diff --git a/core/java/android/view/textclassifier/ActionsSuggestionsHelper.java b/core/java/android/view/textclassifier/ActionsSuggestionsHelper.java
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+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.view.textclassifier;
+
+import android.annotation.NonNull;
+import android.app.Person;
+import android.text.TextUtils;
+import android.util.ArrayMap;
+
+import com.android.internal.annotations.VisibleForTesting;
+
+import com.google.android.textclassifier.ActionsSuggestionsModel;
+
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.Deque;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/**
+ * Helper class for action suggestions.
+ *
+ * @hide
+ */
+@VisibleForTesting(visibility = VisibleForTesting.Visibility.PACKAGE)
+public final class ActionsSuggestionsHelper {
+    private static final int USER_LOCAL = 0;
+    private static final int FIRST_NON_LOCAL_USER = 1;
+
+    private ActionsSuggestionsHelper() {}
+
+    /**
+     * Converts the messages to a list of native messages object that the model can understand.
+     * <p>
+     * User id encoding - local user is represented as 0, Other users are numbered according to
+     * how far before they spoke last time in the conversation. For example, considering this
+     * conversation:
+     * <ul>
+     * <li> User A: xxx
+     * <li> Local user: yyy
+     * <li> User B: zzz
+     * </ul>
+     * User A will be encoded as 2, user B will be encoded as 1 and local user will be encoded as 0.
+     */
+    @NonNull
+    public static ActionsSuggestionsModel.ConversationMessage[] toNativeMessages(
+            @NonNull List<ConversationActions.Message> messages) {
+        List<ConversationActions.Message> messagesWithText =
+                messages.stream()
+                        .filter(message -> !TextUtils.isEmpty(message.getText()))
+                        .collect(Collectors.toCollection(ArrayList::new));
+        if (messagesWithText.isEmpty()) {
+            return new ActionsSuggestionsModel.ConversationMessage[0];
+        }
+        int size = messagesWithText.size();
+        // If the last message (the most important one) does not have the Person object, we will
+        // just use the last message and consider this message is sent from a remote user.
+        ConversationActions.Message lastMessage = messages.get(size - 1);
+        boolean useLastMessageOnly = lastMessage.getAuthor() == null;
+        if (useLastMessageOnly) {
+            return new ActionsSuggestionsModel.ConversationMessage[]{
+                    new ActionsSuggestionsModel.ConversationMessage(
+                            FIRST_NON_LOCAL_USER,
+                            lastMessage.getText().toString())};
+        }
+
+        // Encode the messages in the reverse order, stop whenever the Person object is missing.
+        Deque<ActionsSuggestionsModel.ConversationMessage> nativeMessages = new ArrayDeque<>();
+        PersonEncoder personEncoder = new PersonEncoder();
+        for (int i = size - 1; i >= 0; i--) {
+            ConversationActions.Message message = messagesWithText.get(i);
+            if (message.getAuthor() == null) {
+                break;
+            }
+            nativeMessages.push(new ActionsSuggestionsModel.ConversationMessage(
+                    personEncoder.encode(message.getAuthor()),
+                    message.getText().toString()));
+        }
+        return nativeMessages.toArray(
+                new ActionsSuggestionsModel.ConversationMessage[nativeMessages.size()]);
+    }
+
+    private static final class PersonEncoder {
+        private final Map<Person, Integer> mMapping = new ArrayMap<>();
+        private int mNextUserId = FIRST_NON_LOCAL_USER;
+
+        private int encode(Person person) {
+            if (ConversationActions.Message.PERSON_USER_LOCAL.equals(person)) {
+                return USER_LOCAL;
+            }
+            Integer result = mMapping.get(person);
+            if (result == null) {
+                mMapping.put(person, mNextUserId);
+                result = mNextUserId;
+                mNextUserId++;
+            }
+            return result;
+        }
+    }
+}