feat: add preferences and send empty state

shared/src/iosMain/kotlin/com/vnidrop/app/core/FilePicker.ios.kt

@@ -8,6 +8,7 @@ import platform.UIKit.UIApplication
 import platform.UIKit.UIDocumentPickerDelegateProtocol
 import platform.UIKit.UIDocumentPickerViewController
 import platform.UIKit.UIModalPresentationFormSheet
+import platform.UniformTypeIdentifiers.UTTypeFolder
 import platform.UniformTypeIdentifiers.UTTypeItem
 import platform.darwin.NSObject
 
@@ -37,6 +38,41 @@ actual fun rememberShareFilePicker(
 	}
 }
 
+@Composable
+actual fun rememberReceiveFolderPicker(
+	onFolderPicked: (ReceiveFolder) -> Unit,
+	onError: (String) -> Unit,
+): ReceiveFolderPicker = remember(onFolderPicked, onError) {
+	object : ReceiveFolderPicker {
+		@OptIn(ExperimentalForeignApi::class)
+		override fun pickFolder() {
+			val presenter = UIApplication.sharedApplication.keyWindow?.rootViewController
+			if (presenter == null) {
+				onError("Could not find an iOS view controller for the folder picker")
+				return
+			}
+
+			val picker = UIDocumentPickerViewController(forOpeningContentTypes = listOf(UTTypeFolder), asCopy = false)
+			val delegate = DocumentPickerDelegate(
+				onFilePicked = { folder ->
+					onFolderPicked(
+						ReceiveFolder(
+							kind = ReceiveFolderKind.IosSecurityScopedUrl,
+							value = folder.value,
+							displayName = folder.displayName,
+						),
+					)
+				},
+				onError = onError,
+			)
+			retainedPickerDelegate = delegate
+			picker.delegate = delegate
+			picker.modalPresentationStyle = UIModalPresentationFormSheet
+			presenter.presentViewController(picker, animated = true, completion = null)
+		}
+	}
+}
+
 actual suspend fun sharePickedFile(
 	repository: CoreRepository,
 	file: PickedShareFile,

shared/src/iosMain/kotlin/com/vnidrop/app/core/FileSystemService.ios.kt

@@ -0,0 +1,59 @@
+package com.vnidrop.app.core
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
+import platform.Foundation.NSFileManager
+import platform.Foundation.NSDocumentDirectory
+import platform.Foundation.NSSearchPathForDirectoriesInDomains
+import platform.Foundation.NSURL
+import platform.Foundation.NSUserDomainMask
+import uniffi.vnidrop.ReceiveOutputSink
+
+@Composable
+actual fun rememberFileSystemService(): FileSystemService =
+	remember { IosFileSystemService() }
+
+private class IosFileSystemService : FileSystemService {
+	override fun defaultReceiveFolder(): ReceiveFolder {
+		val path = NSSearchPathForDirectoriesInDomains(
+			NSDocumentDirectory,
+			NSUserDomainMask,
+			true,
+		).firstOrNull() as? String ?: ""
+		return ReceiveFolder(
+			kind = ReceiveFolderKind.FileSystemPath,
+			value = path,
+			displayName = "Documents",
+		)
+	}
+
+	override suspend fun validateReceiveFolder(folder: ReceiveFolder): FolderAccessStatus =
+		when (folder.kind) {
+			ReceiveFolderKind.FileSystemPath -> {
+				if (NSFileManager.defaultManager.isWritableFileAtPath(folder.value)) {
+					FolderAccessStatus.Writable
+				} else {
+					FolderAccessStatus.Unavailable
+				}
+			}
+			ReceiveFolderKind.IosSecurityScopedUrl -> validateSecurityScopedUrl(folder.value)
+			ReceiveFolderKind.AndroidTreeUri -> FolderAccessStatus.Unavailable
+		}
+
+	override fun createReceiveOutputSink(folder: ReceiveFolder): ReceiveOutputSink? = null
+
+	private fun validateSecurityScopedUrl(value: String): FolderAccessStatus {
+		val url = NSURL.URLWithString(value) ?: NSURL.fileURLWithPath(value)
+		val didStartAccess = url.startAccessingSecurityScopedResource()
+		return try {
+			val path = url.path
+			if (path != null && NSFileManager.defaultManager.isWritableFileAtPath(path)) {
+				FolderAccessStatus.Writable
+			} else {
+				FolderAccessStatus.PermissionRequired
+			}
+		} finally {
+			if (didStartAccess) url.stopAccessingSecurityScopedResource()
+		}
+	}
+}