defmodule Odinsea.Shop.MTS do
  @moduledoc """
  Maple Trading System (MTS) implementation.

  The MTS allows players to:
  - List items for sale (buy now)
  - Purchase items from other players
  - Search for items
  - Manage their MTS cart

  Ported from handling/cashshop/handler/MTSOperation.java
  and server/MTSStorage.java / server/MTSCart.java
  """

  use GenServer
  require Logger

  alias Odinsea.Game.Inventory

  # MTS opcodes
  @mts_sell 2
  @mts_page 5
  @mts_search 6
  @mts_cancel 7
  @mts_transfer 8
  @mts_add_cart 9
  @mts_del_cart 10
  @mts_buy_now 16
  @mts_buy_cart 17

  # MTS Constants
  @min_price 100
  @mts_meso 5000
  @listing_duration_days 7

  # ETS tables
  @mts_items :odinsea_mts_items
  @mts_carts :odinsea_mts_carts

  defstruct [
    :id,
    :item,
    :price,
    :seller_id,
    :seller_name,
    :expiration,
    :buyer_id
  ]

  ## Public API

  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
  end

  @doc """
  Gets or creates a cart for a character.
  """
  @spec get_cart(integer()) :: map()
  def get_cart(character_id) do
    case :ets.lookup(@mts_carts, character_id) do
      [{^character_id, cart}] ->
        cart

      [] ->
        cart = %{
          character_id: character_id,
          cart: [],
          inventory: [],
          not_yet_sold: [],
          owed_nx: 0,
          tab: 0,
          page: 0,
          type: 0,
          current_view: []
        }

        :ets.insert(@mts_carts, {character_id, cart})
        cart
    end
  end

  @doc """
  Updates cart view settings.
  """
  @spec change_cart_info(integer(), integer(), integer(), integer()) :: :ok
  def change_cart_info(character_id, tab, page, type) do
    cart = get_cart(character_id)

    new_cart = %{
      cart
      | tab: tab,
        page: page,
        type: type
    }

    :ets.insert(@mts_carts, {character_id, new_cart})
    :ok
  end

  @doc """
  Updates current view (search results).
  """
  @spec change_current_view(integer(), [map()]) :: :ok
  def change_current_view(character_id, items) do
    cart = get_cart(character_id)
    new_cart = %{cart | current_view: items}
    :ets.insert(@mts_carts, {character_id, new_cart})
    :ok
  end

  @doc """
  Lists an item for sale on the MTS.
  """
  @spec list_item(integer(), map(), integer(), String.t()) ::
          {:ok, integer()} | {:error, atom()}
  def list_item(seller_id, item, price, seller_name) do
    if price < @min_price do
      {:error, :price_too_low}
    else
      expiration = Odinsea.now() + @listing_duration_days * 24 * 60 * 60 * 1000

      listing = %__MODULE__{
        id: generate_listing_id(),
        item: item,
        price: price,
        seller_id: seller_id,
        seller_name: seller_name,
        expiration: expiration,
        buyer_id: nil
      }

      :ets.insert(@mts_items, {listing.id, listing})

      # Add to seller's "not yet sold" list
      cart = get_cart(seller_id)
      new_not_yet_sold = [listing.id | cart.not_yet_sold]
      new_cart = %{cart | not_yet_sold: new_not_yet_sold}
      :ets.insert(@mts_carts, {seller_id, new_cart})

      {:ok, listing.id}
    end
  end

  @doc """
  Gets a single MTS item by ID.
  """
  @spec get_item(integer()) :: map() | nil
  def get_item(id) do
    case :ets.lookup(@mts_items, id) do
      [{^id, item}] -> item
      [] -> nil
    end
  end

  @doc """
  Removes an item from the MTS.
  Returns the item to the seller's transfer inventory if canceling.
  """
  @spec remove_item(integer(), integer(), boolean()) :: boolean()
  def remove_item(id, character_id, cancel) do
    case get_item(id) do
      nil ->
        false

      item ->
        if item.seller_id != character_id do
          false
        else
          :ets.delete(@mts_items, id)

          if cancel do
            # Return item to seller's transfer inventory
            cart = get_cart(character_id)
            new_inventory = [item.item | cart.inventory]
            new_not_yet_sold = List.delete(cart.not_yet_sold, id)

            new_cart = %{
              cart
              | inventory: new_inventory,
                not_yet_sold: new_not_yet_sold
            }

