defmodule Odinsea.Channel.Handler.InterServer do
  @moduledoc """
  Inter-server migration handler.
  Handles players migrating into the channel server from login or other channels.
  
  Ported from Java handling.channel.handler.InterServerHandler.MigrateIn
  """

  require Logger

  alias Odinsea.Database.Context
  alias Odinsea.World.Migration
  alias Odinsea.Channel.Packets

  @doc """
  Handles character migration into the channel server.
  
  ## Parameters
  - character_id: The character ID migrating in
  - client_state: The client connection state
  
  ## Returns
  - {:ok, new_state} on success
  - {:error, reason, state} on failure
  - {:disconnect, reason} on critical failure
  """
  def migrate_in(character_id, %{socket: socket, ip: ip} = state) do
    Logger.info("Migrate in: character_id=#{character_id} from #{ip}")
    
    # Check if character is already online in this channel
    if Odinsea.Channel.Players.is_online?(character_id) do
      Logger.error("Character #{character_id} already online, disconnecting")
      {:disconnect, :already_online}
    else
      # Check for pending migration token
      token = Migration.get_pending_character(character_id)
      
      if token do
        # Validate the token
        case Migration.validate_migration_token(token.id, character_id, :channel) do
          {:ok, valid_token} ->
            # Use transfer data if available
            do_migrate_in(character_id, valid_token.account_id, state, valid_token.character_data)
            
          {:error, reason} ->
            Logger.warning("Migration token validation failed: #{inspect(reason)}")
            # Fall back to database load
            do_migrate_in(character_id, nil, state, %{})
        end
      else
        # No token, load directly from database (direct login)
        do_migrate_in(character_id, nil, state, %{})
      end
    end
  end

  @doc """
  Handles channel change request from client.
  
  ## Parameters
  - target_channel: The target channel (1-20)
  - state: Client state
  
  ## Returns
  - {:ok, new_state} - Will disconnect client for migration
  """
  def change_channel(target_channel, %{character_id: char_id, account_id: acc_id} = state) do
    Logger.info("Change channel: character=#{char_id} to channel #{target_channel}")
    
    # Check server capacity
    if Migration.pending_count() >= 10 do
      Logger.warning("Server busy, rejecting channel change")
      response = Packets.server_blocked(2)
      send_packet(state, response)
      send_packet(state, Packets.enable_actions())
      {:ok, state}
    else
      # TODO: Check if player has blocked inventory, is in event, etc.
      
      # Save character to database
      Context.update_character_position(char_id, state.map_id, state.spawn_point)
      
      # Create migration token
      character_data = %{
        map_id: state.map_id,
        hp: state.hp,
        mp: state.mp,
        buffs: state.buffs || []
      }
      
      case Migration.create_migration_token(char_id, acc_id, :channel, target_channel, character_data) do
        {:ok, token_id} ->
          # Get channel IP and port
          channel_ip = get_channel_ip(target_channel)
          channel_port = get_channel_port(target_channel)
          
          # Send migration command
          response = Packets.get_channel_change(channel_ip, channel_port, char_id)
          send_packet(state, response)
          
          # Update login state
          Context.update_login_state(acc_id, 3, state.ip)  # CHANGE_CHANNEL
          
          # Remove player from current channel storage
          Odinsea.Channel.Players.remove_player(char_id)
          
          # Disconnect will happen after packet is sent
          {:disconnect, :changing_channel}
          
        {:error, reason} ->
          Logger.error("Failed to create migration token: #{inspect(reason)}")
          send_packet(state, Packets.server_blocked(2))
          send_packet(state, Packets.enable_actions())
          {:ok, state}
      end
    end
  end

  # ==================================================================================================
  # Private Functions
  # ==================================================================================================

  defp do_migrate_in(character_id, account_id, state, transfer_data) do
    # Load character from database
    character = Context.load_character(character_id)
    
    if is_nil(character) do
      Logger.error("Character #{character_id} not found in database")
      {:disconnect, :character_not_found}
    else
      # Verify account ownership if account_id provided
      if account_id && character.accountid != account_id do
        Logger.error("Character account mismatch: expected #{account_id}, got #{character.accountid}")
        {:disconnect, :account_mismatch}
      else
        # Check login state
        login_state = Context.get_login_state(character.accountid)
        
        allow_login = 
          login_state in [0, 1, 3]  # NOTLOGGEDIN, SERVER_TRANSITION, or CHANGE_CHANNEL
          # TODO: Check if character is already connected on another account's session
        
        if allow_login do
          complete_migration(character, state, transfer_data)
        else
          Logger.warning("Character #{character_id} already logged in elsewhere")
          {:disconnect, :already_logged_in}
        end
      end
    end
  end

  defp complete_migration(character, state, transfer_data) do
    # Update login state to logged in
    Context.update_login_state(character.accountid, 2, state.ip)
    
    # Add to channel player storage
    :ok = Odinsea.Channel.Players.add_player(character.id, %{
      character_id: character.id,
      account_id: character.accountid,
      name: character.name,
      map_id: character.map,
      level: character.level,
      job: character.job,
      socket: state.socket
    })
    
    # Restore buffs/cooldowns from transfer data or storage
    restored_buffs = transfer_data[:buffs] || []
    
    # Send character info packet
    char_info = Packets.get_char_info(character, restored_buffs)
    send_packet(state, char_info)
    
    # Send cash shop enable packet
    send_packet(state, Packets.enable_cash_shop())
    
    # TODO: Send buddy list, guild info, etc.
    
    new_state = 
      state
      |> Map.put(:character_id, character.id)
      |> Map.put(:account_id, character.accountid)
      |> Map.put(:character_name, character.name)
      |> Map.put(:map_id, character.map)
      |> Map.put(:hp, character.hp)
      |> Map.put(:mp, character.mp)
      |> Map.put(:level, character.level)
      |> Map.put(:job, character.job)
      |> Map.put(:logged_in, true)
    
    Logger.info("Character #{character.name} (#{character.id}) successfully migrated in")
    
    {:ok, new_state}
  end

  defp send_packet(%{socket: socket}, packet_data) do
    packet_length = byte_size(packet_data)
    header = <<packet_length::little-size(16)>>
    
    case :gen_tcp.send(socket, header <> packet_data) do
      :ok -> :ok
      {:error, reason} ->
        Logger.error("Failed to send packet: #{inspect(reason)}")
        :error
    end
  end
  
  defp send_packet(_, _), do: :error

  defp get_channel_ip(channel_id) do
    # TODO: Get from configuration
    Application.get_env(:odinsea, :channel_ip, "127.0.0.1")
  end

  defp get_channel_port(channel_id) do
    # TODO: Get from configuration
    base_port = Application.get_env(:odinsea, :channel_base_port, 8585)
    base_port + channel_id - 1
  end
end