defmodule Codex.AppServer.Mcp do
  @moduledoc """
  MCP (Model Context Protocol) server management for app-server connections.

  This module provides functions to interact with MCP servers configured in
  the Codex app-server, including listing server status and handling OAuth
  authentication flows.
  """

  alias Codex.AppServer.Connection
  alias Codex.AppServer.Params
  alias Codex.Config.Defaults
  alias Codex.MCP.Config, as: MCPConfig
  alias Codex.MCP.OAuth

  @type connection :: pid()

  @doc """
  Lists configured MCP servers with their tools, resources, and auth status.

  Supports cursor-based pagination via `:cursor` and `:limit` options.

  ## Compatibility

  This function tries the new `mcpServerStatus/list` method first. If the server
  returns a "method not found" (`-32601`) or "unknown variant" (`-32600`) error
  (older servers), it falls back to the legacy `mcpServers/list` method
  automatically.
  """
  @spec list_servers(connection(), keyword()) :: {:ok, map()} | {:error, term()}
  def list_servers(conn, opts \\ []) when is_pid(conn) and is_list(opts) do
    params =
      %{}
      |> Params.put_optional("cursor", Keyword.get(opts, :cursor))
      |> Params.put_optional("limit", Keyword.get(opts, :limit))

    case Connection.request(conn, "mcpServerStatus/list", params,
           timeout_ms: Defaults.mcp_server_request_timeout_ms()
         ) do
      {:error, %{"code" => -32_601}} ->
        Connection.request(conn, "mcpServers/list", params,
          timeout_ms: Defaults.mcp_server_request_timeout_ms()
        )

      {:error, %{code: -32_601}} ->
        Connection.request(conn, "mcpServers/list", params,
          timeout_ms: Defaults.mcp_server_request_timeout_ms()
        )

      {:error, error} ->
        if unknown_variant_mcp_server_status_list?(error) do
          Connection.request(conn, "mcpServers/list", params,
            timeout_ms: Defaults.mcp_server_request_timeout_ms()
          )
        else
          {:error, error}
        end

      result ->
        result
    end
  end

  @doc """
  Alias for `list_servers/2`. Returns MCP server status information.
  """
  @spec list_server_statuses(connection(), keyword()) :: {:ok, map()} | {:error, term()}
  def list_server_statuses(conn, opts \\ []), do: list_servers(conn, opts)

  @doc """
  Starts an OAuth login flow for a streamable HTTP MCP server.

  OAuth credentials are stored using the configured MCP credentials store. Use
  `oauth_tokens/3` to load them after login completes.
  """
  @spec oauth_login(connection(), keyword()) :: {:ok, map()} | {:error, term()}
  def oauth_login(conn, opts) when is_pid(conn) and is_list(opts) do
    name = Keyword.fetch!(opts, :name)

    params =
      %{"name" => name}
      |> Params.put_optional("scopes", Keyword.get(opts, :scopes))
      |> Params.put_optional("timeoutSecs", Keyword.get(opts, :timeout_secs))

    Connection.request(conn, "mcpServer/oauth/login", params,
      timeout_ms: Defaults.mcp_server_request_timeout_ms()
    )
  end

  @doc """
  Loads stored OAuth tokens for a configured MCP server.

  Returns `{:error, :server_not_found}` if the server is not configured, or
  `{:error, :missing_url}` if the server is not a streamable HTTP server.
  """
  @spec oauth_tokens(connection(), String.t(), keyword()) ::
          {:ok, OAuth.tokens() | nil} | {:error, term()}
  def oauth_tokens(conn, name, opts \\ [])
      when is_pid(conn) and is_binary(name) and is_list(opts) do
    store_mode = Keyword.get(opts, :store_mode)

    with {:ok, servers} <- MCPConfig.list_servers(conn, opts),
         {:ok, server} <- Map.fetch(servers, name),
         url when is_binary(url) <- fetch_server_url(server) do
      {:ok, OAuth.load_tokens(name, url, store_mode)}
    else
      :error -> {:error, :server_not_found}
      false -> {:error, :missing_url}
      nil -> {:error, :missing_url}
      {:error, _} = error -> error
    end
  end

  @doc """
  Deletes stored OAuth tokens for a configured MCP server.

  Returns `{:error, :server_not_found}` if the server is not configured, or
  `{:error, :missing_url}` if the server is not a streamable HTTP server.
  """
  @spec oauth_logout(connection(), String.t(), keyword()) :: :ok | {:error, term()}
  def oauth_logout(conn, name, opts \\ [])
      when is_pid(conn) and is_binary(name) and is_list(opts) do
    store_mode = Keyword.get(opts, :store_mode)

    with {:ok, servers} <- MCPConfig.list_servers(conn, opts),
         {:ok, server} <- Map.fetch(servers, name),
         url when is_binary(url) <- fetch_server_url(server) do
      OAuth.delete_tokens(name, url, store_mode)
    else
      :error -> {:error, :server_not_found}
      false -> {:error, :missing_url}
      nil -> {:error, :missing_url}
      {:error, _} = error -> error
    end
  end

  @doc """
  Requests MCP servers to reload configuration and refresh cached tools.
  """
  @spec reload(connection()) :: {:ok, map()} | {:error, term()}
  def reload(conn) when is_pid(conn) do
    Connection.request(conn, "config/mcpServer/reload", %{},
      timeout_ms: Defaults.mcp_server_request_timeout_ms()
    )
  end

  defp unknown_variant_mcp_server_status_list?(%{"code" => -32_600, "message" => message})
       when is_binary(message) do
    String.contains?(message, "unknown variant") and
      String.contains?(message, "mcpServerStatus/list")
  end

  defp unknown_variant_mcp_server_status_list?(%{code: -32_600, message: message})
       when is_binary(message) do
    String.contains?(message, "unknown variant") and
      String.contains?(message, "mcpServerStatus/list")
  end

  defp unknown_variant_mcp_server_status_list?(_error), do: false

  defp fetch_server_url(%{} = server) do
    Map.get(server, "url") || Map.get(server, :url)
  end
end