Rewrite of factorio mod turrets-range 1.1.1

control.lua

require "defines"

global.active_turret_range_entities = {}
global.nearby_turret_map = {}

local function draw_turret_range(turret_type, sx, sy, r)
  -- what is this voodoo?
  local function round(x)
    return x + 0.5 - (x + 0.5) % 1
  end

  local x = 0
  local y = 0
  local angle = 0
  local drawmap = {}
  local turret_range_entities = {}

  sx = round(sx) - 1
  sy = round(sy) - 1

  -- would it be better to use the range instead of the type? (considering 3rd party mods)
  if turret_type == "electric-turret" then
    turret_type = "laser-turret-range-overlay"
  else
    turret_type = "gun-turret-range-overlay"
  end

  while angle < math.pi * 2 do
    angle = angle + 0.03
    x = round(math.cos(angle) * r + sx)
    y = round(math.sin(angle) * r + sy)

    if drawmap[x .. "x" .. y] == nil then
      drawmap[x .. "x" .. y] = true
      local indicator = game.get_surface(1).create_entity {
        name = turret_type,
        position = { x = x, y = y },
      }
      table.insert(turret_range_entities, indicator)
    end
  end
  return turret_range_entities
end

local turret_whitelist = {
  ["electric-turret"] = true,
  ["ammo-turret"] = true,
  -- ["turret"] = true,
}

local function turret_key(turret)
  return turret.position.x .. "x" .. turret.position.y
end

-- adds turrets to the table `map`
local function map_turrets_arround_player(map, player, range)
  range = range or 5
  local area = {
    { player.position.x-range, player.position.y-range },
    { player.position.x+range, player.position.y+range }
  }

  -- if turret is selected, add it
  if player.selected and turret_whitelist[player.selected.type] then
    map[turret_key(player.selected)] = player.selected
  end

  -- find all turrets in a square of raidus `range` centered on the player
  local surface = game.get_surface(1)
  for name, _ in pairs(turret_whitelist) do
    local turrets = surface.find_entities_filtered { area = area, type = name }
    for i, turret in ipairs(turrets) do map[turret_key(turret)] = turret end -- use ipairs?
  end
end

local function update_range_indicators()
  local map = {}
  local prev_map = global.nearby_turret_map or {}

  -- create a  `Set` of turrets near all players
  for _, player in ipairs(game.players) do
    map_turrets_arround_player(map, player)
  end

  -- draw all new turrets
  for key, turret in pairs(map) do
    if not prev_map[key] then
      local entities = draw_turret_range(turret.type, turret.position.x, turret.position.y, turret.prototype.turret_range)
      global.active_turret_range_entities[key] = entities
    end
  end

  -- remove old turrets not in new map
  for key, turret in pairs(prev_map) do
    if not map[key] then
      for _, entity in ipairs(global.active_turret_range_entities[key]) do
        entity.destroy()
      end
      global.active_turret_range_entities[key] = nil
    end
  end

  -- update map
  global.nearby_turret_map = map
end

-- wire it up
game.on_event(defines.events.on_tick, function(event)
  if event.tick % 10 == 0 then
    -- game.player.print("TICK "..event.tick)
    update_range_indicators()
  end
end)

game.on_load(function()
  -- reset old plugin's data
  for i = 1, #global.turret_range_entities do
    global.turret_range_entities[i].destroy()
  end
  global.turret_range_entities = {}

  -- init?
  if not global.active_turret_range_entities then
    global.active_turret_range_entities = {}
  end
end)