            :ets.insert(@mts_carts, {character_id, new_cart})
          end

          true
        end
    end
  end

  @doc """
  Buys an item from the MTS.
  """
  @spec buy_item(integer(), integer(), integer()) ::
          {:ok, map()} | {:error, atom()}
  def buy_item(id, buyer_id, offered_price) do
    case get_item(id) do
      nil ->
        {:error, :not_found}

      item ->
        if item.seller_id == buyer_id do
          {:error, :own_item}
        else
          if offered_price < item.price do
            {:error, :insufficient_funds}
          else
            # Mark as sold and transfer to buyer
            :ets.delete(@mts_items, id)

            # Add to buyer's transfer inventory
            buyer_cart = get_cart(buyer_id)
            new_buyer_inventory = [item.item | buyer_cart.inventory]
            new_buyer_cart = %{buyer_cart | inventory: new_buyer_inventory}
            :ets.insert(@mts_carts, {buyer_id, new_buyer_cart})

            # Credit seller with NX
            seller_cart = get_cart(item.seller_id)
            new_owed = seller_cart.owed_nx + item.price
            new_not_yet_sold = List.delete(seller_cart.not_yet_sold, id)

            new_seller_cart = %{
              seller_cart
              | owed_nx: new_owed,
                not_yet_sold: new_not_yet_sold
            }

            :ets.insert(@mts_carts, {item.seller_id, new_seller_cart})

            {:ok, item}
          end
        end
    end
  end

  @doc """
  Searches for items in the MTS.
  """
  @spec search(boolean(), String.t(), integer(), integer()) :: [map()]
  def search(_cash_search, search_string, type, tab) do
    # Get all items
    all_items =
      :ets.select(@mts_items, [{{:_, :"$1"}, [], [:"$1"]}])
      |> Enum.filter(&is_nil(&1.buyer_id))

    # Apply filters
    items =
      cond do
        # Tab 0 = all items
        tab == 0 ->
          all_items

        # Tab 1 = search by name
        tab == 1 && search_string != "" ->
          Enum.filter(all_items, fn item ->
            item_name = get_item_name(item.item.item_id)
            String.contains?(String.downcase(item_name), String.downcase(search_string))
          end)

        # Type filtering
        type > 0 ->
          Enum.filter(all_items, fn item ->
            get_item_type(item.item.item_id) == type
          end)

        true ->
          all_items
      end

    # Sort by newest first
    Enum.sort_by(items, & &1.id, :desc)
  end

  @doc """
  Adds an item to the cart.
  """
  @spec add_to_cart(integer(), integer()) :: boolean()
  def add_to_cart(character_id, item_id) do
    cart = get_cart(character_id)

    if item_id in cart.cart do
      false
    else
      new_cart = %{cart | cart: [item_id | cart.cart]}
      :ets.insert(@mts_carts, {character_id, new_cart})
      true
    end
  end

  @doc """
  Removes an item from the cart.
  """
  @spec remove_from_cart(integer(), integer()) :: boolean()
  def remove_from_cart(character_id, item_id) do
    cart = get_cart(character_id)

    if item_id in cart.cart do
      new_cart = %{cart | cart: List.delete(cart.cart, item_id)}
      :ets.insert(@mts_carts, {character_id, new_cart})
      true
    else
      false
    end
  end

  @doc """
  Transfers an item from MTS inventory to game inventory.
  """
  @spec transfer_item(integer(), integer()) :: {:ok, map()} | {:error, atom()}
  def transfer_item(character_id, index) do
    cart = get_cart(character_id)

    if index < 0 || index >= length(cart.inventory) do
      {:error, :invalid_index}
    else
      item = Enum.at(cart.inventory, index)
      new_inventory = List.delete_at(cart.inventory, index)
      new_cart = %{cart | inventory: new_inventory}
      :ets.insert(@mts_carts, {character_id, new_cart})
      {:ok, item}
    end
  end

  @doc """
  Claims owed NX for a character.
  """
  @spec claim_nx(integer()) :: integer()
  def claim_nx(character_id) do
    cart = get_cart(character_id)
    owed = cart.owed_nx

    if owed > 0 do
      new_cart = %{cart | owed_nx: 0}
      :ets.insert(@mts_carts, {character_id, new_cart})
    end

    owed
  end

  @doc """
  Checks and removes expired listings.
  """
  @spec check_expirations() :: :ok
  def check_expirations do
    now = Odinsea.now()

    expired =
      :ets.select(@mts_items, [{{:_, :"$1"}, [], [:"$1"]}])
      |> Enum.filter(fn item -> item.expiration < now end)

