defmodule Odinsea.Login.Packets do
  @moduledoc """
  Login server packet builders.
  Ported from Java LoginPacket.java

  Builds outgoing packets for the login server:
  - Authentication responses
  - Server/world lists
  - Character lists
  - Character creation/deletion responses
  """

  alias Odinsea.Net.Packet.Out
  alias Odinsea.Net.Opcodes
  alias Odinsea.Constants.Server

  # ==================================================================================================
  # Connection & Handshake
  # ==================================================================================================

  @doc """
  Builds the initial hello/handshake packet sent to the client.
  Contains maple version, patch version, send/recv IVs, and locale.

  ## Parameters
  - `maple_version` - MapleStory version (342 for GMS v342)
  - `send_iv` - 4-byte send IV for encryption
  - `recv_iv` - 4-byte recv IV for encryption

  ## Returns
  Raw binary packet (with length header prepended)
  """
  def get_hello(maple_version, send_iv, recv_iv) when byte_size(send_iv) == 4 and byte_size(recv_iv) == 4 do
    packet_length = 13 + byte_size(Server.maple_patch())

    Out.new()
    |> Out.encode_short(packet_length)
    |> Out.encode_short(maple_version)
    |> Out.encode_string(Server.maple_patch())
    |> Out.encode_buffer(recv_iv)
    |> Out.encode_buffer(send_iv)
    |> Out.encode_byte(Server.maple_locale())
    |> Out.to_data()
  end

  @doc """
  Builds a ping/alive request packet.
  Client should respond with CP_AliveAck.
  """
  def get_ping do
    Out.new(Opcodes.lp_alive_req())
    |> Out.to_data()
  end

  @doc """
  Sends the login background image path to the client.
  """
  def get_login_background(background_path) do
    # Note: In Java this uses LoopbackPacket.LOGIN_AUTH
    # Need to verify the correct opcode for this
    Out.new(Opcodes.lp_set_client_key())  # TODO: Verify opcode
    |> Out.encode_string(background_path)
    |> Out.to_data()
  end

  @doc """
  Sends the RSA public key to the client for password encryption.
  """
  def get_rsa_key(public_key) do
    Out.new(Opcodes.lp_set_client_key())
    |> Out.encode_string(public_key)
    |> Out.to_data()
  end

  # ==================================================================================================
  # Authentication
  # ==================================================================================================

  @doc """
  Login failed response with reason code.

  ## Reason Codes
  - 3: ID deleted or blocked
  - 4: Incorrect password
  - 5: Not a registered ID
  - 6: System error
  - 7: Already logged in
  - 8: System error
  - 10: Cannot process so many connections
  - 13: Unable to log on as master at this IP
  - 16: Please verify your account through email
  - 32: IP blocked
  """
  def get_login_failed(reason) do
    packet =
      Out.new(Opcodes.lp_check_password_result())
      |> Out.encode_byte(reason)

    packet =
      cond do
        reason == 84 ->
          # Password change required
          Out.encode_long(packet, get_time(-2))

        reason == 7 ->
          # Already logged in
          Out.encode_bytes(packet, <<0, 0, 0, 0, 0>>)

        true ->
          packet
      end

    Out.to_data(packet)
  end

  @doc """
  Permanent ban response.
  """
  def get_perm_ban(reason) do
    Out.new(Opcodes.lp_check_password_result())
    |> Out.encode_short(2)  # Account is banned
    |> Out.encode_int(0)
    |> Out.encode_short(reason)
    |> Out.encode_buffer(<<1, 1, 1, 1, 0>>)
    |> Out.to_data()
  end

  @doc """
  Temporary ban response.
  """
  def get_temp_ban(timestamp_till, reason) do
    Out.new(Opcodes.lp_check_password_result())
    |> Out.encode_int(2)
    |> Out.encode_short(0)
    |> Out.encode_byte(reason)
    |> Out.encode_long(timestamp_till)
    |> Out.to_data()
  end

  @doc """
  Successful authentication response.

