defmodule Odinsea.Database.Redis do
  @moduledoc """
  Redis client for Odinsea.
  Provides key-value storage, pub/sub, and caching functionality.
  """

  require Logger

  # ==================================================================================================
  # Connection
  # ==================================================================================================

  defp conn do
    # Get Redis connection from application environment
    # In production, this would be a persistent connection pool
    host = Application.get_env(:odinsea, :redis_host, "localhost")
    port = Application.get_env(:odinsea, :redis_port, 6379)
    database = Application.get_env(:odinsea, :redis_database, 0)
    password = Application.get_env(:odinsea, :redis_password, nil)
    
    opts = [host: host, port: port, database: database]
    opts = if password, do: Keyword.put(opts, :password, password), else: opts
    
    case Redix.start_link(opts) do
      {:ok, conn} -> conn
      {:error, _} -> nil
    end
  end

  # ==================================================================================================
  # Key-Value Operations
  # ==================================================================================================

  @doc """
  Gets a value by key.
  """
  @spec get(String.t()) :: {:ok, String.t() | nil} | {:error, term()}
  def get(key) do
    with conn when not is_nil(conn) <- conn(),
         {:ok, value} <- Redix.command(conn, ["GET", key]) do
      {:ok, value}
    else
      nil -> {:error, :no_connection}
      {:error, reason} -> {:error, reason}
    end
  after
    close_conn()
  end

  @doc """
  Sets a key to a value.
  """
  @spec set(String.t(), String.t()) :: :ok | {:error, term()}
  def set(key, value) do
    with conn when not is_nil(conn) <- conn(),
         {:ok, _} <- Redix.command(conn, ["SET", key, value]) do
      :ok
    else
      nil -> {:error, :no_connection}
      {:error, reason} -> {:error, reason}
    end
  after
    close_conn()
  end

  @doc """
  Sets a key to a value with expiration (in seconds).
  """
  @spec setex(String.t(), integer(), String.t()) :: :ok | {:error, term()}
  def setex(key, seconds, value) do
    with conn when not is_nil(conn) <- conn(),
         {:ok, _} <- Redix.command(conn, ["SETEX", key, seconds, value]) do
      :ok
    else
      nil -> {:error, :no_connection}
      {:error, reason} -> {:error, reason}
    end
  after
    close_conn()
  end

  @doc """
  Deletes a key.
  """
  @spec del(String.t()) :: :ok | {:error, term()}
  def del(key) do
    with conn when not is_nil(conn) <- conn(),
         {:ok, _} <- Redix.command(conn, ["DEL", key]) do
      :ok
    else
      nil -> {:error, :no_connection}
      {:error, reason} -> {:error, reason}
    end
  after
    close_conn()
  end

  @doc """
  Checks if a key exists.
  """
  @spec exists?(String.t()) :: boolean()
  def exists?(key) do
    with conn when not is_nil(conn) <- conn(),
         {:ok, count} <- Redix.command(conn, ["EXISTS", key]) do
      count > 0
    else
      _ -> false
    end
  after
    close_conn()
  end

  @doc """
  Sets expiration on a key (in seconds).
  """
  @spec expire(String.t(), integer()) :: :ok | {:error, term()}
  def expire(key, seconds) do
    with conn when not is_nil(conn) <- conn(),
         {:ok, _} <- Redix.command(conn, ["EXPIRE", key, seconds]) do
      :ok
    else
      nil -> {:error, :no_connection}
      {:error, reason} -> {:error, reason}
    end
  after
    close_conn()
  end

  # ==================================================================================================
  # Pub/Sub Operations
  # ==================================================================================================

  @doc """
  Publishes a message to a channel.
  The message is automatically JSON-encoded.
  """
  @spec publish(String.t(), map()) :: :ok | {:error, term()}
  def publish(channel, message) do
    json_message = Jason.encode!(message)
    
    with conn when not is_nil(conn) <- conn(),
         {:ok, _} <- Redix.command(conn, ["PUBLISH", channel, json_message]) do
      :ok
    else
      nil -> {:error, :no_connection}
      {:error, reason} -> {:error, reason}
    end
  after
    close_conn()
  end

  @doc """
  Subscribes to channels and handles messages with a callback function.
  This is a blocking operation that should be run in a separate process.
  """
  @spec subscribe([String.t()], (String.t(), map() -> any())) :: :ok | {:error, term()}
  def subscribe(channels, callback) when is_list(channels) and is_function(callback, 2) do
    # Pub/Sub in Redix requires a separate connection
    host = Application.get_env(:odinsea, :redis_host, "localhost")
    port = Application.get_env(:odinsea, :redis_port, 6379)
    
    opts = [host: host, port: port]
    
    case Redix.PubSub.start_link(opts) do
      {:ok, pubsub} ->
        # Subscribe to channels
        Enum.each(channels, fn channel ->
          Redix.PubSub.subscribe(pubsub, channel, self())
        end)
        
        # Message loop
        message_loop(pubsub, callback)
        
      {:error, reason} ->
        {:error, reason}
    end
  end

  defp message_loop(pubsub, callback) do
    receive do
      {:redix_pubsub, ^pubsub, :message, %{channel: channel, payload: payload}} ->
        # Decode JSON payload
        case Jason.decode(payload) do
          {:ok, decoded} -> callback.(channel, decoded)
          {:error, _} -> callback.(channel, %{"raw" => payload})
        end
        message_loop(pubsub, callback)
        
      {:redix_pubsub, ^pubsub, :subscribed, %{channel: _channel}} ->
        message_loop(pubsub, callback)
        
      _ ->
        message_loop(pubsub, callback)
    end
  end

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

  defp close_conn do
    # Note: In a production setup with connection pooling,
    # this would return the connection to the pool instead of closing
    :ok
  end

  @doc """
  Gets the online count for a world.
  """
  @spec get_world_online_count(integer()) :: integer()
  def get_world_online_count(world_id) do
    case get("world:#{world_id}:online_count") do
      {:ok, nil} -> 0
      {:ok, count} -> String.to_integer(count)
      {:error, _} -> 0
    end
  end

  @doc """
  Updates the online count for a world.
  """
  @spec update_world_online_count(integer(), integer()) :: :ok
  def update_world_online_count(world_id, count) do
    set("world:#{world_id}:online_count", to_string(count))
    :ok
  end

  @doc """
  Registers a player as online.
  """
  @spec register_player_online(integer(), integer(), String.t()) :: :ok
  def register_player_online(character_id, world_id, channel) do
    setex("player:#{character_id}:online", 60, Jason.encode!(%{
      world_id: world_id,
      channel: channel,
      timestamp: System.system_time(:second)
    }))
    :ok
  end

  @doc """
  Unregisters a player as online.
  """
  @spec unregister_player_online(integer()) :: :ok
  def unregister_player_online(character_id) do
    del("player:#{character_id}:online")
    :ok
  end

  @doc """
  Checks if a player is online.
  """
  @spec player_online?(integer()) :: boolean()
  def player_online?(character_id) do
    exists?("player:#{character_id}:online")
  end
end