improvement: Support "Follow system theme" option for Flatpak users #382

common/src/androidMain/kotlin/com/artemchep/keyguard/platform/theme/PlatformTheme.android.kt

@@ -0,0 +1,8 @@
+package com.artemchep.keyguard.platform.theme
+
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.runtime.Composable
+import com.artemchep.keyguard.platform.Platform
+
+@Composable
+actual fun Platform.hasDarkThemeEnabled(): Boolean = isSystemInDarkTheme()

common/src/commonMain/kotlin/com/artemchep/keyguard/platform/theme/PlatformTheme.kt

@@ -0,0 +1,7 @@
+package com.artemchep.keyguard.platform.theme
+
+import androidx.compose.runtime.Composable
+import com.artemchep.keyguard.platform.Platform
+
+@Composable
+expect fun Platform.hasDarkThemeEnabled(): Boolean

common/src/commonMain/kotlin/com/artemchep/keyguard/ui/theme/Theme.kt

@@ -22,6 +22,8 @@ import com.artemchep.keyguard.common.usecase.GetColors
 import com.artemchep.keyguard.common.usecase.GetFont
 import com.artemchep.keyguard.common.usecase.GetTheme
 import com.artemchep.keyguard.common.usecase.GetThemeUseAmoledDark
+import com.artemchep.keyguard.platform.CurrentPlatform
+import com.artemchep.keyguard.platform.theme.hasDarkThemeEnabled
 import com.artemchep.keyguard.res.Res
 import com.artemchep.keyguard.res.*
 import com.artemchep.keyguard.ui.theme.monet.ColorSchemeFactory
@@ -275,7 +277,7 @@ fun KeyguardTheme(
     val isDarkColorScheme = when (theme) {
         AppTheme.DARK -> true
         AppTheme.LIGHT -> false
-        null -> isSystemInDarkTheme()
+        null -> CurrentPlatform.hasDarkThemeEnabled()
     }
 
     val scheme = kotlin.run {

common/src/desktopMain/kotlin/com/artemchep/keyguard/platform/theme/PlatformTheme.desktop.kt

@@ -0,0 +1,69 @@
+package com.artemchep.keyguard.platform.theme
+
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import com.artemchep.keyguard.platform.Platform
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.ensureActive
+import kotlinx.coroutines.withContext
+import java.util.concurrent.TimeUnit
+
+@Composable
+actual fun Platform.hasDarkThemeEnabled(): Boolean = when (this) {
+    is Platform.Desktop.Linux -> isLinuxPortalInDarkTheme()
+    else -> isSystemInDarkTheme()
+}
+
+@Composable
+private fun isLinuxPortalInDarkTheme(): Boolean {
+    val darkThemeDefault = isSystemInDarkTheme()
+    var darkThemeState by remember {
+        mutableStateOf(darkThemeDefault)
+    }
+    LaunchedEffect(Unit) {
+        while (true) {
+            kotlin.runCatching {
+                darkThemeState = readLinuxPortalInDarkTheme()
+            }.getOrElse {
+                // Stop checking for the appearance, just use
+                // whatever Compose provides.
+                darkThemeState = darkThemeDefault
+                return@LaunchedEffect
+            }
+
+            delay(2000L)
+            ensureActive()
+        }
+    }
+    return darkThemeState
+}
+
+private suspend fun readLinuxPortalInDarkTheme() = withContext(Dispatchers.IO) {
+    val command = listOf(
+        "gdbus",
+        "call",
+        "--session",
+        "--dest=org.freedesktop.portal.Desktop",
+        "--object-path=/org/freedesktop/portal/desktop",
+        "--method=org.freedesktop.portal.Settings.Read",
+        "org.freedesktop.appearance",
+        "color-scheme",
+    )
+    val pb = ProcessBuilder(command)
+        .redirectError(ProcessBuilder.Redirect.INHERIT)
+    val process = pb.start().apply {
+        waitFor(60, TimeUnit.MINUTES)
+    }
+
+    val result = process.inputStream.reader().readText()
+    // 0: No preference
+    // 1: Prefer dark appearance
+    // 2: Prefer light appearance
+    result[10] == '1'
+}