defmodule Carny.Statement do
  @moduledoc """
  Associates a bucket of resources with an "allow" or "deny". On their own not so useful main
  use is to be composed into Policies.
  """

  alias __MODULE__
  alias Carny.Identifier

  defstruct effect: "allow", resources: [], privileges: []

  @doc """
  Checks if an identifier passes a statement.

  ## Examples

      iex> Carny.Statement.passes?("start", %Carny.Identifier{}, %Carny.Statement{privileges: ["start"], resources: [%Carny.Identifier{}]})
      true
  """
  def passes?(
        privilege,
        %Identifier{} = identifier,
        %Statement{resources: resources, privileges: privileges, effect: "allow"}
      )
      when length(resources) > 0 do
    case privilege in privileges do
      true ->
        Enum.reduce_while(resources, true, fn
          resource, true ->
            {:cont, Identifier.validate_against(identifier, resource)}

          _resource, false ->
            {:halt, false}
        end)

      false ->
        false
    end
  end

  def passes?(
        %Identifier{} = identifier,
        %Statement{resources: resources, effect: "deny"} = statement
      )
      when length(resources) > 0 do
    not passes?(identifier, statement)
  end

  def passes?(_, _), do: false

  def from_map(%{"resources" => resources} = statement) do
    resources =
      Enum.map(resources, fn id ->
        id |> atom_map() |> Identifier.from_map()
      end)

    struct(Statement, atom_map(%{statement | "resources" => resources}))
  end

  def from_map(statement), do: struct(Statement, statement)
  defp atom_map(t), do: Map.new(t, fn {k, v} -> {String.to_atom(k), v} end)
end