/*
 * Copyright (C) 2012 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.makedict;

import com.android.inputmethod.annotations.UsedForTesting;
import com.android.inputmethod.latin.Constants;
import com.android.inputmethod.latin.makedict.BinaryDictInputOutput.CharEncoding;
import com.android.inputmethod.latin.makedict.BinaryDictInputOutput.FusionDictionaryBufferInterface;
import com.android.inputmethod.latin.makedict.FormatSpec.FileHeader;
import com.android.inputmethod.latin.makedict.FormatSpec.FormatOptions;
import com.android.inputmethod.latin.makedict.FusionDictionary.CharGroup;
import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.channels.FileChannel;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.Map;
import java.util.Stack;

public final class BinaryDictIOUtils {
    private static final boolean DBG = false;
    private static final int MSB24 = 0x800000;
    private static final int SINT24_MAX = 0x7FFFFF;
    private static final int MAX_JUMPS = 10000;

    private BinaryDictIOUtils() {
        // This utility class is not publicly instantiable.
    }

    private static final class Position {
        public static final int NOT_READ_GROUPCOUNT = -1;

        public int mAddress;
        public int mNumOfCharGroup;
        public int mPosition;
        public int mLength;

        public Position(int address, int length) {
            mAddress = address;
            mLength = length;
            mNumOfCharGroup = NOT_READ_GROUPCOUNT;
        }
    }

    /**
     * Tours all node without recursive call.
     */
    private static void readUnigramsAndBigramsBinaryInner(
            final FusionDictionaryBufferInterface buffer, final int headerSize,
            final Map<Integer, String> words, final Map<Integer, Integer> frequencies,
            final Map<Integer, ArrayList<PendingAttribute>> bigrams,
            final FormatOptions formatOptions) {
        int[] pushedChars = new int[FormatSpec.MAX_WORD_LENGTH + 1];

        Stack<Position> stack = new Stack<Position>();
        int index = 0;

        Position initPos = new Position(headerSize, 0);
        stack.push(initPos);

        while (!stack.empty()) {
            Position p = stack.peek();

            if (DBG) {
                MakedictLog.d("read: address=" + p.mAddress + ", numOfCharGroup=" +
                        p.mNumOfCharGroup + ", position=" + p.mPosition + ", length=" + p.mLength);
            }

            if (buffer.position() != p.mAddress) buffer.position(p.mAddress);
            if (index != p.mLength) index = p.mLength;

            if (p.mNumOfCharGroup == Position.NOT_READ_GROUPCOUNT) {
                p.mNumOfCharGroup = BinaryDictInputOutput.readCharGroupCount(buffer);
                p.mAddress += BinaryDictInputOutput.getGroupCountSize(p.mNumOfCharGroup);
                p.mPosition = 0;
            }
            if (p.mNumOfCharGroup == 0) {
                stack.pop();
                continue;
            }
            CharGroupInfo info = BinaryDictInputOutput.readCharGroup(buffer,
                    p.mAddress - headerSize, formatOptions);
            for (int i = 0; i < info.mCharacters.length; ++i) {
                pushedChars[index++] = info.mCharacters[i];
            }
            p.mPosition++;

            final boolean isMovedGroup = BinaryDictInputOutput.isMovedGroup(info.mFlags,
                    formatOptions);
            final boolean isDeletedGroup = BinaryDictInputOutput.isDeletedGroup(info.mFlags,
                    formatOptions);
            if (!isMovedGroup && !isDeletedGroup
                    && info.mFrequency != FusionDictionary.CharGroup.NOT_A_TERMINAL) {// found word
                words.put(info.mOriginalAddress, new String(pushedChars, 0, index));
                frequencies.put(info.mOriginalAddress, info.mFrequency);
                if (info.mBigrams != null) bigrams.put(info.mOriginalAddress, info.mBigrams);
            }

            if (p.mPosition == p.mNumOfCharGroup) {
                if (formatOptions.mSupportsDynamicUpdate) {
                    final int forwardLinkAddress = buffer.readUnsignedInt24();
                    if (forwardLinkAddress != FormatSpec.NO_FORWARD_LINK_ADDRESS) {
                        // the node has a forward link.
                        p.mNumOfCharGroup = Position.NOT_READ_GROUPCOUNT;
                        p.mAddress = forwardLinkAddress;
                    } else {
                        stack.pop();
                    }
                } else {
                    stack.pop();
                }
            } else {
                // the node has more groups.
                p.mAddress = buffer.position();
            }

            if (!isMovedGroup && BinaryDictInputOutput.hasChildrenAddress(info.mChildrenAddress)) {
                Position childrenPos = new Position(info.mChildrenAddress + headerSize, index);
                stack.push(childrenPos);
            }
        }
    }

    /**
     * Reads unigrams and bigrams from the binary file.
     * Doesn't make the memory representation of the dictionary.
     *
     * @param buffer the buffer to read.
     * @param words the map to store the address as a key and the word as a value.
     * @param frequencies the map to store the address as a key and the frequency as a value.
     * @param bigrams the map to store the address as a key and the list of address as a value.
     * @throws IOException
     * @throws UnsupportedFormatException
     */
    public static void readUnigramsAndBigramsBinary(final FusionDictionaryBufferInterface buffer,
            final Map<Integer, String> words, final Map<Integer, Integer> frequencies,
            final Map<Integer, ArrayList<PendingAttribute>> bigrams) throws IOException,
            UnsupportedFormatException {
        // Read header
        final FileHeader header = BinaryDictInputOutput.readHeader(buffer);
        readUnigramsAndBigramsBinaryInner(buffer, header.mHeaderSize, words, frequencies, bigrams,
                header.mFormatOptions);
    }