  ## Parameters
  - `account_id` - Account ID
  - `account_name` - Account username
  - `gender` - Gender (0=male, 1=female, 2=unset)
  - `is_gm` - Admin/GM status
  - `second_password` - Second password (nil if not set)
  """
  def get_auth_success(account_id, account_name, gender, is_gm, second_password) do
    admin_byte = if is_gm, do: 1, else: 0
    spw_byte = get_second_password_byte(second_password)

    Out.new(Opcodes.lp_check_password_result())
    |> Out.encode_bytes(<<0, 0, 0, 0, 0, 0>>)  # GMS specific
    |> Out.encode_int(account_id)
    |> Out.encode_byte(gender)
    |> Out.encode_byte(admin_byte)  # Admin byte - Find, Trade, etc.
    |> Out.encode_short(2)  # GMS: 2 for existing accounts, 0 for new
    |> Out.encode_byte(admin_byte)  # Admin byte - Commands
    |> Out.encode_string(account_name)
    |> Out.encode_int(3)  # 3 for existing accounts, 0 for new
    |> Out.encode_bytes(<<0, 0, 0, 0, 0, 0>>)
    |> Out.encode_long(get_time(System.system_time(:millisecond)))  # Account creation date
    |> Out.encode_int(4)  # 4 for existing accounts, 0 for new
    |> Out.encode_byte(1)  # 1 = PIN disabled, 0 = PIN enabled
    |> Out.encode_byte(spw_byte)  # Second password status
    |> Out.encode_long(:rand.uniform(1_000_000_000_000_000_000))  # Random long for anti-hack
    |> Out.to_data()
  end

  # ==================================================================================================
  # World/Server List
  # ==================================================================================================

  @doc """
  Sends a single world/server entry to the client.

  ## Parameters
  - `server_id` - World ID (0-based)
  - `world_name` - World name (e.g., "Scania")
  - `flag` - World flag/ribbon (0=none, 1=event, 2=new, 3=hot)
  - `event_message` - Event message shown on world
  - `channel_load` - Map of channel_id => population
  """
  def get_server_list(server_id, world_name, flag, event_message, channel_load) do
    last_channel = get_last_channel(channel_load)

    packet =
      Out.new(Opcodes.lp_world_information())
      |> Out.encode_byte(server_id)
      |> Out.encode_string(world_name)
      |> Out.encode_byte(flag)
      |> Out.encode_string(event_message)
      |> Out.encode_short(100)  # EXP rate display
      |> Out.encode_short(100)  # Drop rate display
      |> Out.encode_byte(0)  # GMS specific
      |> Out.encode_byte(last_channel)

    # Encode channel list
    packet =
      Enum.reduce(1..last_channel, packet, fn channel_id, acc ->
        load = Map.get(channel_load, channel_id, 1200)

        acc
        |> Out.encode_string("#{world_name}-#{channel_id}")
        |> Out.encode_int(load)
        |> Out.encode_byte(server_id)
        |> Out.encode_short(channel_id - 1)
      end)

    packet
    |> Out.encode_short(0)  # Balloon message size
    |> Out.encode_int(0)
    |> Out.to_data()
  end

  @doc """
  Sends the end-of-server-list marker.
  """
  def get_end_of_server_list do
    Out.new(Opcodes.lp_world_information())
    |> Out.encode_byte(0xFF)
    |> Out.to_data()
  end

  @doc """
  Sends server status (population indicator).

  ## Status codes
  - 0: Normal
  - 1: Highly populated
  - 2: Full
  """
  def get_server_status(status) do
    Out.new(Opcodes.lp_select_world_result())
    |> Out.encode_short(status)
    |> Out.to_data()
  end

  @doc """
  Sends latest connected world ID.
  """
  def get_latest_connected_world(world_id) do
    Out.new(Opcodes.lp_latest_connected_world())
    |> Out.encode_int(world_id)
    |> Out.to_data()
  end

  @doc """
  Sends recommended world message.
  """
  def get_recommend_world_message(world_id, message) do
    packet = Out.new(Opcodes.lp_recommend_world_message())

    packet =
      if message do
        packet
        |> Out.encode_byte(1)
        |> Out.encode_int(world_id)
        |> Out.encode_string(message)
      else
        Out.encode_byte(packet, 0)
      end

    Out.to_data(packet)
  end

  # ==================================================================================================
  # Character List
  # ==================================================================================================

  @doc """
  Sends character list for selected world.

