[Android] Add support for text processing actions (flutter#44579)

## Description

This Android related PR adds a channel buffer and a plugin to interact with Android 'process text' feature. It makes it possible to query text processing actions and to run those actions (for instance 'calling' Google translate).
Text actions that outputs a processed text are supported.

The implementation is based on the great sample provided by @gualse , see flutter/flutter#107603 (comment). 

In order to return a non empty list of text actions, the implementation will require adding a section to the Android manifest file (see flutter/flutter#107603 (comment)).
Adding this section automatically to new or existing Flutter apps is not part of this PR but will be tackled in a future PR.

## Related Issue

Android engine side for flutter/flutter#107603

## Tests

Adds 3 tests.

Author: bleroux

ci/licenses_golden/licenses_flutter

@@ -3091,6 +3091,7 @@ ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/syst
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/NavigationChannel.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/PlatformChannel.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/PlatformViewsChannel.java + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/ProcessTextChannel.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/RestorationChannel.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/SpellCheckChannel.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/SystemChannel.java + ../../../flutter/LICENSE
@@ -3133,6 +3134,7 @@ ORIGIN: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/Platf
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/PlatformViewsController.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/SingleViewPresentation.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/VirtualDisplayController.java + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/android/io/flutter/plugin/text/ProcessTextPlugin.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/util/HandlerCompat.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/util/PathUtils.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/util/Preconditions.java + ../../../flutter/LICENSE
@@ -5861,6 +5863,7 @@ FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/system
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/NavigationChannel.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/PlatformChannel.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/PlatformViewsChannel.java
+FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/ProcessTextChannel.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/RestorationChannel.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/SettingsChannel.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/SpellCheckChannel.java
@@ -5908,6 +5911,7 @@ FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/Platfor
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/SingleViewPresentation.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/SurfaceTexturePlatformViewRenderTarget.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/VirtualDisplayController.java
+FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/text/ProcessTextPlugin.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/util/HandlerCompat.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/util/PathUtils.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/util/Preconditions.java

shell/platform/android/AndroidManifest.xml

@@ -24,4 +24,12 @@
             </intent-filter>
         </activity>
     </application>
+
+    <!-- Required for io.flutter.plugin.text.ProcessTextPlugin to query activities that can process text. -->
+    <queries>
+        <intent>
+            <action android:name="android.intent.action.PROCESS_TEXT" />
+            <data android:mimeType="text/plain" />
+        </intent>
+    </queries>
  </manifest>

shell/platform/android/BUILD.gn

@@ -265,6 +265,7 @@ android_java_sources = [
   "io/flutter/embedding/engine/systemchannels/NavigationChannel.java",
   "io/flutter/embedding/engine/systemchannels/PlatformChannel.java",
   "io/flutter/embedding/engine/systemchannels/PlatformViewsChannel.java",
+  "io/flutter/embedding/engine/systemchannels/ProcessTextChannel.java",
   "io/flutter/embedding/engine/systemchannels/RestorationChannel.java",
   "io/flutter/embedding/engine/systemchannels/SettingsChannel.java",
   "io/flutter/embedding/engine/systemchannels/SpellCheckChannel.java",
@@ -312,6 +313,7 @@ android_java_sources = [
   "io/flutter/plugin/platform/SingleViewPresentation.java",
   "io/flutter/plugin/platform/SurfaceTexturePlatformViewRenderTarget.java",
   "io/flutter/plugin/platform/VirtualDisplayController.java",
+  "io/flutter/plugin/text/ProcessTextPlugin.java",
   "io/flutter/util/HandlerCompat.java",
   "io/flutter/util/PathUtils.java",
   "io/flutter/util/Preconditions.java",

