defmodule Odinsea.Game.Character do
  @moduledoc """
  Represents an in-game character (player) with stats, position, inventory, skills, etc.
  This is a GenServer that manages character state while the player is logged into a channel.

  Unlike the database schema (Odinsea.Database.Schema.Character), this module represents
  the live, mutable game state including position, buffs, equipment effects, etc.
  """
  use GenServer
  require Logger

  alias Odinsea.Database.Schema.Character, as: CharacterDB
  alias Odinsea.Game.Map, as: GameMap
  alias Odinsea.Game.{Inventory, InventoryType, Pet}
  alias Odinsea.Net.Packet.Out

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

  defmodule Stats do
    @moduledoc "Character stats (base + equipped + buffed)"
    defstruct [
      # Base stats
      :str,
      :dex,
      :int,
      :luk,
      :hp,
      :max_hp,
      :mp,
      :max_mp,
      # Computed stats (from equipment + buffs)
      :weapon_attack,
      :magic_attack,
      :weapon_defense,
      :magic_defense,
      :accuracy,
      :avoidability,
      :speed,
      :jump
    ]

    @type t :: %__MODULE__{
            str: non_neg_integer(),
            dex: non_neg_integer(),
            int: non_neg_integer(),
            luk: non_neg_integer(),
            hp: non_neg_integer(),
            max_hp: non_neg_integer(),
            mp: non_neg_integer(),
            max_mp: non_neg_integer(),
            weapon_attack: non_neg_integer(),
            magic_attack: non_neg_integer(),
            weapon_defense: non_neg_integer(),
            magic_defense: non_neg_integer(),
            accuracy: non_neg_integer(),
            avoidability: non_neg_integer(),
            speed: non_neg_integer(),
            jump: non_neg_integer()
          }
  end

  defmodule Position do
    @moduledoc "Character position and stance"
    defstruct [:x, :y, :foothold, :stance]

    @type t :: %__MODULE__{
            x: integer(),
            y: integer(),
            foothold: non_neg_integer(),
            stance: byte()
          }
  end

  defmodule State do
    @moduledoc "In-game character state"
    defstruct [
      # Identity
      :character_id,
      :account_id,
      :name,
      :world_id,
      :channel_id,
      # Character data
      :level,
      :job,
      :exp,
      :meso,
      :fame,
      :gender,
      :skin_color,
      :hair,
      :face,
      # GM Level (0 = normal player, >0 = GM)
      :gm,
      # Stats
      :stats,
      # Position & Map
      :map_id,
      :position,
      :spawn_point,
      # AP/SP
      :remaining_ap,
      :remaining_sp,
      # Client connection
      :client_pid,
      # Inventory (TODO)
      :inventories,
      # Skills (TODO)
      :skills,
      # Buffs (TODO)
      :buffs,
      # Pets (TODO)
      :pets,
      # Timestamps
      :created_at,
      :updated_at
    ]

    @type t :: %__MODULE__{
            character_id: pos_integer(),
            account_id: pos_integer(),
            name: String.t(),
            world_id: byte(),
            channel_id: byte(),
            level: non_neg_integer(),
            job: non_neg_integer(),
            exp: non_neg_integer(),
            meso: non_neg_integer(),
            fame: integer(),
            gender: byte(),
            skin_color: byte(),
            hair: non_neg_integer(),
            face: non_neg_integer(),
            gm: non_neg_integer(),
            stats: Stats.t(),
            map_id: non_neg_integer(),
            position: Position.t(),
            spawn_point: byte(),
            remaining_ap: non_neg_integer(),
            remaining_sp: list(non_neg_integer()),
            client_pid: pid() | nil,
            inventories: map(),
            skills: map(),
            buffs: list(),
            pets: list(),
            created_at: DateTime.t(),
            updated_at: DateTime.t()
          }
  end

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

  @doc """
  Starts a character GenServer for an in-game player.
  """
  def start_link(opts) do
    character_id = Keyword.fetch!(opts, :character_id)
    GenServer.start_link(__MODULE__, opts, name: via_tuple(character_id))
  end

