hasBackButton feature on Android browser

Author: Aitor Cubeles Torres

android/src/main/java/com/proyecto26/inappbrowser/RNInAppBrowser.java

@@ -7,9 +7,11 @@
 import android.content.Context;
 import android.content.Intent;
 import android.graphics.Color;
+import android.graphics.BitmapFactory;
 import android.provider.Browser;
 import androidx.annotation.Nullable;
 import androidx.browser.customtabs.CustomTabsIntent;
+import androidx.core.graphics.ColorUtils;
 
 import com.facebook.react.bridge.Arguments;
 import com.facebook.react.bridge.Promise;
@@ -38,8 +40,10 @@ public class RNInAppBrowser {
   private static final String KEY_ANIMATION_START_EXIT = "startExit";
   private static final String KEY_ANIMATION_END_ENTER = "endEnter";
   private static final String KEY_ANIMATION_END_EXIT = "endExit";
+  private static final String HASBACKBUTTON = "hasBackButton";
 
   private @Nullable Promise mOpenBrowserPromise;
+  private Boolean isLightTheme;
   private Activity currentActivity;
   private static final Pattern animationIdentifierPattern = Pattern.compile("^.+:.+/");
 
@@ -66,6 +70,7 @@ public void open(Context context, final ReadableMap options, final Promise promi
       final String colorString = options.getString(KEY_TOOLBAR_COLOR);
       try {
         builder.setToolbarColor(Color.parseColor(colorString));
+        isLightTheme = toolbarIsLight(colorString);
       } catch (IllegalArgumentException e) {
         throw new JSApplicationIllegalArgumentException(
                 "Invalid toolbar color '" + colorString + "': " + e.getMessage());
@@ -92,6 +97,11 @@ public void open(Context context, final ReadableMap options, final Promise promi
       final ReadableMap animations = options.getMap(KEY_ANIMATIONS);
       applyAnimation(context, builder, animations);
     }
+    if (options.hasKey(HASBACKBUTTON) &&
+            options.getBoolean(HASBACKBUTTON)) {
+      builder.setCloseButtonIcon(BitmapFactory.decodeResource(
+            context.getResources(), isLightTheme ? R.drawable.ic_arrow_back_black : R.drawable.ic_arrow_back_white));
+    }
 
     CustomTabsIntent customTabsIntent = builder.build();
 
@@ -218,4 +228,8 @@ private void unRegisterEventBus() {
       EventBus.getDefault().unregister(this);
     }
   }
+
+  private Boolean toolbarIsLight(String themeColor) {
+    return ColorUtils.calculateLuminance(Color.parseColor(themeColor)) > 0.5;
+  }
 }