taler-android

NfcTotpWriter.kt (5958B)

---

 /*
  * This file is part of GNU Taler
  * (C) 2026 Taler Systems S.A.
  *
  * GNU Taler is free software; you can redistribute it and/or modify it under the
  * terms of the GNU General Public License as published by the Free Software
  * Foundation; either version 3, or (at your option) any later version.
  *
  * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
  * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License along with
  * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
  */
 
 package net.taler.wallet.payment
 
 import android.app.Activity
 import android.nfc.NdefMessage
 import android.nfc.NdefRecord
 import android.nfc.NfcAdapter
 import android.nfc.tech.Ndef
 import android.nfc.tech.NfcA
 import android.widget.Toast
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
 import androidx.compose.material3.Button
 import androidx.compose.material3.ButtonDefaults
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.DisposableEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment.Companion.CenterHorizontally
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.text.font.FontFamily
 import androidx.compose.ui.unit.dp
 import net.taler.wallet.R
 import java.io.ByteArrayOutputStream
 
 private const val NFC_READER_FLAGS = NfcAdapter.FLAG_READER_NFC_A or NfcAdapter.FLAG_READER_NFC_V
 
 private fun formatTotpPayload(totpString: String): ByteArray {
     val codes = totpString.split("\n").mapNotNull { it.toUIntOrNull() }
     val out = ByteArrayOutputStream()
     out.write(0x42)
     for (code in codes) {
         val v = code.toInt()
         out.write(v shr 0 and 0xFF)
         out.write(v shr 8 and 0xFF)
         out.write(v shr 16 and 0xFF)
         out.write(v shr 24 and 0xFF)
     }
     return out.toByteArray()
 }
 
 @Composable
 fun TotpNfcWriter(
     totpString: String,
     modifier: Modifier = Modifier,
 ) {
     val context = LocalContext.current
     val activity = context as? Activity
     var isWriting by remember { mutableStateOf(false) }
 
     DisposableEffect(activity) {
         onDispose {
             if (isWriting && activity != null) {
                 NfcAdapter.getDefaultAdapter(context)?.disableReaderMode(activity)
             }
         }
     }
 
     val ndefMessage = remember(totpString) {
         val payload = formatTotpPayload(totpString)
         val record = NdefRecord(
             NdefRecord.TNF_WELL_KNOWN,
             "T".encodeToByteArray(),
             ByteArray(0),
             payload,
         )
         NdefMessage(arrayOf(record))
     }
 
     Column(modifier = modifier, horizontalAlignment = CenterHorizontally) {
         Text(
             modifier = Modifier.padding(top = 16.dp, start = 16.dp, end = 16.dp),
             text = stringResource(R.string.payment_confirmation_code),
             style = MaterialTheme.typography.bodyMedium,
         )
 
         Text(
             modifier = Modifier.padding(top = 8.dp, start = 16.dp, end = 16.dp, bottom = 8.dp),
             text = totpString,
             fontFamily = FontFamily.Monospace,
             fontSize = MaterialTheme.typography.titleLarge.fontSize,
         )
 
         Button(
             onClick = {
                 val nfcAdapter = NfcAdapter.getDefaultAdapter(context)
                 val act = activity
                 if (nfcAdapter == null || act == null) {
                     Toast.makeText(context, R.string.nfc_not_available, Toast.LENGTH_SHORT).show()
                     return@Button
                 }
                 isWriting = true
                 nfcAdapter.enableReaderMode(act, { tag ->
                     val ndef = Ndef.get(tag)
                     if (ndef != null) {
                         try {
                             ndef.connect()
                             ndef.writeNdefMessage(ndefMessage)
                             act.runOnUiThread {
                                 Toast.makeText(context, R.string.nfc_write_success, Toast.LENGTH_SHORT).show()
                             }
                         } catch (e: Exception) {
                             act.runOnUiThread {
                                 Toast.makeText(context, "${e.message}", Toast.LENGTH_SHORT).show()
                             }
                         } finally {
                             act.runOnUiThread {
                                 isWriting = false
                                 nfcAdapter.disableReaderMode(act)
                             }
                         }
                     } else {
                         act.runOnUiThread {
                             isWriting = false
                             nfcAdapter.disableReaderMode(act)
                             Toast.makeText(context, R.string.nfc_tag_not_ndef, Toast.LENGTH_SHORT).show()
                         }
                     }
                 }, NFC_READER_FLAGS, null)
             },
             modifier = Modifier.fillMaxWidth().padding(horizontal = 32.dp).padding(top = 4.dp),
             enabled = !isWriting,
         ) {
             Text(if (isWriting) stringResource(R.string.nfc_writing) else stringResource(R.string.nfc_write_button))
         }
 
         if (!isWriting) {
             Spacer(Modifier.height(ButtonDefaults.IconSpacing))
         }
     }
 }