Revert "Use PrevWordsInfo for get/add/remove n-gram(bigram) entry."

This reverts commit ff50b39176370ab80a33bfdcf9979603c08a88b3.

Bug: 14119293
Bug: 14425059
Bug: 15102610

Change-Id: If278b4ab236e38d20d8cdc0761b0438911bd4ff9

10 files changed, 89 insertions, 100 deletions

diff --git a/java/src/com/android/inputmethod/latin/BinaryDictionary.java b/java/src/com/android/inputmethod/latin/BinaryDictionary.java
index e7ab02ac1..b8cf3f89c 100644
--- a/java/src/com/android/inputmethod/latin/BinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/BinaryDictionary.java
@@ -359,16 +359,14 @@ public final class BinaryDictionary extends Dictionary {
     }
 
     @UsedForTesting
-    public boolean isValidNgram(final PrevWordsInfo prevWordsInfo, final String word) {
-        return getNgramProbability(prevWordsInfo, word) != NOT_A_PROBABILITY;
+    public boolean isValidBigram(final String word0, final String word1) {
+        return getBigramProbability(word0, word1) != NOT_A_PROBABILITY;
     }
 
-    public int getNgramProbability(final PrevWordsInfo prevWordsInfo, final String word) {
-        if (TextUtils.isEmpty(prevWordsInfo.mPrevWord) || TextUtils.isEmpty(word)) {
-            return NOT_A_PROBABILITY;
-        }
-        final int[] codePoints0 = StringUtils.toCodePointArray(prevWordsInfo.mPrevWord);
-        final int[] codePoints1 = StringUtils.toCodePointArray(word);
+    public int getBigramProbability(final String word0, final String word1) {
+        if (TextUtils.isEmpty(word0) || TextUtils.isEmpty(word1)) return NOT_A_PROBABILITY;
+        final int[] codePoints0 = StringUtils.toCodePointArray(word0);
+        final int[] codePoints1 = StringUtils.toCodePointArray(word1);
         return getBigramProbabilityNative(mNativeDict, codePoints0, codePoints1);
     }
 
@@ -419,7 +417,7 @@ public final class BinaryDictionary extends Dictionary {
     }
 
     // Add a unigram entry to binary dictionary with unigram attributes in native code.
-    public void addUnigramEntry(final String word, final int probability,
+    public void addUnigramWord(final String word, final int probability,
             final String shortcutTarget, final int shortcutProbability, final boolean isNotAWord,
             final boolean isBlacklisted, final int timestamp) {
         if (TextUtils.isEmpty(word)) {
@@ -433,26 +431,25 @@ public final class BinaryDictionary extends Dictionary {
         mHasUpdated = true;
     }
 
-    // Add an n-gram entry to the binary dictionary with timestamp in native code.
-    public void addNgramEntry(final PrevWordsInfo prevWordsInfo, final String word,
-            final int probability,
+    // Add a bigram entry to binary dictionary with timestamp in native code.
+    public void addBigramWords(final String word0, final String word1, final int probability,
             final int timestamp) {
-        if (TextUtils.isEmpty(prevWordsInfo.mPrevWord) || TextUtils.isEmpty(word)) {
+        if (TextUtils.isEmpty(word0) || TextUtils.isEmpty(word1)) {
             return;
         }
-        final int[] codePoints0 = StringUtils.toCodePointArray(prevWordsInfo.mPrevWord);
-        final int[] codePoints1 = StringUtils.toCodePointArray(word);
+        final int[] codePoints0 = StringUtils.toCodePointArray(word0);
+        final int[] codePoints1 = StringUtils.toCodePointArray(word1);
         addBigramWordsNative(mNativeDict, codePoints0, codePoints1, probability, timestamp);
         mHasUpdated = true;
     }
 
