/*
 * Copyright (C) 2007 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 android.text;

import android.content.res.Resources;
import android.content.res.XmlResourceParser;
import com.android.internal.util.XmlUtils;
import android.view.View;

import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;

import java.io.IOException;
import java.util.Locale;

/**
 * This class accesses a dictionary of corrections to frequent misspellings.
 */
public class AutoText {
    // struct trie {
    //     char c;
    //     int off;
    //     struct trie *child;
    //     struct trie *next;
    // };

    private static final int TRIE_C = 0;
    private static final int TRIE_OFF = 1;
    private static final int TRIE_CHILD = 2;
    private static final int TRIE_NEXT = 3;

    private static final int TRIE_SIZEOF = 4;
    private static final char TRIE_NULL = (char) -1;
    private static final int TRIE_ROOT = 0;

    private static final int INCREMENT = 1024;

    private static final int DEFAULT = 14337; // Size of the Trie 13 Aug 2007

    private static final int RIGHT = 9300; // Size of 'right' 13 Aug 2007

    private static AutoText sInstance = new AutoText(Resources.getSystem());
    private static Object sLock = new Object();

    // TODO:
    //
    // Note the assumption that the destination strings total less than
    // 64K characters and that the trie for the source side totals less
    // than 64K chars/offsets/child pointers/next pointers.
    //
    // This seems very safe for English (currently 7K of destination,
    // 14K of trie) but may need to be revisited.

    private char[] mTrie;
    private char mTrieUsed;
    private String mText;
    private Locale mLocale;
    private int mSize;

    private AutoText(Resources resources) {
        mLocale = resources.getConfiguration().locale;
        init(resources);
    }

    /**
     * Returns the instance of AutoText. If the locale has changed, it will create a new
     * instance of AutoText for the locale.
     * @param view to get the resources from
     * @return the single instance of AutoText
     */
    private static AutoText getInstance(View view) {
        Resources res = view.getContext().getResources();
        Locale locale = res.getConfiguration().locale;
        AutoText instance;

        synchronized (sLock) {
            instance = sInstance;

            if (!locale.equals(instance.mLocale)) {
                instance = new AutoText(res);
                sInstance = instance;
            }
        }
        
        return instance;
    }
    
    /**
     * Retrieves a possible spelling correction for the specified range
     * of text.  Returns null if no correction can be found.
     * The View is used to get the current Locale and Resources.
     */
    public static String get(CharSequence src, final int start, final int end,
                             View view) {
        return getInstance(view).lookup(src, start, end);
    }

    /**
     * Returns the size of the auto text dictionary. The return value can be zero if there is
     * no auto correction data available for the current locale.
     * @param view used to retrieve the current Locale and Resources.
     * @return the number of entries in the auto text dictionary
     */
    public static int getSize(View view) {

        return getInstance(view).getSize(); 
    }

    /**
     * Returns the size of the dictionary.
     */
    private int getSize() {
        return mSize;
    }

    private String lookup(CharSequence src, final int start, final int end) {
        int here = mTrie[TRIE_ROOT];

        for (int i = start; i < end; i++) {
            char c = src.charAt(i);

            for (; here != TRIE_NULL; here = mTrie[here + TRIE_NEXT]) {
                if (c == mTrie[here + TRIE_C]) {
                    if ((i == end - 1) 
                            && (mTrie[here + TRIE_OFF] != TRIE_NULL)) {
                        int off = mTrie[here + TRIE_OFF];
                        int len = mText.charAt(off);

                        return mText.substring(off + 1, off + 1 + len);
                    }

                    here = mTrie[here + TRIE_CHILD];
                    break;
                }
            }

            if (here == TRIE_NULL) {
                return null;
            }
        }

        return null;
    }

    private void init(Resources r) {
        XmlResourceParser parser = r.getXml(com.android.internal.R.xml.autotext);

        StringBuilder right = new StringBuilder(RIGHT);
        mTrie = new char[DEFAULT];
        mTrie[TRIE_ROOT] = TRIE_NULL;
        mTrieUsed = TRIE_ROOT + 1;

        try {
            XmlUtils.beginDocument(parser, "words");
            String odest = "";
            char ooff = 0;

            while (true) {
                XmlUtils.nextElement(parser);

                String element = parser.getName(); 
                if (element == null || !(element.equals("word"))) {
                    break;
                }

                String src = parser.getAttributeValue(null, "src");
                if (parser.next() == XmlPullParser.TEXT) {
                    String dest = parser.getText();
                    char off;

                    if (dest.equals(odest)) {
                        off = ooff;
                    } else {
                        off = (char) right.length();
                        right.append((char) dest.length());
                        right.append(dest);
                    }

                    add(src, off);
                }
            }

            // Don't let Resources cache a copy of all these strings.
            r.flushLayoutCache();
        } catch (XmlPullParserException e) {
            throw new RuntimeException(e);
        } catch (IOException e) {
            throw new RuntimeException(e);
        } finally {
            parser.close();
        }

        mText = right.toString();
    }

    private void add(String src, char off) {
        int slen = src.length();
        int herep = TRIE_ROOT;
        // Keep track of the size of the dictionary
        mSize++;
        
        for (int i = 0; i < slen; i++) {
            char c = src.charAt(i);
            boolean found = false;

            for (; mTrie[herep] != TRIE_NULL;
                    herep = mTrie[herep] + TRIE_NEXT) {
                if (c == mTrie[mTrie[herep] + TRIE_C]) {
                    // There is a node for this letter, and this is the
                    // end, so fill in the right hand side fields.

                    if (i == slen - 1) {
                        mTrie[mTrie[herep] + TRIE_OFF] = off;
                        return;
                    }

                    // There is a node for this letter, and we need
                    // to go deeper into it to fill in the rest.

                    herep = mTrie[herep] + TRIE_CHILD;
                    found = true;
                    break;
                }
            }

            if (!found) {
                // No node for this letter yet.  Make one.

                char node = newTrieNode();
                mTrie[herep] = node;

                mTrie[mTrie[herep] + TRIE_C] = c;
                mTrie[mTrie[herep] + TRIE_OFF] = TRIE_NULL;
                mTrie[mTrie[herep] + TRIE_NEXT] = TRIE_NULL;
                mTrie[mTrie[herep] + TRIE_CHILD] = TRIE_NULL;

                // If this is the end of the word, fill in the offset.

                if (i == slen - 1) {
                    mTrie[mTrie[herep] + TRIE_OFF] = off;
                    return;
                }

                // Otherwise, step in deeper and go to the next letter.

                herep = mTrie[herep] + TRIE_CHILD;
            }
        }
    }

    private char newTrieNode() {
        if (mTrieUsed + TRIE_SIZEOF > mTrie.length) {
            char[] copy = new char[mTrie.length + INCREMENT];
            System.arraycopy(mTrie, 0, copy, 0, mTrie.length);
            mTrie = copy;
        }

        char ret = mTrieUsed;
        mTrieUsed += TRIE_SIZEOF;

        return ret;
    }
}
