.select(1)
      turtle.digDown()
      f.write("Found down: ")
      f.writeLine(item.name)
    end
  end
  turtle.turnLeft()
  success, item=turtle.inspect()
  if success then
    if check(item.name) then
      turtle.select(1)
      turtle.dig()
      f.write("Found left: ")
      f.writeLine(item.name)
    end
  end
  turtle.turnRight()
  turtle.turnRight()
  success, item=turtle.inspect()
  if success then
    if check(item.name) then
      turtle.select(1)
      turtle.dig()
      f.write("Found right: ")
      f.writeLine(item.name)
    end
  end
  turtle.turnLeft()
  success, item=turtle.inspect()
  if success then
    if check(item.name) then
      turtle.select(1)
      turtle.dig()
      f.write("Found forward: ")
      f.writeLine(item.name)
    end
  end
end

local x=0
local y=0
local state = "up"
while x<maxX do --a
  while y<maxY do
    f.write("X=")
    f.write(x)
    f.write(" Y=")
    f.writeLine(y)
    local leftY=maxY-y
    local dist
    if state=="up" then
      dist=x+y
    else
      dist=x+leftY
    end
    local fuelLevel = turtle.getFuelLevel()
    if fuelLevel<= dist then --c
      local fuelFound=false
      local currSelected=1
      repeat
        turtle.select(currSelected)
        fuelFound = turtle.refuel()
        currSelected = currSelected+1
      until fuelFound == true or currSelected>16
      if fuelFound==false then
        f.writeLine("Fuel not found")
      else f.writeLine("Refueled")
      end
    end --c
    local nCoal=0
    freeSlots = 0
    for c=1,16 do --d
      local item=turtle.getItemDetail(c)
      if item then
        if item.name=="minecraft:coal" then
          nCoal = nCoal+item.count
        end
        if not check(item.name) then
          turtle.select(c)
          turtle.drop()
          freeSlots=freeSlots+1
        end
      else
          freeSlots=freeSlots+1
      end
    end --
    nCoal = nCoal*80+turtle.getFuelLevel()-4
    noCoal=true
    if nCoal<=dist or freeSlots <=1 then
      if nCoal<=dist then
        f.write("Not enough coal for the journey, returning home (left:")
        f.write(nCoal)
        f.write(", coord(")
        f.write(x)
        f.write(",")
        f.write(y)
        f.writeLine("))")
      end
      if freeSlots <=1 then f.writeLine("Not enough slots, returning home") end
      if state=="up" then
       turtle.turnLeft()
       turtle.turnLeft()
      else
       y=leftY
      end
      stopx=x
      stopy=y
      while y>0 do
        while turtle.detect() do
          turtle.select(1)
          turtle.dig()
        end
        clearInventory()
        if turtle.getFuelLevel()<2 then refuel() end
        turtle.forward()
        y=y-1
        f.write("X=")
        f.write(x)
        f.write(" Y=")
        f.writeLine(y)
      end
      turtle.turnRight()
      while x>0 do
        while turtle.detect() do
          turtle.select(1)
          turtle.dig()
        end
        clearInventory()
        if turtle.getFuelLevel()<2 then refuel() end
        turtle.forward()
        x=x-1
        f.write("X=")
        f.write(x)
        f.write(" Y=")
        f.writeLine(y)
      end
      success,storage=turtle.inspect()
      if success and storage.name=="minecraft:chest" then
        f.writeLine("Chest found")
        for c=1,16 do
          turtle.select(c)
          item=turtle.getItemDetail()
          if item and not item.name=="minecraft:coal" then
            dropSuccess=turtle.drop()
            if dropSuccess then
              f.write(item.name)
              f.writeLine(" dropped in chest")
            else
              f.writeLine("Chest full!! Shutting down...")
              f.close()
              os.shutdown()
            end
          end
        end
        if noCoal then
          success=turtle.suckUp()
          if not success then
            f.writeLine("no coal chest or coal, shutting down...")
            f.close()
            os.shutdown()
          else f.writeLine("Refueled from chest")
          end
        end
        f.write("Returning to the last point (")
        f.write(stopx)
        f.write(", ")
        f.write(stopy)
        f.writeLine(")")
        turtle.turnRight()
        turtle.turnRight()
        while x<stopx do
          find()
          if turtle.getFuelLevel()<2 then refuel() end
          while turtle.detect() do
            turtle.select(1)
            turtle.dig()
          end
          clearInventory()
          turtle.forward()
          x=x+1
          f.write("X=")
          f.write(x)
          f.write(" Y=")
          f.writeLine(y)
        end
        f.writeLine("Turning left for y")
        turtle.turnLeft()
        while y<stopy do
          find()
          if turtle.getFuelLevel()<2 then refuel() end
          while turtle.detect() do
            turtle.select(1)
            turtle.dig()
          end
          clearInventory()
          turtle.forward()
          y=y+1
          f.write("X=")
          f.write(x)
          f.write(" Y=")
          f.writeLinw(y)
        end
        if state==down then
          f.writeLine("Turning to the original state")
          turtle.turnLeft()
          turtle.turnLeft()
          y=maxY-leftY
        end
      else
        f.writeLine("No chest, shutting down...")
        f.close()
        os.shutdown()
      end
    end
    find()
    while turtle.detect() do
      turtle.select(1)
      turtle.dig()
    end
    turtle.forward()
    y=y+1
  end
  f.write("Ended x ")
  f.writeLine(x)
  if state=="up" then
    turtle.turnRight()
  else turtle.turnLeft()
  end
  for i=1, 3 do
    find()
    while turtle.detect() do
      turtle.select(1)
      turtle.dig()
    end
    turtle.forward()
    x=x+1
  end
  if state=="up" then
  turtle.turnRight()
    state="down"
  else
    turtle.turnLeft()
    state="up"
  end
end --a
f.writeLine("Returning home")
if state=="up" then
  turtle.turnLeft()
  turtle.turnLeft()
else
  y=maxY-y
end
while y>0 do
  find()
  if turtle.getFuelLevel()<2 then refuel() end
  while turtle.detect() do
    turtle.select(1)
    turtle.dig()
  end
  turtle.forward()
  y=y-1
  f.write("X=") f.write(x) f.write(" Y=") f.writeLine(y)
  clearInventory()
end
turtle.turnRight()
while x>0 do
  if turtle.getFuelLevel()<2 then refuel() end
  find()
  while turtle.detect() do
    turtle.select(1)
    turtle.dig()
  end
  turtle.forward()
  x=x-1
  f.write("X=") f.write(x) f.write(" Y=") f.writeLine(y)
  clearInventory()
end
f.writeLine("Arrived! Dropping loot into chest")
success, item = turtle.inspect()
if  item.name == "minecraft:chest" then
  f.writeLine("Chest found, beginning transfusion...")
  for c=1, 16 do
    turtle.select(c)
    item=turtle.getItemDetail()
    if item and item.name=="minecraft:coal" then
      success1=turtle.dropUp()
      t=1
    else
      if item then
        success2=turtle.drop()
        t=2
      end
    end
    if item and (success1 and t==1 or success2 and t==2) then
      f.write("Dropped ")
      f.write(item.count)
      f.write(" ")
      f.writeLine(item.name)
    else
      if item and t==1 then
        f.writeLine("Coal inventory full!!")
      else
        if item then
          f.writeLine("Item invetory full!!")
        end
      end
    end
  end
end
f.writeLine("Shutting down...")
f.close()
os.shutdown()