-    // Remove an n-gram entry from the binary dictionary in native code.
-    public void removeNgramEntry(final PrevWordsInfo prevWordsInfo, final String word) {
-        if (TextUtils.isEmpty(prevWordsInfo.mPrevWord) || TextUtils.isEmpty(word)) {
+    // Remove a bigram entry form binary dictionary in native code.
+    public void removeBigramWords(final String word0, final String word1) {
+        if (TextUtils.isEmpty(word0) || TextUtils.isEmpty(word1)) {
             return;
         }
-        final int[] codePoints0 = StringUtils.toCodePointArray(prevWordsInfo.mPrevWord);
-        final int[] codePoints1 = StringUtils.toCodePointArray(word);
+        final int[] codePoints0 = StringUtils.toCodePointArray(word0);
+        final int[] codePoints1 = StringUtils.toCodePointArray(word1);
         removeBigramWordsNative(mNativeDict, codePoints0, codePoints1);
         mHasUpdated = true;
     }
diff --git a/java/src/com/android/inputmethod/latin/ContactsBinaryDictionary.java b/java/src/com/android/inputmethod/latin/ContactsBinaryDictionary.java
index 3fb76b142..e04fcda27 100644
--- a/java/src/com/android/inputmethod/latin/ContactsBinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/ContactsBinaryDictionary.java
@@ -142,7 +142,7 @@ public class ContactsBinaryDictionary extends ExpandableBinaryDictionary {
                 Log.d(TAG, "loadAccountVocabulary: " + word);
             }
             runGCIfRequiredLocked(true /* mindsBlockByGC */);
-            addUnigramLocked(word, FREQUENCY_FOR_CONTACTS, null /* shortcut */,
+            addWordDynamicallyLocked(word, FREQUENCY_FOR_CONTACTS, null /* shortcut */,
                     0 /* shortcutFreq */, false /* isNotAWord */, false /* isBlacklisted */,
                     BinaryDictionary.NOT_A_VALID_TIMESTAMP);
         }
@@ -224,7 +224,7 @@ public class ContactsBinaryDictionary extends ExpandableBinaryDictionary {
      */
     private void addNameLocked(final String name) {
         int len = StringUtils.codePointCount(name);
-        PrevWordsInfo prevWordsInfo = new PrevWordsInfo(null);
+        String prevWord = null;
         // TODO: Better tokenization for non-Latin writing systems
         for (int i = 0; i < len; i++) {
             if (Character.isLetter(name.codePointAt(i))) {
@@ -239,19 +239,19 @@ public class ContactsBinaryDictionary extends ExpandableBinaryDictionary {
                 final int wordLen = StringUtils.codePointCount(word);
                 if (wordLen < MAX_WORD_LENGTH && wordLen > 1) {
                     if (DEBUG) {
-                        Log.d(TAG, "addName " + name + ", " + word + ", "
-                                + prevWordsInfo.mPrevWord);
+                        Log.d(TAG, "addName " + name + ", " + word + ", " + prevWord);
                     }
                     runGCIfRequiredLocked(true /* mindsBlockByGC */);
-                    addUnigramLocked(word, FREQUENCY_FOR_CONTACTS,
+                    addWordDynamicallyLocked(word, FREQUENCY_FOR_CONTACTS,
                             null /* shortcut */, 0 /* shortcutFreq */, false /* isNotAWord */,
                             false /* isBlacklisted */, BinaryDictionary.NOT_A_VALID_TIMESTAMP);
-                    if (!TextUtils.isEmpty(prevWordsInfo.mPrevWord) && mUseFirstLastBigrams) {
+                    if (!TextUtils.isEmpty(prevWord) && mUseFirstLastBigrams) {
                         runGCIfRequiredLocked(true /* mindsBlockByGC */);
-                        addNgramEntryLocked(prevWordsInfo, word, FREQUENCY_FOR_CONTACTS_BIGRAM,
+                        addBigramDynamicallyLocked(prevWord, word,
+                                FREQUENCY_FOR_CONTACTS_BIGRAM,
                                 BinaryDictionary.NOT_A_VALID_TIMESTAMP);
                     }
-                    prevWordsInfo = new PrevWordsInfo(word);
+                    prevWord = word;
                 }
             }
         }
diff --git a/java/src/com/android/inputmethod/latin/DictionaryFacilitatorForSuggest.java b/java/src/com/android/inputmethod/latin/DictionaryFacilitatorForSuggest.java
index 301b832b6..14c8bb6c3 100644
--- a/java/src/com/android/inputmethod/latin/DictionaryFacilitatorForSuggest.java
+++ b/java/src/com/android/inputmethod/latin/DictionaryFacilitatorForSuggest.java
@@ -370,23 +370,22 @@ public class DictionaryFacilitatorForSuggest {
     }
 
