content: /*
   * 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.ailiwean.core.zxing.core.common;
  
  import com.ailiwean.core.zxing.core.DecodeHintType;
  
  import java.nio.charset.Charset;
  import java.util.Map;
  
  
  /**
   * 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;
    }
  
  }
  