defmodule Odinsea.Game.Map do
  @moduledoc """
  Represents a game map instance.

  Each map is a GenServer that manages all objects on the map:
  - Players
  - Monsters (mobs)
  - NPCs
  - Items (drops)
  - Reactors
  - Portals

  Maps are registered by map_id and belong to a specific channel.
  """
  use GenServer
  require Logger

  alias Odinsea.Game.Character
  alias Odinsea.Channel.Packets, as: ChannelPackets

  # ============================================================================
  # Data Structures
  # ============================================================================

  defmodule State do
    @moduledoc "Map instance state"
    defstruct [
      # Map identity
      :map_id,
      :channel_id,
      # Objects on map (by type)
      :players,
      # Map stores character_id => %{oid: integer(), character: Character.State}
      :monsters,
      # Map stores oid => Monster
      :npcs,
      # Map stores oid => NPC
      :items,
      # Map stores oid => Item
      :reactors,
      # Map stores oid => Reactor
      # Object ID counter
      :next_oid,
      # Map properties (TODO: load from WZ data)
      :return_map,
      :forced_return,
      :time_limit,
      :field_limit,
      :mob_rate,
      :drop_rate,
      # Timestamps
      :created_at
    ]

    @type t :: %__MODULE__{
            map_id: non_neg_integer(),
            channel_id: byte(),
            players: %{pos_integer() => map()},
            monsters: %{pos_integer() => any()},
            npcs: %{pos_integer() => any()},
            items: %{pos_integer() => any()},
            reactors: %{pos_integer() => any()},
            next_oid: pos_integer(),
            return_map: non_neg_integer() | nil,
            forced_return: non_neg_integer() | nil,
            time_limit: non_neg_integer() | nil,
            field_limit: non_neg_integer() | nil,
            mob_rate: float(),
            drop_rate: float(),
            created_at: DateTime.t()
          }
  end

  # ============================================================================
  # Client API
  # ============================================================================

  @doc """
  Starts a map GenServer.
  """
  def start_link(opts) do
    map_id = Keyword.fetch!(opts, :map_id)
    channel_id = Keyword.fetch!(opts, :channel_id)

    GenServer.start_link(__MODULE__, opts, name: via_tuple(map_id, channel_id))
  end

  @doc """
  Ensures a map is loaded for the given channel.
  """
  def ensure_map(map_id, channel_id) do
    case Registry.lookup(Odinsea.MapRegistry, {map_id, channel_id}) do
      [{pid, _}] ->
        {:ok, pid}

      [] ->
        # Start map via DynamicSupervisor
        spec = {__MODULE__, map_id: map_id, channel_id: channel_id}

        case DynamicSupervisor.start_child(Odinsea.MapSupervisor, spec) do
          {:ok, pid} -> {:ok, pid}
          {:error, {:already_started, pid}} -> {:ok, pid}
          error -> error
        end
    end
  end

  @doc """
  Adds a player to the map.
  """
  def add_player(map_id, character_id) do
    # TODO: Get channel_id from somewhere
    channel_id = 1
    {:ok, _pid} = ensure_map(map_id, channel_id)
    GenServer.call(via_tuple(map_id, channel_id), {:add_player, character_id})
  end

  @doc """
  Removes a player from the map.
  """
  def remove_player(map_id, character_id) do
    # TODO: Get channel_id from somewhere
    channel_id = 1

    case Registry.lookup(Odinsea.MapRegistry, {map_id, channel_id}) do
      [{_pid, _}] ->
        GenServer.call(via_tuple(map_id, channel_id), {:remove_player, character_id})

      [] ->
        :ok
    end
  end

  @doc """
  Broadcasts a packet to all players on the map.
  """
  def broadcast(map_id, channel_id, packet) do
    GenServer.cast(via_tuple(map_id, channel_id), {:broadcast, packet})
  end

  @doc """
  Broadcasts a packet to all players except the specified character.
  """
  def broadcast_except(map_id, channel_id, except_character_id, packet) do
    GenServer.cast(via_tuple(map_id, channel_id), {:broadcast_except, except_character_id, packet})
  end

