weather = {
  -- weather states, 'none' is default, other states depends from active mods
  state = "none",
  
  -- player list for saving player meta info
  players = {},
  
  -- default weather recalculation interval
  check_interval = 300,
  
  -- weather min duration
  min_duration = 600,
  
  -- weather max duration
  max_duration = 9000,
  
  -- weather calculated end time
  end_time = nil,
  
  -- registered weathers
  reg_weathers = {},

  -- automaticly calculates intervals and swap weathers 
  auto_mode = true,
  
  -- global flag to disable/enable ABM logic. 
  allow_abm = true,
}

weather.reg_weathers["none"] = {
  min_duration = weather.min_duration,
  max_duration = weather.max_duration,
  transitions = {
    [50] = "rain",
    [100] = "snow",
  },
  clear = function() end,
}

weather.get_rand_end_time = function(min_duration, max_duration)
  local r
  if min_duration ~= nil and max_duration ~= nil then
    r = math.random(min_duration, max_duration);
  else
    r = math.random(weather.min_duration, weather.max_duration);
  end 
  return minetest.get_gametime() + r
end

-- Returns true if pos is outdoor.
-- Outdoor is defined as any node in the Overworld under open sky.
-- FIXME: Nodes below glass also count as “outdoor”, this should not be the case.
weather.is_outdoor = function(pos)
  local cpos = {x=pos.x, y=pos.y+1, z=pos.z}
  local _, dim = mcl_util.y_to_layer(cpos.y)
  if minetest.get_node_light(cpos, 0.5) == 15 and dim == "overworld" then
    return true
  end
  return false
end

-- checks if player is undewater. This is needed in order to
-- turn off weather particles generation.
weather.is_underwater = function(player)
    local ppos = player:getpos()
    local offset = player:get_eye_offset()
    local player_eye_pos = {x = ppos.x + offset.x, 
                            y = ppos.y + offset.y + 1.5, 
                            z = ppos.z + offset.z}
    local node_level = minetest.get_node_level(player_eye_pos)
    if node_level == 8 or node_level == 7 then
      return true
    end
    return false
end

-- trying to locate position for particles by player look direction for performance reason.
-- it is costly to generate many particles around player so goal is focus mainly on front view.  
weather.get_random_pos_by_player_look_dir = function(player)
  local look_dir = player:get_look_dir()
  local player_pos = player:getpos()

  local random_pos_x = 0
  local random_pos_y = 0
  local random_pos_z = 0

  if look_dir.x > 0 then
    if look_dir.z > 0 then
      random_pos_x = math.random() + math.random(player_pos.x - 2.5, player_pos.x + 5)
      random_pos_z = math.random() + math.random(player_pos.z - 2.5, player_pos.z + 5)
    else
      random_pos_x = math.random() + math.random(player_pos.x - 2.5, player_pos.x + 5)
      random_pos_z = math.random() + math.random(player_pos.z - 5, player_pos.z + 2.5)
    end
  else
    if look_dir.z > 0 then
      random_pos_x = math.random() + math.random(player_pos.x - 5, player_pos.x + 2.5)
      random_pos_z = math.random() + math.random(player_pos.z - 2.5, player_pos.z + 5)
    else
      random_pos_x = math.random() + math.random(player_pos.x - 5, player_pos.x + 2.5)
      random_pos_z = math.random() + math.random(player_pos.z - 5, player_pos.z + 2.5)
    end
  end

  random_pos_y = math.random() + math.random(player_pos.y + 1, player_pos.y + 3)
  return random_pos_x, random_pos_y, random_pos_z
end

minetest.register_globalstep(function(dtime)
  if weather.auto_mode == false then
    return 0
  end

  if weather.end_time == nil then
    weather.end_time = weather.get_rand_end_time()
  end
  -- recalculate weather
  if weather.end_time <= minetest.get_gametime() then
    weather.set_random_weather(weather.state, weather.reg_weathers[weather.state])
  end
end)

-- sets random weather (which could be 'regular' (no weather)).
weather.set_random_weather = function(weather_name, weather_meta)
  if (weather_meta ~= nil) then
    local transitions = weather_meta.transitions
    local random_roll = math.random(0,100)
    local new_weather
    for v, weather in pairs(transitions) do
      if random_roll < v then
        new_weather = weather
        break
      end
    end
    if new_weather then
      weather.state = new_weather
      weather.end_time = weather.get_rand_end_time(weather.reg_weathers[weather.state].min_duration, weather.reg_weathers[weather.state].max_duration)
      weather.reg_weathers[weather_name].clear()
    end
  end
end

minetest.register_privilege("weather_manager", {
  description = "Gives ability to control weather",
  give_to_singleplayer = false
})

-- Weather command definition. Set 
minetest.register_chatcommand("weather", {
  params = "clear | rain | snow | thunder",
  description = "Changes the weather to the specified parameter.",
  privs = {weather_manager = true},
  func = function(name, param)
    if (param == "") then
      minetest.chat_send_player(name, "Error: No weather specified.")
      return
    end
    local success = false
    if (param == "clear") then
      weather.reg_weathers[weather.state].clear()
      weather.state = "none"
      weather.end_time = weather.get_rand_end_time()
      success = true
      return
    end
  
    if (weather.reg_weathers ~= nil and weather.reg_weathers[param] ~= nil) then
      if (weather.state ~= nil and weather.state ~= "none" and weather.reg_weathers[weather.state] ~= nil) then
        weather.reg_weathers[weather.state].clear()
        local weather_meta = weather.reg_weathers[weather.state]
        weather.end_time = weather.get_rand_end_time(weather_meta.min_duration, weather_meta.max_duration)
      end
      weather.state = param
      return
    else
      minetest.chat_send_player(name, "Error: Invalid weather specified. Use “clear”, “rain”, “snow” or “thunder”.")
    end
  end
})

minetest.register_chatcommand("toggledownfall", {
  params = "",
  description = "Toggles between clear weather and weather with downfall (randomly rain, thunderstorm or snow)",
  privs = {weather_manager = true},
  func = function(name, param)
    -- Currently rain/thunder/snow: Set weather to clear
    if weather.state ~= "none" then
       weather.reg_weathers[weather.state].clear()
       weather.state = "none"
       weather.end_time = weather.get_rand_end_time()

    -- Currently clear: Set weather randomly to rain/thunder/snow
    else
       local new = { "rain", "thunder", "snow" }
       local r = math.random(1, #new)
       weather.reg_weathers[weather.state].clear()
       weather.state = new[r]
       local weather_meta = weather.reg_weathers[weather.state]
       weather.end_time = weather.get_rand_end_time(weather_meta.min_duration, weather_meta.max_duration)
    end
  end
})

-- Configuration setting which allows user to disable ABM for weathers (if they use it).
-- Weather mods expected to be use this flag before registering ABM.
local weather_allow_abm = minetest.settings:get_bool("weather_allow_abm")
if weather_allow_abm ~= nil and weather_allow_abm == false then
  weather.allow_abm = false
end