    /**
     * Gets the address of the last CharGroup of the exact matching word in the dictionary.
     * If no match is found, returns NOT_VALID_WORD.
     *
     * @param buffer the buffer to read.
     * @param word the word we search for.
     * @return the address of the terminal node.
     * @throws IOException
     * @throws UnsupportedFormatException
     */
    @UsedForTesting
    public static int getTerminalPosition(final FusionDictionaryBufferInterface buffer,
            final String word) throws IOException, UnsupportedFormatException {
        if (word == null) return FormatSpec.NOT_VALID_WORD;
        if (buffer.position() != 0) buffer.position(0);

        final FileHeader header = BinaryDictInputOutput.readHeader(buffer);
        int wordPos = 0;
        final int wordLen = word.codePointCount(0, word.length());
        for (int depth = 0; depth < Constants.Dictionary.MAX_WORD_LENGTH; ++depth) {
            if (wordPos >= wordLen) return FormatSpec.NOT_VALID_WORD;

            do {
                final int charGroupCount = BinaryDictInputOutput.readCharGroupCount(buffer);
                boolean foundNextCharGroup = false;
                for (int i = 0; i < charGroupCount; ++i) {
                    final int charGroupPos = buffer.position();
                    final CharGroupInfo currentInfo = BinaryDictInputOutput.readCharGroup(buffer,
                            buffer.position(), header.mFormatOptions);
                    final boolean isMovedGroup =
                            BinaryDictInputOutput.isMovedGroup(currentInfo.mFlags,
                                    header.mFormatOptions);
                    final boolean isDeletedGroup =
                            BinaryDictInputOutput.isDeletedGroup(currentInfo.mFlags,
                                    header.mFormatOptions);
                    if (isMovedGroup) continue;
                    boolean same = true;
                    for (int p = 0, j = word.offsetByCodePoints(0, wordPos);
                            p < currentInfo.mCharacters.length;
                            ++p, j = word.offsetByCodePoints(j, 1)) {
                        if (wordPos + p >= wordLen
                                || word.codePointAt(j) != currentInfo.mCharacters[p]) {
                            same = false;
                            break;
                        }
                    }

                    if (same) {
                        // found the group matches the word.
                        if (wordPos + currentInfo.mCharacters.length == wordLen) {
                            if (currentInfo.mFrequency == CharGroup.NOT_A_TERMINAL
                                    || isDeletedGroup) {
                                return FormatSpec.NOT_VALID_WORD;
                            } else {
                                return charGroupPos;
                            }
                        }
                        wordPos += currentInfo.mCharacters.length;
                        if (currentInfo.mChildrenAddress == FormatSpec.NO_CHILDREN_ADDRESS) {
                            return FormatSpec.NOT_VALID_WORD;
                        }
                        foundNextCharGroup = true;
                        buffer.position(currentInfo.mChildrenAddress);
                        break;
                    }
                }

                // If we found the next char group, it is under the file pointer.
                // But if not, we are at the end of this node so we expect to have
                // a forward link address that we need to consult and possibly resume
                // search on the next node in the linked list.
                if (foundNextCharGroup) break;
                if (!header.mFormatOptions.mSupportsDynamicUpdate) {
                    return FormatSpec.NOT_VALID_WORD;
                }

                final int forwardLinkAddress = buffer.readUnsignedInt24();
                if (forwardLinkAddress == FormatSpec.NO_FORWARD_LINK_ADDRESS) {
                    return FormatSpec.NOT_VALID_WORD;
                }
                buffer.position(forwardLinkAddress);
            } while(true);
        }
        return FormatSpec.NOT_VALID_WORD;
    }

    private static int markAsDeleted(final int flags) {
        return (flags & (~FormatSpec.MASK_GROUP_ADDRESS_TYPE)) | FormatSpec.FLAG_IS_DELETED;
    }

    /**
     * Delete the word from the binary file.
     *
     * @param buffer the buffer to write.
     * @param word the word we delete
     * @throws IOException
     * @throws UnsupportedFormatException
     */
    @UsedForTesting
    public static void deleteWord(final FusionDictionaryBufferInterface buffer,
            final String word) throws IOException, UnsupportedFormatException {
        buffer.position(0);
        final FileHeader header = BinaryDictInputOutput.readHeader(buffer);
        final int wordPosition = getTerminalPosition(buffer, word);
        if (wordPosition == FormatSpec.NOT_VALID_WORD) return;

        buffer.position(wordPosition);
        final int flags = buffer.readUnsignedByte();
        buffer.position(wordPosition);
        buffer.put((byte)markAsDeleted(flags));
    }

    /**
     * @return the size written, in bytes. Always 3 bytes.
     */
    private static int writeSInt24ToBuffer(final FusionDictionaryBufferInterface buffer,
            final int value) {
        final int absValue = Math.abs(value);
        buffer.put((byte)(((value < 0 ? 0x80 : 0) | (absValue >> 16)) & 0xFF));
        buffer.put((byte)((absValue >> 8) & 0xFF));
        buffer.put((byte)(absValue & 0xFF));
        return 3;
    }