     public void addToUserHistory(final String suggestion, final boolean wasAutoCapitalized,
-            final PrevWordsInfo prevWordsInfo, final int timeStampInSeconds,
+            final String previousWord, final int timeStampInSeconds,
             final boolean blockPotentiallyOffensive) {
         final Dictionaries dictionaries = mDictionaries;
         final String[] words = suggestion.split(Constants.WORD_SEPARATOR);
         for (int i = 0; i < words.length; i++) {
             final String currentWord = words[i];
-            final PrevWordsInfo prevWordsInfoForCurrentWord =
-                    (i == 0) ? prevWordsInfo : new PrevWordsInfo(words[i - 1]);
+            final String prevWord = (i == 0) ? previousWord : words[i - 1];
             final boolean wasCurrentWordAutoCapitalized = (i == 0) ? wasAutoCapitalized : false;
-            addWordToUserHistory(dictionaries, prevWordsInfoForCurrentWord, currentWord,
+            addWordToUserHistory(dictionaries, prevWord, currentWord,
                     wasCurrentWordAutoCapitalized, timeStampInSeconds, blockPotentiallyOffensive);
         }
     }
 
-    private void addWordToUserHistory(final Dictionaries dictionaries,
-            final PrevWordsInfo prevWordsInfo, final String word, final boolean wasAutoCapitalized,
-            final int timeStampInSeconds, final boolean blockPotentiallyOffensive) {
+    private void addWordToUserHistory(final Dictionaries dictionaries, final String prevWord,
+            final String word, final boolean wasAutoCapitalized, final int timeStampInSeconds,
+            final boolean blockPotentiallyOffensive) {
         final ExpandableBinaryDictionary userHistoryDictionary =
                 dictionaries.getSubDict(Dictionary.TYPE_USER_HISTORY);
         if (userHistoryDictionary == null) {
@@ -431,16 +430,15 @@ public class DictionaryFacilitatorForSuggest {
         // We demote unrecognized words (frequency < 0, below) by specifying them as "invalid".
         // We don't add words with 0-frequency (assuming they would be profanity etc.).
         final boolean isValid = maxFreq > 0;
-        UserHistoryDictionary.addToDictionary(userHistoryDictionary, prevWordsInfo, secondWord,
+        UserHistoryDictionary.addToDictionary(userHistoryDictionary, prevWord, secondWord,
                 isValid, timeStampInSeconds);
     }
 
-    public void cancelAddingUserHistory(final PrevWordsInfo prevWordsInfo,
-            final String committedWord) {
+    public void cancelAddingUserHistory(final String previousWord, final String committedWord) {
         final ExpandableBinaryDictionary userHistoryDictionary =
                 mDictionaries.getSubDict(Dictionary.TYPE_USER_HISTORY);
         if (userHistoryDictionary != null) {
-            userHistoryDictionary.removeNgramDynamically(prevWordsInfo, committedWord);
+            userHistoryDictionary.removeBigramDynamically(previousWord, committedWord);
         }
     }
 
diff --git a/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java b/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
index d67253c3b..629f3fd18 100644
--- a/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
@@ -269,9 +269,9 @@ abstract public class ExpandableBinaryDictionary extends Dictionary {
     }
 
     /**
-     * Adds unigram information of a word to the dictionary. May overwrite an existing entry.
+     * Dynamically adds a word unigram to the dictionary. May overwrite an existing entry.
      */
-    public void addUnigramEntry(final String word, final int frequency,
+    public void addWordDynamically(final String word, final int frequency,
             final String shortcutTarget, final int shortcutFreq, final boolean isNotAWord,
             final boolean isBlacklisted, final int timestamp) {
         reloadDictionaryIfRequired();
@@ -282,23 +282,23 @@ abstract public class ExpandableBinaryDictionary extends Dictionary {
                     return;
                 }
                 runGCIfRequiredLocked(true /* mindsBlockByGC */);
-                addUnigramLocked(word, frequency, shortcutTarget, shortcutFreq,
+                addWordDynamicallyLocked(word, frequency, shortcutTarget, shortcutFreq,
                         isNotAWord, isBlacklisted, timestamp);
             }
         });
     }
 
