defmodule Odinsea.Login.Handler do
  @moduledoc """
  Login server packet handlers.
  Ported from Java CharLoginHandler.java

  Handles all login-related operations:
  - Authentication (login/password)
  - World/server selection
  - Character list
  - Character creation/deletion
  - Character selection (migration to channel)
  """

  require Logger

  alias Odinsea.Net.Packet.{In, Out}
  alias Odinsea.Net.Cipher.LoginCrypto
  alias Odinsea.Login.Packets
  alias Odinsea.Constants.Server
  alias Odinsea.Database.Context

  # ==================================================================================================
  # Permission Request (Client Hello / Version Check)
  # ==================================================================================================

  @doc """
  Handles permission request (initial client hello).
  Validates client version, locale, and patch.

  Packet structure:
  - byte: locale
  - short: major version
  - short: minor version (patch)
  """
  def on_permission_request(packet, state) do
    {locale, packet} = In.decode_byte(packet)
    {major, packet} = In.decode_short(packet)
    {minor, _packet} = In.decode_short(packet)

    # Validate version
    if locale != Server.maple_locale() or
       major != Server.maple_version() or
       Integer.to_string(minor) != Server.maple_patch() do
      Logger.warning("Invalid client version: locale=#{locale}, major=#{major}, minor=#{minor}")
      {:disconnect, :invalid_version}
    else
      Logger.debug("Permission request validated")
      {:ok, state}
    end
  end

  # ==================================================================================================
  # Password Check (Authentication)
  # ==================================================================================================

  @doc """
  Handles password check (login authentication).

  Packet structure:
  - string: username
  - string: password (RSA encrypted if enabled)
  """
  def on_check_password(packet, state) do
    {username, packet} = In.decode_string(packet)
    {password_encrypted, _packet} = In.decode_string(packet)

    # Decrypt password if encryption is enabled
    password =
      if Application.get_env(:odinsea, :encrypt_passwords, false) do
        case LoginCrypto.decrypt_rsa(password_encrypted) do
          {:ok, decrypted} -> decrypted
          {:error, _} -> password_encrypted
        end
      else
        password_encrypted
      end

    Logger.info("Login attempt: username=#{username} from #{state.ip}")

    # Check if IP/MAC is banned
    # TODO: Implement IP/MAC ban checking
    is_banned = false

    # Authenticate with database
    case Context.authenticate_user(username, password, state.ip) do
      {:ok, account_info} ->
        # TODO: Check if account is banned or temp banned
        # TODO: Check if already logged in (kick other session)

        # Send success response
        response = Packets.get_auth_success(
          account_info.account_id,
          account_info.username,
          account_info.gender,
          account_info.is_gm,
          account_info.second_password
        )

        new_state =
          state
          |> Map.put(:logged_in, true)
          |> Map.put(:account_id, account_info.account_id)
          |> Map.put(:account_name, account_info.username)
          |> Map.put(:gender, account_info.gender)
          |> Map.put(:is_gm, account_info.is_gm)
          |> Map.put(:second_password, account_info.second_password)
          |> Map.put(:login_attempts, 0)

        send_packet(state, response)
        {:ok, new_state}

      {:error, :invalid_credentials} ->
        # Increment login attempts
        login_attempts = Map.get(state, :login_attempts, 0) + 1

        if login_attempts > 5 do
          Logger.warning("Too many login attempts from #{state.ip}")
          {:disconnect, :too_many_attempts}
        else
          # Send login failed (reason 4 = incorrect password)
          response = Packets.get_login_failed(4)
          send_packet(state, response)

          new_state = Map.put(state, :login_attempts, login_attempts)
          {:ok, new_state}
        end

      {:error, :account_not_found} ->
        # Send login failed (reason 5 = not registered ID)
        response = Packets.get_login_failed(5)
        send_packet(state, response)
        {:ok, state}

      {:error, :already_logged_in} ->
        # Send login failed (reason 7 = already logged in)
        response = Packets.get_login_failed(7)
        send_packet(state, response)
        {:ok, state}

      {:error, :banned} ->
        # TODO: Check temp ban vs perm ban
        response = Packets.get_perm_ban(0)
        send_packet(state, response)
        {:ok, state}
    end
  end

  # ==================================================================================================
  # World Info Request (Server List)
  # ==================================================================================================

  @doc """
  Handles world info request.
  Sends the list of available worlds/servers and channels.
  """
  def on_world_info_request(state) do
    # TODO: Get actual channel load from World server
    # For now, send a stub response
    channel_load = get_channel_load()

    # Send server list
    server_list = Packets.get_server_list(
      0,  # server_id
      "Odinsea",  # world_name
      0,  # flag (0=normal, 1=event, 2=new, 3=hot)
      "Welcome to Odinsea!",  # event_message
      channel_load
    )

    send_packet(state, server_list)