    /**
     * @return the size written, in bytes. Always 3 bytes.
     */
    private static int writeSInt24ToStream(final OutputStream destination, final int value)
            throws IOException {
        final int absValue = Math.abs(value);
        destination.write((byte)(((value < 0 ? 0x80 : 0) | (absValue >> 16)) & 0xFF));
        destination.write((byte)((absValue >> 8) & 0xFF));
        destination.write((byte)(absValue & 0xFF));
        return 3;
    }

    /**
     * @return the size written, in bytes. 1, 2, or 3 bytes.
     */
    private static int writeVariableAddress(final OutputStream destination, final int value)
            throws IOException {
        switch (BinaryDictInputOutput.getByteSize(value)) {
        case 1:
            destination.write((byte)value);
            break;
        case 2:
            destination.write((byte)(0xFF & (value >> 8)));
            destination.write((byte)(0xFF & value));
            break;
        case 3:
            destination.write((byte)(0xFF & (value >> 16)));
            destination.write((byte)(0xFF & (value >> 8)));
            destination.write((byte)(0xFF & value));
            break;
        }
        return BinaryDictInputOutput.getByteSize(value);
    }

    /**
     * Update a parent address in a CharGroup that is referred to by groupOriginAddress.
     *
     * @param buffer the buffer to write.
     * @param groupOriginAddress the address of the group.
     * @param newParentAddress the absolute address of the parent.
     * @param formatOptions file format options.
     */
    public static void updateParentAddress(final FusionDictionaryBufferInterface buffer,
            final int groupOriginAddress, final int newParentAddress,
            final FormatOptions formatOptions) {
        final int originalPosition = buffer.position();
        buffer.position(groupOriginAddress);
        if (!formatOptions.mSupportsDynamicUpdate) {
            throw new RuntimeException("this file format does not support parent addresses");
        }
        final int flags = buffer.readUnsignedByte();
        if (BinaryDictInputOutput.isMovedGroup(flags, formatOptions)) {
            // if the group is moved, the parent address is stored in the destination group.
            // We are guaranteed to process the destination group later, so there is no need to
            // update anything here.
            buffer.position(originalPosition);
            return;
        }
        if (DBG) {
            MakedictLog.d("update parent address flags=" + flags + ", " + groupOriginAddress);
        }
        final int parentOffset = newParentAddress - groupOriginAddress;
        writeSInt24ToBuffer(buffer, parentOffset);
        buffer.position(originalPosition);
    }

    private static void skipCharGroup(final FusionDictionaryBufferInterface buffer,
            final FormatOptions formatOptions) {
        final int flags = buffer.readUnsignedByte();
        BinaryDictInputOutput.readParentAddress(buffer, formatOptions);
        skipString(buffer, (flags & FormatSpec.FLAG_HAS_MULTIPLE_CHARS) != 0);
        BinaryDictInputOutput.readChildrenAddress(buffer, flags, formatOptions);
        if ((flags & FormatSpec.FLAG_IS_TERMINAL) != 0) buffer.readUnsignedByte();
        if ((flags & FormatSpec.FLAG_HAS_SHORTCUT_TARGETS) != 0) {
            final int shortcutsSize = buffer.readUnsignedShort();
            buffer.position(buffer.position() + shortcutsSize
                    - FormatSpec.GROUP_SHORTCUT_LIST_SIZE_SIZE);
        }
        if ((flags & FormatSpec.FLAG_HAS_BIGRAMS) != 0) {
            int bigramCount = 0;
            while (bigramCount++ < FormatSpec.MAX_BIGRAMS_IN_A_GROUP) {
                final int bigramFlags = buffer.readUnsignedByte();
                switch (bigramFlags & FormatSpec.MASK_ATTRIBUTE_ADDRESS_TYPE) {
                    case FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE:
                        buffer.readUnsignedByte();
                        break;
                    case FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_TWOBYTES:
                        buffer.readUnsignedShort();
                        break;
                    case FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_THREEBYTES:
                        buffer.readUnsignedInt24();
                        break;
                }
                if ((bigramFlags & FormatSpec.FLAG_ATTRIBUTE_HAS_NEXT) == 0) break;
            }
            if (bigramCount >= FormatSpec.MAX_BIGRAMS_IN_A_GROUP) {
                throw new RuntimeException("Too many bigrams in a group.");
            }
        }
    }

    /**
     * Update parent addresses in a Node that is referred to by nodeOriginAddress.
     *
     * @param buffer the buffer to be modified.
     * @param nodeOriginAddress the address of a modified Node.
     * @param newParentAddress the address to be written.
     * @param formatOptions file format options.
     */
    public static void updateParentAddresses(final FusionDictionaryBufferInterface buffer,
            final int nodeOriginAddress, final int newParentAddress,
            final FormatOptions formatOptions) {
        final int originalPosition = buffer.position();
        buffer.position(nodeOriginAddress);
        do {
            final int count = BinaryDictInputOutput.readCharGroupCount(buffer);
            for (int i = 0; i < count; ++i) {
                updateParentAddress(buffer, buffer.position(), newParentAddress, formatOptions);
                skipCharGroup(buffer, formatOptions);
            }
            final int forwardLinkAddress = buffer.readUnsignedInt24();
            buffer.position(forwardLinkAddress);
        } while (formatOptions.mSupportsDynamicUpdate
                && buffer.position() != FormatSpec.NO_FORWARD_LINK_ADDRESS);
        buffer.position(originalPosition);
    }

    private static void skipString(final FusionDictionaryBufferInterface buffer,
            final boolean hasMultipleChars) {
        if (hasMultipleChars) {
            int character = CharEncoding.readChar(buffer);
            while (character != FormatSpec.INVALID_CHARACTER) {
                character = CharEncoding.readChar(buffer);
            }
        } else {
            CharEncoding.readChar(buffer);
        }
    }

