feat(ios): enable QR and NFC invitation share/receive

Wire Core NFC entitlements and implement invitation ticket export,
QR presentation, and NDEF read/write on iOS so send/receive parity
matches Android.

iosApp/iosApp.xcodeproj/project.pbxproj

@@ -296,6 +296,7 @@
 				ARCHS = arm64;
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				ASSETCATALOG_COMPILER_GLOBAL_ACCENT_COLOR_NAME = AccentColor;
+				CODE_SIGN_ENTITLEMENTS = iosApp/vnidrop.entitlements;
 				CODE_SIGN_IDENTITY = "Apple Development";
 				CODE_SIGN_STYLE = Automatic;
 				DEVELOPMENT_ASSET_PATHS = "\"iosApp/Preview Content\"";
@@ -303,6 +304,8 @@
 				ENABLE_PREVIEWS = YES;
 				GENERATE_INFOPLIST_FILE = YES;
 				INFOPLIST_FILE = iosApp/Info.plist;
+				INFOPLIST_KEY_NFCReaderUsageDescription = "VniDrop uses NFC to read transfer invitation tags.";
+				INFOPLIST_KEY_NSCameraUsageDescription = "VniDrop uses the camera to scan transfer QR codes.";
 				INFOPLIST_KEY_UIApplicationSceneManifest_Generation = YES;
 				INFOPLIST_KEY_UIApplicationSupportsIndirectInputEvents = YES;
 				INFOPLIST_KEY_UILaunchScreen_Generation = YES;
@@ -318,6 +321,10 @@
 					SystemConfiguration,
 					"-framework",
 					Network,
+					"-framework",
+					CoreNFC,
+					"-framework",
+					AVFoundation,
 				);
 				SWIFT_EMIT_LOC_STRINGS = YES;
 				SWIFT_VERSION = 5.0;
@@ -331,6 +338,7 @@
 				ARCHS = arm64;
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				ASSETCATALOG_COMPILER_GLOBAL_ACCENT_COLOR_NAME = AccentColor;
+				CODE_SIGN_ENTITLEMENTS = iosApp/vnidrop.entitlements;
 				CODE_SIGN_IDENTITY = "Apple Development";
 				CODE_SIGN_STYLE = Automatic;
 				DEVELOPMENT_ASSET_PATHS = "\"iosApp/Preview Content\"";
@@ -338,6 +346,8 @@
 				ENABLE_PREVIEWS = YES;
 				GENERATE_INFOPLIST_FILE = YES;
 				INFOPLIST_FILE = iosApp/Info.plist;
+				INFOPLIST_KEY_NFCReaderUsageDescription = "VniDrop uses NFC to read transfer invitation tags.";
+				INFOPLIST_KEY_NSCameraUsageDescription = "VniDrop uses the camera to scan transfer QR codes.";
 				INFOPLIST_KEY_UIApplicationSceneManifest_Generation = YES;
 				INFOPLIST_KEY_UIApplicationSupportsIndirectInputEvents = YES;
 				INFOPLIST_KEY_UILaunchScreen_Generation = YES;
@@ -353,6 +363,10 @@
 					SystemConfiguration,
 					"-framework",
 					Network,
+					"-framework",
+					CoreNFC,
+					"-framework",
+					AVFoundation,
 				);
 				SWIFT_EMIT_LOC_STRINGS = YES;
 				SWIFT_VERSION = 5.0;

iosApp/iosApp/Info.plist

@@ -43,6 +43,10 @@
 	</array>
 	<key>LSSupportsOpeningDocumentsInPlace</key>
 	<true/>
+	<key>NSCameraUsageDescription</key>
+	<string>VniDrop uses the camera to scan transfer QR codes.</string>
+	<key>NFCReaderUsageDescription</key>
+	<string>VniDrop uses NFC to read transfer invitation tags.</string>
 	<key>UIViewControllerBasedStatusBarAppearance</key>
 	<true/>
 </dict>

iosApp/iosApp/vnidrop.entitlements

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>com.apple.developer.nfc.readersession.formats</key>
+	<array>
+		<string>NDEF</string>
+	</array>
+</dict>
+</plist>

shared/src/iosMain/kotlin/com/vnidrop/app/feature/receive/ReceiveInvitationActions.ios.kt