  @doc """
  Loads a character from the database and starts their GenServer.
  """
  def load(character_id, account_id, world_id, channel_id, client_pid) do
    case Odinsea.Database.Context.get_character(character_id) do
      nil ->
        {:error, :character_not_found}

      db_char ->
        # Verify ownership
        if db_char.account_id != account_id do
          {:error, :unauthorized}
        else
          state = from_database(db_char, world_id, channel_id, client_pid)

          case start_link(character_id: character_id, state: state) do
            {:ok, pid} -> {:ok, pid, state}
            {:error, {:already_started, pid}} -> {:ok, pid, state}
            error -> error
          end
        end
    end
  end

  @doc """
  Gets the current character state.
  """
  def get_state(character_id) do
    GenServer.call(via_tuple(character_id), :get_state)
  end

  @doc """
  Updates character position (from movement packet).
  """
  def update_position(character_id, position) do
    GenServer.cast(via_tuple(character_id), {:update_position, position})
  end

  @doc """
  Changes the character's map.
  """
  def change_map(character_id, new_map_id, spawn_point \\ 0) do
    GenServer.call(via_tuple(character_id), {:change_map, new_map_id, spawn_point})
  end

  @doc """
  Gets the character's current map ID.
  """
  def get_map_id(character_id) do
    GenServer.call(via_tuple(character_id), :get_map_id)
  end

  @doc """
  Gets the character's client PID.
  """
  def get_client_pid(character_id) do
    GenServer.call(via_tuple(character_id), :get_client_pid)
  end

  @doc """
  Saves character to database.
  """
  def save(character_id) do
    GenServer.call(via_tuple(character_id), :save)
  end

  @doc """
  Stops the character GenServer (logout).
  """
  def logout(character_id) do
    GenServer.stop(via_tuple(character_id), :normal)
  end

  # ============================================================================
  # Inventory API
  # ============================================================================

  @doc """
  Gets a specific inventory.
  """
  def get_inventory(character_id, inv_type) do
    GenServer.call(via_tuple(character_id), {:get_inventory, inv_type})
  end

  @doc """
  Gets an item from a specific inventory slot.
  """
  def get_item(character_id, inv_type, position) do
    GenServer.call(via_tuple(character_id), {:get_item, inv_type, position})
  end

  @doc """
  Moves an item within or between inventories.
  """
  def move_item(character_id, inv_type, src_slot, dst_slot, slot_max \\ 100) do
    GenServer.call(via_tuple(character_id), {:move_item, inv_type, src_slot, dst_slot, slot_max})
  end

  @doc """
  Equips an item (moves from EQUIP inventory to EQUIPPED).
  """
  def equip_item(character_id, src_slot, dst_slot) do
    GenServer.call(via_tuple(character_id), {:equip_item, src_slot, dst_slot})
  end

  @doc """
  Unequips an item (moves from EQUIPPED to EQUIP inventory).
  """
  def unequip_item(character_id, src_slot, dst_slot) do
    GenServer.call(via_tuple(character_id), {:unequip_item, src_slot, dst_slot})
  end

  @doc """
  Drops an item from inventory.
  """
  def drop_item(character_id, inv_type, position, quantity \\ 1) do
    GenServer.call(via_tuple(character_id), {:drop_item, inv_type, position, quantity})
  end

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

  @impl true
  def init(opts) do
    state = Keyword.fetch!(opts, :state)
    Logger.debug("Character loaded: #{state.name} (ID: #{state.character_id})")
    {:ok, state}
  end

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

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

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

  @impl true
  def handle_call({:change_map, new_map_id, spawn_point}, _from, state) do
    old_map_id = state.map_id

    # Remove from old map
    if old_map_id do
      GameMap.remove_player(old_map_id, state.character_id)
    end

    # Update state
    new_state = %{
      state
      | map_id: new_map_id,
        spawn_point: spawn_point,
        updated_at: DateTime.utc_now()
    }

