package sh.lajo.buddy

import android.Manifest
import android.content.Context
import android.content.Intent
import android.net.Uri
import android.net.ConnectivityManager
import android.net.NetworkCapabilities
import android.os.Build
import android.os.PowerManager
import android.provider.Settings
import androidx.activity.compose.rememberLauncherForActivityResult
import androidx.activity.result.contract.ActivityResultContracts
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.Spacer
import androidx.compose.foundation.layout.fillMaxSize
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.MaterialTheme
import androidx.compose.material3.OutlinedButton
import androidx.compose.material3.OutlinedTextField
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
import androidx.compose.ui.Modifier
import androidx.compose.ui.platform.LocalContext
import androidx.compose.ui.platform.LocalLifecycleOwner
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleEventObserver
import androidx.compose.ui.unit.dp
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.launch
import kotlinx.coroutines.withContext
import androidx.compose.runtime.rememberCoroutineScope
import androidx.compose.ui.res.stringResource

import okhttp3.Request
import kotlinx.serialization.Serializable
import kotlinx.serialization.json.Json
import kotlinx.serialization.encodeToString
import okhttp3.RequestBody.Companion.toRequestBody
import sh.lajo.buddy.ApiConfig.BASE_URL
import sh.lajo.buddy.HttpClient.JSON

@Serializable
data class KidLinkRequest(
    val code: String,
)

@Serializable
data class KidLinkResponse(
    val success: Boolean,
    val token: String? = null,
    val reason: String? = null,
)

private val networkJson = Json {
    ignoreUnknownKeys = true
    isLenient = true
}

@Composable
fun OnboardingStep1Screen(
    onNext: () -> Unit,
) {
    OnboardingScaffold(
        title = stringResource(R.string.onboarding_step1_title),
        body = stringResource(R.string.onboarding_step1_body),
        primaryButtonText = stringResource(R.string.onboarding_next),
        onPrimary = onNext,
        showBack = false,
        onBack = null,
    )
}

@Composable
fun OnboardingStep2Screen(
    onBack: () -> Unit,
    onNext: () -> Unit,
) {
    val context = LocalContext.current

    var postNotificationsGranted by remember { mutableStateOf(isPostNotificationsGranted(context)) }
    var notificationListenerEnabled by remember { mutableStateOf(isNotificationListenerEnabled(context)) }

    val permissionLauncher = rememberLauncherForActivityResult(
        contract = ActivityResultContracts.RequestPermission(),
        onResult = { granted -> postNotificationsGranted = granted }
    )

    // Refresh when coming back from system settings screens.
    val lifecycleOwner = LocalLifecycleOwner.current
    DisposableEffect(lifecycleOwner, context) {
        val observer = LifecycleEventObserver { _, event ->
            if (event == Lifecycle.Event.ON_RESUME) {
                postNotificationsGranted = isPostNotificationsGranted(context)
                notificationListenerEnabled = isNotificationListenerEnabled(context)
            }
        }
        lifecycleOwner.lifecycle.addObserver(observer)
        onDispose { lifecycleOwner.lifecycle.removeObserver(observer) }
    }

    val canProceed = postNotificationsGranted && notificationListenerEnabled

    val notificationPermissionText = stringResource(
        R.string.onboarding_notification_permission_status,
        stringResource(if (postNotificationsGranted) R.string.onboarding_permission_granted else R.string.onboarding_permission_not_granted)
    )
    val notificationListenerText = stringResource(
        R.string.onboarding_notification_listener_status,
        stringResource(if (notificationListenerEnabled) R.string.onboarding_permission_enabled else R.string.onboarding_permission_not_enabled)
    )

    val statusText = "$notificationPermissionText\n$notificationListenerText"

    OnboardingScaffold(
        title = stringResource(R.string.onboarding_step2_title),
        body = stringResource(R.string.onboarding_step2_body),
        primaryButtonText = stringResource(R.string.onboarding_next),
        onPrimary = {
            if (canProceed) onNext()
        },
        primaryEnabled = canProceed,
        showBack = true,
        onBack = onBack,
        extraContent = {
            Text(statusText, style = MaterialTheme.typography.bodySmall)
            Spacer(Modifier.height(12.dp))

            if (!postNotificationsGranted) {
                Button(
                    onClick = { permissionLauncher.launch(Manifest.permission.POST_NOTIFICATIONS) }
                ) {
                    Text(stringResource(R.string.onboarding_grant_notification_permission))
                }
            }