@@ -2,30 +2,91 @@ package com.vnidrop.app.feature.receive
 
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.remember
+import kotlinx.cinterop.BetaInteropApi
 import kotlinx.cinterop.ExperimentalForeignApi
+import kotlinx.cinterop.ObjCAction
+import kotlinx.cinterop.ObjCObjectVar
+import kotlinx.cinterop.alloc
+import kotlinx.cinterop.memScoped
+import kotlinx.cinterop.ptr
 import kotlinx.cinterop.readBytes
+import kotlinx.cinterop.value
+import platform.AVFoundation.AVAuthorizationStatusAuthorized
+import platform.AVFoundation.AVAuthorizationStatusDenied
+import platform.AVFoundation.AVAuthorizationStatusNotDetermined
+import platform.AVFoundation.AVAuthorizationStatusRestricted
+import platform.AVFoundation.AVCaptureDevice
+import platform.AVFoundation.AVCaptureDeviceInput
+import platform.AVFoundation.AVCaptureMetadataOutput
+import platform.AVFoundation.AVCaptureMetadataOutputObjectsDelegateProtocol
+import platform.AVFoundation.AVCaptureOutput
+import platform.AVFoundation.AVCaptureConnection
+import platform.AVFoundation.AVCaptureSession
+import platform.AVFoundation.AVCaptureSessionPresetHigh
+import platform.AVFoundation.AVCaptureVideoPreviewLayer
+import platform.AVFoundation.AVLayerVideoGravityResizeAspectFill
+import platform.AVFoundation.AVMediaTypeVideo
+import platform.AVFoundation.AVMetadataMachineReadableCodeObject
+import platform.AVFoundation.AVMetadataObjectTypeQRCode
+import platform.AVFoundation.authorizationStatusForMediaType
+import platform.AVFoundation.requestAccessForMediaType
+import platform.CoreGraphics.CGRectMake
+import platform.CoreNFC.NFCNDEFMessage
+import platform.CoreNFC.NFCNDEFPayload
+import platform.CoreNFC.NFCNDEFReaderSession
+import platform.CoreNFC.NFCNDEFReaderSessionDelegateProtocol
+import platform.CoreNFC.NFCTypeNameFormatMedia
+import platform.Foundation.NSData
+import platform.Foundation.NSError
 import platform.Foundation.NSFileManager
 import platform.Foundation.NSURL
+import platform.UIKit.NSTextAlignmentCenter
 import platform.UIKit.UIApplication
+import platform.UIKit.UIButton
+import platform.UIKit.UIButtonTypeSystem
+import platform.UIKit.UIColor
+import platform.UIKit.UIControlEventTouchUpInside
+import platform.UIKit.UIControlStateNormal
 import platform.UIKit.UIDocumentPickerDelegateProtocol
 import platform.UIKit.UIDocumentPickerViewController
+import platform.UIKit.UILabel
 import platform.UIKit.UIModalPresentationFormSheet
+import platform.UIKit.UIModalPresentationFullScreen
+import platform.UIKit.UIViewAutoresizingFlexibleHeight
+import platform.UIKit.UIViewAutoresizingFlexibleWidth
+import platform.UIKit.UIViewController
 import platform.UniformTypeIdentifiers.UTTypeData
+import platform.darwin.DISPATCH_QUEUE_PRIORITY_DEFAULT
 import platform.darwin.NSObject
+import platform.darwin.dispatch_async
+import platform.darwin.dispatch_get_global_queue
+import platform.darwin.dispatch_get_main_queue
 
 private var retainedInvitationDelegate: InvitationDocumentDelegate? = null
+private var retainedQrScanner: QrScannerViewController? = null
+private var retainedNfcReader: InvitationNfcReader? = null
 