    # Add to new map
    GameMap.add_player(new_map_id, state.character_id)

    {:reply, :ok, new_state}
  end

  @impl true
  def handle_call(:save, _from, state) do
    result = save_to_database(state)
    {:reply, result, state}
  end

  @impl true
  def handle_call({:get_inventory, inv_type}, _from, state) do
    inventory = Map.get(state.inventories, inv_type, Inventory.new(inv_type))
    {:reply, inventory, state}
  end

  @impl true
  def handle_call({:get_item, inv_type, position}, _from, state) do
    inventory = Map.get(state.inventories, inv_type, Inventory.new(inv_type))
    item = Inventory.get_item(inventory, position)
    {:reply, item, state}
  end

  @impl true
  def handle_call({:move_item, inv_type, src_slot, dst_slot, slot_max}, _from, state) do
    inventory = Map.get(state.inventories, inv_type, Inventory.new(inv_type))
    
    case Inventory.move(inventory, src_slot, dst_slot, slot_max) do
      {:ok, new_inventory} ->
        new_inventories = Map.put(state.inventories, inv_type, new_inventory)
        new_state = %{state | inventories: new_inventories, updated_at: DateTime.utc_now()}
        {:reply, :ok, new_state}
      
      {:error, reason} ->
        {:reply, {:error, reason}, state}
    end
  end

  @impl true
  def handle_call({:equip_item, src_slot, dst_slot}, _from, state) do
    # Move from EQUIP to EQUIPPED
    equip_inv = Map.get(state.inventories, :equip, Inventory.new(:equip))
    equipped_inv = Map.get(state.inventories, :equipped, Inventory.new(:equipped))
    
    case Inventory.move(equip_inv, src_slot, dst_slot, 1) do
      {:ok, new_equip_inv} ->
        new_inventories = 
          state.inventories
          |> Map.put(:equip, new_equip_inv)
          |> Map.put(:equipped, equipped_inv)
        
        # TODO: Recalculate stats based on new equipment
        new_state = %{state | inventories: new_inventories, updated_at: DateTime.utc_now()}
        {:reply, :ok, new_state}
      
      {:error, reason} ->
        {:reply, {:error, reason}, state}
    end
  end

  @impl true
  def handle_call({:unequip_item, src_slot, dst_slot}, _from, state) do
    # Move from EQUIPPED to EQUIP
    equipped_inv = Map.get(state.inventories, :equipped, Inventory.new(:equipped))
    equip_inv = Map.get(state.inventories, :equip, Inventory.new(:equip))
    
    case Inventory.move(equipped_inv, src_slot, dst_slot, 1) do
      {:ok, new_equipped_inv} ->
        new_inventories = 
          state.inventories
          |> Map.put(:equipped, new_equipped_inv)
          |> Map.put(:equip, equip_inv)
        
        # TODO: Recalculate stats based on removed equipment
        new_state = %{state | inventories: new_inventories, updated_at: DateTime.utc_now()}
        {:reply, :ok, new_state}
      
      {:error, reason} ->
        {:reply, {:error, reason}, state}
    end
  end

  @impl true
  def handle_call({:drop_item, inv_type, position, quantity}, _from, state) do
    inventory = Map.get(state.inventories, inv_type, Inventory.new(inv_type))
    
    case Inventory.drop(inventory, position, quantity) do
      {:ok, dropped_item, new_inventory} ->
        new_inventories = Map.put(state.inventories, inv_type, new_inventory)
        new_state = %{state | inventories: new_inventories, updated_at: DateTime.utc_now()}
        {:reply, {:ok, dropped_item}, new_state}
      
      {:error, reason} ->
        {:reply, {:error, reason}, state}
    end
  end

  @impl true
  def handle_cast({:update_position, position}, state) do
    new_state = %{
      state
      | position: position,
        updated_at: DateTime.utc_now()
    }

    {:noreply, new_state}
  end

  @impl true
  def terminate(reason, state) do
    Logger.debug(
      "Character logout: #{state.name} (ID: #{state.character_id}), reason: #{inspect(reason)}"
    )