shell/platform/android/io/flutter/embedding/engine/FlutterEngine.java

@@ -31,13 +31,15 @@
 import io.flutter.embedding.engine.systemchannels.MouseCursorChannel;
 import io.flutter.embedding.engine.systemchannels.NavigationChannel;
 import io.flutter.embedding.engine.systemchannels.PlatformChannel;
+import io.flutter.embedding.engine.systemchannels.ProcessTextChannel;
 import io.flutter.embedding.engine.systemchannels.RestorationChannel;
 import io.flutter.embedding.engine.systemchannels.SettingsChannel;
 import io.flutter.embedding.engine.systemchannels.SpellCheckChannel;
 import io.flutter.embedding.engine.systemchannels.SystemChannel;
 import io.flutter.embedding.engine.systemchannels.TextInputChannel;
 import io.flutter.plugin.localization.LocalizationPlugin;
 import io.flutter.plugin.platform.PlatformViewsController;
+import io.flutter.plugin.text.ProcessTextPlugin;
 import io.flutter.util.ViewUtils;
 import java.util.HashSet;
 import java.util.List;
@@ -95,6 +97,7 @@ public class FlutterEngine implements ViewUtils.DisplayUpdater {
   @NonNull private final NavigationChannel navigationChannel;
   @NonNull private final RestorationChannel restorationChannel;
   @NonNull private final PlatformChannel platformChannel;
+  @NonNull private final ProcessTextChannel processTextChannel;
   @NonNull private final SettingsChannel settingsChannel;
   @NonNull private final SpellCheckChannel spellCheckChannel;
   @NonNull private final SystemChannel systemChannel;
@@ -329,6 +332,7 @@ public FlutterEngine(
     mouseCursorChannel = new MouseCursorChannel(dartExecutor);
     navigationChannel = new NavigationChannel(dartExecutor);
     platformChannel = new PlatformChannel(dartExecutor);
+    processTextChannel = new ProcessTextChannel(dartExecutor, context.getPackageManager());
     restorationChannel = new RestorationChannel(dartExecutor, waitForRestorationData);
     settingsChannel = new SettingsChannel(dartExecutor);
     spellCheckChannel = new SpellCheckChannel(dartExecutor);
@@ -384,6 +388,9 @@ public FlutterEngine(
     }
 
     ViewUtils.calculateMaximumDisplayMetrics(context, this);
+
+    ProcessTextPlugin processTextPlugin = new ProcessTextPlugin(this.getProcessTextChannel());
+    this.pluginRegistry.add(processTextPlugin);
   }
 
   private void attachToJni() {
@@ -545,6 +552,12 @@ public PlatformChannel getPlatformChannel() {
     return platformChannel;
   }
 
+  /** System channel that sends text processing requests from Flutter to Android. */
+  @NonNull
+  public ProcessTextChannel getProcessTextChannel() {
+    return processTextChannel;
+  }
+
   /**
    * System channel to exchange restoration data between framework and engine.
    *

shell/platform/android/io/flutter/embedding/engine/systemchannels/ProcessTextChannel.java

