1 files changed, 33 insertions, 3 deletions

diff --git a/java/src/com/android/inputmethod/latin/NgramContext.java b/java/src/com/android/inputmethod/latin/NgramContext.java
index b47731229..86155e0be 100644
--- a/java/src/com/android/inputmethod/latin/NgramContext.java
+++ b/java/src/com/android/inputmethod/latin/NgramContext.java
@@ -19,9 +19,10 @@ package com.android.inputmethod.latin;
 import android.text.TextUtils;
 
 import com.android.inputmethod.annotations.UsedForTesting;
-import com.android.inputmethod.latin.common.Constants;
 import com.android.inputmethod.latin.common.StringUtils;
+import com.android.inputmethod.latin.define.DecoderSpecificConstants;
 
+import java.util.ArrayList;
 import java.util.Arrays;
 
 import javax.annotation.Nonnull;
@@ -38,6 +39,10 @@ public class NgramContext {
     public static final NgramContext BEGINNING_OF_SENTENCE =
             new NgramContext(WordInfo.BEGINNING_OF_SENTENCE_WORD_INFO);
 
+    public static final String BEGINNING_OF_SENTENCE_TAG = "<S>";
+
+    public static final String CONTEXT_SEPARATOR = " ";
+
     /**
      * Word information used to represent previous words information.
      */
@@ -106,14 +111,39 @@ public class NgramContext {
     // Create next prevWordsInfo using current prevWordsInfo.
     @Nonnull
     public NgramContext getNextNgramContext(final WordInfo wordInfo) {
-        final int nextPrevWordCount = Math.min(Constants.MAX_PREV_WORD_COUNT_FOR_N_GRAM,
-                mPrevWordsCount + 1);
+        final int nextPrevWordCount = Math.min(
+                DecoderSpecificConstants.MAX_PREV_WORD_COUNT_FOR_N_GRAM, mPrevWordsCount + 1);
         final WordInfo[] prevWordsInfo = new WordInfo[nextPrevWordCount];
         prevWordsInfo[0] = wordInfo;
         System.arraycopy(mPrevWordsInfo, 0, prevWordsInfo, 1, nextPrevWordCount - 1);
         return new NgramContext(prevWordsInfo);
     }
 
+
+    /**
+     * Extracts the previous words context.
+     *
+     * @return a String with the previous words separated by white space.
+     */
+    public String extractPrevWordsContext() {
+        final ArrayList<String> terms = new ArrayList<>();
+        for (int i = mPrevWordsInfo.length - 1; i >= 0; --i) {
+            if (mPrevWordsInfo[i] != null && mPrevWordsInfo[i].isValid()) {
+                final NgramContext.WordInfo wordInfo = mPrevWordsInfo[i];
+                if (wordInfo.mIsBeginningOfSentence) {
+                    terms.add(BEGINNING_OF_SENTENCE_TAG);
+                } else {
+                    final String term = wordInfo.mWord.toString();
+                    if (!term.isEmpty()) {
+                        terms.add(term);
+                    }
+                }
+            }
+        }
+        return terms.size() == 0 ? BEGINNING_OF_SENTENCE_TAG
+                : TextUtils.join(CONTEXT_SEPARATOR, terms);
+    }
+
     public boolean isValid() {
         return mPrevWordsCount > 0 && mPrevWordsInfo[0].isValid();
     }