    # Remove from map
    if state.map_id do
      GameMap.remove_player(state.map_id, state.character_id)
    end

    # Save to database
    save_to_database(state)

    :ok
  end

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

  defp via_tuple(character_id) do
    {:via, Registry, {Odinsea.CharacterRegistry, character_id}}
  end

  @doc """
  Converts database character to in-game state.
  """
  def from_database(%CharacterDB{} = db_char, world_id, channel_id, client_pid) do
    stats = %Stats{
      str: db_char.str,
      dex: db_char.dex,
      int: db_char.int,
      luk: db_char.luk,
      hp: db_char.hp,
      max_hp: db_char.max_hp,
      mp: db_char.mp,
      max_mp: db_char.max_mp,
      # Computed stats - TODO: calculate from equipment
      weapon_attack: 0,
      magic_attack: 0,
      weapon_defense: 0,
      magic_defense: 0,
      accuracy: 0,
      avoidability: 0,
      speed: 100,
      jump: 100
    }

    position = %Position{
      x: 0,
      y: 0,
      foothold: 0,
      stance: 0
    }

    # Parse remaining_sp (stored as comma-separated string in Java version)
    remaining_sp =
      case db_char.remaining_sp do
        nil -> [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
        sp_str when is_binary(sp_str) -> parse_sp_string(sp_str)
        sp_list when is_list(sp_list) -> sp_list
      end

    # Load inventories from database
    inventories = load_inventories(db_char.id)

    %State{
      character_id: db_char.id,
      account_id: db_char.account_id,
      name: db_char.name,
      world_id: world_id,
      channel_id: channel_id,
      level: db_char.level,
      job: db_char.job,
      exp: db_char.exp,
      meso: db_char.meso,
      fame: db_char.fame,
      gender: db_char.gender,
      skin_color: db_char.skin_color,
      hair: db_char.hair,
      face: db_char.face,
      gm: db_char.gm,
      stats: stats,
      map_id: db_char.map_id,
      position: position,
      spawn_point: db_char.spawn_point,
      remaining_ap: db_char.remaining_ap,
      remaining_sp: remaining_sp,
      client_pid: client_pid,
      inventories: inventories,
      skills: %{},
      buffs: [],
      pets: [],
      created_at: db_char.inserted_at,
      updated_at: DateTime.utc_now()
    }
  end

  defp load_inventories(character_id) do
    # Initialize empty inventories for all types
    base_inventories = 
      InventoryType.all_types()
      |> Map.new(fn type -> {type, Inventory.new(type)} end)
    
    # Load items from database
    case Odinsea.Database.Context.load_character_inventory(character_id) do
      nil -> 
        base_inventories
      
      items_by_type ->
        # Add items to appropriate inventories
        Enum.reduce(items_by_type, base_inventories, fn {type, items}, acc ->
          inventory = 
            Enum.reduce(items, Inventory.new(type), fn item, inv ->
              Inventory.add_from_db(inv, item)
            end)
          
          Map.put(acc, type, inventory)
        end)
    end
  end

  defp parse_sp_string(sp_str) do
    sp_str
    |> String.split(",")
    |> Enum.map(&String.to_integer/1)
    |> Kernel.++(List.duplicate(0, 10))
    |> Enum.take(10)
  rescue
    _ -> [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
  end

  @doc """
  Saves character state to database.
  """
  def save_to_database(%State{} = state) do
    # Convert remaining_sp list to comma-separated string for database
    sp_string = Enum.join(state.remaining_sp, ",")

    attrs = %{
      level: state.level,
      job: state.job,
      exp: state.exp,
      str: state.stats.str,
      dex: state.stats.dex,
      int: state.stats.int,
      luk: state.stats.luk,
      hp: state.stats.hp,
      max_hp: state.stats.max_hp,
      mp: state.stats.mp,
      max_mp: state.stats.max_mp,
      meso: state.meso,
      fame: state.fame,
      map_id: state.map_id,
      spawn_point: state.spawn_point,
      remaining_ap: state.remaining_ap,
      remaining_sp: sp_string
    }