  @doc """
  Gets all players on the map.
  """
  def get_players(map_id, channel_id) do
    GenServer.call(via_tuple(map_id, channel_id), :get_players)
  end

  # ============================================================================
  # GenServer Callbacks
  # ============================================================================

  @impl true
  def init(opts) do
    map_id = Keyword.fetch!(opts, :map_id)
    channel_id = Keyword.fetch!(opts, :channel_id)

    state = %State{
      map_id: map_id,
      channel_id: channel_id,
      players: %{},
      monsters: %{},
      npcs: %{},
      items: %{},
      reactors: %{},
      next_oid: 500_000,
      return_map: nil,
      forced_return: nil,
      time_limit: nil,
      field_limit: 0,
      mob_rate: 1.0,
      drop_rate: 1.0,
      created_at: DateTime.utc_now()
    }

    Logger.debug("Map loaded: #{map_id} (channel #{channel_id})")
    {:ok, state}
  end

  @impl true
  def handle_call({:add_player, character_id}, _from, state) do
    # Allocate OID for this player
    oid = state.next_oid

    # Get character state
    case Character.get_state(character_id) do
      %Character.State{} = char_state ->
        # Add player to map
        player_entry = %{
          oid: oid,
          character: char_state
        }

        new_players = Map.put(state.players, character_id, player_entry)

        # Broadcast spawn packet to other players
        spawn_packet = ChannelPackets.spawn_player(oid, char_state)
        broadcast_to_players(new_players, spawn_packet, except: character_id)

        # Send existing players to new player
        client_pid = char_state.client_pid

        if client_pid do
          send_existing_players(client_pid, new_players, except: character_id)
        end

        new_state = %{
          state
          | players: new_players,
            next_oid: oid + 1
        }

        {:reply, {:ok, oid}, new_state}

      nil ->
        {:reply, {:error, :character_not_found}, state}
    end
  end

  @impl true
  def handle_call({:remove_player, character_id}, _from, state) do
    case Map.get(state.players, character_id) do
      nil ->
        {:reply, :ok, state}

      player_entry ->
        # Broadcast despawn packet
        despawn_packet = ChannelPackets.remove_player(player_entry.oid)
        broadcast_to_players(state.players, despawn_packet, except: character_id)

        # Remove from map
        new_players = Map.delete(state.players, character_id)
        new_state = %{state | players: new_players}

        {:reply, :ok, new_state}
    end
  end

  @impl true
  def handle_call(:get_players, _from, state) do
    {:reply, state.players, state}
  end

  @impl true
  def handle_cast({:broadcast, packet}, state) do
    broadcast_to_players(state.players, packet)
    {:noreply, state}
  end

  @impl true
  def handle_cast({:broadcast_except, except_character_id, packet}, state) do
    broadcast_to_players(state.players, packet, except: except_character_id)
    {:noreply, state}
  end

  # ============================================================================
  # Helper Functions
  # ============================================================================

  defp via_tuple(map_id, channel_id) do
    {:via, Registry, {Odinsea.MapRegistry, {map_id, channel_id}}}
  end

  defp broadcast_to_players(players, packet, opts \\ []) do
    except_char_id = Keyword.get(opts, :except)

    Enum.each(players, fn
      {char_id, %{character: char_state}} when char_id != except_char_id ->
        if char_state.client_pid do
          send_packet(char_state.client_pid, packet)
        end

      _ ->
        :ok
    end)
  end

  defp send_existing_players(client_pid, players, opts) do
    except_char_id = Keyword.get(opts, :except)

    Enum.each(players, fn
      {char_id, %{oid: oid, character: char_state}} when char_id != except_char_id ->
        spawn_packet = ChannelPackets.spawn_player(oid, char_state)
        send_packet(client_pid, spawn_packet)

      _ ->
        :ok
    end)
  end

  defp send_packet(client_pid, packet) do
    send(client_pid, {:send_packet, packet})
  end
end