adjust icon and text color of status/navigation bar if API is provided.

app/src/main/java/jp/juggler/subwaytooter/App1.kt

@@ -13,6 +13,7 @@ import android.graphics.Color
 import android.net.Uri
 import android.os.Build
 import android.util.Log
+import android.view.View
 import android.view.WindowManager
 import androidx.browser.customtabs.CustomTabsIntent
 import com.bumptech.glide.Glide
@@ -48,6 +49,7 @@ import java.util.concurrent.atomic.AtomicInteger
 import java.util.regex.Pattern
 import kotlin.math.max
 import kotlin.math.min
+import kotlin.math.pow
 
 class App1 : Application() {
 	
@@ -643,18 +645,88 @@ class App1 : Application() {
 			//			}
 		}
 		
+		private fun rgbToLab(rgb : Int) : Triple<Float, Float, Float> {
+			
+			fun Int.revGamma() : Float {
+				val v = toFloat() / 255f
+				return when {
+					v > 0.04045f -> ((v + 0.055f) / 1.055f).pow(2.4f)
+					else -> v / 12.92f
+				}
+			}
+			
+			val r = Color.red(rgb).revGamma()
+			val g = Color.green(rgb).revGamma()
+			val b = Color.blue(rgb).revGamma()
+			
+			//https://en.wikipedia.org/wiki/Lab_color_space#CIELAB-CIEXYZ_conversions
+			
+			fun f(src : Float, k : Float) : Float {
+				val v = src * k
+				return when {
+					v > 0.008856f -> v.pow(1f / 3f)
+					else -> (7.787f * v) + (4f / 29f)
+				}
+			}
+			
+			val x = f(r * 0.4124f + g * 0.3576f + b * 0.1805f, 100f / 95.047f)
+			val y = f(r * 0.2126f + g * 0.7152f + b * 0.0722f, 100f / 100f)
+			val z = f(r * 0.0193f + g * 0.1192f + b * 0.9505f, 100f / 108.883f)
+			
+			return Triple(
+				(116 * y) - 16, // L
+				500 * (x - y), // a
+				200 * (y - z) //b
+			)
+		}
+		
 		fun setStatusBarColor(activity : Activity) {
 			
 			activity.window?.apply {
-				var c = Pref.ipStatusBarColor(pref).notZero() ?: getAttributeColor(activity,R.attr.colorPrimaryDark)
+				
 				clearFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS)
+				clearFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_NAVIGATION)
 				addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS)
+
+				var c = Pref.ipStatusBarColor(pref).notZero() ?: getAttributeColor(
+					activity,
+					R.attr.colorPrimaryDark
+				)
 				statusBarColor = c or Color.BLACK
 				
+				if(Build.VERSION.SDK_INT >= 23) {
+					val min = rgbToLab(Color.BLACK)
+					val max = rgbToLab(Color.WHITE)
+					val current = rgbToLab(c)
+					
+					decorView.systemUiVisibility =
+						if(current.first >= (min.first + max.first) / 2f) {
+							//Dark Text to show up on your light status bar
+							decorView.systemUiVisibility or View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR
+						} else {
+							//Light Text to show up on your dark status bar
+							decorView.systemUiVisibility and View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR.inv()
+						}
+				}
+				
 				c = Pref.ipNavigationBarColor(pref)
 				if(c != 0) {
 					navigationBarColor = c or Color.BLACK
+					
+					if( Build.VERSION.SDK_INT >= 26){
+						val current = rgbToLab(c)
+
+						decorView.systemUiVisibility =
+							if(current.first >= 50) {
+								//Dark Text to show up on your light status bar
+								decorView.systemUiVisibility or View.SYSTEM_UI_FLAG_LIGHT_NAVIGATION_BAR
+							} else {
+								//Light Text to show up on your dark status bar
+								decorView.systemUiVisibility and View.SYSTEM_UI_FLAG_LIGHT_NAVIGATION_BAR.inv()
+							}
+					}
 				} // else: need restart app.
+				
 			}
 		}
 	}

app/src/main/res/values-ja/strings.xml

@@ -936,7 +936,7 @@
     <string name="show_in_directory">ディレクトリに表示</string>
     <string name="featured_hashtags">注目のハッシュタグ</string>
     <string name="custom_emoji">カスタム絵文字</string>
-    <string name="status_bar_color">ステータスバーの色(アプリ再起動が必要)</string>
-    <string name="navigation_bar_color">ナビゲーションバーの色(アプリ再起動が必要)</string>
+    <string name="status_bar_color">ステータスバーの色(アプリ再起動が必要。Android 6未満はアイコンやテキストの色を調整できません)</string>
+    <string name="navigation_bar_color">ナビゲーションバーの色(アプリ再起動が必要。Android 8未満はアイコンの色を調整できません)</string>
 
 </resources>

app/src/main/res/values/strings.xml

@@ -929,7 +929,6 @@
     <string name="show_in_directory">Show in directory</string>
     <string name="featured_hashtags">Featured hashtags</string>
     <string name="custom_emoji">Custom emoji</string>
-    <string name="status_bar_color">Status bar color (app restart required)</string>
-    <string name="navigation_bar_color">Navigation bar color (app restart required)</string>
-
+    <string name="status_bar_color">Status bar color (app restart required. pre-Android 6 can\'t adjust icon and text color)</string>
+    <string name="navigation_bar_color">Navigation bar color (app restart required. pre-Android 8 can\'t adjust icon color)</string>
 </resources>