-    protected void addUnigramLocked(final String word, final int frequency,
+    protected void addWordDynamicallyLocked(final String word, final int frequency,
             final String shortcutTarget, final int shortcutFreq, final boolean isNotAWord,
             final boolean isBlacklisted, final int timestamp) {
-        mBinaryDictionary.addUnigramEntry(word, frequency, shortcutTarget, shortcutFreq,
+        mBinaryDictionary.addUnigramWord(word, frequency, shortcutTarget, shortcutFreq,
                 isNotAWord, isBlacklisted, timestamp);
     }
 
     /**
-     * Adds n-gram information of a word to the dictionary. May overwrite an existing entry.
+     * Dynamically adds a word bigram in the dictionary. May overwrite an existing entry.
      */
-    public void addNgramEntry(final PrevWordsInfo prevWordsInfo, final String word,
+    public void addBigramDynamically(final String word0, final String word1,
             final int frequency, final int timestamp) {
         reloadDictionaryIfRequired();
         asyncExecuteTaskWithWriteLock(new Runnable() {
@@ -308,20 +308,20 @@ abstract public class ExpandableBinaryDictionary extends Dictionary {
                     return;
                 }
                 runGCIfRequiredLocked(true /* mindsBlockByGC */);
-                addNgramEntryLocked(prevWordsInfo, word, frequency, timestamp);
+                addBigramDynamicallyLocked(word0, word1, frequency, timestamp);
             }
         });
     }
 
-    protected void addNgramEntryLocked(final PrevWordsInfo prevWordsInfo, final String word,
+    protected void addBigramDynamicallyLocked(final String word0, final String word1,
             final int frequency, final int timestamp) {
-        mBinaryDictionary.addNgramEntry(prevWordsInfo, word, frequency, timestamp);
+        mBinaryDictionary.addBigramWords(word0, word1, frequency, timestamp);
     }
 
     /**
-     * Dynamically remove the n-gram entry in the dictionary.
+     * Dynamically remove a word bigram in the dictionary.
      */
-    public void removeNgramDynamically(final PrevWordsInfo prevWordsInfo, final String word1) {
+    public void removeBigramDynamically(final String word0, final String word1) {
         reloadDictionaryIfRequired();
         asyncExecuteTaskWithWriteLock(new Runnable() {
             @Override
@@ -330,7 +330,7 @@ abstract public class ExpandableBinaryDictionary extends Dictionary {
                     return;
                 }
                 runGCIfRequiredLocked(true /* mindsBlockByGC */);
-                mBinaryDictionary.removeNgramEntry(prevWordsInfo, word1);
+                mBinaryDictionary.removeBigramWords(word0, word1);
             }
         });
     }
@@ -428,9 +428,9 @@ abstract public class ExpandableBinaryDictionary extends Dictionary {
         return mBinaryDictionary.isValidWord(word);
     }
 
-    protected boolean isValidNgramLocked(final PrevWordsInfo prevWordsInfo, final String word) {
+    protected boolean isValidBigramLocked(final String word1, final String word2) {
         if (mBinaryDictionary == null) return false;
-        return mBinaryDictionary.isValidNgram(prevWordsInfo, word);
+        return mBinaryDictionary.isValidBigram(word1, word2);
     }
 
