Comunicación bidireccional sin Internet

implementation 'com.google.android.gms:play-services-nearby:LATEST_VERSION'

android {
   ...
   buildFeatures {
       viewBinding true
   }
}

<vector xmlns:android="http://schemas.android.com/apk/res/android"
   android:height="24dp"
   android:tintMode="multiply"
   android:viewportHeight="48.0"
   android:viewportWidth="48.0"
   android:width="24dp">
 <path
     android:fillColor="#ffffff"
     android:pathData="M28,12l-7.5,10 5.7,7.6L23,32c-3.38,-4.5 -9,-12 -9,-12L2,36h44L28,12z"/>
</vector>

<vector xmlns:android="http://schemas.android.com/apk/res/android"
   android:height="24dp"
   android:tintMode="multiply"
   android:viewportHeight="48.0"
   android:viewportWidth="48.0"
   android:width="24dp">
 <path
     android:fillColor="#ffffff"
     android:pathData="M28,4L12,4C9.79,4 8.02,5.79 8.02,8L8,40c0,2.21 1.77,4 3.98,4L36,44c2.21,0 4,-1.79 4,-4L40,16L28,4zM26,18L26,7l11,11L26,18z"/>
</vector>

<vector xmlns:android="http://schemas.android.com/apk/res/android"
   android:width="24dp"
   android:height="24dp"
   android:tintMode="multiply"
   android:viewportWidth="48.0"
   android:viewportHeight="48.0">
   <path
       android:fillColor="#ffffff"
       android:pathData="M19.28,15.28c0.45,-1 0.72,-2.11 0.72,-3.28 0,-4.42 -3.58,-8 -8,-8s-8,3.58 -8,8 3.58,8 8,8c1.17,0 2.28,-0.27 3.28,-0.72L20,24l-4.72,4.72c-1,-0.45 -2.11,-0.72 -3.28,-0.72 -4.42,0 -8,3.58 -8,8s3.58,8 8,8 8,-3.58 8,-8c0,-1.17 -0.27,-2.28 -0.72,-3.28L24,28l14,14h6v-2L19.28,15.28zM12,16c-2.21,0 -4,-1.79 -4,-4s1.79,-4 4,-4 4,1.79 4,4 -1.79,4 -4,4zM12,40c-2.21,0 -4,-1.79 -4,-4s1.79,-4 4,-4 4,1.79 4,4 -1.79,4 -4,4zM24,25c-0.55,0 -1,-0.45 -1,-1s0.45,-1 1,-1 1,0.45 1,1 -0.45,1 -1,1zM38,6L26,18l4,4L44,8L44,6z" />
</vector>

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
   xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:app="http://schemas.android.com/apk/res-auto"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   tools:context=".MainActivity">

   <TextView
       android:id="@+id/status"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:padding="16dp"
       android:text="searching..."
       app:layout_constraintBottom_toTopOf="@+id/myName"
       app:layout_constraintEnd_toEndOf="parent"
       app:layout_constraintStart_toStartOf="parent"
       app:layout_constraintTop_toTopOf="parent"
       />

   <TextView
       android:id="@+id/myName"
       android:layout_width="0dp"
       android:layout_height="wrap_content"
       android:layout_gravity="center"
       android:text="You (codeName)"
       android:textAlignment="center"
       android:textAppearance="?android:textAppearanceMedium"
       app:layout_constraintEnd_toStartOf="@+id/opponentName"
       app:layout_constraintStart_toStartOf="parent"
       app:layout_constraintTop_toBottomOf="@+id/status"
       />

   <TextView
       android:id="@+id/opponentName"
       android:layout_width="0dp"
       android:layout_height="wrap_content"
       android:layout_gravity="center"
       android:text="Opponent (codeName)"
       android:textAlignment="center"
       android:textAppearance="?android:textAppearanceMedium"
       app:layout_constraintEnd_toEndOf="parent"
       app:layout_constraintStart_toEndOf="@+id/myName"
       app:layout_constraintTop_toBottomOf="@+id/status"
       />