 @Composable
 actual fun rememberReceiveInvitationActions(): ReceiveInvitationActions = remember {
 	object : ReceiveInvitationActions {
 		override val fileAvailability = ReceiveMethodAvailability.Available
-		// Hide unfinished iOS methods so the method list only shows what works.
-		override val qrAvailability = ReceiveMethodAvailability.Hidden
-		override val nfcAvailability = ReceiveMethodAvailability.Hidden
+		override val qrAvailability =
+			if (AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo) != null) {
+				ReceiveMethodAvailability.Available
+			} else {
+				ReceiveMethodAvailability.Unavailable
+			}
+		override val nfcAvailability =
+			if (NFCNDEFReaderSession.readingAvailable) {
+				ReceiveMethodAvailability.Available
+			} else {
+				ReceiveMethodAvailability.Unavailable
+			}
 
 		@OptIn(ExperimentalForeignApi::class)
 		override fun pickInvitation(onResult: (Result<String>) -> Unit) {
-			val presenter = UIApplication.sharedApplication.keyWindow?.rootViewController
+			cancel()
+			val presenter = topPresenter()
 				?: return onResult(Result.failure(IllegalStateException("Could not find an iOS view controller")))
 			val picker = UIDocumentPickerViewController(forOpeningContentTypes = listOf(UTTypeData), asCopy = true)
 			val delegate = InvitationDocumentDelegate(onResult)
@@ -35,13 +96,67 @@ actual fun rememberReceiveInvitationActions(): ReceiveInvitationActions = rememb
 			presenter.presentViewController(picker, animated = true, completion = null)
 		}
 
-		override fun scanQrCode(onResult: (Result<String>) -> Unit) =
-			onResult(Result.failure(UnsupportedOperationException("QR scanning is not enabled for this iOS build")))
+		override fun scanQrCode(onResult: (Result<String>) -> Unit) {
+			cancel()
+			val presenter = topPresenter()
+				?: return onResult(Result.failure(IllegalStateException("Could not find an iOS view controller")))
+			ensureCameraAccess { granted ->
+				if (!granted) {
+					onResult(Result.failure(IllegalStateException("Camera access is required to scan QR codes")))
+					return@ensureCameraAccess
+				}
+				val scanner = QrScannerViewController { result ->
+					retainedQrScanner = null
+					onResult(result)
+				}
+				retainedQrScanner = scanner
+				scanner.modalPresentationStyle = UIModalPresentationFullScreen
+				presenter.presentViewController(scanner, animated = true, completion = null)
+			}
+		}
 
-		override fun readNfcInvitation(onResult: (Result<String>) -> Unit) =
-			onResult(Result.failure(UnsupportedOperationException("NFC reading is not enabled for this iOS build")))
+		override fun readNfcInvitation(onResult: (Result<String>) -> Unit) {
+			cancel()
+			if (!NFCNDEFReaderSession.readingAvailable) {
+				onResult(Result.failure(UnsupportedOperationException("NFC reading is unavailable on this device")))
+				return
+			}
+			val reader = InvitationNfcReader { result ->
+				retainedNfcReader = null
+				onResult(result)
+			}
+			retainedNfcReader = reader
+			reader.start()
+		}
 
-		override fun cancel() = Unit
+		override fun cancel() {
+			retainedNfcReader?.cancel()
+			retainedNfcReader = null
+			retainedQrScanner?.cancelScan()
+			retainedQrScanner = null
+			retainedInvitationDelegate = null
+		}
+	}
+}
+
+private fun topPresenter(): UIViewController? {
+	var controller = UIApplication.sharedApplication.keyWindow?.rootViewController
+	while (controller?.presentedViewController != null) {
+		controller = controller?.presentedViewController
+	}
+	return controller
+}
+
+private fun ensureCameraAccess(onResult: (Boolean) -> Unit) {
+	when (AVCaptureDevice.authorizationStatusForMediaType(AVMediaTypeVideo)) {
+		AVAuthorizationStatusAuthorized -> onResult(true)
+		AVAuthorizationStatusNotDetermined -> {
+			AVCaptureDevice.requestAccessForMediaType(AVMediaTypeVideo) { granted ->
+				dispatch_async(dispatch_get_main_queue()) { onResult(granted) }
+			}
+		}
+		AVAuthorizationStatusDenied, AVAuthorizationStatusRestricted -> onResult(false)
+		else -> onResult(false)
 	}
 }
 