    # Send end of server list
    end_list = Packets.get_end_of_server_list()
    send_packet(state, end_list)

    # Send latest connected world
    latest_world = Packets.get_latest_connected_world(0)
    send_packet(state, latest_world)

    # Send recommended world message
    recommend = Packets.get_recommend_world_message(0, "Join now!")
    send_packet(state, recommend)

    {:ok, state}
  end

  # ==================================================================================================
  # Check User Limit (Server Capacity)
  # ==================================================================================================

  @doc """
  Handles check user limit request.
  Returns server population status.
  """
  def on_check_user_limit(state) do
    # TODO: Get actual user count from World server
    {users_online, user_limit} = get_user_count()

    status =
      cond do
        users_online >= user_limit -> 2  # Full
        users_online * 2 >= user_limit -> 1  # Highly populated
        true -> 0  # Normal
      end

    response = Packets.get_server_status(status)
    send_packet(state, response)

    {:ok, state}
  end

  # ==================================================================================================
  # Select World (Load Character List)
  # ==================================================================================================

  @doc """
  Handles world selection.
  Validates world/channel and sends character list.

  Packet structure:
  - byte: world_id
  - byte: channel_id (0-based, add 1 for actual channel)
  """
  def on_select_world(packet, state) do
    if not Map.get(state, :logged_in, false) do
      Logger.warning("Select world: not logged in")
      {:disconnect, :not_logged_in}
    else
      {world_id, packet} = In.decode_byte(packet)
      {channel_id, _packet} = In.decode_byte(packet)

      actual_channel = channel_id + 1

      # Validate world
      if world_id != 0 do
        Logger.warning("Invalid world ID: #{world_id}")
        response = Packets.get_login_failed(10)
        send_packet(state, response)
        {:ok, state}
      else
        # TODO: Check if channel is available
        # if not World.is_channel_available(actual_channel) do
        #   response = Packets.get_login_failed(10)
        #   send_packet(state, response)
        #   {:ok, state}
        # else

        # TODO: Load character list from database
        characters = load_characters(state.account_id, world_id)

        response = Packets.get_char_list(
          characters,
          state.second_password,
          3  # character slots
        )

        send_packet(state, response)

        new_state =
          state
          |> Map.put(:world, world_id)
          |> Map.put(:channel, actual_channel)

        {:ok, new_state}
      end
    end
  end

  # ==================================================================================================
  # Check Duplicated ID (Character Name Availability)
  # ==================================================================================================

  @doc """
  Handles character name availability check.

  Packet structure:
  - string: character_name
  """
  def on_check_duplicated_id(packet, state) do
    if not Map.get(state, :logged_in, false) do
      {:disconnect, :not_logged_in}
    else
      {char_name, _packet} = In.decode_string(packet)

      # TODO: Check if name is forbidden or already exists
      name_used = check_name_used(char_name, state)

      response = Packets.get_char_name_response(char_name, name_used)
      send_packet(state, response)

      {:ok, state}
    end
  end

  # ==================================================================================================
  # Create New Character
  # ==================================================================================================

  @doc """
  Handles character creation.

  Packet structure:
  - string: name
  - int: job_type (0=Resistance, 1=Adventurer, 2=Cygnus, 3=Aran, 4=Evan)
  - short: dual_blade (1=DB, 0=Adventurer)
  - byte: gender (GMS only)
  - int: face
  - int: hair
  - int: hair_color
  - int: skin_color
  - int: top
  - int: bottom
  - int: shoes
  - int: weapon
  """
  def on_create_new_character(packet, state) do
    if not Map.get(state, :logged_in, false) do
      {:disconnect, :not_logged_in}
    else
      {name, packet} = In.decode_string(packet)
      {job_type, packet} = In.decode_int(packet)
      {_dual_blade, packet} = In.decode_short(packet)
      {gender, packet} = In.decode_byte(packet)
      {face, packet} = In.decode_int(packet)
      {hair, packet} = In.decode_int(packet)
      {hair_color, packet} = In.decode_int(packet)
      {skin_color, packet} = In.decode_int(packet)
      {top, packet} = In.decode_int(packet)
      {bottom, packet} = In.decode_int(packet)
      {shoes, packet} = In.decode_int(packet)
      {weapon, _packet} = In.decode_int(packet)

      Logger.info("Create character: name=#{name}, job_type=#{job_type}")

      # TODO: Validate appearance items
      # TODO: Create character in database
      # TODO: Add default items and quests

      # For now, send success stub
      response = Packets.get_add_new_char_entry(%{}, false)  # TODO: Pass actual character
      send_packet(state, response)

      {:ok, state}
    end
  end

  # ==================================================================================================
  # Create Ultimate (Cygnus Knight → Ultimate Adventurer)
  # ==================================================================================================

  @doc """
  Handles ultimate adventurer creation (Cygnus Knight transformation).
  """
  def on_create_ultimate(_packet, state) do
    # TODO: Implement ultimate creation
    # Requires level 120 Cygnus Knight in Ereve
    Logger.debug("Create ultimate request (not implemented)")
    {:ok, state}
  end

  # ==================================================================================================
  # Delete Character
  # ==================================================================================================

  @doc """
  Handles character deletion.