     /**
diff --git a/java/src/com/android/inputmethod/latin/LastComposedWord.java b/java/src/com/android/inputmethod/latin/LastComposedWord.java
index 9caec3e01..232bf7407 100644
--- a/java/src/com/android/inputmethod/latin/LastComposedWord.java
+++ b/java/src/com/android/inputmethod/latin/LastComposedWord.java
@@ -48,7 +48,7 @@ public final class LastComposedWord {
     public final String mTypedWord;
     public final CharSequence mCommittedWord;
     public final String mSeparatorString;
-    public final PrevWordsInfo mPrevWordsInfo;
+    public final String mPrevWord;
     public final int mCapitalizedMode;
     public final InputPointers mInputPointers =
             new InputPointers(Constants.DICTIONARY_MAX_WORD_LENGTH);
@@ -64,7 +64,7 @@ public final class LastComposedWord {
     public LastComposedWord(final ArrayList<Event> events,
             final InputPointers inputPointers, final String typedWord,
             final CharSequence committedWord, final String separatorString,
-            final PrevWordsInfo prevWordsInfo, final int capitalizedMode) {
+            final String prevWord, final int capitalizedMode) {
         if (inputPointers != null) {
             mInputPointers.copy(inputPointers);
         }
@@ -73,7 +73,7 @@ public final class LastComposedWord {
         mCommittedWord = committedWord;
         mSeparatorString = separatorString;
         mActive = true;
-        mPrevWordsInfo = prevWordsInfo;
+        mPrevWord = prevWord;
         mCapitalizedMode = capitalizedMode;
     }
 
diff --git a/java/src/com/android/inputmethod/latin/UserBinaryDictionary.java b/java/src/com/android/inputmethod/latin/UserBinaryDictionary.java
index b89ab84b2..c8ffbe443 100644
--- a/java/src/com/android/inputmethod/latin/UserBinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/UserBinaryDictionary.java
@@ -258,12 +258,12 @@ public class UserBinaryDictionary extends ExpandableBinaryDictionary {
                 // Safeguard against adding really long words.
                 if (word.length() < MAX_WORD_LENGTH) {
                     runGCIfRequiredLocked(true /* mindsBlockByGC */);
-                    addUnigramLocked(word, adjustedFrequency, null /* shortcutTarget */,
+                    addWordDynamicallyLocked(word, adjustedFrequency, null /* shortcutTarget */,
                             0 /* shortcutFreq */, false /* isNotAWord */,
                             false /* isBlacklisted */, BinaryDictionary.NOT_A_VALID_TIMESTAMP);
                     if (null != shortcut && shortcut.length() < MAX_WORD_LENGTH) {
                         runGCIfRequiredLocked(true /* mindsBlockByGC */);
-                        addUnigramLocked(shortcut, adjustedFrequency, word,
+                        addWordDynamicallyLocked(shortcut, adjustedFrequency, word,
                                 USER_DICT_SHORTCUT_FREQUENCY, true /* isNotAWord */,
                                 false /* isBlacklisted */, BinaryDictionary.NOT_A_VALID_TIMESTAMP);
                     }
diff --git a/java/src/com/android/inputmethod/latin/WordComposer.java b/java/src/com/android/inputmethod/latin/WordComposer.java
index 09e905481..227b42bde 100644
--- a/java/src/com/android/inputmethod/latin/WordComposer.java
+++ b/java/src/com/android/inputmethod/latin/WordComposer.java
@@ -294,10 +294,11 @@ public final class WordComposer {
      * This will register NOT_A_COORDINATE for X and Ys, and use the passed keyboard for proximity.
      * @param codePoints the code points to set as the composing word.
      * @param coordinates the x, y coordinates of the key in the CoordinateUtils format
-     * @param prevWordsInfo the information of previous words, to use as context for suggestions
+     * @param previousWord the previous word, to use as context for suggestions. Can be null if
+     *   the context is nil (typically, at start of text).
      */
     public void setComposingWord(final int[] codePoints, final int[] coordinates,
-            final PrevWordsInfo prevWordsInfo) {
+            final CharSequence previousWord) {
         reset();
         final int length = codePoints.length;
         for (int i = 0; i < length; ++i) {
@@ -306,7 +307,7 @@ public final class WordComposer {
                     CoordinateUtils.yFromArray(coordinates, i)));
         }
         mIsResumed = true;
-        mPrevWordsInfo = prevWordsInfo;
+        mPrevWordsInfo = new PrevWordsInfo(null == previousWord ? null : previousWord.toString());
     }
 