    # Save character base data
    result = Odinsea.Database.Context.update_character(state.character_id, attrs)

    # Save inventories
    Odinsea.Database.Context.save_character_inventory(state.character_id, state.inventories)

    result
  end

  @doc """
  Gives EXP to the character.
  Handles level-up, EXP calculation, and packet broadcasting.
  """
  def gain_exp(character_pid, exp_amount, is_highest_damage \\ false) when is_pid(character_pid) do
    GenServer.cast(character_pid, {:gain_exp, exp_amount, is_highest_damage})
  end

  # ============================================================================
  # Pet API
  # ============================================================================

  @doc """
  Gets a pet by slot index (0-2 for the 3 pet slots).
  """
  def get_pet(character_id, slot) do
    GenServer.call(via_tuple(character_id), {:get_pet, slot})
  end

  @doc """
  Gets all summoned pets.
  """
  def get_summoned_pets(character_id) do
    GenServer.call(via_tuple(character_id), :get_summoned_pets)
  end

  @doc """
  Spawns a pet from inventory to the map.
  """
  def spawn_pet(character_id, inventory_slot, lead \\ false) do
    GenServer.call(via_tuple(character_id), {:spawn_pet, inventory_slot, lead})
  end

  @doc """
  Despawns a pet from the map.
  """
  def despawn_pet(character_id, slot) do
    GenServer.call(via_tuple(character_id), {:despawn_pet, slot})
  end

  @doc """
  Updates a pet's data (after feeding, command, etc.).
  """
  def update_pet(character_id, pet) do
    GenServer.cast(via_tuple(character_id), {:update_pet, pet})
  end

  @doc """
  Updates a pet's position.
  """
  def update_pet_position(character_id, slot, position) do
    GenServer.cast(via_tuple(character_id), {:update_pet_position, slot, position})
  end

  def gain_exp(character_id, exp_amount, is_highest_damage) when is_integer(character_id) do
    case Registry.lookup(Odinsea.CharacterRegistry, character_id) do
      [{pid, _}] -> gain_exp(pid, exp_amount, is_highest_damage)
      [] -> {:error, :character_not_found}
    end
  end

  # ============================================================================
  # GenServer Callbacks - EXP Gain
  # ============================================================================

  @impl true
  def handle_cast({:gain_exp, exp_amount, is_highest_damage}, state) do
    # Calculate EXP needed for next level
    exp_needed = calculate_exp_needed(state.level)

    # Add EXP
    new_exp = state.exp + exp_amount

    # Check for level up
    {new_state, leveled_up} =
      if new_exp >= exp_needed and state.level < 200 do
        # Level up!
        new_level = state.level + 1

        # Calculate stat gains (simple formula for now)
        # TODO: Use job-specific stat gain formulas
        hp_gain = 10 + div(state.stats.str, 10)
        mp_gain = 5 + div(state.stats.int, 10)

        new_stats = %{
          state.stats
          | max_hp: state.stats.max_hp + hp_gain,
            max_mp: state.stats.max_mp + mp_gain,
            hp: state.stats.max_hp + hp_gain,
            mp: state.stats.max_mp + mp_gain
        }

        updated_state = %{
          state
          | level: new_level,
            exp: new_exp - exp_needed,
            stats: new_stats,
            remaining_ap: state.remaining_ap + 5
        }

        Logger.info("Character #{state.name} leveled up to #{new_level}!")

        # TODO: Send level-up packet to client
        # TODO: Broadcast level-up effect to map

        {updated_state, true}
      else
        {%{state | exp: new_exp}, false}
      end

    # TODO: Send EXP gain packet to client
    # TODO: If highest damage, send bonus message

    Logger.debug(
      "Character #{state.name} gained #{exp_amount} EXP (total: #{new_state.exp}, level: #{new_state.level})"
    )

    {:noreply, new_state}
  end

  # ============================================================================
  # GenServer Callbacks - Pet Functions
  # ============================================================================