   <TextView
       android:id="@+id/score"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:layout_gravity="center"
       android:layout_margin="16dp"
       android:text=":"
       android:textAlignment="center"
       android:textSize="80sp"
       app:layout_constraintEnd_toEndOf="parent"
       app:layout_constraintStart_toStartOf="parent"
       app:layout_constraintTop_toBottomOf="@+id/myName"
       />

   <androidx.appcompat.widget.AppCompatButton
       android:id="@+id/rock"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:drawableTop="@drawable/rock"
       android:text="Rock"
       app:layout_constraintEnd_toStartOf="@+id/paper"
       app:layout_constraintHorizontal_chainStyle="spread"
       app:layout_constraintStart_toStartOf="parent"
       app:layout_constraintTop_toBottomOf="@+id/score"
       />

   <androidx.appcompat.widget.AppCompatButton
       android:id="@+id/paper"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:drawableTop="@drawable/paper"
       android:text="Paper"
       app:layout_constraintEnd_toStartOf="@+id/scissors"
       app:layout_constraintStart_toEndOf="@+id/rock"
       app:layout_constraintTop_toBottomOf="@+id/score"
       />

   <androidx.appcompat.widget.AppCompatButton
       android:id="@+id/scissors"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:drawableTop="@drawable/scissors"
       android:text="Scissors"
       app:layout_constraintEnd_toEndOf="parent"
       app:layout_constraintStart_toEndOf="@+id/paper"
       app:layout_constraintTop_toBottomOf="@+id/score"
       />

   <androidx.appcompat.widget.AppCompatButton
       android:id="@+id/disconnect"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:layout_margin="32dp"
       android:text="disconnect"
       app:layout_constraintBottom_toBottomOf="parent"
       app:layout_constraintEnd_toEndOf="parent"
       app:layout_constraintStart_toStartOf="parent"
       app:layout_constraintTop_toBottomOf="@+id/paper"
       />

   <androidx.appcompat.widget.AppCompatButton
       android:id="@+id/findOpponent"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:layout_margin="32dp"
       android:text="find opponent"
       app:layout_constraintBottom_toBottomOf="parent"
       app:layout_constraintEnd_toEndOf="parent"
       app:layout_constraintStart_toStartOf="parent"
       app:layout_constraintTop_toBottomOf="@+id/paper"
       />

</androidx.constraintlayout.widget.ConstraintLayout>

<!-- Required for Nearby Connections →

<!--    Because ACCESS_FINE_LOCATION is a dangerous permission, the app will have to-->
<!--    request it at runtime, and the user will be prompted to grant or deny access.-->

<uses-permission android:name="android.permission.BLUETOOTH"/>
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE"/>
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>

/**
* Enum class for defining the winning rules for Rock-Paper-Scissors. Each player will make a
* choice, then the beats function in this class will be used to determine whom to reward the
* point to.
*/
private enum class GameChoice {
   ROCK, PAPER, SCISSORS;

   fun beats(other: GameChoice): Boolean =
       (this == ROCK && other == SCISSORS)
               || (this == SCISSORS && other == PAPER)
               || (this == PAPER && other == ROCK)
}

/**
* Instead of having each player enter a name, in this sample we will conveniently generate
* random human readable names for players.
*/
internal object CodenameGenerator {
   private val COLORS = arrayOf(
       "Red", "Orange", "Yellow", "Green", "Blue", "Indigo", "Violet", "Purple", "Lavender"
   )
   private val TREATS = arrayOf(
       "Cupcake", "Donut", "Eclair", "Froyo", "Gingerbread", "Honeycomb",
       "Ice Cream Sandwich", "Jellybean", "Kit Kat", "Lollipop", "Marshmallow", "Nougat",
       "Oreo", "Pie"
   )
   private val generator = Random()

   /** Generate a random Android agent codename  */
   fun generate(): String {
       val color = COLORS[generator.nextInt(COLORS.size)]
       val treat = TREATS[generator.nextInt(TREATS.size)]
       return "$color $treat"
   }
}