            Spacer(Modifier.height(8.dp))

            if (!notificationListenerEnabled) {
                Button(
                    onClick = {
                        safeStartActivity(context, Intent(Settings.ACTION_NOTIFICATION_LISTENER_SETTINGS))
                    }
                ) {
                    Text(stringResource(R.string.onboarding_enable_notification_access))
                }
            }

            if (!canProceed) {
                Spacer(Modifier.height(12.dp))
                Text(
                    stringResource(R.string.onboarding_complete_steps),
                    style = MaterialTheme.typography.bodySmall,
                )
            }
        }
    )
}

@Composable
fun OnboardingStep3Screen(
    onBack: () -> Unit,
    onNext: () -> Unit
) {
    val context = LocalContext.current

    var accessibilityServiceEnabled by remember {
        mutableStateOf(isAccessibilityServiceEnabled(context))
    }

    // Refresh when coming back from system settings screens.
    val lifecycleOwner = LocalLifecycleOwner.current
    DisposableEffect(lifecycleOwner, context) {
        val observer = LifecycleEventObserver { _, event ->
            if (event == Lifecycle.Event.ON_RESUME) {
                accessibilityServiceEnabled = isAccessibilityServiceEnabled(context)
            }
        }
        lifecycleOwner.lifecycle.addObserver(observer)
        onDispose { lifecycleOwner.lifecycle.removeObserver(observer) }
    }

    val canProceed = accessibilityServiceEnabled

    OnboardingScaffold(
        title = stringResource(R.string.onboarding_step3_title),
        body = stringResource(R.string.onboarding_step3_body),
        primaryButtonText = stringResource(R.string.onboarding_next),
        onPrimary = {
            if (canProceed) onNext()
        },
        primaryEnabled = canProceed,
        showBack = true,
        onBack = onBack,
        extraContent = {
            Text(
                stringResource(
                    R.string.onboarding_accessibility_service_status,
                    stringResource(if (accessibilityServiceEnabled) R.string.onboarding_permission_enabled else R.string.onboarding_permission_not_enabled)
                ),
                style = MaterialTheme.typography.bodySmall
            )
            Spacer(Modifier.height(12.dp))

            if (!accessibilityServiceEnabled) {
                Button(
                    onClick = {
                        safeStartActivity(context, Intent(Settings.ACTION_ACCESSIBILITY_SETTINGS))
                    }
                ) {
                    Text(stringResource(R.string.onboarding_enable_accessibility_access))
                }
            }

            if (!canProceed) {
                Spacer(Modifier.height(12.dp))
                Text(
                    stringResource(R.string.onboarding_enable_accessibility_to_continue),
                    style = MaterialTheme.typography.bodySmall,
                )
            }
        }
    )
}

@Composable
fun OnboardingStep4Screen(
    onBack: () -> Unit,
    onNext: () -> Unit
) {
    val context = LocalContext.current

    var ignoringBatteryOptimizations by remember {
        mutableStateOf(isIgnoringBatteryOptimizations(context))
    }

    // Refresh when coming back from system settings screens.
    val lifecycleOwner = LocalLifecycleOwner.current
    DisposableEffect(lifecycleOwner, context) {
        val observer = LifecycleEventObserver { _, event ->
            if (event == Lifecycle.Event.ON_RESUME) {
                ignoringBatteryOptimizations = isIgnoringBatteryOptimizations(context)
            }
        }
        lifecycleOwner.lifecycle.addObserver(observer)
        onDispose { lifecycleOwner.lifecycle.removeObserver(observer) }
    }

    val canProceed = ignoringBatteryOptimizations

    OnboardingScaffold(
        title = stringResource(R.string.onboarding_step4_title),
        body = stringResource(R.string.onboarding_step4_body),
        primaryButtonText = stringResource(R.string.onboarding_next),
        onPrimary = {
            if (canProceed) onNext()
        },
        primaryEnabled = canProceed,
        showBack = true,
        onBack = onBack,
        extraContent = {
            Text(
                stringResource(
                    R.string.onboarding_battery_optimization_status,
                    stringResource(if (ignoringBatteryOptimizations) R.string.onboarding_battery_optimization_disabled else R.string.onboarding_battery_optimization_enabled)
                ),
                style = MaterialTheme.typography.bodySmall
            )
            Spacer(Modifier.height(12.dp))