    /**
     * Write a string to a stream.
     *
     * @param destination the stream to write.
     * @param word the string to be written.
     * @return the size written, in bytes.
     * @throws IOException
     */
    private static int writeString(final OutputStream destination, final String word)
            throws IOException {
        int size = 0;
        final int length = word.length();
        for (int i = 0; i < length; i = word.offsetByCodePoints(i, 1)) {
            final int codePoint = word.codePointAt(i);
            if (CharEncoding.getCharSize(codePoint) == 1) {
                destination.write((byte)codePoint);
                size++;
            } else {
                destination.write((byte)(0xFF & (codePoint >> 16)));
                destination.write((byte)(0xFF & (codePoint >> 8)));
                destination.write((byte)(0xFF & codePoint));
                size += 3;
            }
        }
        destination.write((byte)FormatSpec.GROUP_CHARACTERS_TERMINATOR);
        size += FormatSpec.GROUP_TERMINATOR_SIZE;
        return size;
    }

    /**
     * Update a children address in a CharGroup that is addressed by groupOriginAddress.
     *
     * @param buffer the buffer to write.
     * @param groupOriginAddress the address of the group.
     * @param newChildrenAddress the absolute address of the child.
     * @param formatOptions file format options.
     */
    public static void updateChildrenAddress(final FusionDictionaryBufferInterface buffer,
            final int groupOriginAddress, final int newChildrenAddress,
            final FormatOptions formatOptions) {
        final int originalPosition = buffer.position();
        buffer.position(groupOriginAddress);
        final int flags = buffer.readUnsignedByte();
        final int parentAddress = BinaryDictInputOutput.readParentAddress(buffer, formatOptions);
        skipString(buffer, (flags & FormatSpec.FLAG_HAS_MULTIPLE_CHARS) != 0);
        if ((flags & FormatSpec.FLAG_IS_TERMINAL) != 0) buffer.readUnsignedByte();
        final int childrenOffset = newChildrenAddress == FormatSpec.NO_CHILDREN_ADDRESS
                ? FormatSpec.NO_CHILDREN_ADDRESS : newChildrenAddress - buffer.position();
        writeSInt24ToBuffer(buffer, childrenOffset);
        buffer.position(originalPosition);
    }

    /**
     * Write a char group to an output stream.
     * A char group is an in-memory representation of a node in trie.
     * A char group info is an on-disk representation of a node.
     *
     * @param destination the stream to write.
     * @param info the char group info to be written.
     * @return the size written, in bytes.
     */
    public static int writeCharGroup(final OutputStream destination, final CharGroupInfo info)
            throws IOException {
        int size = FormatSpec.GROUP_FLAGS_SIZE;
        destination.write((byte)info.mFlags);
        final int parentOffset = info.mParentAddress == FormatSpec.NO_PARENT_ADDRESS ?
                FormatSpec.NO_PARENT_ADDRESS : info.mParentAddress - info.mOriginalAddress;
        size += writeSInt24ToStream(destination, parentOffset);

        for (int i = 0; i < info.mCharacters.length; ++i) {
            if (CharEncoding.getCharSize(info.mCharacters[i]) == 1) {
                destination.write((byte)info.mCharacters[i]);
                size++;
            } else {
                size += writeSInt24ToStream(destination, info.mCharacters[i]);
            }
        }
        if (info.mCharacters.length > 1) {
            destination.write((byte)FormatSpec.GROUP_CHARACTERS_TERMINATOR);
            size++;
        }

        if ((info.mFlags & FormatSpec.FLAG_IS_TERMINAL) != 0) {
            destination.write((byte)info.mFrequency);
            size++;
        }

        if (DBG) {
            MakedictLog.d("writeCharGroup origin=" + info.mOriginalAddress + ", size=" + size
                    + ", child=" + info.mChildrenAddress + ", characters ="
                    + new String(info.mCharacters, 0, info.mCharacters.length));
        }
        final int childrenOffset = info.mChildrenAddress == FormatSpec.NO_CHILDREN_ADDRESS ?
                0 : info.mChildrenAddress - (info.mOriginalAddress + size);
        writeSInt24ToStream(destination, childrenOffset);
        size += FormatSpec.SIGNED_CHILDREN_ADDRESS_SIZE;

        if (info.mShortcutTargets != null && info.mShortcutTargets.size() > 0) {
            final int shortcutListSize =
                    BinaryDictInputOutput.getShortcutListSize(info.mShortcutTargets);
            destination.write((byte)(shortcutListSize >> 8));
            destination.write((byte)(shortcutListSize & 0xFF));
            size += 2;
            final Iterator<WeightedString> shortcutIterator = info.mShortcutTargets.iterator();
            while (shortcutIterator.hasNext()) {
                final WeightedString target = shortcutIterator.next();
                destination.write((byte)BinaryDictInputOutput.makeShortcutFlags(
                        shortcutIterator.hasNext(), target.mFrequency));
                size++;
                size += writeString(destination, target.mWord);
            }
        }