/**
* Strategy for telling the Nearby Connections API how we want to discover and connect to
* other nearby devices. A star shaped strategy means we want to discover multiple devices but
* only connect to and communicate with one at a time.
*/
private val STRATEGY = Strategy.P2P_STAR

/**
* Our handle to the [Nearby Connections API][ConnectionsClient].
*/
private lateinit var connectionsClient: ConnectionsClient

/**
* The request code for verifying our call to [requestPermissions]. Recall that calling
* [requestPermissions] leads to a callback to [onRequestPermissionsResult]
*/
private val REQUEST_CODE_REQUIRED_PERMISSIONS = 1

/*
The following variables are convenient ways of tracking the data of the opponent that we
choose to play against.
*/
private var opponentName: String? = null
private var opponentEndpointId: String? = null
private var opponentScore = 0
private var opponentChoice: GameChoice? = null

/*
The following variables are for tracking our own data
*/
private var myCodeName: String = CodenameGenerator.generate()
private var myScore = 0
private var myChoice: GameChoice? = null

/**
* This is for wiring and interacting with the UI views.
*/
private lateinit var binding: ActivityMainBinding

override fun onCreate(savedInstanceState: Bundle?) {
   super.onCreate(savedInstanceState)
   binding = ActivityMainBinding.inflate(layoutInflater)
   setContentView(binding.root)
   connectionsClient = Nearby.getConnectionsClient(this)
}

@CallSuper
override fun onStart() {
   super.onStart()
   if (checkSelfPermission(Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
       requestPermissions(
           arrayOf(Manifest.permission.ACCESS_FINE_LOCATION),
           REQUEST_CODE_REQUIRED_PERMISSIONS
       )
   }
}

@CallSuper
override fun onRequestPermissionsResult(
   requestCode: Int,
   permissions: Array<out String>,
   grantResults: IntArray
) {
   super.onRequestPermissionsResult(requestCode, permissions, grantResults)
   val errMsg = "Cannot start without required permissions"
   if (requestCode == REQUEST_CODE_REQUIRED_PERMISSIONS) {
       grantResults.forEach {
           if (it == PackageManager.PERMISSION_DENIED) {
               Toast.makeText(this, errMsg, Toast.LENGTH_LONG).show()
               finish()
               return
           }
       }
       recreate()
   }
}

/** Sends the user's selection of rock, paper, or scissors to the opponent. */
private fun sendGameChoice(choice: GameChoice) {
   myChoice = choice
   connectionsClient.sendPayload(
       opponentEndpointId!!,
       Payload.fromBytes(choice.name.toByteArray(UTF_8))
   )
   binding.status.text = "You chose ${choice.name}"
   // For fair play, we will disable the game controller so that users don't change their
   // choice in the middle of a game.
   setGameControllerEnabled(false)
}

/**
* Enables/Disables the rock, paper and scissors buttons. Disabling the game controller
* prevents users from changing their minds after making a choice.
*/
private fun setGameControllerEnabled(state: Boolean) {
   binding.apply {
       rock.isEnabled = state
       paper.isEnabled = state
       scissors.isEnabled = state
   }
}

/** callback for receiving payloads */
private val payloadCallback: PayloadCallback = object : PayloadCallback() {
   override fun onPayloadReceived(endpointId: String, payload: Payload) {
       payload.asBytes()?.let {
           opponentChoice = GameChoice.valueOf(String(it, UTF_8))
       }
   }

   override fun onPayloadTransferUpdate(endpointId: String, update: PayloadTransferUpdate) {
       // Determines the winner and updates game state/UI after both players have chosen.
       // Feel free to refactor and extract this code into a different method
       if (update.status == PayloadTransferUpdate.Status.SUCCESS
           && myChoice != null && opponentChoice != null) {
           val mc = myChoice!!
           val oc = opponentChoice!!
           when {
               mc.beats(oc) -> { // Win!
                   binding.status.text = "${mc.name} beats ${oc.name}"
                   myScore++
               }
               mc == oc -> { // Tie
                   binding.status.text = "You both chose ${mc.name}"
               }
               else -> { // Loss
                   binding.status.text = "${mc.name} loses to ${oc.name}"
                   opponentScore++
               }
           }
           binding.score.text = "$myScore : $opponentScore"
           myChoice = null
           opponentChoice = null
           setGameControllerEnabled(true)
       }
   }
}