@@ -50,9 +165,9 @@ private class InvitationDocumentDelegate(
 ) : NSObject(), UIDocumentPickerDelegateProtocol {
 	@OptIn(ExperimentalForeignApi::class)
 	override fun documentPicker(controller: UIDocumentPickerViewController, didPickDocumentsAtURLs: List<*>) {
-		val url = didPickDocumentsAtURLs.firstOrNull() as? NSURL
 		onResult(runCatching {
-			requireNotNull(url) { "The selected invitation URL was invalid" }
+			val url = didPickDocumentsAtURLs.firstOrNull() as? NSURL
+				?: error("The selected invitation URL was invalid")
 			val path = url.path ?: error("The invitation path was invalid")
 			val data = NSFileManager.defaultManager.contentsAtPath(path) ?: error("The invitation could not be opened")
 			val length = data.length.toInt()
@@ -67,3 +182,203 @@ private class InvitationDocumentDelegate(
 		retainedInvitationDelegate = null
 	}
 }
+
+@OptIn(ExperimentalForeignApi::class, BetaInteropApi::class)
+private class QrScannerViewController(
+	private val onResult: (Result<String>) -> Unit,
+) : UIViewController(nibName = null, bundle = null), AVCaptureMetadataOutputObjectsDelegateProtocol {
+	private val session = AVCaptureSession()
+	private var previewLayer: AVCaptureVideoPreviewLayer? = null
+	private var finished = false
+	private val closeTarget = ButtonTarget { cancelScan() }
+
+	override fun viewDidLoad() {
+		super.viewDidLoad()
+		view.backgroundColor = UIColor.blackColor
+
+		val hint = UILabel(frame = view.bounds).apply {
+			text = "Point the camera at a VniDrop QR code"
+			textColor = UIColor.whiteColor
+			textAlignment = NSTextAlignmentCenter
+			numberOfLines = 0
+			autoresizingMask = UIViewAutoresizingFlexibleWidth or UIViewAutoresizingFlexibleHeight
+		}
+		view.addSubview(hint)
+
+		val close = UIButton.buttonWithType(UIButtonTypeSystem).apply {
+			setTitle("Cancel", forState = UIControlStateNormal)
+			setTitleColor(UIColor.whiteColor, forState = UIControlStateNormal)
+			addTarget(closeTarget, platform.objc.sel_registerName("invoke"), UIControlEventTouchUpInside)
+			setFrame(CGRectMake(16.0, 52.0, 88.0, 36.0))
+		}
+		view.addSubview(close)
+		configureSession()
+	}
+
+	override fun viewDidLayoutSubviews() {
+		super.viewDidLayoutSubviews()
+		previewLayer?.setFrame(view.bounds)
+	}
+
+	override fun viewWillDisappear(animated: Boolean) {
+		super.viewWillDisappear(animated)
+		if (session.running) session.stopRunning()
+	}
+
+	fun cancelScan() {
+		finish(Result.failure(IllegalStateException("QR scanning was cancelled")))
+	}
+
+	private fun configureSession() {
+		val device = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)
+			?: return finish(Result.failure(IllegalStateException("No camera is available")))
+
+		memScoped {
+			val errorPtr = alloc<ObjCObjectVar<NSError?>>()
+			val input = AVCaptureDeviceInput.deviceInputWithDevice(device, errorPtr.ptr)
+			if (input == null) {
+				finish(
+					Result.failure(
+						IllegalStateException(errorPtr.value?.localizedDescription ?: "Could not open the camera"),
+					),
+				)
+				return
+			}
+			if (!session.canAddInput(input)) {
+				finish(Result.failure(IllegalStateException("Could not configure the camera input")))
+				return
+			}
+			session.addInput(input)
+		}
+
+		val output = AVCaptureMetadataOutput()
+		if (!session.canAddOutput(output)) {
+			finish(Result.failure(IllegalStateException("Could not configure the QR scanner")))
+			return
+		}
+		session.addOutput(output)
+		output.setMetadataObjectsDelegate(this, queue = dispatch_get_main_queue())
+		output.metadataObjectTypes = listOf(AVMetadataObjectTypeQRCode)
+
+		val layer = AVCaptureVideoPreviewLayer(session = session).apply {