        if (info.mBigrams != null) {
            // TODO: Consolidate this code with the code that computes the size of the bigram list
            //        in BinaryDictionaryInputOutput#computeActualNodeSize
            for (int i = 0; i < info.mBigrams.size(); ++i) {

                final int bigramFrequency = info.mBigrams.get(i).mFrequency;
                int bigramFlags = (i < info.mBigrams.size() - 1)
                        ? FormatSpec.FLAG_ATTRIBUTE_HAS_NEXT : 0;
                size++;
                final int bigramOffset = info.mBigrams.get(i).mAddress - (info.mOriginalAddress
                        + size);
                bigramFlags |= (bigramOffset < 0) ? FormatSpec.FLAG_ATTRIBUTE_OFFSET_NEGATIVE : 0;
                switch (BinaryDictInputOutput.getByteSize(bigramOffset)) {
                case 1:
                    bigramFlags |= FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE;
                    break;
                case 2:
                    bigramFlags |= FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_TWOBYTES;
                    break;
                case 3:
                    bigramFlags |= FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_THREEBYTES;
                    break;
                }
                bigramFlags |= bigramFrequency & FormatSpec.FLAG_ATTRIBUTE_FREQUENCY;
                destination.write((byte)bigramFlags);
                size += writeVariableAddress(destination, Math.abs(bigramOffset));
            }
        }
        return size;
    }

    @SuppressWarnings("unused")
    private static void updateForwardLink(final FusionDictionaryBufferInterface buffer,
            final int nodeOriginAddress, final int newNodeAddress,
            final FormatOptions formatOptions) {
        buffer.position(nodeOriginAddress);
        int jumpCount = 0;
        while (jumpCount++ < MAX_JUMPS) {
            final int count = BinaryDictInputOutput.readCharGroupCount(buffer);
            for (int i = 0; i < count; ++i) skipCharGroup(buffer, formatOptions);
            final int forwardLinkAddress = buffer.readUnsignedInt24();
            if (forwardLinkAddress == FormatSpec.NO_FORWARD_LINK_ADDRESS) {
                buffer.position(buffer.position() - FormatSpec.FORWARD_LINK_ADDRESS_SIZE);
                writeSInt24ToBuffer(buffer, newNodeAddress);
                return;
            }
            buffer.position(forwardLinkAddress);
        }
        if (DBG && jumpCount >= MAX_JUMPS) {
            throw new RuntimeException("too many jumps, probably a bug.");
        }
    }

    /**
     * Helper method to move a char group to the tail of the file.
     */
    private static int moveCharGroup(final OutputStream destination,
            final FusionDictionaryBufferInterface buffer, final CharGroupInfo info,
            final int nodeOriginAddress, final int oldGroupAddress,
            final FormatOptions formatOptions) throws IOException {
        updateParentAddress(buffer, oldGroupAddress, buffer.limit() + 1, formatOptions);
        buffer.position(oldGroupAddress);
        final int currentFlags = buffer.readUnsignedByte();
        buffer.position(oldGroupAddress);
        buffer.put((byte)(FormatSpec.FLAG_IS_MOVED | (currentFlags
                & (~FormatSpec.MASK_MOVE_AND_DELETE_FLAG))));
        int size = FormatSpec.GROUP_FLAGS_SIZE;
        updateForwardLink(buffer, nodeOriginAddress, buffer.limit(), formatOptions);
        size += writeNode(destination, new CharGroupInfo[] { info });
        return size;
    }

    /**
     * Compute the size of the char group.
     */
    private static int computeGroupSize(final CharGroupInfo info,
            final FormatOptions formatOptions) {
        int size = FormatSpec.GROUP_FLAGS_SIZE + FormatSpec.PARENT_ADDRESS_SIZE
                + BinaryDictInputOutput.getGroupCharactersSize(info.mCharacters)
                + BinaryDictInputOutput.getChildrenAddressSize(info.mFlags, formatOptions);
        if ((info.mFlags & FormatSpec.FLAG_IS_TERMINAL) != 0) {
            size += FormatSpec.GROUP_FREQUENCY_SIZE;
        }
        if (info.mShortcutTargets != null && !info.mShortcutTargets.isEmpty()) {
            size += BinaryDictInputOutput.getShortcutListSize(info.mShortcutTargets);
        }
        if (info.mBigrams != null) {
            for (final PendingAttribute attr : info.mBigrams) {
                size += FormatSpec.GROUP_FLAGS_SIZE;
                size += BinaryDictInputOutput.getByteSize(attr.mAddress);
            }
        }
        return size;
    }

    /**
     * Write a node to the stream.
     *
     * @param destination the stream to write.
     * @param infos groups to be written.
     * @return the size written, in bytes.
     * @throws IOException
     */
    private static int writeNode(final OutputStream destination, final CharGroupInfo[] infos)
            throws IOException {
        int size = BinaryDictInputOutput.getGroupCountSize(infos.length);
        switch (BinaryDictInputOutput.getGroupCountSize(infos.length)) {
            case 1:
                destination.write((byte)infos.length);
                break;
            case 2:
                destination.write((byte)(infos.length >> 8));
                destination.write((byte)(infos.length & 0xFF));
                break;
            default:
                throw new RuntimeException("Invalid group count size.");
        }
        for (final CharGroupInfo info : infos) size += writeCharGroup(destination, info);
        writeSInt24ToStream(destination, FormatSpec.NO_FORWARD_LINK_ADDRESS);
        return size + FormatSpec.FORWARD_LINK_ADDRESS_SIZE;
    }

