/*
 * 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.makedict;

import com.android.inputmethod.annotations.UsedForTesting;
import com.android.inputmethod.latin.makedict.BinaryDictDecoderUtils.CharEncoding;
import com.android.inputmethod.latin.makedict.BinaryDictDecoderUtils.DictBuffer;
import com.android.inputmethod.latin.makedict.FormatSpec.FormatOptions;
import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;

import android.util.Log;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;

/**
 * An implementation of DictDecoder for version 2 binary dictionary.
 */
@UsedForTesting
public class Ver2DictDecoder extends AbstractDictDecoder {
    private static final String TAG = Ver2DictDecoder.class.getSimpleName();

    /**
     * A utility class for reading a PtNode.
     */
    protected static class PtNodeReader {
        private static ProbabilityInfo readProbabilityInfo(final DictBuffer dictBuffer) {
            // Ver2 dicts don't contain historical information.
            return new ProbabilityInfo(dictBuffer.readUnsignedByte());
        }

        protected static int readPtNodeOptionFlags(final DictBuffer dictBuffer) {
            return dictBuffer.readUnsignedByte();
        }

        protected static int readChildrenAddress(final DictBuffer dictBuffer,
                final int ptNodeFlags) {
            switch (ptNodeFlags & FormatSpec.MASK_CHILDREN_ADDRESS_TYPE) {
                case FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_ONEBYTE:
                    return dictBuffer.readUnsignedByte();
                case FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_TWOBYTES:
                    return dictBuffer.readUnsignedShort();
                case FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_THREEBYTES:
                    return dictBuffer.readUnsignedInt24();
                case FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_NOADDRESS:
                default:
                    return FormatSpec.NO_CHILDREN_ADDRESS;
            }
        }

        // Reads shortcuts and returns the read length.
        protected static int readShortcut(final DictBuffer dictBuffer,
                final ArrayList<WeightedString> shortcutTargets) {
            final int pointerBefore = dictBuffer.position();
            dictBuffer.readUnsignedShort(); // skip the size
            while (true) {
                final int targetFlags = dictBuffer.readUnsignedByte();
                final String word = CharEncoding.readString(dictBuffer);
                shortcutTargets.add(new WeightedString(word,
                        targetFlags & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_FREQUENCY));
                if (0 == (targetFlags & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_HAS_NEXT)) break;
            }
            return dictBuffer.position() - pointerBefore;
        }

        protected static int readBigramAddresses(final DictBuffer dictBuffer,
                final ArrayList<PendingAttribute> bigrams, final int baseAddress) {
            int readLength = 0;
            int bigramCount = 0;
            while (bigramCount++ < FormatSpec.MAX_BIGRAMS_IN_A_PTNODE) {
                final int bigramFlags = dictBuffer.readUnsignedByte();
                ++readLength;
                final int sign = 0 == (bigramFlags & FormatSpec.FLAG_BIGRAM_ATTR_OFFSET_NEGATIVE)
                        ? 1 : -1;
                int bigramAddress = baseAddress + readLength;
                switch (bigramFlags & FormatSpec.MASK_BIGRAM_ATTR_ADDRESS_TYPE) {
                    case FormatSpec.FLAG_BIGRAM_ATTR_ADDRESS_TYPE_ONEBYTE:
                        bigramAddress += sign * dictBuffer.readUnsignedByte();
                        readLength += 1;
                        break;
                    case FormatSpec.FLAG_BIGRAM_ATTR_ADDRESS_TYPE_TWOBYTES:
                        bigramAddress += sign * dictBuffer.readUnsignedShort();
                        readLength += 2;
                        break;
                    case FormatSpec.FLAG_BIGRAM_ATTR_ADDRESS_TYPE_THREEBYTES:
                        bigramAddress += sign * dictBuffer.readUnsignedInt24();
                        readLength += 3;
                        break;
                    default:
                        throw new RuntimeException("Has bigrams with no address");
                }
                bigrams.add(new PendingAttribute(
                        bigramFlags & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_FREQUENCY,
                        bigramAddress));
                if (0 == (bigramFlags & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_HAS_NEXT)) break;
            }
            return readLength;
        }
    }

    protected final File mDictionaryBinaryFile;
    private final DictionaryBufferFactory mBufferFactory;
    protected DictBuffer mDictBuffer;

    /* package */ Ver2DictDecoder(final File file, final int factoryFlag) {
        mDictionaryBinaryFile = file;
        mDictBuffer = null;

        if ((factoryFlag & MASK_DICTBUFFER) == USE_READONLY_BYTEBUFFER) {
            mBufferFactory = new DictionaryBufferFromReadOnlyByteBufferFactory();
        } else if ((factoryFlag  & MASK_DICTBUFFER) == USE_BYTEARRAY) {
            mBufferFactory = new DictionaryBufferFromByteArrayFactory();
        } else if ((factoryFlag & MASK_DICTBUFFER) == USE_WRITABLE_BYTEBUFFER) {
            mBufferFactory = new DictionaryBufferFromWritableByteBufferFactory();
        } else {
            mBufferFactory = new DictionaryBufferFromReadOnlyByteBufferFactory();
        }
    }

    /* package */ Ver2DictDecoder(final File file, final DictionaryBufferFactory factory) {
        mDictionaryBinaryFile = file;
        mBufferFactory = factory;
    }

    @Override
    public void openDictBuffer() throws FileNotFoundException, IOException {
        mDictBuffer = mBufferFactory.getDictionaryBuffer(mDictionaryBinaryFile);
    }

    @Override
    public boolean isDictBufferOpen() {
        return mDictBuffer != null;
    }

    /* package */ DictBuffer getDictBuffer() {
        return mDictBuffer;
    }

    @UsedForTesting
    /* package */ DictBuffer openAndGetDictBuffer() throws FileNotFoundException, IOException {
        openDictBuffer();
        return getDictBuffer();
    }