            Button(
                onClick = {
                    val intent = Intent(Settings.ACTION_REQUEST_IGNORE_BATTERY_OPTIMIZATIONS).apply {
                        data = Uri.parse("package:${context.packageName}")
                    }
                    safeStartActivity(context, intent)
                }
            ) {
                Text(stringResource(R.string.onboarding_allow_running_in_background))
            }

            Spacer(Modifier.height(8.dp))

            OutlinedButton(
                onClick = {
                    safeStartActivity(context, Intent(Settings.ACTION_IGNORE_BATTERY_OPTIMIZATION_SETTINGS))
                }
            ) {
                Text(stringResource(R.string.onboarding_open_battery_optimization_settings))
            }

            if (!canProceed) {
                Spacer(Modifier.height(12.dp))
                Text(
                    stringResource(R.string.onboarding_disable_battery_optimization_to_continue),
                    style = MaterialTheme.typography.bodySmall,
                )
            }
        }
    )
}

@Composable
fun OnboardingStep5Screen(
    onBack: () -> Unit,
    onNext: () -> Unit
) {
    val context = LocalContext.current

    var contactsPermissionGranted by remember {
        mutableStateOf(isContactsPermissionGranted(context))
    }

    val permissionLauncher = rememberLauncherForActivityResult(
        contract = ActivityResultContracts.RequestPermission(),
        onResult = { granted -> contactsPermissionGranted = granted }
    )

    // Refresh when coming back from system settings screens.
    val lifecycleOwner = LocalLifecycleOwner.current
    DisposableEffect(lifecycleOwner, context) {
        val observer = LifecycleEventObserver { _, event ->
            if (event == Lifecycle.Event.ON_RESUME) {
                contactsPermissionGranted = isContactsPermissionGranted(context)
            }
        }
        lifecycleOwner.lifecycle.addObserver(observer)
        onDispose { lifecycleOwner.lifecycle.removeObserver(observer) }
    }

    val canProceed = contactsPermissionGranted

    OnboardingScaffold(
        title = stringResource(R.string.onboarding_step5_title),
        body = stringResource(R.string.onboarding_step5_body),
        primaryButtonText = stringResource(R.string.onboarding_next),
        onPrimary = {
            if (canProceed) onNext()
        },
        primaryEnabled = canProceed,
        showBack = true,
        onBack = onBack,
        extraContent = {
            Text(
                stringResource(
                    R.string.onboarding_contacts_permission_status,
                    stringResource(if (contactsPermissionGranted) R.string.onboarding_permission_granted else R.string.onboarding_permission_not_granted)
                ),
                style = MaterialTheme.typography.bodySmall
            )
            Spacer(Modifier.height(12.dp))

            if (!contactsPermissionGranted) {
                Button(
                    onClick = { permissionLauncher.launch(Manifest.permission.READ_CONTACTS) }
                ) {
                    Text(stringResource(R.string.onboarding_grant_contacts_permission))
                }
            }

            if (!canProceed) {
                Spacer(Modifier.height(12.dp))
                Text(
                    stringResource(R.string.onboarding_grant_contacts_to_continue),
                    style = MaterialTheme.typography.bodySmall,
                )
            }
        }
    )
}

@Composable
fun OnboardingStep6Screen(
    onBack: () -> Unit,
    onNext: () -> Unit,
) {
    val context = LocalContext.current

    // Best-effort detection: some OEMs hide details, so we also allow manual confirmation.
    var vpnActive by remember { mutableStateOf(isVpnActive(context)) }
    var userConfirmed by remember { mutableStateOf(false) }

