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.{ClientCrypto, LoginCrypto}
  alias Odinsea.Net.PacketLogger
  alias Odinsea.Login.Packets
  alias Odinsea.Constants.Server
  alias Odinsea.Database.Context
  alias Odinsea.Game.{JobType, InventoryType}

  # ==================================================================================================
  # 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
    features = Application.get_env(:odinsea, :features, [])
    skip_maccheck = Keyword.get(features, :skip_maccheck, false)

    ip_banned = Context.ip_banned?(state.ip)
    mac_banned = if skip_maccheck or state.macs == [] do
      false
    else
      Enum.any?(state.macs, &Context.mac_banned?/1)
    end

    if (ip_banned || mac_banned) do
      Logger.warning("Banned IP/MAC attempted login: ip=#{state.ip}, macs=#{inspect(state.macs)}")

      # If MAC banned, also ban the IP for enforcement
      if mac_banned do
        Context.ban_ip_address(state.ip, "Enforcing account ban, account #{username}", false, 4)
      end

      response = Packets.get_login_failed(3)
      state = send_packet(state, response)
      {:ok, state}
    else
      # Authenticate with database
      case Context.authenticate_user(username, password, state.ip) do
        {:ok, account_info} ->
          # Check if account is banned (perm or temp)
          temp_ban_info = Context.get_temp_ban_info(account_info.account_id)
          
          if temp_ban_info do
            Logger.warning("Temp banned account attempted login: #{username}")
            response = Packets.get_temp_ban(
              format_timestamp(temp_ban_info.expires),
              temp_ban_info.reason || ""
            )
            state = send_packet(state, response)
            {:ok, state}
          else
            # Check if already logged in - kick other session
            login_state = Context.get_login_state(account_info.account_id)
            
            if login_state > 0 do
              Logger.warning("Account already logged in, kicking other session: #{username}")
              # Kick the existing session
              kick_existing_session(account_info.account_id, username)
              # Small delay to allow kick to process
              Process.sleep(100)
            end
            
            # Update login state to logged in
            Context.update_login_state(account_info.account_id, 2, state.ip)

            # 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
            )

            state = send_packet(state, response)

            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 world info immediately after auth success (Java: LoginWorker.registerClient)
            on_world_info_request(new_state)
          end

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

        {:error, :already_logged_in} ->
          # Try to kick the existing session and allow retry
          Logger.warning("Already logged in, attempting to kick session for: #{username}")
          kick_existing_session_by_name(username)
          Process.sleep(100)
          
          # Send login failed (reason 7 = already logged in) but client can retry
          response = Packets.get_login_failed(7)
          state = send_packet(state, response)
          {:ok, state}

        {:error, :banned} ->
          response = Packets.get_perm_ban(0)
          state = send_packet(state, response)
          {:ok, state}
      end
    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
    )

    state = send_packet(state, server_list)

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

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

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

        # Load character list from database
        characters = load_characters(state.account_id, world_id)
        
        # Store character IDs in state for later validation
        char_ids = Enum.map(characters, & &1.id)

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

        state = send_packet(state, response)

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

        {: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)

      # 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)
      state = 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_int, 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_int}")
      
      # Validate name is not forbidden and doesn't exist
      if check_name_used(name, state) do
        response = Packets.get_add_new_char_entry(nil, false)
        state = send_packet(state, response)
        {:ok, state}
      else
        # TODO: Validate appearance items are eligible for gender/job type
        # For now, accept the items as provided
        
        # Create character with default stats
        job_type = JobType.from_int(job_type_int)
        default_stats = Context.get_default_stats_for_job(job_type_int, dual_blade)
        default_map = Context.get_default_map_for_job(job_type_int)
        
        # Combine hair with hair color
        final_hair = hair + hair_color
        
        # Build character attributes
        attrs = Map.merge(default_stats, %{
          name: name,
          accountid: state.account_id,
          world: state.world,
          face: face,
          hair: final_hair,
          gender: gender,
          skin: skin_color,
          map: default_map
        })
        
        case Context.create_character(attrs) do
          {:ok, character} ->
            # Add default items to character inventory
            :ok = add_default_items(character.id, top, bottom, shoes, weapon, job_type_int)
            
            # Add job-specific starter items and quests
            :ok = add_job_specific_starters(character.id, job_type_int)
            
            Logger.info("Character created successfully: id=#{character.id}, name=#{name}")
            
            # Reload character with full data
            char_data = Context.load_character(character.id)
            response = Packets.get_add_new_char_entry(char_data, true)
            state = send_packet(state, response)

            # Add character ID to state's character list
            new_char_ids = [character.id | Map.get(state, :character_ids, [])]
            new_state = Map.put(state, :character_ids, new_char_ids)
            {:ok, new_state}
            