    /**
     * Move a group that is referred to by oldGroupOrigin to the tail of the file.
     * And set the children address to the byte after the group.
     *
     * @param nodeOrigin the address of the tail of the file.
     * @param characters
     * @param length
     * @param flags
     * @param frequency
     * @param parentAddress
     * @param shortcutTargets
     * @param bigrams
     * @param destination the stream representing the tail of the file.
     * @param buffer the buffer representing the (constant-size) body of the file.
     * @param oldNodeOrigin
     * @param oldGroupOrigin
     * @param formatOptions
     * @return the size written, in bytes.
     * @throws IOException
     */
    private static int moveGroup(final int nodeOrigin, final int[] characters, final int length,
            final int flags, final int frequency, final int parentAddress,
            final ArrayList<WeightedString> shortcutTargets,
            final ArrayList<PendingAttribute> bigrams, final OutputStream destination,
            final FusionDictionaryBufferInterface buffer, final int oldNodeOrigin,
            final int oldGroupOrigin, final FormatOptions formatOptions) throws IOException {
        int size = 0;
        final int newGroupOrigin = nodeOrigin + 1;
        final int[] writtenCharacters = Arrays.copyOfRange(characters, 0, length);
        final CharGroupInfo tmpInfo = new CharGroupInfo(newGroupOrigin, -1 /* endAddress */,
                flags, writtenCharacters, frequency, parentAddress, FormatSpec.NO_CHILDREN_ADDRESS,
                shortcutTargets, bigrams);
        size = computeGroupSize(tmpInfo, formatOptions);
        final CharGroupInfo newInfo = new CharGroupInfo(newGroupOrigin, newGroupOrigin + size,
                flags, writtenCharacters, frequency, parentAddress,
                nodeOrigin + 1 + size + FormatSpec.FORWARD_LINK_ADDRESS_SIZE, shortcutTargets,
                bigrams);
        moveCharGroup(destination, buffer, newInfo, oldNodeOrigin, oldGroupOrigin, formatOptions);
        return 1 + size + FormatSpec.FORWARD_LINK_ADDRESS_SIZE;
    }

    /**
     * Insert a word into a binary dictionary.
     *
     * @param buffer
     * @param destination
     * @param word
     * @param frequency
     * @param bigramStrings
     * @param shortcuts
     * @throws IOException
     * @throws UnsupportedFormatException
     */
    // TODO: Support batch insertion.
    // TODO: Remove @UsedForTesting once UserHistoryDictionary is implemented by BinaryDictionary.
    @UsedForTesting
    public static void insertWord(final FusionDictionaryBufferInterface buffer,
            final OutputStream destination, final String word, final int frequency,
            final ArrayList<WeightedString> bigramStrings,
            final ArrayList<WeightedString> shortcuts, final boolean isNotAWord,
            final boolean isBlackListEntry)
                    throws IOException, UnsupportedFormatException {
        final ArrayList<PendingAttribute> bigrams = new ArrayList<PendingAttribute>();
        if (bigramStrings != null) {
            for (final WeightedString bigram : bigramStrings) {
                int position = getTerminalPosition(buffer, bigram.mWord);
                if (position == FormatSpec.NOT_VALID_WORD) {
                    // TODO: figure out what is the correct thing to do here.
                } else {
                    bigrams.add(new PendingAttribute(bigram.mFrequency, position));
                }
            }
        }

        final boolean isTerminal = true;
        final boolean hasBigrams = !bigrams.isEmpty();
        final boolean hasShortcuts = shortcuts != null && !shortcuts.isEmpty();

        // find the insert position of the word.
        if (buffer.position() != 0) buffer.position(0);
        final FileHeader header = BinaryDictInputOutput.readHeader(buffer);

        int wordPos = 0, address = buffer.position(), nodeOriginAddress = buffer.position();
        final int[] codePoints = FusionDictionary.getCodePoints(word);
        final int wordLen = codePoints.length;

        for (int depth = 0; depth < Constants.Dictionary.MAX_WORD_LENGTH; ++depth) {
            if (wordPos >= wordLen) break;
            nodeOriginAddress = buffer.position();
            int nodeParentAddress = -1;
            final int charGroupCount = BinaryDictInputOutput.readCharGroupCount(buffer);
            boolean foundNextGroup = false;

            for (int i = 0; i < charGroupCount; ++i) {
                address = buffer.position();
                final CharGroupInfo currentInfo = BinaryDictInputOutput.readCharGroup(buffer,
                        buffer.position(), header.mFormatOptions);
                final boolean isMovedGroup = BinaryDictInputOutput.isMovedGroup(currentInfo.mFlags,
                        header.mFormatOptions);
                if (isMovedGroup) continue;
                nodeParentAddress = (currentInfo.mParentAddress == FormatSpec.NO_PARENT_ADDRESS)
                        ? FormatSpec.NO_PARENT_ADDRESS : currentInfo.mParentAddress + address;
                boolean matched = true;
                for (int p = 0; p < currentInfo.mCharacters.length; ++p) {
                    if (wordPos + p >= wordLen) {
                        /*
                         * splitting
                         * before
                         *  abcd - ef
                         *
                         * insert "abc"
                         *
                         * after
                         *  abc - d - ef
                         */
                        final int newNodeAddress = buffer.limit();
                        final int flags = BinaryDictInputOutput.makeCharGroupFlags(p > 1,
                                isTerminal, 0, hasShortcuts, hasBigrams, false /* isNotAWord */,
                                false /* isBlackListEntry */, header.mFormatOptions);
                        int written = moveGroup(newNodeAddress, currentInfo.mCharacters, p, flags,
                                frequency, nodeParentAddress, shortcuts, bigrams, destination,
                                buffer, nodeOriginAddress, address, header.mFormatOptions);