    // Refresh when coming back from system settings screens.
    val lifecycleOwner = LocalLifecycleOwner.current
    DisposableEffect(lifecycleOwner, context) {
        val observer = LifecycleEventObserver { _, event ->
            if (event == Lifecycle.Event.ON_RESUME) {
                vpnActive = isVpnActive(context)
            }
        }
        lifecycleOwner.lifecycle.addObserver(observer)
        onDispose { lifecycleOwner.lifecycle.removeObserver(observer) }
    }

    val canProceed = vpnActive || userConfirmed

    OnboardingScaffold(
        title = stringResource(R.string.onboarding_step6_title),
        body = stringResource(R.string.onboarding_step6_body),
        primaryButtonText = stringResource(R.string.onboarding_next),
        onPrimary = {
            if (canProceed) onNext()
        },
        primaryEnabled = canProceed,
        showBack = true,
        onBack = onBack,
        extraContent = {
            Text(
                stringResource(
                    R.string.onboarding_vpn_status,
                    stringResource(if (vpnActive) R.string.onboarding_vpn_status_active else R.string.onboarding_vpn_status_not_detected)
                ),
                style = MaterialTheme.typography.bodySmall
            )
            Spacer(Modifier.height(12.dp))

            Button(
                onClick = {
                    // This opens the system VPN settings page.
                    safeStartActivity(context, Intent(Settings.ACTION_VPN_SETTINGS))
                }
            ) {
                Text(stringResource(R.string.onboarding_open_vpn_settings))
            }

            Spacer(Modifier.height(8.dp))

            OutlinedButton(
                onClick = { userConfirmed = true }
            ) {
                Text(stringResource(R.string.onboarding_i_enabled_vpn))
            }

            if (!canProceed) {
                Spacer(Modifier.height(12.dp))
                Text(
                    stringResource(R.string.onboarding_enable_vpn_to_continue),
                    style = MaterialTheme.typography.bodySmall,
                )
            }
        }
    )
}

@Composable
fun OnboardingStepMediaScreen(
    onBack: () -> Unit,
    onNext: () -> Unit
) {
    val context = LocalContext.current
    var isMediaGranted by remember { mutableStateOf(isMediaPermissionGranted(context)) }

    val mediaPermissionLauncher = rememberLauncherForActivityResult(
        ActivityResultContracts.RequestPermission()
    ) { isGranted ->
        isMediaGranted = isGranted
    }

    // Use LifecycleObserver to refresh state when returning from settings
    val lifecycleOwner = LocalLifecycleOwner.current
    DisposableEffect(lifecycleOwner) {
        val observer = LifecycleEventObserver { _, event ->
            if (event == Lifecycle.Event.ON_RESUME) {
                isMediaGranted = isMediaPermissionGranted(context)
            }
        }
        lifecycleOwner.lifecycle.addObserver(observer)
        onDispose {
            lifecycleOwner.lifecycle.removeObserver(observer)
        }
    }

    OnboardingScaffold(
        title = stringResource(R.string.onboarding_step_media_title),
        body = stringResource(R.string.onboarding_step_media_body),
        primaryButtonText = stringResource(R.string.onboarding_next),
        onPrimary = onNext,
        primaryEnabled = isMediaGranted,
        showBack = true,
        onBack = onBack,
        extraContent = {
            Column(
                modifier = Modifier.fillMaxWidth(),
                verticalArrangement = Arrangement.spacedBy(8.dp)
            ) {
                Text(
                    text = stringResource(
                        R.string.onboarding_media_permission_status,
                        if (isMediaGranted) stringResource(R.string.onboarding_permission_granted)
                        else stringResource(R.string.onboarding_permission_not_granted)
                    ),
                    style = MaterialTheme.typography.bodyMedium
                )

                if (!isMediaGranted) {
                    Button(
                        onClick = {
                            val permission = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
                                Manifest.permission.READ_MEDIA_IMAGES
                            } else {
                                Manifest.permission.READ_EXTERNAL_STORAGE
                            }
                            mediaPermissionLauncher.launch(permission)
                        },
                        modifier = Modifier.fillMaxWidth()
                    ) {
                        Text(stringResource(R.string.onboarding_grant_media_permission))
                    }
                }

                if (!isMediaGranted) {
                    Spacer(Modifier.height(12.dp))
                    Text(
                        stringResource(R.string.onboarding_grant_media_to_continue),
                        style = MaterialTheme.typography.bodySmall,
                    )
                }
            }
        }
    )
}