    Enum.each(expired, fn item ->
      :ets.delete(@mts_items, item.id)

      # Return item to seller
      cart = get_cart(item.seller_id)
      new_inventory = [item.item | cart.inventory]
      new_not_yet_sold = List.delete(cart.not_yet_sold, item.id)

      new_cart = %{
        cart
        | inventory: new_inventory,
          not_yet_sold: new_not_yet_sold
      }

      :ets.insert(@mts_carts, {item.seller_id, new_cart})
    end)

    :ok
  end

  @doc """
  Gets current MTS listings for display.
  """
  @spec get_current_mts(map()) :: [map()]
  def get_current_mts(cart) do
    page_size = 16
    start_idx = cart.page * page_size

    items =
      if cart.tab == 0 do
        :ets.select(@mts_items, [{{:_, :"$1"}, [], [:"$1"]}])
      else
        cart.current_view
      end

    items
    |> Enum.filter(&is_nil(&1.buyer_id))
    |> Enum.slice(start_idx, page_size)
  end

  @doc """
  Gets "not yet sold" listings for a character.
  """
  @spec get_not_yet_sold(integer()) :: [map()]
  def get_not_yet_sold(character_id) do
    cart = get_cart(character_id)

    Enum.map(cart.not_yet_sold, &get_item/1)
    |> Enum.filter(&(&1 != nil))
  end

  @doc """
  Gets transfer inventory for a character.
  """
  @spec get_transfer(integer()) :: [map()]
  def get_transfer(character_id) do
    cart = get_cart(character_id)
    cart.inventory
  end

  @doc """
  Checks if an item is in the cart.
  """
  @spec in_cart?(integer(), integer()) :: boolean()
  def in_cart?(character_id, item_id) do
    cart = get_cart(character_id)
    item_id in cart.cart
  end

  @doc """
  Handles MTS operation packets.
  """
  @spec handle(In.t(), map()) :: map()
  def handle(packet, client_state) do
    if In.remaining(packet) == 0 do
      # Empty packet - just refresh
      send_mts_packets(client_state)
    else
      {op, packet} = In.decode_byte(packet)
      handle_op(op, packet, client_state)
    end
  end

  ## GenServer Callbacks

  @impl true
  def init(_opts) do
    :ets.new(@mts_items, [:set, :public, :named_table, read_concurrency: true])
    :ets.new(@mts_carts, [:set, :public, :named_table])

    # Schedule expiration check
    schedule_expiration_check()

    {:ok, %{}}
  end

  @impl true
  def handle_info(:check_expirations, state) do
    check_expirations()
    schedule_expiration_check()
    {:noreply, state}
  end

  ## Private Functions

  defp handle_op(@mts_sell, packet, client_state) do
    {inv_type, packet} = In.decode_byte(packet)
    {item_id, packet} = In.decode_int(packet)
    {has_unique_id, packet} = In.decode_byte(packet)

    if has_unique_id != 0 || (inv_type != 1 && inv_type != 2) do
      send_mts_fail_sell(client_state)
      client_state
    else
      # Parse item data from packet
      {item_data, packet} = parse_item_data(packet, inv_type)
      {price, _packet} = In.decode_int(packet)

      character = client_state.character

      # Validate item can be sold
      with :ok <- validate_mts_item(character, item_id, item_data, inv_type),
           :ok <- check_meso_fee(character),
           true <- length(get_cart(character.id).not_yet_sold) < 10 do
        # Create item copy
        item = create_mts_item(character, item_id, item_data)

