policy-service/lib/policy_service_web/plugs/authorization_plug.ex

defmodule PolicyServiceWeb.Plugs.AuthorizationPlug do
  @moduledoc """
  Authorization plug for enforcing role-based access control.

  This plug checks if authenticated users have the required roles
  and scopes to access protected resources.
  """

  import Plug.Conn
  require Logger

  @doc """
  Initializes the authorization plug.

  ## Options
  - :required_roles - List of roles that can access the resource (optional)
  - :required_scopes - List of scopes required to access the resource (optional)
  - :resource_owner_check - Function to check if user owns the resource (optional)
  """
  def init(opts) do
    %{
      required_roles: Keyword.get(opts, :required_roles, []),
      required_scopes: Keyword.get(opts, :required_scopes, []),
      resource_owner_check: Keyword.get(opts, :resource_owner_check, nil)
    }
  end

  @doc """
  Authorizes the request by checking roles and scopes.

  Verifies that the authenticated user has the required roles and scopes
  to access the requested resource.
  """
  def call(conn, config) do
    user_roles = conn.assigns[:roles] || []
    user_scopes = conn.assigns[:scopes] || []
    user_id = conn.assigns[:user_id]
    org_id = conn.assigns[:org_id]

    with :ok <- check_roles(user_roles, config.required_roles),
         :ok <- check_scopes(user_scopes, config.required_scopes),
         :ok <- check_resource_ownership(conn, config.resource_owner_check, user_id, org_id) do
      conn
    else
      {:error, :insufficient_role} ->
        handle_insufficient_role(conn, config.required_roles)

      {:error, :insufficient_scope} ->
        handle_insufficient_scope(conn, config.required_scopes)

      {:error, :not_owner} ->
        handle_not_owner(conn)
    end
  end

  defp check_roles(_user_roles, required_roles) when required_roles == [] do
    :ok
  end

  defp check_roles(user_roles, required_roles) do
    if has_any_role?(user_roles, required_roles) do
      :ok
    else
      Logger.warning(
        "User with roles #{inspect(user_roles)} lacks required roles: #{inspect(required_roles)}"
      )

      {:error, :insufficient_role}
    end
  end

  defp check_scopes(_user_scopes, required_scopes) when required_scopes == [] do
    :ok
  end

  defp check_scopes(user_scopes, required_scopes) do
    if has_all_scopes?(user_scopes, required_scopes) do
      :ok
    else
      Logger.warning(
        "User with scopes #{inspect(user_scopes)} lacks required scopes: #{inspect(required_scopes)}"
      )

      {:error, :insufficient_scope}
    end
  end

  defp check_resource_ownership(_conn, nil, _user_id, _org_id) do
    :ok
  end

  defp check_resource_ownership(conn, check_function, user_id, org_id) do
    try do
      if check_function.(conn, user_id, org_id) do
        :ok
      else
        {:error, :not_owner}
      end
    rescue
      error ->
        Logger.error("Resource ownership check failed: #{inspect(error)}")
        {:error, :not_owner}
    end
  end

  @doc """
  Checks if the user has any of the required roles.

  Supports role hierarchy where admin has all permissions.
  """
  def has_any_role?(user_roles, required_roles) do
    cond do
      "admin" in user_roles ->
        true

      Enum.any?(required_roles, fn role -> role in user_roles end) ->
        true

      true ->
        false
    end
  end

  @doc """
  Checks if the user has all of the required scopes.
  """
  def has_all_scopes?(user_scopes, required_scopes) do
    Enum.all?(required_scopes, fn scope -> scope in user_scopes end)
  end

  @doc """
  Checks if the user can access a specific resource based on ownership.

  Admins can access any resource. Other users can only access their own resources.
  """
  def can_access_resource?(user_roles, resource_user_id, current_user_id) do
    cond do
      "admin" in user_roles ->
        true

      resource_user_id == current_user_id ->
        true

      true ->
        false
    end
  end

  defp handle_insufficient_role(conn, required_roles) do
    conn
    |> put_resp_content_type("application/json")
    |> send_resp(
      403,
      Jason.encode!(%{
        error: "Insufficient permissions",
        required_roles: required_roles
      })
    )
    |> halt()
  end

  defp handle_insufficient_scope(conn, required_scopes) do
    conn
    |> put_resp_content_type("application/json")
    |> send_resp(
      403,
      Jason.encode!(%{
        error: "Insufficient permissions",
        required_scopes: required_scopes
      })
    )
    |> halt()
  end

  defp handle_not_owner(conn) do
    conn
    |> put_resp_content_type("application/json")
    |> send_resp(
      403,
      Jason.encode!(%{error: "You do not have permission to access this resource"})
    )
    |> halt()
  end
end