          {:error, changeset} ->
            Logger.error("Failed to create character: #{inspect(changeset.errors)}")
            response = Packets.get_add_new_char_entry(nil, false)
            state = send_packet(state, response)
            {:ok, state}
        end
      end
    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:
  - byte: has_spw (1 if second password provided)
  - string: second_password (if enabled)
  - string: asia_password (legacy, usually empty)
  - int: character_id
  """
  def on_delete_character(packet, state) do
    if not Map.get(state, :logged_in, false) do
      {:disconnect, :not_logged_in}
    else
      {has_spw, packet} = In.decode_byte(packet)
      
      # Read second password if enabled
      {spw, packet} = 
        if has_spw > 0 do
          In.decode_string(packet)
        else
          {"", packet}
        end
        
      {_asia_pw, packet} = In.decode_string(packet)
      {character_id, _packet} = In.decode_int(packet)

      Logger.info("Delete character: character_id=#{character_id}, account=#{state.account_name}")
      
      # Validate second password if account has one
      spw_valid = validate_second_password(state, spw)
      
      result = 
        cond do
          not spw_valid ->
            Logger.warning("Delete character: invalid second password")
            12  # Wrong Password
            
          not character_belongs_to_account?(character_id, state) ->
            Logger.warning("Delete character: character does not belong to account")
            1  # General error
            
          true ->
            # Attempt to delete character
            case Context.delete_character(character_id) do
              :ok ->
                Logger.info("Character deleted successfully: id=#{character_id}")
                # Remove from state's character list
                0  # Success
                
              {:error, reason} ->
                Logger.error("Failed to delete character: #{inspect(reason)}")
                1  # General error
            end
        end

      response = Packets.get_delete_char_response(character_id, result)
      state = send_packet(state, response)

      # Update state if successful
      new_state = 
        if result == 0 do
          new_char_ids = Enum.reject(Map.get(state, :character_ids, []), &(&1 == character_id))
          Map.put(state, :character_ids, new_char_ids)
        else
          state
        end

      {:ok, new_state}
    end
  end

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

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

  Packet structure:
  - byte: set_spw (1 if setting second password)
  - int: character_id
  """
  def on_select_character(packet, state) do
    if not Map.get(state, :logged_in, false) do
      {:disconnect, :not_logged_in}
    else
      {set_spw, packet} = In.decode_byte(packet)
      {character_id, _packet} = In.decode_int(packet)

      Logger.info("Select character: character_id=#{character_id}, channel=#{state.channel}")
      
      # Validate character belongs to account
      unless character_belongs_to_account?(character_id, state) do
        Logger.warning("Select character: character does not belong to account")
        {:disconnect, :invalid_character}
      else
        # Handle setting second password if requested
        if set_spw > 0 do
          {new_spw, _} = In.decode_string(packet)
          
          # Validate second password length
          if String.length(new_spw) < 6 || String.length(new_spw) > 16 do
            response = Packets.get_second_pw_error(0x14)
            state = send_packet(state, response)
            {:ok, state}
          else
            # Update second password
            Context.update_second_password(state.account_id, new_spw)
            Logger.info("Second password set for account: #{state.account_name}")
            
            # Continue with character selection
            do_character_migration(character_id, state)
          end
        else
          do_character_migration(character_id, state)
        end
      end
    end
  end
  
  defp do_character_migration(character_id, state) do
    # Load character data
    case Context.load_character(character_id) do
      nil ->
        Logger.error("Failed to load character: id=#{character_id}")
        {:disconnect, :character_not_found}
        
      character ->
        # Register migration token with channel server
        migration_token = generate_migration_token()
        
        # Store migration info in Redis/ETS for channel server
        :ok = register_migration_token(
          migration_token,
          character_id,
          state.account_id,
          state.channel
        )
        
        # Update login state to server transition
        Context.update_login_state(state.account_id, 1, state.ip)
        
        # Get channel IP and port
        {channel_ip, channel_port} = get_channel_endpoint(state.channel)
        
        Logger.info("Character migration: char=#{character.name} to channel #{state.channel} (#{channel_ip}:#{channel_port})")
        
        # Send migration command
        response = Packets.get_server_ip(false, channel_ip, channel_port, character_id)
        state = send_packet(state, response)

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

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

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

  Packet structure:
  - string: second_password
  - int: character_id
  """
  def on_check_spw_request(packet, state) do
    {spw, packet} = In.decode_string(packet)
    {character_id, _packet} = In.decode_int(packet)
    
    # Validate character belongs to account
    unless character_belongs_to_account?(character_id, state) do
      {:disconnect, :invalid_character}
    else
      stored_spw = Map.get(state, :second_password)

      if stored_spw == nil or stored_spw == spw do
        # Success - migrate to channel
        do_character_migration(character_id, state)
      else
        # Failure - send error
        response = Packets.get_second_pw_error(15)  # Incorrect SPW
        state = send_packet(state, response)
        {:ok, state}
      end
    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
    bg_response = Packets.get_login_background(Server.maplogin_default())
    state = send_packet(state, bg_response)

    # Send RSA public key
    key_response = Packets.get_rsa_key(Server.pub_key())
    state = send_packet(state, key_response)

    {:ok, state}
  end

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

  defp send_packet(%{socket: socket, crypto: crypto} = state, packet_data) do
    # Flatten iodata to binary for pattern matching
    packet_data = IO.iodata_to_binary(packet_data)