     /**
@@ -412,13 +413,13 @@ public final class WordComposer {
     // `type' should be one of the LastComposedWord.COMMIT_TYPE_* constants above.
     // committedWord should contain suggestion spans if applicable.
     public LastComposedWord commitWord(final int type, final CharSequence committedWord,
-            final String separatorString, final PrevWordsInfo prevWordsInfo) {
+            final String separatorString, final String prevWord) {
         // Note: currently, we come here whenever we commit a word. If it's a MANUAL_PICK
         // or a DECIDED_WORD we may cancel the commit later; otherwise, we should deactivate
         // the last composed word to ensure this does not happen.
         final LastComposedWord lastComposedWord = new LastComposedWord(mEvents,
                 mInputPointers, mTypedWordCache.toString(), committedWord, separatorString,
-                prevWordsInfo, mCapitalizedMode);
+                prevWord, mCapitalizedMode);
         mInputPointers.reset();
         if (type != LastComposedWord.COMMIT_TYPE_DECIDED_WORD
                 && type != LastComposedWord.COMMIT_TYPE_MANUAL_PICK) {
diff --git a/java/src/com/android/inputmethod/latin/inputlogic/InputLogic.java b/java/src/com/android/inputmethod/latin/inputlogic/InputLogic.java
index 58b101254..ea58abc14 100644
--- a/java/src/com/android/inputmethod/latin/inputlogic/InputLogic.java
+++ b/java/src/com/android/inputmethod/latin/inputlogic/InputLogic.java
@@ -37,7 +37,6 @@ import com.android.inputmethod.latin.InputPointers;
 import com.android.inputmethod.latin.LastComposedWord;
 import com.android.inputmethod.latin.LatinIME;
 import com.android.inputmethod.latin.LatinImeLogger;
-import com.android.inputmethod.latin.PrevWordsInfo;
 import com.android.inputmethod.latin.RichInputConnection;
 import com.android.inputmethod.latin.Suggest;
 import com.android.inputmethod.latin.Suggest.OnGetSuggestedWordsCallback;
@@ -1234,7 +1233,7 @@ public final class InputLogic {
     }
 
     private void performAdditionToUserHistoryDictionary(final SettingsValues settingsValues,
-            final String suggestion, final PrevWordsInfo prevWordsInfo) {
+            final String suggestion, final String prevWord) {
         // If correction is not enabled, we don't add words to the user history dictionary.
         // That's to avoid unintended additions in some sensitive fields, or fields that
         // expect to receive non-words.
@@ -1245,8 +1244,8 @@ public final class InputLogic {
                 mWordComposer.wasAutoCapitalized() && !mWordComposer.isMostlyCaps();
         final int timeStampInSeconds = (int)TimeUnit.MILLISECONDS.toSeconds(
                 System.currentTimeMillis());
-        mSuggest.mDictionaryFacilitator.addToUserHistory(suggestion, wasAutoCapitalized,
-                prevWordsInfo, timeStampInSeconds, settingsValues.mBlockPotentiallyOffensive);
+        mSuggest.mDictionaryFacilitator.addToUserHistory(suggestion, wasAutoCapitalized, prevWord,
+                timeStampInSeconds, settingsValues.mBlockPotentiallyOffensive);
     }
 
