/*
 * Copyright (C) 2010 ZXing authors
 *
 * 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.sobot.chat.widget.zxing.common;

import java.nio.charset.Charset;
import java.util.Map;

import com.sobot.chat.widget.zxing.DecodeHintType;

/**
 * Common string-related functions.
 *
 * @author Sean Owen
 * @author Alex Dupre
 */
public final class StringUtils {

    private static final String PLATFORM_DEFAULT_ENCODING = Charset.defaultCharset().name();
    public static final String SHIFT_JIS = "SJIS";
    public static final String GB2312 = "GB2312";
    private static final String EUC_JP = "EUC_JP";
    private static final String UTF8 = "UTF8";
    private static final String ISO88591 = "ISO8859_1";
    private static final boolean ASSUME_SHIFT_JIS =
            SHIFT_JIS.equalsIgnoreCase(PLATFORM_DEFAULT_ENCODING) ||
                    EUC_JP.equalsIgnoreCase(PLATFORM_DEFAULT_ENCODING);

    private StringUtils() {
    }

    /**
     * @param bytes bytes encoding a string, whose encoding should be guessed
     * @param hints decode hints if applicable
     * @return name of guessed encoding; at the moment will only guess one of:
     * {@link #SHIFT_JIS}, {@link #UTF8}, {@link #ISO88591}, or the platform
     * default encoding if none of these can possibly be correct
     */
    public static String guessEncoding(byte[] bytes, Map<DecodeHintType, ?> hints) {
        if (hints != null && hints.containsKey(DecodeHintType.CHARACTER_SET)) {
            return hints.get(DecodeHintType.CHARACTER_SET).toString();
        }
        // For now, merely tries to distinguish ISO-8859-1, UTF-8 and Shift_JIS,
        // which should be by far the most common encodings.
        int length = bytes.length;
        boolean canBeISO88591 = true;
        boolean canBeShiftJIS = true;
        boolean canBeUTF8 = true;
        int utf8BytesLeft = 0;
        int utf2BytesChars = 0;
        int utf3BytesChars = 0;
        int utf4BytesChars = 0;
        int sjisBytesLeft = 0;
        int sjisKatakanaChars = 0;
        int sjisCurKatakanaWordLength = 0;
        int sjisCurDoubleBytesWordLength = 0;
        int sjisMaxKatakanaWordLength = 0;
        int sjisMaxDoubleBytesWordLength = 0;
        int isoHighOther = 0;

        boolean utf8bom = bytes.length > 3 &&
                bytes[0] == (byte) 0xEF &&
                bytes[1] == (byte) 0xBB &&
                bytes[2] == (byte) 0xBF;

        for (int i = 0;
             i < length && (canBeISO88591 || canBeShiftJIS || canBeUTF8);
             i++) {

            int value = bytes[i] & 0xFF;

            // UTF-8 stuff
            if (canBeUTF8) {
                if (utf8BytesLeft > 0) {
                    if ((value & 0x80) == 0) {
                        canBeUTF8 = false;
                    } else {
                        utf8BytesLeft--;
                    }
                } else if ((value & 0x80) != 0) {
                    if ((value & 0x40) == 0) {
                        canBeUTF8 = false;
                    } else {
                        utf8BytesLeft++;
                        if ((value & 0x20) == 0) {
                            utf2BytesChars++;
                        } else {
                            utf8BytesLeft++;
                            if ((value & 0x10) == 0) {
                                utf3BytesChars++;
                            } else {
                                utf8BytesLeft++;
                                if ((value & 0x08) == 0) {
                                    utf4BytesChars++;
                                } else {
                                    canBeUTF8 = false;
                                }
                            }
                        }
                    }
                }
            }

            // ISO-8859-1 stuff
            if (canBeISO88591) {
                if (value > 0x7F && value < 0xA0) {
                    canBeISO88591 = false;
                } else if (value > 0x9F && (value < 0xC0 || value == 0xD7 || value == 0xF7)) {
                    isoHighOther++;
                }
            }

            // Shift_JIS stuff
            if (canBeShiftJIS) {
                if (sjisBytesLeft > 0) {
                    if (value < 0x40 || value == 0x7F || value > 0xFC) {
                        canBeShiftJIS = false;
                    } else {
                        sjisBytesLeft--;
                    }
                } else if (value == 0x80 || value == 0xA0 || value > 0xEF) {
                    canBeShiftJIS = false;
                } else if (value > 0xA0 && value < 0xE0) {
                    sjisKatakanaChars++;
                    sjisCurDoubleBytesWordLength = 0;
                    sjisCurKatakanaWordLength++;
                    if (sjisCurKatakanaWordLength > sjisMaxKatakanaWordLength) {
                        sjisMaxKatakanaWordLength = sjisCurKatakanaWordLength;
                    }
                } else if (value > 0x7F) {
                    sjisBytesLeft++;
                    //sjisDoubleBytesChars++;
                    sjisCurKatakanaWordLength = 0;
                    sjisCurDoubleBytesWordLength++;
                    if (sjisCurDoubleBytesWordLength > sjisMaxDoubleBytesWordLength) {
                        sjisMaxDoubleBytesWordLength = sjisCurDoubleBytesWordLength;
                    }
                } else {
                    //sjisLowChars++;
                    sjisCurKatakanaWordLength = 0;
                    sjisCurDoubleBytesWordLength = 0;
                }
            }
        }

        if (canBeUTF8 && utf8BytesLeft > 0) {
            canBeUTF8 = false;
        }
        if (canBeShiftJIS && sjisBytesLeft > 0) {
            canBeShiftJIS = false;
        }

        // Easy -- if there is BOM or at least 1 valid not-single byte character (and no evidence it can't be UTF-8), done
        if (canBeUTF8 && (utf8bom || utf2BytesChars + utf3BytesChars + utf4BytesChars > 0)) {
            return UTF8;
        }
        // Easy -- if assuming Shift_JIS or >= 3 valid consecutive not-ascii characters (and no evidence it can't be), done
        if (canBeShiftJIS && (ASSUME_SHIFT_JIS || sjisMaxKatakanaWordLength >= 3 || sjisMaxDoubleBytesWordLength >= 3)) {
            return SHIFT_JIS;
        }
        // Distinguishing Shift_JIS and ISO-8859-1 can be a little tough for short words. The crude heuristic is:
        // - If we saw
        //   - only two consecutive katakana chars in the whole text, or
        //   - at least 10% of bytes that could be "upper" not-alphanumeric Latin1,
        // - then we conclude Shift_JIS, else ISO-8859-1
        if (canBeISO88591 && canBeShiftJIS) {
            return (sjisMaxKatakanaWordLength == 2 && sjisKatakanaChars == 2) || isoHighOther * 10 >= length
                    ? SHIFT_JIS : ISO88591;
        }

        // Otherwise, try in order ISO-8859-1, Shift JIS, UTF-8 and fall back to default platform encoding
        if (canBeISO88591) {
            return ISO88591;
        }
        if (canBeShiftJIS) {
            return SHIFT_JIS;
        }
        if (canBeUTF8) {
            return UTF8;
        }
        // Otherwise, we take a wild guess with platform encoding
        return PLATFORM_DEFAULT_ENCODING;
    }

}