// Callbacks for connections to other devices
private val connectionLifecycleCallback = object : ConnectionLifecycleCallback() {
   override fun onConnectionInitiated(endpointId: String, info: ConnectionInfo) {
       // Accepting a connection means you want to receive messages. Hence, the API expects
       // that you attach a PayloadCall to the acceptance
       connectionsClient.acceptConnection(endpointId, payloadCallback)
       opponentName = "Opponent\n(${info.endpointName})"
   }

   override fun onConnectionResult(endpointId: String, result: ConnectionResolution) {
       if (result.status.isSuccess) {
           connectionsClient.stopAdvertising()
           connectionsClient.stopDiscovery()
           opponentEndpointId = endpointId
           binding.opponentName.text = opponentName
           binding.status.text = "Connected"
           setGameControllerEnabled(true) // we can start playing
       }
   }

   override fun onDisconnected(endpointId: String) {
       resetGame()
   }
}

/** Wipes all game state and updates the UI accordingly. */
private fun resetGame() {
   // reset data
   opponentEndpointId = null
   opponentName = null
   opponentChoice = null
   opponentScore = 0
   myChoice = null
   myScore = 0
   // reset state of views
   binding.disconnect.visibility = View.GONE
   binding.findOpponent.visibility = View.VISIBLE
   setGameControllerEnabled(false)
   binding.opponentName.text="opponent\n(none yet)"
   binding.status.text ="..."
   binding.score.text = ":"
}

private fun startAdvertising() {
   val options = AdvertisingOptions.Builder().setStrategy(STRATEGY).build()
   // Note: Advertising may fail. To keep this demo simple, we don't handle failures.
   connectionsClient.startAdvertising(
       myCodeName,
       packageName,
       connectionLifecycleCallback,
       options
   )
}

// Callbacks for finding other devices
private val endpointDiscoveryCallback = object : EndpointDiscoveryCallback() {
   override fun onEndpointFound(endpointId: String, info: DiscoveredEndpointInfo) {
       connectionsClient.requestConnection(myCodeName, endpointId, connectionLifecycleCallback)
   }

   override fun onEndpointLost(endpointId: String) {
   }
}

private fun startDiscovery(){
   val options = DiscoveryOptions.Builder().setStrategy(STRATEGY).build()
   connectionsClient.startDiscovery(packageName,endpointDiscoveryCallback,options)
}

override fun onCreate(savedInstanceState: Bundle?) {
   super.onCreate(savedInstanceState)
   binding = ActivityMainBinding.inflate(layoutInflater)
   setContentView(binding.root)
   connectionsClient = Nearby.getConnectionsClient(this)

   binding.myName.text = "You\n($myCodeName)"
   binding.findOpponent.setOnClickListener {
       startAdvertising()
       startDiscovery()
       binding.status.text = "Searching for opponents..."
       // "find opponents" is the opposite of "disconnect" so they don't both need to be
       // visible at the same time
       binding.findOpponent.visibility = View.GONE
       binding.disconnect.visibility = View.VISIBLE
   }
   // wire the controller buttons
   binding.apply {
       rock.setOnClickListener { sendGameChoice(GameChoice.ROCK) }
       paper.setOnClickListener { sendGameChoice(GameChoice.PAPER) }
       scissors.setOnClickListener { sendGameChoice(GameChoice.SCISSORS) }
   }
   binding.disconnect.setOnClickListener {
       opponentEndpointId?.let { connectionsClient.disconnectFromEndpoint(it) }
       resetGame()
   }

   resetGame() // we are about to start a new game
}

@CallSuper
override fun onStop(){
   connectionsClient.apply {
       stopAdvertising()
       stopDiscovery()
       stopAllEndpoints()
   }
   resetGame()
   super.onStop()
}