     public void performUpdateSuggestionStripSync(final SettingsValues settingsValues) {
@@ -1371,15 +1370,13 @@ public final class InputLogic {
             }
         }
         final int[] codePoints = StringUtils.toCodePointArray(typedWord);
-        // We want the previous word for suggestion. If we have chars in the word
-        // before the cursor, then we want the word before that, hence 2; otherwise,
-        // we want the word immediately before the cursor, hence 1.
-        final String prevWord = getNthPreviousWordForSuggestion(
-                settingsValues.mSpacingAndPunctuations,
-                0 == numberOfCharsInWordBeforeCursor ? 1 : 2).toString();
         mWordComposer.setComposingWord(codePoints,
                 mLatinIME.getCoordinatesForCurrentKeyboard(codePoints),
-                new PrevWordsInfo(prevWord));
+                getNthPreviousWordForSuggestion(settingsValues.mSpacingAndPunctuations,
+                        // We want the previous word for suggestion. If we have chars in the word
+                        // before the cursor, then we want the word before that, hence 2; otherwise,
+                        // we want the word immediately before the cursor, hence 1.
+                        0 == numberOfCharsInWordBeforeCursor ? 1 : 2));
         mWordComposer.setCursorPositionWithinWord(
                 typedWord.codePointCount(0, numberOfCharsInWordBeforeCursor));
         mConnection.setComposingRegion(expectedCursorPosition - numberOfCharsInWordBeforeCursor,
@@ -1434,7 +1431,7 @@ public final class InputLogic {
      * @param inputTransaction The transaction in progress.
      */
     private void revertCommit(final InputTransaction inputTransaction) {
-        final PrevWordsInfo prevWordsInfo = mLastComposedWord.mPrevWordsInfo;
+        final String previousWord = mLastComposedWord.mPrevWord;
         final CharSequence originallyTypedWord = mLastComposedWord.mTypedWord;
         final CharSequence committedWord = mLastComposedWord.mCommittedWord;
         final String committedWordString = committedWord.toString();
@@ -1456,9 +1453,9 @@ public final class InputLogic {
             }
         }
         mConnection.deleteSurroundingText(deleteLength, 0);
-        if (!TextUtils.isEmpty(prevWordsInfo.mPrevWord) && !TextUtils.isEmpty(committedWord)) {
+        if (!TextUtils.isEmpty(previousWord) && !TextUtils.isEmpty(committedWord)) {
             mSuggest.mDictionaryFacilitator.cancelAddingUserHistory(
-                    prevWordsInfo, committedWordString);
+                    previousWord, committedWordString);
         }
         final String stringToCommit = originallyTypedWord + mLastComposedWord.mSeparatorString;
         final SpannableString textToCommit = new SpannableString(stringToCommit);
@@ -1507,7 +1504,7 @@ public final class InputLogic {
             // with the typed word, so we need to resume suggestions right away.
             final int[] codePoints = StringUtils.toCodePointArray(stringToCommit);
             mWordComposer.setComposingWord(codePoints,
-                    mLatinIME.getCoordinatesForCurrentKeyboard(codePoints), prevWordsInfo);
+                    mLatinIME.getCoordinatesForCurrentKeyboard(codePoints), previousWord);
             mConnection.setComposingText(textToCommit, 1);
         }
         if (inputTransaction.mSettingsValues.mIsInternal) {
@@ -1971,17 +1968,17 @@ public final class InputLogic {
                         suggestedWords);
         // Use the 2nd previous word as the previous word because the 1st previous word is the word
         // to be committed.
-        final PrevWordsInfo prevWordsInfo = new PrevWordsInfo(mConnection.getNthPreviousWord(
-                settingsValues.mSpacingAndPunctuations, 2));
+        final String prevWord = mConnection.getNthPreviousWord(
+                settingsValues.mSpacingAndPunctuations, 2);
         mConnection.commitText(chosenWordWithSuggestions, 1);
         // Add the word to the user history dictionary
-        performAdditionToUserHistoryDictionary(settingsValues, chosenWord, prevWordsInfo);
+        performAdditionToUserHistoryDictionary(settingsValues, chosenWord, prevWord);
         // TODO: figure out here if this is an auto-correct or if the best word is actually
         // what user typed. Note: currently this is done much later in
         // LastComposedWord#didCommitTypedWord by string equality of the remembered
         // strings.
         mLastComposedWord = mWordComposer.commitWord(commitType,
-                chosenWordWithSuggestions, separatorString, prevWordsInfo);
+                chosenWordWithSuggestions, separatorString, prevWord);
         final boolean shouldDiscardPreviousWordForSuggestion;
         if (0 == StringUtils.codePointCount(separatorString)) {
             // Separator is 0-length, we can keep the previous word for suggestion. Either this
diff --git a/java/src/com/android/inputmethod/latin/personalization/UserHistoryDictionary.java b/java/src/com/android/inputmethod/latin/personalization/UserHistoryDictionary.java
index f89caf921..818cd9a5f 100644
--- a/java/src/com/android/inputmethod/latin/personalization/UserHistoryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/personalization/UserHistoryDictionary.java
@@ -22,7 +22,6 @@ import com.android.inputmethod.annotations.UsedForTesting;
 import com.android.inputmethod.latin.Constants;
 import com.android.inputmethod.latin.Dictionary;
 import com.android.inputmethod.latin.ExpandableBinaryDictionary;
-import com.android.inputmethod.latin.PrevWordsInfo;
 
