Support Wi-Fi keep alives

mobile/src/main/java/be/mygod/vpnhotspot/net/wifi/WifiDoubleLock.kt

@@ -0,0 +1,61 @@
+package be.mygod.vpnhotspot.net.wifi
+
+import android.annotation.SuppressLint
+import android.content.SharedPreferences
+import android.net.wifi.WifiManager
+import android.os.PowerManager
+import androidx.core.content.getSystemService
+import be.mygod.vpnhotspot.App.Companion.app
+
+/**
+ * This mechanism is used to maximize profit. Source: https://stackoverflow.com/a/29657230/2245107
+ */
+class WifiDoubleLock(lockType: Int) : AutoCloseable {
+    companion object : SharedPreferences.OnSharedPreferenceChangeListener {
+        private const val KEY = "service.wifiLock"
+        private val lockType get() =
+            WifiDoubleLock.Mode.valueOf(app.pref.getString(KEY, WifiDoubleLock.Mode.Full.toString()) ?: "").lockType
+        private val service by lazy { app.getSystemService<PowerManager>()!! }
+
+        private var referenceCount = 0
+        private var lock: WifiDoubleLock? = null
+
+        fun acquire() = synchronized(this) {
+            if (referenceCount == 0) {
+                app.pref.registerOnSharedPreferenceChangeListener(this)
+                val lockType = lockType
+                if (lockType != null) lock = WifiDoubleLock(lockType)
+            }
+            referenceCount += 1
+        }
+        fun release() = synchronized(this) {
+            referenceCount -= 1
+            if (referenceCount == 0) {
+                lock?.close()
+                lock = null
+                app.pref.unregisterOnSharedPreferenceChangeListener(this)
+            }
+        }
+
+        override fun onSharedPreferenceChanged(sharedPreferences: SharedPreferences?, key: String?) {
+            if (key == KEY) synchronized(this) {
+                lock?.close()
+                val lockType = lockType
+                lock = if (lockType == null) null else WifiDoubleLock(lockType)
+            }
+        }
+    }
+
+    enum class Mode(val lockType: Int? = null) {
+        None, Full(WifiManager.WIFI_MODE_FULL), HighPerf(WifiManager.WIFI_MODE_FULL_HIGH_PERF)
+    }
+
+    private val wifi = app.wifi.createWifiLock(lockType, "vpnhotspot:wifi").apply { acquire() }
+    @SuppressLint("WakelockTimeout")
+    private val power = service.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "vpnhotspot:power").apply { acquire() }
+
+    override fun close() {
+        wifi.release()
+        power.release()
+    }
+}