[Factorio] Convert mined entity into blueprint

local building_prototype_name = "small-factory"

script.on_event(defines.events.on_preplayer_mined_item, function(event)
  --event.entity
  --event.player_index
  if EntityOk(event.entity) and building.name == building_prototype_name and PlayerOk(game.players[event.player_index]) then
    StoreBuilding(game.players[event.player_index], event.entity)
  end
end)

function StoreBuilding(player, building)
  player.print(building_prototype_name .. " is being mined")
  local blueprint_simple_stack = {name = "blueprint", count = 1}
  local inv = player.get_inventory(defines.inventory.player_main)
  if inv.can_insert(blueprint_simple_stack) then
    inv.insert(blueprint_simple_stack)
    for slot_index = 1, #inv, 1 do
      local item_stack = inv[slot_index]
      if item_stack.valid and item_stack.valid_for_read and item_stack.name == "blueprint" then
        local bp_entities = item_stack.get_blueprint_entities()
        if not bp_entities then
          local blueprint = item_stack
          local entities = {}
          local ent = {entity_number = 1--[[unique number in current blueprint]], name = building_prototype_name, position = {1,1}}
          table.insert(entities, ent)
          blueprint.set_blueprint_entities(entities)
          local blueprint_name
          if building.backer_name and string.len(building.backer_name) > 0 then
            blueprint_name = building.backer_name
          else
            blueprint_name = building_prototype_name --or surface name, or smth else
          end
          blueprint.label = blueprint_name
          blueprint.allow_manual_label_change = false -- blueprint cannot be renamed
          building.destroy()
          return
        end
      end
    end
  end
end

function EntityOk(entity)
  return (entity and entity.valid)
end

function PlayerOk(entity)
  return (entity and entity.valid and entity.connected)
end