                        final int[] characters2 = Arrays.copyOfRange(currentInfo.mCharacters, p,
                                currentInfo.mCharacters.length);
                        if (currentInfo.mChildrenAddress != FormatSpec.NO_CHILDREN_ADDRESS) {
                            updateParentAddresses(buffer, currentInfo.mChildrenAddress,
                                    newNodeAddress + written + 1, header.mFormatOptions);
                        }
                        final CharGroupInfo newInfo2 = new CharGroupInfo(
                                newNodeAddress + written + 1, -1 /* endAddress */,
                                currentInfo.mFlags, characters2, currentInfo.mFrequency,
                                newNodeAddress + 1, currentInfo.mChildrenAddress,
                                currentInfo.mShortcutTargets, currentInfo.mBigrams);
                        writeNode(destination, new CharGroupInfo[] { newInfo2 });
                        return;
                    } else if (codePoints[wordPos + p] != currentInfo.mCharacters[p]) {
                        if (p > 0) {
                            /*
                             * splitting
                             * before
                             *   ab - cd
                             *
                             * insert "ac"
                             *
                             * after
                             *   a - b - cd
                             *     |
                             *     - c
                             */

                            final int newNodeAddress = buffer.limit();
                            final int childrenAddress = currentInfo.mChildrenAddress;

                            // move prefix
                            final int prefixFlags = BinaryDictInputOutput.makeCharGroupFlags(p > 1,
                                    false /* isTerminal */, 0 /* childrenAddressSize*/,
                                    false /* hasShortcut */, false /* hasBigrams */,
                                    false /* isNotAWord */, false /* isBlackListEntry */,
                                    header.mFormatOptions);
                            int written = moveGroup(newNodeAddress, currentInfo.mCharacters, p,
                                    prefixFlags, -1 /* frequency */, nodeParentAddress, null, null,
                                    destination, buffer, nodeOriginAddress, address,
                                    header.mFormatOptions);

                            final int[] suffixCharacters = Arrays.copyOfRange(
                                    currentInfo.mCharacters, p, currentInfo.mCharacters.length);
                            if (currentInfo.mChildrenAddress != FormatSpec.NO_CHILDREN_ADDRESS) {
                                updateParentAddresses(buffer, currentInfo.mChildrenAddress,
                                        newNodeAddress + written + 1, header.mFormatOptions);
                            }
                            final int suffixFlags = BinaryDictInputOutput.makeCharGroupFlags(
                                    suffixCharacters.length > 1,
                                    (currentInfo.mFlags & FormatSpec.FLAG_IS_TERMINAL) != 0,
                                    0 /* childrenAddressSize */,
                                    (currentInfo.mFlags & FormatSpec.FLAG_HAS_SHORTCUT_TARGETS)
                                            != 0,
                                    (currentInfo.mFlags & FormatSpec.FLAG_HAS_BIGRAMS) != 0,
                                    isNotAWord, isBlackListEntry, header.mFormatOptions);
                            final CharGroupInfo suffixInfo = new CharGroupInfo(
                                    newNodeAddress + written + 1, -1 /* endAddress */, suffixFlags,
                                    suffixCharacters, currentInfo.mFrequency, newNodeAddress + 1,
                                    currentInfo.mChildrenAddress, currentInfo.mShortcutTargets,
                                    currentInfo.mBigrams);
                            written += computeGroupSize(suffixInfo, header.mFormatOptions) + 1;

                            final int[] newCharacters = Arrays.copyOfRange(codePoints, wordPos + p,
                                    codePoints.length);
                            final int flags = BinaryDictInputOutput.makeCharGroupFlags(
                                    newCharacters.length > 1, isTerminal,
                                    0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
                                    isNotAWord, isBlackListEntry, header.mFormatOptions);
                            final CharGroupInfo newInfo = new CharGroupInfo(
                                    newNodeAddress + written, -1 /* endAddress */, flags,
                                    newCharacters, frequency, newNodeAddress + 1,
                                    FormatSpec.NO_CHILDREN_ADDRESS, shortcuts, bigrams);
                            writeNode(destination, new CharGroupInfo[] { suffixInfo, newInfo });
                            return;
                        }
                        matched = false;
                        break;
                    }
                }