  Packet structure:
  - string: second_password (if enabled)
  - int: character_id
  """
  def on_delete_character(packet, state) do
    if not Map.get(state, :logged_in, false) do
      {:disconnect, :not_logged_in}
    else
      # TODO: Read second password if enabled
      {_spw, packet} = In.decode_string(packet)
      {character_id, _packet} = In.decode_int(packet)

      Logger.info("Delete character: character_id=#{character_id}")

      # TODO: Validate second password
      # TODO: Check if character belongs to account
      # TODO: Delete character from database

      # For now, send success stub
      response = Packets.get_delete_char_response(character_id, 0)
      send_packet(state, response)

      {:ok, state}
    end
  end

  # ==================================================================================================
  # Select Character (Enter Game / Migrate to Channel)
  # ==================================================================================================

  @doc """
  Handles character selection (enter game).
  Initiates migration to the selected channel.

  Packet structure:
  - int: character_id
  """
  def on_select_character(packet, state) do
    if not Map.get(state, :logged_in, false) do
      {:disconnect, :not_logged_in}
    else
      {character_id, _packet} = In.decode_int(packet)

      Logger.info("Select character: character_id=#{character_id}, channel=#{state.channel}")

      # TODO: Validate character belongs to account
      # TODO: Load character data
      # TODO: Register migration token with channel server

      # Send migration command to connect to channel
      # TODO: Get actual channel IP/port
      channel_ip = "127.0.0.1"
      channel_port = 8585 + (state.channel - 1)

      response = Packets.get_server_ip(false, channel_ip, channel_port, character_id)
      send_packet(state, response)

      new_state = Map.put(state, :character_id, character_id)
      {:ok, new_state}
    end
  end

  # ==================================================================================================
  # Check Second Password
  # ==================================================================================================

  @doc """
  Handles second password verification (SPW / PIC).

  Packet structure:
  - string: second_password
  """
  def on_check_spw_request(packet, state) do
    {spw, _packet} = In.decode_string(packet)

    # TODO: Validate second password
    stored_spw = Map.get(state, :second_password)

    if stored_spw == nil or stored_spw == spw do
      # Success - continue with operation
      {:ok, state}
    else
      # Failure - send error
      response = Packets.get_second_pw_error(15)  # Incorrect SPW
      send_packet(state, response)
      {:ok, state}
    end
  end

  # ==================================================================================================
  # RSA Key Request
  # ==================================================================================================

  @doc """
  Handles RSA key request.
  Sends RSA public key and login background.
  """
  def on_rsa_key(_packet, state) do
    # TODO: Check if custom client is enabled
    # TODO: Send damage cap packet if custom client

    # Send login background
    background = Application.get_env(:odinsea, :login_background, "MapLogin")
    bg_response = Packets.get_login_background(background)
    send_packet(state, bg_response)

    # Send RSA public key
    pub_key = Application.get_env(:odinsea, :rsa_public_key, "")
    key_response = Packets.get_rsa_key(pub_key)
    send_packet(state, key_response)

    {:ok, state}
  end

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

  defp send_packet(%{socket: socket} = state, packet_data) do
    # Add header (2 bytes: packet length)
    packet_length = byte_size(packet_data)
    header = <<packet_length::little-size(16)>>
    full_packet = header <> packet_data

    case :gen_tcp.send(socket, full_packet) do
      :ok ->
        Logger.debug("Sent packet: #{packet_length} bytes")
        :ok

      {:error, reason} ->
        Logger.error("Failed to send packet: #{inspect(reason)}")
        {:error, reason}
    end
  end

  defp send_packet(_state, _packet_data) do
    # Socket not available in state
    Logger.error("Cannot send packet: socket not in state")
    :error
  end

  defp authenticate_user(username, password, _state) do
    # Delegated to Context.authenticate_user/3
    Context.authenticate_user(username, password)
  end

  defp get_channel_load do
    # TODO: Get actual channel load from World server
    # For now, return stub data
    %{
      1 => 100,
      2 => 200,
      3 => 150
    }
  end

  defp get_user_count do
    # TODO: Get actual user count from World server
    {50, 1000}
  end

  defp load_characters(account_id, world_id) do
    Context.load_character_entries(account_id, world_id)
  end

  defp check_name_used(char_name, _state) do
    # Check if name is forbidden or already exists
    Context.forbidden_name?(char_name) or
      Context.character_name_exists?(char_name)
  end
end