    @Override
    public DictionaryHeader readHeader() throws IOException, UnsupportedFormatException {
        if (mDictBuffer == null) {
            openDictBuffer();
        }
        final DictionaryHeader header = super.readHeader(mDictBuffer);
        final int version = header.mFormatOptions.mVersion;
        if (version != FormatSpec.VERSION2) {
            throw new UnsupportedFormatException("File header has a wrong version : " + version);
        }
        return header;
    }

    // TODO: Make this buffer multi thread safe.
    private final int[] mCharacterBuffer = new int[FormatSpec.MAX_WORD_LENGTH];
    @Override
    public PtNodeInfo readPtNode(final int ptNodePos, final FormatOptions options) {
        int addressPointer = ptNodePos;
        final int flags = PtNodeReader.readPtNodeOptionFlags(mDictBuffer);
        addressPointer += FormatSpec.PTNODE_FLAGS_SIZE;
        final int characters[];
        if (0 != (flags & FormatSpec.FLAG_HAS_MULTIPLE_CHARS)) {
            int index = 0;
            int character = CharEncoding.readChar(mDictBuffer);
            addressPointer += CharEncoding.getCharSize(character);
            while (FormatSpec.INVALID_CHARACTER != character) {
                // FusionDictionary is making sure that the length of the word is smaller than
                // MAX_WORD_LENGTH.
                // So we'll never write past the end of mCharacterBuffer.
                mCharacterBuffer[index++] = character;
                character = CharEncoding.readChar(mDictBuffer);
                addressPointer += CharEncoding.getCharSize(character);
            }
            characters = Arrays.copyOfRange(mCharacterBuffer, 0, index);
        } else {
            final int character = CharEncoding.readChar(mDictBuffer);
            addressPointer += CharEncoding.getCharSize(character);
            characters = new int[] { character };
        }
        final ProbabilityInfo probabilityInfo;
        if (0 != (FormatSpec.FLAG_IS_TERMINAL & flags)) {
            probabilityInfo = PtNodeReader.readProbabilityInfo(mDictBuffer);
            addressPointer += FormatSpec.PTNODE_FREQUENCY_SIZE;
        } else {
            probabilityInfo = null;
        }
        int childrenAddress = PtNodeReader.readChildrenAddress(mDictBuffer, flags);
        if (childrenAddress != FormatSpec.NO_CHILDREN_ADDRESS) {
            childrenAddress += addressPointer;
        }
        addressPointer += BinaryDictIOUtils.getChildrenAddressSize(flags, options);
        final ArrayList<WeightedString> shortcutTargets;
        if (0 != (flags & FormatSpec.FLAG_HAS_SHORTCUT_TARGETS)) {
            // readShortcut will add shortcuts to shortcutTargets.
            shortcutTargets = new ArrayList<WeightedString>();
            addressPointer += PtNodeReader.readShortcut(mDictBuffer, shortcutTargets);
        } else {
            shortcutTargets = null;
        }

        final ArrayList<PendingAttribute> bigrams;
        if (0 != (flags & FormatSpec.FLAG_HAS_BIGRAMS)) {
            bigrams = new ArrayList<PendingAttribute>();
            addressPointer += PtNodeReader.readBigramAddresses(mDictBuffer, bigrams,
                    addressPointer);
            if (bigrams.size() >= FormatSpec.MAX_BIGRAMS_IN_A_PTNODE) {
                throw new RuntimeException("Too many bigrams in a PtNode (" + bigrams.size()
                        + " but max is " + FormatSpec.MAX_BIGRAMS_IN_A_PTNODE + ")");
            }
        } else {
            bigrams = null;
        }
        return new PtNodeInfo(ptNodePos, addressPointer, flags, characters, probabilityInfo,
                FormatSpec.NO_PARENT_ADDRESS, childrenAddress, shortcutTargets, bigrams);
    }

    @Override
    public FusionDictionary readDictionaryBinary(final FusionDictionary dict,
            final boolean deleteDictIfBroken)
            throws FileNotFoundException, IOException, UnsupportedFormatException {
        if (mDictBuffer == null) {
            openDictBuffer();
        }
        try {
            return BinaryDictDecoderUtils.readDictionaryBinary(this, dict);
        } catch (IOException e) {
            Log.e(TAG, "The dictionary " + mDictionaryBinaryFile.getName() + " is broken.", e);
            if (deleteDictIfBroken && !mDictionaryBinaryFile.delete()) {
                Log.e(TAG, "Failed to delete the broken dictionary.");
            }
            throw e;
        } catch (UnsupportedFormatException e) {
            Log.e(TAG, "The dictionary " + mDictionaryBinaryFile.getName() + " is broken.", e);
            if (deleteDictIfBroken && !mDictionaryBinaryFile.delete()) {
                Log.e(TAG, "Failed to delete the broken dictionary.");
            }
            throw e;
        }
    }

    @Override
    public void setPosition(int newPos) {
        mDictBuffer.position(newPos);
    }

    @Override
    public int getPosition() {
        return mDictBuffer.position();
    }

    @Override
    public int readPtNodeCount() {
        return BinaryDictDecoderUtils.readPtNodeCount(mDictBuffer);
    }

    @Override
    public boolean readAndFollowForwardLink() {
        final int nextAddress = mDictBuffer.readUnsignedInt24();
        if (nextAddress >= 0 && nextAddress < mDictBuffer.limit()) {
            mDictBuffer.position(nextAddress);
            return true;
        }
        return false;
    }

    @Override
    public boolean hasNextPtNodeArray() {
        return mDictBuffer.position() != FormatSpec.NO_FORWARD_LINK_ADDRESS;
    }
}