+			videoGravity = AVLayerVideoGravityResizeAspectFill
+			setFrame(view.bounds)
+		}
+		view.layer.insertSublayer(layer, atIndex = 0u)
+		previewLayer = layer
+		session.sessionPreset = AVCaptureSessionPresetHigh
+
+		dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT.toLong(), 0u)) {
+			session.startRunning()
+		}
+	}
+
+	override fun captureOutput(
+		output: AVCaptureOutput,
+		didOutputMetadataObjects: List<*>,
+		fromConnection: AVCaptureConnection,
+	) {
+		val code = didOutputMetadataObjects
+			.mapNotNull { it as? AVMetadataMachineReadableCodeObject }
+			.firstOrNull { it.type == AVMetadataObjectTypeQRCode }
+		val value = code?.stringValue?.trim().orEmpty()
+		if (value.isNotEmpty()) {
+			finish(Result.success(value))
+		}
+	}
+
+	private fun finish(result: Result<String>) {
+		if (finished) return
+		finished = true
+		if (session.running) session.stopRunning()
+		if (presentingViewController != null) {
+			dismissViewControllerAnimated(true) { onResult(result) }
+		} else {
+			onResult(result)
+		}
+	}
+}
+
+@OptIn(BetaInteropApi::class)
+private class ButtonTarget(
+	private val onClick: () -> Unit,
+) : NSObject() {
+	@ObjCAction
+	fun invoke() {
+		onClick()
+	}
+}
+
+@OptIn(ExperimentalForeignApi::class)
+private class InvitationNfcReader(
+	private val onResult: (Result<String>) -> Unit,
+) : NSObject(), NFCNDEFReaderSessionDelegateProtocol {
+	private var session: NFCNDEFReaderSession? = null
+	private var finished = false
+
+	fun start() {
+		val reader = NFCNDEFReaderSession(this, dispatch_get_main_queue(), invalidateAfterFirstRead = true)
+		reader.alertMessage = "Hold your iPhone near a VniDrop invitation tag"
+		session = reader
+		reader.beginSession()
+	}
+
+	fun cancel() {
+		session?.invalidateSession()
+		session = null
+	}
+
+	override fun readerSession(session: NFCNDEFReaderSession, didInvalidateWithError: NSError) {
+		if (finished) return
+		// NFCReaderError.readerSessionInvalidationErrorUserCanceled == 200
+		val cancelled = didInvalidateWithError.code == 200L
+		finish(
+			if (cancelled) {
+				Result.failure(IllegalStateException("NFC reading was cancelled"))
+			} else {
+				Result.failure(
+					IllegalStateException(didInvalidateWithError.localizedDescription ?: "NFC reading failed"),
+				)
+			},
+		)
+	}
+
+	override fun readerSession(session: NFCNDEFReaderSession, didDetectNDEFs: List<*>) {
+		val ticket = runCatching {
+			val messages = didDetectNDEFs.mapNotNull { it as? NFCNDEFMessage }
+			messages
+				.flatMap { message -> message.records.mapNotNull { it as? NFCNDEFPayload } }
+				.firstNotNullOfOrNull(::payloadAsInvitation)
+				?: error("This NFC tag does not contain a VniDrop invitation")
+		}
+		session.invalidateSession()
+		finish(ticket)
+	}
+
+	private fun finish(result: Result<String>) {
+		if (finished) return
+		finished = true
+		session = null
+		dispatch_async(dispatch_get_main_queue()) { onResult(result) }
+	}
+}
+
+@OptIn(ExperimentalForeignApi::class)
+private fun payloadAsInvitation(payload: NFCNDEFPayload): String? {
+	val type = payload.type?.toByteArray()?.decodeToString() ?: return null
+	val data = payload.payload?.toByteArray() ?: return null
+	return when {
+		payload.typeNameFormat == NFCTypeNameFormatMedia && type == InvitationMimeType ->
+			decodeInvitationBytes(data)
+		payload.typeNameFormat == NFCTypeNameFormatMedia && type.startsWith("text/") ->
+			decodeInvitationBytes(data)
+		else -> null
+	}
+}
+
+@OptIn(ExperimentalForeignApi::class)
+private fun NSData.toByteArray(): ByteArray {
+	val length = this.length.toInt()
+	if (length <= 0) return ByteArray(0)
+	return this.bytes?.readBytes(length) ?: ByteArray(0)
+}

