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diff --git a/java/src/com/android/inputmethod/latin/personalization/DynamicPersonalizationDictionaryWriter.java b/java/src/com/android/inputmethod/latin/personalization/DynamicPersonalizationDictionaryWriter.java
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+++ b/java/src/com/android/inputmethod/latin/personalization/DynamicPersonalizationDictionaryWriter.java
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+/*
+ * Copyright (C) 2013 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 com.android.inputmethod.latin.personalization;
+
+import android.content.Context;
+
+import com.android.inputmethod.keyboard.ProximityInfo;
+import com.android.inputmethod.latin.AbstractDictionaryWriter;
+import com.android.inputmethod.latin.ExpandableDictionary;
+import com.android.inputmethod.latin.WordComposer;
+import com.android.inputmethod.latin.ExpandableDictionary.NextWord;
+import com.android.inputmethod.latin.SuggestedWords.SuggestedWordInfo;
+import com.android.inputmethod.latin.makedict.DictEncoder;
+import com.android.inputmethod.latin.makedict.FormatSpec;
+import com.android.inputmethod.latin.makedict.UnsupportedFormatException;
+import com.android.inputmethod.latin.utils.UserHistoryDictIOUtils;
+import com.android.inputmethod.latin.utils.UserHistoryDictIOUtils.BigramDictionaryInterface;
+import com.android.inputmethod.latin.utils.UserHistoryForgettingCurveUtils;
+import com.android.inputmethod.latin.utils.UserHistoryForgettingCurveUtils.ForgettingCurveParams;
+
+import java.io.IOException;
+import java.util.ArrayList;
+
+// Currently this class is used to implement dynamic prodiction dictionary.
+// TODO: Move to native code.
+public class DynamicPersonalizationDictionaryWriter extends AbstractDictionaryWriter {
+    private static final String TAG = DynamicPersonalizationDictionaryWriter.class.getSimpleName();
+    /** Maximum number of pairs. Pruning will start when databases goes above this number. */
+    public static final int MAX_HISTORY_BIGRAMS = 10000;
+
+    /** Any pair being typed or picked */
+    private static final int FREQUENCY_FOR_TYPED = 2;
+
+    private static final int BINARY_DICT_VERSION = 3;
+    private static final FormatSpec.FormatOptions FORMAT_OPTIONS =
+            new FormatSpec.FormatOptions(BINARY_DICT_VERSION, true /* supportsDynamicUpdate */);
+
+    private final UserHistoryDictionaryBigramList mBigramList =
+            new UserHistoryDictionaryBigramList();
+    private final ExpandableDictionary mExpandableDictionary;
+
+    public DynamicPersonalizationDictionaryWriter(final Context context, final String dictType) {
+        super(context, dictType);
+        mExpandableDictionary = new ExpandableDictionary(context, dictType);
+    }
+
+    @Override
+    public void clear() {
+        mBigramList.evictAll();
+        mExpandableDictionary.clearDictionary();
+    }
+
+    /**
+     * Adds a word unigram to the fusion dictionary. Call updateBinaryDictionary when all changes
+     * are done to update the binary dictionary.
+     */
+    @Override
+    public void addUnigramWord(final String word, final String shortcutTarget, final int frequency,
+            final boolean isNotAWord) {
+        mExpandableDictionary.addWord(word, shortcutTarget, frequency);
+        mBigramList.addBigram(null, word, (byte)frequency);
+    }
+
+    @Override
+    public void addBigramWords(final String word0, final String word1, final int frequency,
+            final boolean isValid, final long lastModifiedTime) {
+        if (lastModifiedTime > 0) {
+            mExpandableDictionary.setBigramAndGetFrequency(word0, word1,
+                    new ForgettingCurveParams(frequency, System.currentTimeMillis(),
+                            lastModifiedTime));
+            mBigramList.addBigram(word0, word1, (byte)frequency);
+        } else {
+            mExpandableDictionary.setBigramAndGetFrequency(word0, word1,
+                    new ForgettingCurveParams(isValid));
+            mBigramList.addBigram(word0, word1, (byte)frequency);
+        }
+    }
+
+    @Override
+    public void removeBigramWords(final String word0, final String word1) {
+        if (mBigramList.removeBigram(word0, word1)) {
+            mExpandableDictionary.removeBigram(word0, word1);
+        }
+    }
+
+    @Override
+    protected void writeDictionary(final DictEncoder dictEncoder)
+            throws IOException, UnsupportedFormatException {
+        UserHistoryDictIOUtils.writeDictionary(dictEncoder,
+                new FrequencyProvider(mBigramList, mExpandableDictionary), mBigramList,
+                        FORMAT_OPTIONS);
+    }
+
+    private static class FrequencyProvider implements BigramDictionaryInterface {
+        final private UserHistoryDictionaryBigramList mBigramList;
+        final private ExpandableDictionary mExpandableDictionary;
+
+        public FrequencyProvider(final UserHistoryDictionaryBigramList bigramList,
+                final ExpandableDictionary expandableDictionary) {
+            mBigramList = bigramList;
+            mExpandableDictionary = expandableDictionary;
+        }
+        @Override
+        public int getFrequency(final String word0, final String word1) {
+            final int freq;
+            if (word0 == null) { // unigram
+                freq = FREQUENCY_FOR_TYPED;
+            } else { // bigram
+                final NextWord nw = mExpandableDictionary.getBigramWord(word0, word1);
+                if (nw != null) {
+                    final ForgettingCurveParams forgettingCurveParams = nw.getFcParams();
+                    final byte prevFc = mBigramList.getBigrams(word0).get(word1);
+                    final byte fc = forgettingCurveParams.getFc();
+                    final boolean isValid = forgettingCurveParams.isValid();
+                    if (prevFc > 0 && prevFc == fc) {
+                        freq = fc & 0xFF;
+                    } else if (UserHistoryForgettingCurveUtils.
+                            needsToSave(fc, isValid, mBigramList.size() <= MAX_HISTORY_BIGRAMS)) {
+                        freq = fc & 0xFF;
+                    } else {
+                        // Delete this entry
+                        freq = -1;
+                    }
+                } else {
+                    // Delete this entry
+                    freq = -1;
+                }
+            }
+            return freq;
+        }
+    }
+
+    @Override
+    public ArrayList<SuggestedWordInfo> getSuggestions(final WordComposer composer,
+            final String prevWord, final ProximityInfo proximityInfo,
+            boolean blockOffensiveWords) {
+        return mExpandableDictionary.getSuggestions(composer, prevWord, proximityInfo,
+                blockOffensiveWords);
+    }
+
+    @Override
+    public boolean isValidWord(final String word) {
+        return mExpandableDictionary.isValidWord(word);
+    }
+}