 import java.io.File;
 import java.util.Locale;
@@ -53,32 +52,29 @@ public class UserHistoryDictionary extends DecayingExpandableBinaryDictionaryBas
     }
 
     /**
-     * Add a word to the user history dictionary.
+     * Pair will be added to the user history dictionary.
      *
-     * @param userHistoryDictionary the user history dictionary
-     * @param prevWordsInfo the information of previous words
-     * @param word the word the user inputted
-     * @param isValid whether the word is valid or not
-     * @param timestamp the timestamp when the word has been inputted
+     * The first word may be null. That means we don't know the context, in other words,
+     * it's only a unigram. The first word may also be an empty string : this means start
+     * context, as in beginning of a sentence for example.
+     * The second word may not be null (a NullPointerException would be thrown).
      */
     public static void addToDictionary(final ExpandableBinaryDictionary userHistoryDictionary,
-            final PrevWordsInfo prevWordsInfo, final String word, final boolean isValid,
-            final int timestamp) {
-        final String prevWord = prevWordsInfo.mPrevWord;
-        if (word.length() >= Constants.DICTIONARY_MAX_WORD_LENGTH ||
-                (prevWord != null && prevWord.length() >= Constants.DICTIONARY_MAX_WORD_LENGTH)) {
+            final String word0, final String word1, final boolean isValid, final int timestamp) {
+        if (word1.length() >= Constants.DICTIONARY_MAX_WORD_LENGTH ||
+                (word0 != null && word0.length() >= Constants.DICTIONARY_MAX_WORD_LENGTH)) {
             return;
         }
         final int frequency = isValid ?
                 FREQUENCY_FOR_WORDS_IN_DICTS : FREQUENCY_FOR_WORDS_NOT_IN_DICTS;
-        userHistoryDictionary.addUnigramEntry(word, frequency, null /* shortcutTarget */,
+        userHistoryDictionary.addWordDynamically(word1, frequency, null /* shortcutTarget */,
                 0 /* shortcutFreq */, false /* isNotAWord */, false /* isBlacklisted */, timestamp);
         // Do not insert a word as a bigram of itself
-        if (word.equals(prevWord)) {
+        if (word1.equals(word0)) {
             return;
         }
-        if (null != prevWord) {
-            userHistoryDictionary.addNgramEntry(prevWordsInfo, word, frequency, timestamp);
+        if (null != word0) {
+            userHistoryDictionary.addBigramDynamically(word0, word1, frequency, timestamp);
         }
     }
 }
diff --git a/java/src/com/android/inputmethod/latin/utils/DistracterFilter.java b/java/src/com/android/inputmethod/latin/utils/DistracterFilter.java
index 9ea7e217e..a21953259 100644
--- a/java/src/com/android/inputmethod/latin/utils/DistracterFilter.java
+++ b/java/src/com/android/inputmethod/latin/utils/DistracterFilter.java
@@ -114,7 +114,7 @@ public class DistracterFilter {
         final int[] codePoints = StringUtils.toCodePointArray(testedWord);
         final int[] coordinates;
         coordinates = mKeyboard.getCoordinates(codePoints);
-        composer.setComposingWord(codePoints, coordinates, prevWordsInfo);
+        composer.setComposingWord(codePoints, coordinates, prevWordsInfo.mPrevWord);
 
         final int trailingSingleQuotesCount = StringUtils.getTrailingSingleQuotesCount(testedWord);
         final String consideredWord = trailingSingleQuotesCount > 0 ?