shared/src/iosMain/kotlin/com/vnidrop/app/feature/send/TransferShareActions.ios.kt

@@ -2,27 +2,47 @@ package com.vnidrop.app.feature.send
 
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.remember
-import kotlinx.cinterop.ExperimentalForeignApi
+import com.vnidrop.app.feature.receive.VniDropInvitationMimeType
 import kotlinx.cinterop.BetaInteropApi
+import kotlinx.cinterop.ExperimentalForeignApi
+import kotlinx.cinterop.ObjCSignatureOverride
+import platform.CoreNFC.NFCNDEFMessage
+import platform.CoreNFC.NFCNDEFPayload
+import platform.CoreNFC.NFCNDEFReaderSession
+import platform.CoreNFC.NFCNDEFReaderSessionDelegateProtocol
+import platform.CoreNFC.NFCNDEFStatusNotSupported
+import platform.CoreNFC.NFCNDEFStatusReadOnly
+import platform.CoreNFC.NFCNDEFTagProtocol
+import platform.CoreNFC.NFCTypeNameFormatMedia
+import platform.Foundation.NSData
+import platform.Foundation.NSError
 import platform.Foundation.NSString
 import platform.Foundation.NSTemporaryDirectory
-import platform.Foundation.NSURL
 import platform.Foundation.NSUTF8StringEncoding
+import platform.Foundation.NSURL
 import platform.Foundation.create
+import platform.Foundation.dataUsingEncoding
 import platform.Foundation.writeToFile
 import platform.UIKit.UIActivityViewController
 import platform.UIKit.UIApplication
 import platform.UIKit.UIDocumentPickerViewController
 import platform.UIKit.UIModalPresentationFormSheet
+import platform.darwin.NSObject
+import platform.darwin.dispatch_get_main_queue
+
+private var retainedNfcWriter: InvitationNfcWriter? = null
 
 @OptIn(ExperimentalForeignApi::class)
 @Composable
 actual fun rememberTransferShareActions(): TransferShareActions = remember {
 	object : TransferShareActions {
 		override val canUseNativeShare = true
-		// Core NFC tag writing requires the NFC entitlement. Keep the action
-		// visible but disabled until that capability is provisioned for the app.
-		override val nfcAvailability = NfcShareAvailability.Unavailable
+		override val nfcAvailability =
+			if (NFCNDEFReaderSession.readingAvailable) {
+				NfcShareAvailability.Available
+			} else {
+				NfcShareAvailability.Unavailable
+			}
 
 		override fun exportInvitation(ticket: String, transferName: String, onResult: (Result<Unit>) -> Unit) {
 			onResult(runCatching {
@@ -42,9 +62,23 @@ actual fun rememberTransferShareActions(): TransferShareActions = remember {
 		}
 
 		override fun writeInvitationToNfc(ticket: String, onResult: (Result<Unit>) -> Unit) {
-			onResult(Result.failure(UnsupportedOperationException("NFC tag writing is not enabled for this build")))
+			cancelNfcWrite()
+			if (!NFCNDEFReaderSession.readingAvailable) {
+				onResult(Result.failure(UnsupportedOperationException("NFC is unavailable on this device")))
+				return
+			}
+			val writer = InvitationNfcWriter(ticket) { result ->
+				retainedNfcWriter = null
+				onResult(result)
+			}
+			retainedNfcWriter = writer
+			writer.start()
+		}
+
+		override fun cancelNfcWrite() {
+			retainedNfcWriter?.cancel()
+			retainedNfcWriter = null
 		}
-		override fun cancelNfcWrite() = Unit
 	}
 }
 