  ## Parameters
  - `characters` - List of character maps
  - `second_password` - Second password (nil if not set)
  - `char_slots` - Number of character slots (default 3)
  """
  def get_char_list(characters, second_password, char_slots \\ 3) do
    spw_byte = get_second_password_byte(second_password)

    packet =
      Out.new(Opcodes.lp_select_character_result())
      |> Out.encode_byte(0)
      |> Out.encode_byte(length(characters))

    # TODO: Encode each character entry
    # For now, just encode empty list structure
    packet =
      Enum.reduce(characters, packet, fn _char, acc ->
        # add_char_entry(acc, char)
        acc  # TODO: Implement character encoding
      end)

    packet
    |> Out.encode_byte(spw_byte)
    |> Out.encode_long(char_slots)
    |> Out.to_data()
  end

  @doc """
  Character name check response.
  """
  def get_char_name_response(char_name, name_used) do
    Out.new(Opcodes.lp_check_duplicated_id_result())
    |> Out.encode_string(char_name)
    |> Out.encode_byte(if name_used, do: 1, else: 0)
    |> Out.to_data()
  end

  @doc """
  Character creation response.
  """
  def get_add_new_char_entry(character, worked) do
    Out.new(Opcodes.lp_create_new_character_result())
    |> Out.encode_byte(if worked, do: 0, else: 1)
    # TODO: Add character entry if worked
    |> Out.to_data()
  end

  @doc """
  Character deletion response.
  """
  def get_delete_char_response(character_id, state) do
    Out.new(Opcodes.lp_delete_character_result())
    |> Out.encode_int(character_id)
    |> Out.encode_byte(state)
    |> Out.to_data()
  end

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

  @doc """
  Second password error response.

  ## Mode codes
  - 14: Invalid password
  - 15: Second password is incorrect
  """
  def get_second_pw_error(mode) do
    Out.new(Opcodes.lp_check_spw_result())
    |> Out.encode_byte(mode)
    |> Out.to_data()
  end

  # ==================================================================================================
  # Migration (Channel Change)
  # ==================================================================================================

  @doc """
  Sends migration command to connect to channel/cash shop.

  ## Parameters
  - `is_cash_shop` - true for cash shop, false for channel
  - `host` - IP address to connect to
  - `port` - Port to connect to
  - `character_id` - Character ID for migration
  """
  def get_server_ip(is_cash_shop, host, port, character_id) do
    # Parse IP address
    ip_parts = parse_ip(host)

    Out.new(Opcodes.lp_migrate_command())
    |> Out.encode_short(if is_cash_shop, do: 1, else: 0)
    |> encode_ip(ip_parts)
    |> Out.encode_short(port)
    |> Out.encode_int(character_id)
    |> Out.encode_bytes(<<0, 0>>)
    |> Out.to_data()
  end

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

  defp get_second_password_byte(second_password) do
    cond do
      second_password == nil -> 0
      second_password == "" -> 2
      true -> 1
    end
  end

  defp get_last_channel(channel_load) do
    channel_load
    |> Map.keys()
    |> Enum.max(fn -> 1 end)
  end

  @doc """
  Converts a Unix timestamp (milliseconds) to MapleStory time format.
  MapleStory uses Windows FILETIME (100-nanosecond intervals since 1601-01-01).
  """
  def get_time(timestamp_ms) when timestamp_ms < 0 do
    # Special values
    0
  end

  def get_time(timestamp_ms) do
    # Convert Unix epoch (1970-01-01) to Windows epoch (1601-01-01)
    # Difference: 11644473600 seconds = 11644473600000 milliseconds
    windows_epoch_offset = 11_644_473_600_000

    # Convert to 100-nanosecond intervals
    (timestamp_ms + windows_epoch_offset) * 10_000
  end

  defp parse_ip(host) when is_binary(host) do
    case String.split(host, ".") do
      [a, b, c, d] ->
        {
          String.to_integer(a),
          String.to_integer(b),
          String.to_integer(c),
          String.to_integer(d)
        }

      _ ->
        {127, 0, 0, 1}  # Default to localhost
    end
  end

  defp encode_ip(packet, {a, b, c, d}) do
    packet
    |> Out.encode_byte(a)
    |> Out.encode_byte(b)
    |> Out.encode_byte(c)
    |> Out.encode_byte(d)
  end
end