        # List on MTS
        {:ok, _listing_id} = list_item(character.id, item, price, character.name)

        # Deduct meso and remove from inventory
        new_character = deduct_meso(character, @mts_meso)
        new_character = remove_from_inventory(new_character, inv_type, item_data.slot)

        client_state
        |> Map.put(:character, new_character)
        |> send_mts_confirm_sell()
      else
        _ ->
          send_mts_fail_sell(client_state)
          client_state
      end
    end
  end

  defp handle_op(@mts_page, packet, client_state) do
    {tab, packet} = In.decode_int(packet)
    {page, packet} = In.decode_int(packet)
    {type, _packet} = In.decode_int(packet)

    change_cart_info(client_state.character.id, tab, page, type)
    send_mts_packets(client_state)
  end

  defp handle_op(@mts_search, packet, client_state) do
    {tab, packet} = In.decode_int(packet)
    {page, packet} = In.decode_int(packet)
    {_zero, packet} = In.decode_int(packet)
    {cash_search, packet} = In.decode_int(packet)
    {search_string, _packet} = In.decode_string(packet)

    cart = get_cart(client_state.character.id)
    change_cart_info(client_state.character.id, tab, page, cart.type)

    # Perform search
    results = search(cash_search > 0, search_string, cart.type, tab)
    change_current_view(client_state.character.id, results)

    send_mts_packets(client_state)
  end

  defp handle_op(@mts_cancel, packet, client_state) do
    {id, _packet} = In.decode_int(packet)

    if remove_item(id, client_state.character.id, true) do
      send_mts_confirm_cancel(client_state)
      send_mts_packets(client_state)
    else
      send_mts_fail_cancel(client_state)
      client_state
    end
  end

  defp handle_op(@mts_transfer, packet, client_state) do
    # Fake ID encoding
    {fake_id, _packet} = In.decode_int(packet)
    index = Integer.pow(2, 31) - 1 - fake_id

    case transfer_item(client_state.character.id, index) do
      {:ok, item} ->
        # Add to inventory
        case add_to_inventory(client_state.character, item) do
          {:ok, new_character, position} ->
            client_state
            |> Map.put(:character, new_character)
            |> send_mts_confirm_transfer(item, position)
            |> send_mts_packets()

          {:error, _} ->
            send_mts_fail_buy(client_state)
            client_state
        end

      {:error, _} ->
        send_mts_fail_buy(client_state)
        client_state
    end
  end

  defp handle_op(@mts_add_cart, packet, client_state) do
    {id, _packet} = In.decode_int(packet)

    if in_cart?(client_state.character.id, id) do
      send_cart_message(client_state, true, false)
    else
      if add_to_cart(client_state.character.id, id) do
        send_cart_message(client_state, false, false)
      else
        send_cart_message(client_state, true, false)
      end
    end

    client_state
  end

  defp handle_op(@mts_del_cart, packet, client_state) do
    {id, _packet} = In.decode_int(packet)

    if remove_from_cart(client_state.character.id, id) do
      send_cart_message(client_state, false, true)
    else
      send_cart_message(client_state, true, true)
    end

    client_state
  end

  defp handle_op(op, packet, client_state) when op in [@mts_buy_now, @mts_buy_cart] do
    {id, _packet} = In.decode_int(packet)

    case get_item(id) do
      nil ->
        send_mts_fail_buy(client_state)
        client_state

      item ->
        if item.seller_id == client_state.character.id do
          send_mts_fail_buy(client_state)
          client_state
        else
          # Check buyer has enough NX
          character = client_state.character

          if (character.nx_cash || 0) >= item.price do
            case buy_item(id, character.id, item.price) do
              {:ok, _} ->
                # Deduct NX
                new_character = %{character | nx_cash: character.nx_cash - item.price}

                client_state
                |> Map.put(:character, new_character)
                |> send_mts_confirm_buy()
                |> send_mts_packets()

              {:error, _} ->
                send_mts_fail_buy(client_state)
                client_state
            end
          else
            send_mts_fail_buy(client_state)
            client_state
          end
        end
    end
  end

  defp handle_op(_op, _packet, client_state) do
    # Unknown op - just refresh
    send_mts_packets(client_state)
  end

  defp parse_item_data(packet, 1) do
    # Equipment item data
    packet = In.skip(packet, 32) # Skip various stats
    {_owner, packet} = In.decode_string(packet)
    packet = In.skip(packet, 50)
    {slot, packet} = In.decode_int(packet)
    packet = In.skip(packet, 4)

    {%{slot: slot}, packet}
  end

  defp parse_item_data(packet, 2) do
    # Regular item data
    {stars, packet} = In.decode_short(packet)
    {_owner, packet} = In.decode_string(packet)
    packet = In.skip(packet, 2) # Flag
    {slot, packet} = In.decode_int(packet)
    {quantity, _packet} = In.decode_int(packet)

