local function create_force(player)
  if not (player and player.valid) then
    return
  end

  -- Protect against players having the same name as an existing force
  local name = game.forces[player.name] and "" or player.name

  while name == "" or game.forces[name] do
    name = script.mod_name.."-"..player.name.."-"..math.floor(math.random(100))
  end

  -- Create and assign force
  game.create_force(name)
  player.force = name

  -- Share chart
  player.force.share_chart = true
end

script.on_event(defines.events.on_player_joined_game, function(event)
  local player = game.players[event.player_index]
  local f_name = player.force.name

  if player.name ~= f_name and
      not f_name:match("^"..script.mod_name.."%-"..player.name.."%-%d*$") then

    create_force(player)
    policy(player.force)
  end
end)

local function policy(player_force)
  if not (player_force and player_force.valid) then
    return
  end

  for f, force in pairs(game.forces) do
    -- Ignore player_force and forces without players
    if player_force ~= force and force.name == "player" or next(force.players) then
      player_force.set_cease_fire(force, true)
      player_force.set_friend(force, true)

      force.set_cease_fire(player_force, true)
      force.set_friend(player_force, true)
    end
  end
end

-- Make sure all players are on their own force
local function init()
  local f_name
  for p, player in pairs(game.players) do
    f_name = player.force.name
    if player.name ~= f_name and
        not f_name:match("^"..script.mod_name.."%-"..player.name.."%-%d*$") then

      create_force(player)
      policy(player.force)
    end
  end
end


script.on_event(defines.events.on_player_joined_game, function(event)
  local player = game.players[event.player_index]

  create_force(player)
  policy(player.force)

end)

-- We can't remove the force before the player has been removed, so we store the
-- force name with the player for now.
script.on_event(defines.events.on_pre_player_removed, function(event)
  local player = game.players[event.player_index]

  global.remove_forces = global.remove_forces or {}
  global.remove_forces[player.index] = player.force.name
end)

-- We only get the index of the removed player, but we can remove the force because
-- we've stored its name.
script.on_event(defines.events.on_player_removed, function(event)
  local player = game.players[event.player_index]
  local force = global.remove_forces[player.index]

  -- Merge removed player's force with force "player" (all entities will be moved to
  -- force "player" and the other force will be deleted)
  game.merge_forces(force, "player")

  global.remove_forces[player.index] = nil
  if not next(global.remove_forces) then
    global.remove_forces = nil
  end
end)

script.on_init(init)
script.on_configuration_changed(init)