-- can only harvest wheat.
-- will automatically turn dirt into farmland.
-- farm size has to be 8x8, no water in this area.
-- place turtle on the left side of an edge, one block above ground.
-- place a chest under the turtle, it will fill it.
-- place seeds in the four top slots. in every slot should be at least one seed to prevent bugs.
-- place fuel in the botton right slot.


seedsSlots = {1, 2, 3, 4}
harvestSlots = {5, 6, 7, 8, 9, 10, 11, 12}
fuelSlot = 16
wheat = {name = 'minecraft:wheat', metadata = 7}


function findSlotWithSpace()
  for i = 1, #harvestSlots do
    turtle.select(harvestSlots[i])
    if turtle.getItemSpace() > 0 then
      return true
    end
  end
  return false
end

function findSlotWithSeeds()
  for i = 1, #seedsSlots do
    turtle.select(seedsSlots[i])
    if turtle.getItemCount() > 0 then
      turtle.placeDown()
      return true
    end
  end
  return false
end

function searchForHarvestedSeeds()
  for i = 1, #harvestSlots do
    turtle.select(harvestSlots[i])
    local item = turtle.getItemDetail()
    if item ~= nil and item.name == "minecraft:wheat_seeds" then
      for i = 1, #seedsSlots do
        turtle.transferTo(seedsSlots[i])
      end
    end
  end
end

function harvestAndPlant()
  local success,data = turtle.inspectDown()

  if success == false then -- nothing found
    turtle.digDown() -- changes grass to farmland
  else
    if data.name ~= wheat.name or data.metadata ~= wheat.metadata then
      return
    end
    findSlotWithSpace()
    turtle.digDown()
  end

  if not findSlotWithSeeds() then
    searchForHarvestedSeeds()
    findSlotWithSeeds()
  end
  turtle.placeDown()
end

function forwardAndHarvest(n)
  for i = 1, n do
    turtle.forward()
    harvestAndPlant()
  end
end

function tillEightByEight()
  -- line 1 and turn
  forwardAndHarvest(8)
  turtle.turnRight()
  forwardAndHarvest(1)
  turtle.turnRight()
  -- line 2 and turn
  forwardAndHarvest(7)
  turtle.turnLeft()
  forwardAndHarvest(1)
  turtle.turnLeft()
  -- line 3 and turn
  forwardAndHarvest(7)
  turtle.turnRight()
  forwardAndHarvest(1)
  turtle.turnRight()
  -- line 4 and turn
  forwardAndHarvest(7)
  turtle.turnLeft()
  forwardAndHarvest(1)
  turtle.turnLeft()
  -- line 5 and turn
  forwardAndHarvest(7)
  turtle.turnRight()
  forwardAndHarvest(1)
  turtle.turnRight()
  -- line 6 and turn
  forwardAndHarvest(7)
  turtle.turnLeft()
  forwardAndHarvest(1)
  turtle.turnLeft()
  -- line 7 and turn
  forwardAndHarvest(7)
  turtle.turnRight()
  forwardAndHarvest(1)
  turtle.turnRight()
  -- line 8
  forwardAndHarvest(7)
  -- move to chest
  turtle.turnRight()
  for i = 1, 7 do
    turtle.forward()
  end
  turtle.turnLeft()
  turtle.forward()
  turtle.turnLeft()
  turtle.turnLeft()
end

function unload()
  local seeds = 0
  local wheat = 0
  for i = 1, #harvestSlots do
    turtle.select(harvestSlots[i])
    local item = turtle.getItemDetail()
    if item ~= nil then
      if item.name == "minecraft:wheat_seeds" then
        seeds = seeds + getItemCount()
      elseif item.name == "minecraft:wheat" then
        wheat = wheat + getItemCount()
      else
        print(item.name)
      end
      turtle.dropDown()
    end
  end
  print(seeds.." seeds harvested")
  print(wheat.." wheat harvested")
end

function refuel()
  if turtle.getFuelLevel() < turtle.getFuelLimit() then
    turtle.select(fuelSlot)
    turtle.refuel()
  end
end

'minecraft:wheat'
if item ~= nil and item.name == "minecraft:wheat_seeds" then

-- main program
function main()
  refuel()
  local fuelBegin = turtle.getFuelLevel()
  if fuelBegin < 200 then
    print("Not enough fuel left.")
    return
  end

  tillEightByEight()
  searchForHarvestedSeeds()
  unload()

  local fuelEnd = turtle.getFuelLevel()
  print("fuel consumed: "..(fuelBegin - fuelEnd))
  os.sleep(1)
end

main()