@Composable
fun OnboardingStep7Screen(
    onFinish: () -> Unit,
    onBack: () -> Unit
) {
    var code by remember { mutableStateOf("") }

    var isLoading by remember { mutableStateOf(false) }
    var resultText by remember { mutableStateOf<String?>(null) }
    var errorText by remember { mutableStateOf<String?>(null) }

    val coroutineScope = rememberCoroutineScope()
    val context = LocalContext.current

    OnboardingScaffold(
        title = stringResource(R.string.onboarding_step7_title),
        body = stringResource(R.string.onboarding_step7_body),
        primaryButtonText = if (isLoading) stringResource(R.string.onboarding_linking) else stringResource(R.string.onboarding_link_device),
        onPrimary = {
            if (isLoading) return@OnboardingScaffold

            isLoading = true
            errorText = null
            resultText = null

            coroutineScope.launch {
                try {
                    val client = HttpClient.client

                    val normalizedCode = code.trim().uppercase()
                    val jsonBody = networkJson.encodeToString(KidLinkRequest(normalizedCode))
                    val body = jsonBody.toRequestBody(JSON)

                    val request = Request.Builder()
                        .url("${BASE_URL}/kid/link")
                        .post(body)
                        .build()

                    val rawBody = withContext(Dispatchers.IO) {
                        client.newCall(request).execute().use { response ->
                            val bodyString = response.body?.string().orEmpty()

                            // If we got a non-2xx response, still try to parse a structured error.
                            if (!response.isSuccessful) {
                                val parsed = runCatching {
                                    networkJson.decodeFromString<KidLinkResponse>(bodyString)
                                }.getOrNull()

                                val reason = parsed?.reason?.takeIf { it.isNotBlank() }
                                throw IllegalStateException(reason ?: "HTTP ${response.code}")
                            }

                            bodyString
                        }
                    }

                    val parsed = runCatching {
                        networkJson.decodeFromString<KidLinkResponse>(rawBody)
                    }.getOrElse { t ->
                        throw IllegalStateException("Invalid server response")
                    }

                    if (parsed.success) {
                        val token = parsed.token?.trim().orEmpty()
                        if (token.isBlank()) {
                            throw IllegalStateException("Missing token in server response")
                        }
                        resultText = context.getString(R.string.onboarding_linked_successfully)
                        val prefs = context.getSharedPreferences("app_prefs", Context.MODE_PRIVATE)
                        prefs.edit()
                            .putString("auth_token", token)
                            .putBoolean("onboardingFinished", true)
                            .apply()
                        onFinish()
                    } else {
                        val reason = parsed.reason?.takeIf { it.isNotBlank() } ?: "Unknown error"
                        throw IllegalStateException(reason)
                    }
                } catch (t: Throwable) {
                    errorText = t.message ?: t::class.java.simpleName
                } finally {
                    isLoading = false
                }
            }
        },
        primaryEnabled = !isLoading,
        showBack = true,
        onBack = onBack,
        extraContent = {
            OutlinedTextField(
                value = code,
                onValueChange = { input ->
                    val sanitized = input.uppercase().filter { it.isLetterOrDigit() }
                    val withDash = buildString {
                        sanitized.take(6).forEachIndexed { index, c ->
                            if (index == 3) {
                                append('-')
                            }
                            append(c)
                        }
                    }
                    code = withDash
                },
                label = { Text(stringResource(R.string.onboarding_link_code)) },
                singleLine = true,
                modifier = Modifier.fillMaxWidth(),
                enabled = !isLoading,
            )

            if (errorText != null) {
                Spacer(Modifier.height(12.dp))
                Text(
                    text = stringResource(R.string.onboarding_error, errorText!!),
                    style = MaterialTheme.typography.bodySmall,
                    color = MaterialTheme.colorScheme.error,
                )
            }

            if (resultText != null) {
                Spacer(Modifier.height(12.dp))
                Text(
                    text = resultText!!,
                    style = MaterialTheme.typography.bodySmall,
                )
            }
        }
    )
}