    {%{slot: slot, quantity: quantity, stars: stars}, packet}
  end

  defp validate_mts_item(character, item_id, item_data, inv_type) do
    # Check item exists in inventory
    inventory = Map.get(character.inventories, inv_type, [])

    case Enum.find(inventory, &(&1.position == item_data.slot)) do
      nil ->
        :error

      item ->
        if item.item_id == item_id && item.quantity >= (item_data.quantity || 1) do
          :ok
        else
          :error
        end
    end
  end

  defp check_meso_fee(character) do
    if character.meso >= @mts_meso do
      :ok
    else
      :error
    end
  end

  defp create_mts_item(character, item_id, item_data) do
    %{
      item_id: item_id,
      quantity: item_data.quantity || 1,
      owner: character.name,
      flag: 0
    }
  end

  defp deduct_meso(character, amount) do
    %{character | meso: character.meso - amount}
  end

  defp remove_from_inventory(character, inv_type, slot) do
    inventory = Map.get(character.inventories, inv_type, [])
    new_inventory = Enum.reject(inventory, &(&1.position == slot))
    inventories = Map.put(character.inventories, inv_type, new_inventory)
    %{character | inventories: inventories}
  end

  defp add_to_inventory(character, item) do
    inv_type = Odinsea.Game.InventoryType.from_item_id(item.item_id)

    if Odinsea.Shop.Operation.check_inventory_space(character, item.item_id, item.quantity) == :ok do
      inventory = Map.get(character.inventories, inv_type, [])
      position = Inventory.next_free_slot(inventory)
      new_item = %{item | position: position}
      new_inventory = [new_item | inventory]
      inventories = Map.put(character.inventories, inv_type, new_inventory)
      {:ok, %{character | inventories: inventories}, position}
    else
      {:error, :no_space}
    end
  end

  defp get_item_name(item_id) do
    Odinsea.Game.ItemInfo.get_name(item_id) || "Unknown"
  end

  defp get_item_type(item_id) do
    cond do
      item_id >= 1_000_000 && item_id < 2_000_000 -> 1
      item_id >= 2_000_000 && item_id < 3_000_000 -> 2
      item_id >= 4_000_000 && item_id < 5_000_000 -> 4
      true -> 0
    end
  end

  defp generate_listing_id do
    :erlang.unique_integer([:positive])
  end

  defp schedule_expiration_check do
    # Check every hour
    Process.send_after(self(), :check_expirations, 60 * 60 * 1000)
  end

  # Packet senders
  defp send_mts_packets(client_state) do
    cart = get_cart(client_state.character.id)

    Odinsea.Shop.Packets.send_current_mts(client_state.socket, cart)
    Odinsea.Shop.Packets.send_not_yet_sold(client_state.socket, cart)
    Odinsea.Shop.Packets.send_transfer(client_state.socket, cart)
    Odinsea.Shop.Packets.show_mts_cash(client_state.socket, client_state.character)
    Odinsea.Shop.Packets.enable_cs_use(client_state.socket)

    client_state
  end

  defp send_mts_fail_sell(client_state) do
    Odinsea.Shop.Packets.get_mts_fail_sell(client_state.socket)
  end

  defp send_mts_confirm_sell(client_state) do
    Odinsea.Shop.Packets.get_mts_confirm_sell(client_state.socket)
  end

  defp send_mts_fail_cancel(client_state) do
    Odinsea.Shop.Packets.get_mts_fail_cancel(client_state.socket)
  end

  defp send_mts_confirm_cancel(client_state) do
    Odinsea.Shop.Packets.get_mts_confirm_cancel(client_state.socket)
  end

  defp send_mts_fail_buy(client_state) do
    Odinsea.Shop.Packets.get_mts_fail_buy(client_state.socket)
  end

  defp send_mts_confirm_buy(client_state) do
    Odinsea.Shop.Packets.get_mts_confirm_buy(client_state.socket)
  end

  defp send_mts_confirm_transfer(client_state, _item, position) do
    # This needs the inventory type encoded
    Odinsea.Shop.Packets.get_mts_confirm_transfer(client_state.socket, 1, position)
  end

  defp send_cart_message(client_state, failed, deleted) do
    Odinsea.Shop.Packets.add_to_cart_message(client_state.socket, failed, deleted)
  end
end