@@ -0,0 +1,122 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package io.flutter.embedding.engine.systemchannels;
+
+import android.content.pm.PackageManager;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import io.flutter.embedding.engine.dart.DartExecutor;
+import io.flutter.plugin.common.MethodCall;
+import io.flutter.plugin.common.MethodChannel;
+import io.flutter.plugin.common.StandardMethodCodec;
+import java.util.ArrayList;
+import java.util.Map;
+
+/**
+ * {@link ProcessTextChannel} is a platform channel that is used by the framework to initiate text
+ * processing feature in the embedding and for the embedding to send back the results.
+ *
+ * <p>When the framework needs to query the list of text processing actions (for instance to expose
+ * them in the selected text context menu), it will send to the embedding the message {@code
+ * ProcessText.queryTextActions}. In response, the {@link io.flutter.plugin.text.ProcessTextPlugin}
+ * will return a map of all activities that can process text. The map keys are generated IDs and the
+ * values are the activities labels. On the first request, the {@link
+ * io.flutter.plugin.text.ProcessTextPlugin} will make a call to Android's package manager to query
+ * all activities that can be performed for the {@code Intent.ACTION_PROCESS_TEXT} intent.
+ *
+ * <p>When a text processing action has to be executed, the framework will send to the embedding the
+ * message {@code ProcessText.processTextAction} with the {@code int id} of the choosen text action
+ * and the {@code String} of text to process as arguments. In response, the {@link
+ * io.flutter.plugin.text.ProcessTextPlugin} will make a call to the Android application activity to
+ * start the activity exposing the text action. The {@link io.flutter.plugin.text.ProcessTextPlugin}
+ * will return the processed text if there is one, or null if the activity did not return a
+ * transformed text.
+ *
+ * <p>{@link io.flutter.plugin.text.ProcessTextPlugin} implements {@link ProcessTextMethodHandler}
+ * that parses incoming messages from Flutter.
+ */
+public class ProcessTextChannel {
+  private static final String TAG = "ProcessTextChannel";
+  private static final String CHANNEL_NAME = "flutter/processtext";
+  private static final String METHOD_QUERY_TEXT_ACTIONS = "ProcessText.queryTextActions";
+  private static final String METHOD_PROCESS_TEXT_ACTION = "ProcessText.processTextAction";
+
+  public final MethodChannel channel;
+  public final PackageManager packageManager;
+  private ProcessTextMethodHandler processTextMethodHandler;
+
+  @NonNull
+  public final MethodChannel.MethodCallHandler parsingMethodHandler =
+      new MethodChannel.MethodCallHandler() {
+        @Override
+        public void onMethodCall(@NonNull MethodCall call, @NonNull MethodChannel.Result result) {
+          if (processTextMethodHandler == null) {
+            return;
+          }
+          String method = call.method;
+          Object args = call.arguments;
+          switch (method) {
+            case METHOD_QUERY_TEXT_ACTIONS:
+              try {
+                Map<String, String> actions = processTextMethodHandler.queryTextActions();
+                result.success(actions);
+              } catch (IllegalStateException exception) {
+                result.error("error", exception.getMessage(), null);
+              }
+              break;
+            case METHOD_PROCESS_TEXT_ACTION:
+              try {
+                final ArrayList<Object> argumentList = (ArrayList<Object>) args;
+                String id = (String) (argumentList.get(0));
+                String text = (String) (argumentList.get(1));
+                boolean readOnly = (boolean) (argumentList.get(2));
+                processTextMethodHandler.processTextAction(id, text, readOnly, result);
+              } catch (IllegalStateException exception) {
+                result.error("error", exception.getMessage(), null);
+              }
+              break;
+            default:
+              result.notImplemented();
+              break;
+          }
+        }
+      };
+
+  public ProcessTextChannel(
+      @NonNull DartExecutor dartExecutor, @NonNull PackageManager packageManager) {
+    this.packageManager = packageManager;
+    channel = new MethodChannel(dartExecutor, CHANNEL_NAME, StandardMethodCodec.INSTANCE);
+    channel.setMethodCallHandler(parsingMethodHandler);
+  }
+
+  /**
+   * Sets the {@link ProcessTextMethodHandler} which receives all requests to the text processing
+   * feature sent through this channel.
+   */
+  public void setMethodHandler(@Nullable ProcessTextMethodHandler processTextMethodHandler) {
+    this.processTextMethodHandler = processTextMethodHandler;
+  }
+
+  public interface ProcessTextMethodHandler {
+    /** Requests the map of text actions. Each text action has a unique id and a localized label. */
+    Map<String, String> queryTextActions();
+
+    /**
+     * Requests to run a text action on a given input text.
+     *
+     * @param id The ID of the text action returned by {@code ProcessText.queryTextActions}.
+     * @param input The text to be processed.
+     * @param readOnly Indicates to the activity if the processed text will be used as read-only.
+     *     see
+     *     https://developer.android.com/reference/android/content/Intent#EXTRA_PROCESS_TEXT_READONLY
+     * @param result The method channel result instance used to reply.
+     */
+    void processTextAction(
+        @NonNull String id,
+        @NonNull String input,
+        @NonNull boolean readOnly,
+        @NonNull MethodChannel.Result result);
+  }
+}