@Composable
private fun OnboardingScaffold(
    title: String,
    body: String,
    primaryButtonText: String,
    onPrimary: () -> Unit,
    primaryEnabled: Boolean = true,
    showBack: Boolean,
    onBack: (() -> Unit)?,
    extraContent: @Composable (() -> Unit)? = null,
) {
    Column(
        modifier = Modifier
            .fillMaxSize()
            .padding(24.dp),
    ) {
        Box(
            modifier = Modifier
                .fillMaxSize()
                .weight(1f),
            contentAlignment = Alignment.Center
        ) {
            Column(
                horizontalAlignment = Alignment.CenterHorizontally
            ) {
                Text(title, style = MaterialTheme.typography.headlineMedium)
                Spacer(Modifier.height(12.dp))
                Text(body, style = MaterialTheme.typography.bodyLarge)

                if (extraContent != null) {
                    Spacer(Modifier.height(20.dp))
                    extraContent()
                }
            }
        }

        // No weight here; this row should wrap content and sit at the bottom due to the Box using weight(1f).
        Row(
            modifier = Modifier.fillMaxWidth(),
            horizontalArrangement = if (showBack) Arrangement.SpaceBetween else Arrangement.Absolute.Right,
            verticalAlignment = Alignment.CenterVertically
        ) {
            if (showBack && onBack != null) {
                OutlinedButton(onClick = onBack) { Text(stringResource(R.string.onboarding_back)) }
            }

            Button(
                onClick = onPrimary,
                enabled = primaryEnabled,
            ) { Text(primaryButtonText) }
        }
    }
}

private fun isPostNotificationsGranted(context: Context): Boolean {
    return if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
        context.checkSelfPermission(Manifest.permission.POST_NOTIFICATIONS) ==
                android.content.pm.PackageManager.PERMISSION_GRANTED
    } else {
        true
    }
}

private fun isNotificationListenerEnabled(context: Context): Boolean {
    val enabled = Settings.Secure.getString(
        context.contentResolver,
        "enabled_notification_listeners"
    ) ?: return false
    return enabled.contains(context.packageName)
}

private fun isAccessibilityServiceEnabled(context: Context): Boolean {
    val enabled = Settings.Secure.getString(
        context.contentResolver,
        Settings.Secure.ENABLED_ACCESSIBILITY_SERVICES
    ) ?: return false
    val serviceName = "${context.packageName}/${context.packageName}.BuddyAccessibilityService"
    return enabled.contains(serviceName)
}

private fun isIgnoringBatteryOptimizations(context: Context): Boolean {
    val pm = context.getSystemService(Context.POWER_SERVICE) as? PowerManager ?: return false
    return if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
        pm.isIgnoringBatteryOptimizations(context.packageName)
    } else {
        true
    }
}

private fun isContactsPermissionGranted(context: Context): Boolean {
    return context.checkSelfPermission(Manifest.permission.READ_CONTACTS) ==
            android.content.pm.PackageManager.PERMISSION_GRANTED
}

private fun isMediaPermissionGranted(context: Context): Boolean {
    val permission = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
        Manifest.permission.READ_MEDIA_IMAGES
    } else {
        Manifest.permission.READ_EXTERNAL_STORAGE
    }
    return context.checkSelfPermission(permission) ==
            android.content.pm.PackageManager.PERMISSION_GRANTED
}

private fun isVpnActive(context: Context): Boolean {
    val cm = context.getSystemService(Context.CONNECTIVITY_SERVICE) as? ConnectivityManager
        ?: return false
    val network = cm.activeNetwork ?: return false
    val caps = cm.getNetworkCapabilities(network) ?: return false

    // TRANSPORT_VPN is available on API 21+.
    return caps.hasTransport(NetworkCapabilities.TRANSPORT_VPN)
}

private fun safeStartActivity(context: Context, intent: Intent) {
    val safeIntent = Intent(intent).addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
    if (safeIntent.resolveActivity(context.packageManager) != null) {
        context.startActivity(safeIntent)
    }
}