    # Extract opcode from packet data (first 2 bytes)
    <<opcode::little-16, rest::binary>> = packet_data

    # Log the packet
    context = %{
      ip: state.ip,
      server_type: :login
    }
    PacketLogger.log_server_packet(opcode, rest, context)

    # Encrypt the data (Shanda then AES) and morph send IV
    {updated_crypto, encrypted, header} = ClientCrypto.encrypt(crypto, packet_data)

    # Send encrypted packet with 4-byte crypto header
    full_packet = header <> encrypted

    case :gen_tcp.send(socket, full_packet) do
      :ok ->
        %{state | crypto: updated_crypto}

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

  defp send_packet(state, _packet_data) do
    # Socket not available in state
    Logger.error("Cannot send packet: socket not in state")
    state
  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
  
  defp character_belongs_to_account?(character_id, state) do
    char_ids = Map.get(state, :character_ids, [])
    character_id in char_ids
  end
  
  defp validate_second_password(state, provided_spw) do
    stored_spw = Map.get(state, :second_password)
    
    # If no second password set, accept any
    if stored_spw == nil || stored_spw == "" do
      true
    else
      stored_spw == provided_spw
    end
  end
  
  defp kick_existing_session(account_id, username) do
    # TODO: Implement session kicking via World server or Redis pub/sub
    # For now, just update login state to force disconnect on next tick
    Context.update_login_state(account_id, 0)
    
    # Publish kick message to Redis for other servers
    Odinsea.Database.Redis.publish("kick_session", %{account_id: account_id, username: username})
    :ok
  end
  
  defp kick_existing_session_by_name(username) do
    # Find account by name and kick
    case Context.get_account_by_name(username) do
      nil -> :ok
      account -> kick_existing_session(account.id, username)
    end
  end
  
  defp add_default_items(character_id, top, bottom, shoes, weapon, _job_type) do
    # Add equipped items
    Context.create_inventory_item(character_id, :equipped, %{
      item_id: top,
      position: -5,
      quantity: 1
    })
    
    if bottom > 0 do
      Context.create_inventory_item(character_id, :equipped, %{
        item_id: bottom,
        position: -6,
        quantity: 1
      })
    end
    
    Context.create_inventory_item(character_id, :equipped, %{
      item_id: shoes,
      position: -7,
      quantity: 1
    })
    
    Context.create_inventory_item(character_id, :equipped, %{
      item_id: weapon,
      position: -11,
      quantity: 1
    })
    
    # Add starter potions
    Context.create_inventory_item(character_id, :use, %{
      item_id: 2000013,
      position: 0,
      quantity: 100
    })
    
    Context.create_inventory_item(character_id, :use, %{
      item_id: 2000014,
      position: 0,
      quantity: 100
    })
    
    :ok
  end
  
  defp add_job_specific_starters(character_id, job_type) do
    case job_type do
      0 -> # Resistance
        Context.create_inventory_item(character_id, :etc, %{
          item_id: 4161001,
          position: 0,
          quantity: 1
        })
        
      1 -> # Adventurer
        Context.create_inventory_item(character_id, :etc, %{
          item_id: 4161001,
          position: 0,
          quantity: 1
        })
        
      2 -> # Cygnus
        # Add starter quests
        Context.set_quest_progress(character_id, 20022, 1, "1")
        Context.set_quest_progress(character_id, 20010, 1, nil)
        
        Context.create_inventory_item(character_id, :etc, %{
          item_id: 4161047,
          position: 0,
          quantity: 1
        })
        
      3 -> # Aran
        Context.create_inventory_item(character_id, :etc, %{
          item_id: 4161048,
          position: 0,
          quantity: 1
        })
        
      4 -> # Evan
        Context.create_inventory_item(character_id, :etc, %{
          item_id: 4161052,
          position: 0,
          quantity: 1
        })
        
      _ ->
        :ok
    end
    
    :ok
  end
  
  defp generate_migration_token do
    # Generate a unique migration token
    :crypto.strong_rand_bytes(16) |> Base.encode16(case: :lower)
  end
  
  defp register_migration_token(token, character_id, account_id, channel) do
    # Store in Redis with TTL for channel server to pick up
    Odinsea.Database.Redis.setex(
      "migration:#{token}",
      30,  # 30 second TTL
      Jason.encode!(%{
        character_id: character_id,
        account_id: account_id,
        channel: channel,
        timestamp: System.system_time(:second)
      })
    )
    :ok
  end
  
  defp get_channel_endpoint(channel) do
    # TODO: Get actual channel IP from World server config
    # For now, return localhost with calculated port
    ip = Application.get_env(:odinsea, :channel_ip, "127.0.0.1")
    base_port = Application.get_env(:odinsea, :channel_base_port, 8585)
    port = base_port + (channel - 1)
    {ip, port}
  end
  
  defp format_timestamp(naive_datetime) do
    NaiveDateTime.to_string(naive_datetime)
  end
end