  @impl true
  def handle_call({:get_pet, slot}, _from, state) do
    # Find pet by slot (1, 2, or 3)
    pet = Enum.find(state.pets, fn p -> p.summoned == slot end)

    if pet do
      {:reply, {:ok, pet}, state}
    else
      {:reply, {:error, :pet_not_found}, state}
    end
  end

  @impl true
  def handle_call(:get_summoned_pets, _from, state) do
    # Return list of {slot, pet} tuples for all summoned pets
    summoned = state.pets
    |> Enum.filter(fn p -> p.summoned > 0 end)
    |> Enum.map(fn p -> {p.summoned, p} end)

    {:reply, summoned, state}
  end

  @impl true
  def handle_call({:spawn_pet, inventory_slot, lead}, _from, state) do
    # Get pet from cash inventory
    cash_inv = Map.get(state.inventories, :cash, Inventory.new(:cash))
    item = Inventory.get_item(cash_inv, inventory_slot)

    cond do
      is_nil(item) ->
        {:reply, {:error, :item_not_found}, state}

      is_nil(item.pet) ->
        {:reply, {:error, :not_a_pet}, state}

      true ->
        # Find available slot (1, 2, or 3)
        used_slots = state.pets |> Enum.map(& &1.summoned) |> Enum.filter(& &1 > 0)
        available_slots = [1, 2, 3] -- used_slots

        if available_slots == [] do
          {:reply, {:error, :no_slots_available}, state}
        else
          slot = if lead, do: 1, else: List.first(available_slots)

          # Update pet with summoned slot and position
          pet = item.pet
          |> Pet.set_summoned(slot)
          |> Pet.set_inventory_position(inventory_slot)
          |> Pet.update_position(state.position.x, state.position.y)

          # Add or update pet in state
          existing_index = Enum.find_index(state.pets, fn p -> p.unique_id == pet.unique_id end)

          new_pets = if existing_index do
            List.replace_at(state.pets, existing_index, pet)
          else
            [pet | state.pets]
          end

          new_state = %{state | pets: new_pets, updated_at: DateTime.utc_now()}
          {:reply, {:ok, pet}, new_state}
        end
    end
  end

  @impl true
  def handle_call({:despawn_pet, slot}, _from, state) do
    case Enum.find(state.pets, fn p -> p.summoned == slot end) do
      nil ->
        {:reply, {:error, :pet_not_found}, state}

      pet ->
        # Set summoned to 0
        updated_pet = Pet.set_summoned(pet, 0)

        # Update in state
        pet_index = Enum.find_index(state.pets, fn p -> p.unique_id == pet.unique_id end)
        new_pets = List.replace_at(state.pets, pet_index, updated_pet)

        new_state = %{state | pets: new_pets, updated_at: DateTime.utc_now()}
        {:reply, {:ok, updated_pet}, new_state}
    end
  end

  @impl true
  def handle_cast({:update_pet, pet}, state) do
    # Find and update pet
    pet_index = Enum.find_index(state.pets, fn p -> p.unique_id == pet.unique_id end)

    new_pets = if pet_index do
      List.replace_at(state.pets, pet_index, pet)
    else
      [pet | state.pets]
    end

    {:noreply, %{state | pets: new_pets, updated_at: DateTime.utc_now()}}
  end

  @impl true
  def handle_cast({:update_pet_position, slot, position}, state) do
    # Find pet by slot and update position
    case Enum.find_index(state.pets, fn p -> p.summoned == slot end) do
      nil ->
        {:noreply, state}

      index ->
        pet = Enum.at(state.pets, index)
        updated_pet = Pet.update_position(pet, position.x, position.y, position.fh, position.stance)
        new_pets = List.replace_at(state.pets, index, updated_pet)

        {:noreply, %{state | pets: new_pets}}
    end
  end

  # Calculate EXP needed to reach next level
  defp calculate_exp_needed(level) when level >= 200, do: 0

  defp calculate_exp_needed(level) do
    # Simple formula: level^3 + 100 * level
    # TODO: Use actual MapleStory EXP table
    level * level * level + 100 * level
  end
end