                if (matched) {
                    if (wordPos + currentInfo.mCharacters.length == wordLen) {
                        // the word exists in the dictionary.
                        // only update group.
                        final int newNodeAddress = buffer.limit();
                        final boolean hasMultipleChars = currentInfo.mCharacters.length > 1;
                        final int flags = BinaryDictInputOutput.makeCharGroupFlags(hasMultipleChars,
                                isTerminal, 0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
                                isNotAWord, isBlackListEntry, header.mFormatOptions);
                        final CharGroupInfo newInfo = new CharGroupInfo(newNodeAddress + 1,
                                -1 /* endAddress */, flags, currentInfo.mCharacters, frequency,
                                nodeParentAddress, currentInfo.mChildrenAddress, shortcuts,
                                bigrams);
                        moveCharGroup(destination, buffer, newInfo, nodeOriginAddress, address,
                                header.mFormatOptions);
                        return;
                    }
                    wordPos += currentInfo.mCharacters.length;
                    if (currentInfo.mChildrenAddress == FormatSpec.NO_CHILDREN_ADDRESS) {
                        /*
                         * found the prefix of the word.
                         * make new node and link to the node from this group.
                         *
                         * before
                         * ab - cd
                         *
                         * insert "abcde"
                         *
                         * after
                         * ab - cd - e
                         */
                        final int newNodeAddress = buffer.limit();
                        updateChildrenAddress(buffer, address, newNodeAddress,
                                header.mFormatOptions);
                        final int newGroupAddress = newNodeAddress + 1;
                        final boolean hasMultipleChars = (wordLen - wordPos) > 1;
                        final int flags = BinaryDictInputOutput.makeCharGroupFlags(hasMultipleChars,
                                isTerminal, 0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
                                isNotAWord, isBlackListEntry, header.mFormatOptions);
                        final int[] characters = Arrays.copyOfRange(codePoints, wordPos, wordLen);
                        final CharGroupInfo newInfo = new CharGroupInfo(newGroupAddress, -1, flags,
                                characters, frequency, address, FormatSpec.NO_CHILDREN_ADDRESS,
                                shortcuts, bigrams);
                        writeNode(destination, new CharGroupInfo[] { newInfo });
                        return;
                    }
                    buffer.position(currentInfo.mChildrenAddress);
                    foundNextGroup = true;
                    break;
                }
            }

            if (foundNextGroup) continue;

            // reached the end of the array.
            final int linkAddressPosition = buffer.position();
            int nextLink = buffer.readUnsignedInt24();
            if ((nextLink & MSB24) != 0) {
                nextLink = -(nextLink & SINT24_MAX);
            }
            if (nextLink == FormatSpec.NO_FORWARD_LINK_ADDRESS) {
                /*
                 * expand this node.
                 *
                 * before
                 * ab - cd
                 *
                 * insert "abef"
                 *
                 * after
                 * ab - cd
                 *    |
                 *    - ef
                 */

                // change the forward link address.
                final int newNodeAddress = buffer.limit();
                buffer.position(linkAddressPosition);
                writeSInt24ToBuffer(buffer, newNodeAddress);

                final int[] characters = Arrays.copyOfRange(codePoints, wordPos, wordLen);
                final int flags = BinaryDictInputOutput.makeCharGroupFlags(characters.length > 1,
                        isTerminal, 0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
                        isNotAWord, isBlackListEntry, header.mFormatOptions);
                final CharGroupInfo newInfo = new CharGroupInfo(newNodeAddress + 1,
                        -1 /* endAddress */, flags, characters, frequency, nodeParentAddress,
                        FormatSpec.NO_CHILDREN_ADDRESS, shortcuts, bigrams);
                writeNode(destination, new CharGroupInfo[]{ newInfo });
                return;
            } else {
                depth--;
                buffer.position(nextLink);
            }
        }
    }

    /**
     * Find a word from the buffer.
     *
     * @param buffer the buffer representing the body of the dictionary file.
     * @param word the word searched
     * @return the found group
     * @throws IOException
     * @throws UnsupportedFormatException
     */
    @UsedForTesting
    public static CharGroupInfo findWordFromBuffer(final FusionDictionaryBufferInterface buffer,
            final String word) throws IOException, UnsupportedFormatException {
        int position = getTerminalPosition(buffer, word);
        if (position != FormatSpec.NOT_VALID_WORD) {
            buffer.position(0);
            final FileHeader header = BinaryDictInputOutput.readHeader(buffer);
            buffer.position(position);
            return BinaryDictInputOutput.readCharGroup(buffer, position, header.mFormatOptions);
        }
        return null;
    }

    /**
     * Convenience method to read the header of a binary file.
     *
     * This is quite resource intensive - don't call when performance is critical.
     *
     * @param file The file to read.
     * @param offset The offset in the file where to start reading the data.
     * @param length The length of the data file.
     */
    private static final int HEADER_READING_BUFFER_SIZE = 16384;
    public static FileHeader getDictionaryFileHeader(
            final File file, final long offset, final long length)
            throws FileNotFoundException, IOException, UnsupportedFormatException {
        final byte[] buffer = new byte[HEADER_READING_BUFFER_SIZE];
        final FileInputStream inStream = new FileInputStream(file);
        try {
            inStream.read(buffer);
            final BinaryDictInputOutput.ByteBufferWrapper wrapper =
                    new BinaryDictInputOutput.ByteBufferWrapper(inStream.getChannel().map(
                            FileChannel.MapMode.READ_ONLY, offset, length));
            return BinaryDictInputOutput.readHeader(wrapper);
        } finally {
            inStream.close();
        }
    }

    public static FileHeader getDictionaryFileHeaderOrNull(final File file, final long offset,
            final long length) {
        try {
            final FileHeader header = getDictionaryFileHeader(file, offset, length);
            return header;
        } catch (UnsupportedFormatException e) {
            return null;
        } catch (IOException e) {
            return null;
        }
    }
}