/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * license agreements; and to You under the Apache License, version 2.0:
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * This file is part of the Apache Pekko project, which was derived from Akka.
 */

/*
 * Copyright (C) 2018-2022 Lightbend Inc. <https://www.lightbend.com>
 */

package org.apache.pekko.stream.javadsl

import javax.net.ssl.{ SSLEngine, SSLSession }

import scala.util.Try

import org.apache.pekko
import pekko.NotUsed
import pekko.japi.function
import pekko.stream._
import pekko.stream.TLSProtocol._
import pekko.util.ByteString

/**
 * Stream cipher support based upon JSSE.
 *
 * The underlying SSLEngine has four ports: plaintext input/output and
 * ciphertext input/output. These are modeled as a [[pekko.stream.BidiShape]]
 * element for use in stream topologies, where the plaintext ports are on the
 * left hand side of the shape and the ciphertext ports on the right hand side.
 *
 * Configuring JSSE is a rather complex topic, please refer to the JDK platform
 * documentation or the excellent user guide that is part of the Play Framework
 * documentation. The philosophy of this integration into Pekko Streams is to
 * expose all knobs and dials to client code and therefore not limit the
 * configuration possibilities. In particular the client code will have to
 * provide the SSLEngine, which is typically created from a SSLContext. Handshake
 * parameters and other parameters are defined when creating the SSLEngine.
 *
 * '''IMPORTANT NOTE'''
 *
 * The TLS specification until version 1.2 did not permit half-closing of the user data session
 * that it transports—to be precise a half-close will always promptly lead to a
 * full close. This means that canceling the plaintext output or completing the
 * plaintext input of the SslTls operator will lead to full termination of the
 * secure connection without regard to whether bytes are remaining to be sent or
 * received, respectively. Especially for a client the common idiom of attaching
 * a finite Source to the plaintext input and transforming the plaintext response
 * bytes coming out will not work out of the box due to early termination of the
 * connection. For this reason there is a parameter that determines whether the
 * SslTls operator shall ignore completion and/or cancellation events, and the
 * default is to ignore completion (in view of the client–server scenario). In
 * order to terminate the connection the client will then need to cancel the
 * plaintext output as soon as all expected bytes have been received. When
 * ignoring both types of events the operator will shut down once both events have
 * been received. See also [[TLSClosing]]. For now, half-closing is also not
 * supported with TLS 1.3 where the spec allows it.
 */
object TLS {

  /**
   * Create a StreamTls [[pekko.stream.javadsl.BidiFlow]]. This is a low-level interface.
   *
   * You specify a factory `sslEngineCreator` to create an SSLEngine that must already be configured for
   * client and server mode and with all the parameters for the first session.
   *
   * You can specify a verification function `sessionVerifier` that will be called
   * after every successful handshake to verify additional session information.
   *
   * For a description of the `closing` parameter please refer to [[TLSClosing]].
   */
  def create(
      sslEngineCreator: function.Creator[SSLEngine],
      sessionVerifier: function.Procedure[SSLSession],
      closing: TLSClosing): BidiFlow[SslTlsOutbound, ByteString, ByteString, SslTlsInbound, NotUsed] =
    new javadsl.BidiFlow(
      scaladsl.TLS.apply(() => sslEngineCreator.create(), session => Try(sessionVerifier(session)), closing))

  /**
   * Create a StreamTls [[pekko.stream.javadsl.BidiFlow]]. This is a low-level interface.
   *
   * You specify a factory `sslEngineCreator` to create an SSLEngine that must already be configured for
   * client and server mode and with all the parameters for the first session.
   *
   * For a description of the `closing` parameter please refer to [[TLSClosing]].
   */
  def create(
      sslEngineCreator: function.Creator[SSLEngine],
      closing: TLSClosing): BidiFlow[SslTlsOutbound, ByteString, ByteString, SslTlsInbound, NotUsed] =
    new javadsl.BidiFlow(scaladsl.TLS.apply(() => sslEngineCreator.create(), closing))
}

/**
 * This object holds simple wrapping [[pekko.stream.scaladsl.BidiFlow]] implementations that can
 * be used instead of [[TLS]] when no encryption is desired. The flows will
 * just adapt the message protocol by wrapping into [[SessionBytes]] and
 * unwrapping [[SendBytes]].
 */
object TLSPlacebo {

  /**
   * Returns a reusable [[BidiFlow]] instance representing a [[TLSPlacebo$]].
   */
  def getInstance(): javadsl.BidiFlow[SslTlsOutbound, ByteString, ByteString, SessionBytes, NotUsed] = forJava

  private val forJava: javadsl.BidiFlow[SslTlsOutbound, ByteString, ByteString, SessionBytes, NotUsed] =
    new javadsl.BidiFlow(scaladsl.TLSPlacebo())
}