@@ -64,3 +98,106 @@ private fun presenter() = UIApplication.sharedApplication.keyWindow?.rootViewCon
 private fun present(controller: platform.UIKit.UIViewController) {
 	presenter().presentViewController(controller, animated = true, completion = null)
 }
+
+@OptIn(ExperimentalForeignApi::class, BetaInteropApi::class)
+private class InvitationNfcWriter(
+	private val ticket: String,
+	private val onResult: (Result<Unit>) -> Unit,
+) : NSObject(), NFCNDEFReaderSessionDelegateProtocol {
+	private var session: NFCNDEFReaderSession? = null
+	private var finished = false
+
+	fun start() {
+		val reader = NFCNDEFReaderSession(this, dispatch_get_main_queue(), invalidateAfterFirstRead = false)
+		reader.alertMessage = "Hold your iPhone near a writable NFC tag"
+		session = reader
+		reader.beginSession()
+	}
+
+	fun cancel() {
+		session?.invalidateSession()
+		session = null
+	}
+
+	override fun readerSession(session: NFCNDEFReaderSession, didInvalidateWithError: NSError) {
+		if (finished) return
+		// NFCReaderError.readerSessionInvalidationErrorUserCanceled == 200
+		val cancelled = didInvalidateWithError.code == 200L
+		finish(
+			if (cancelled) {
+				Result.failure(IllegalStateException("NFC writing was cancelled"))
+			} else {
+				Result.failure(
+					IllegalStateException(didInvalidateWithError.localizedDescription),
+				)
+			},
+		)
+	}
+
+	@ObjCSignatureOverride
+	override fun readerSession(session: NFCNDEFReaderSession, didDetectNDEFs: List<*>) {
+		// Prefer tag-based write path via didDetectTags when available.
+	}
+
+	@ObjCSignatureOverride
+	override fun readerSession(session: NFCNDEFReaderSession, didDetectTags: List<*>) {
+		val tag = didDetectTags.firstOrNull() as? NFCNDEFTagProtocol
+			?: return finish(Result.failure(IllegalStateException("No NFC tag was detected")))
+
+		session.connectToTag(tag) { connectError ->
+			if (connectError != null) {
+				finish(Result.failure(IllegalStateException(connectError.localizedDescription)))
+				return@connectToTag
+			}
+			tag.queryNDEFStatusWithCompletionHandler { status, _, queryError ->
+				if (queryError != null) {
+					finish(Result.failure(IllegalStateException(queryError.localizedDescription)))
+					return@queryNDEFStatusWithCompletionHandler
+				}
+				when (status) {
+					NFCNDEFStatusNotSupported -> {
+						finish(Result.failure(IllegalStateException("This NFC tag does not support NDEF")))
+					}
+					NFCNDEFStatusReadOnly -> {
+						finish(Result.failure(IllegalStateException("This NFC tag is read-only")))
+					}
+					else -> {
+						val message = invitationNdefMessage(ticket)
+							?: return@queryNDEFStatusWithCompletionHandler finish(
+								Result.failure(IllegalStateException("Could not encode the invitation for NFC")),
+							)
+						tag.writeNDEF(message) { writeError ->
+							if (writeError != null) {
+								finish(Result.failure(IllegalStateException(writeError.localizedDescription)))
+							} else {
+								session.alertMessage = "Invitation written"
+								session.invalidateSession()
+								finish(Result.success(Unit))
+							}
+						}
+					}
+				}
+			}
+		}
+	}
+
+	private fun finish(result: Result<Unit>) {
+		if (finished) return
+		finished = true
+		session = null
+		onResult(result)
+	}
+}
+
+@OptIn(ExperimentalForeignApi::class, BetaInteropApi::class)
+private fun invitationNdefMessage(ticket: String): NFCNDEFMessage? {
+	val type = NSString.create(string = VniDropInvitationMimeType).dataUsingEncoding(NSUTF8StringEncoding) ?: return null
+	val payload = NSString.create(string = ticket).dataUsingEncoding(NSUTF8StringEncoding) ?: return null
+	val record = NFCNDEFPayload(
+		format = NFCTypeNameFormatMedia,
+		type = type,
+		identifier = NSData(),
+		payload = payload,
+	)
+	return NFCNDEFMessage(nDEFRecords = listOf(record))
+}