defmodule Parc do
  @moduledoc """
  Generic PARC (Principal, Action, Resource, Context) authorization contract,
  independent of any policy framework.

  The contract and engine:

  - `Parc.Request`: the authorization request a decision is made on.
  - `Parc.RequestPreparer`: the behaviour for a pipeline step that prepares the
    request (enrich, telemetry, validate, trace) before the decision.
  - `Parc.PolicyDecider`: the behaviour for the single decision point that turns
    a request into an allow/deny/challenge/error verdict.
  - `Parc.Pipeline`: runs the declared request preparers, then the decider; also
    the `use Parc.Pipeline` builder for declaring a pipeline (`prepare`/`decide`).

  A host adapter builds a `Parc.Request` from its own action representation and runs
  it through the pipeline, mapping the verdict back to the host policy framework.
  Nothing here depends on the adapter or that framework. A decider or preparer is
  written against `Parc.*` alone.
  """
end