/*
 * Copyright 2007 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.jwetherell.quick_response_code.qrcode.decoder;

import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Map;

import com.google.zxing.DecodeHintType;
import com.google.zxing.FormatException;
import com.google.zxing.common.BitSource;
import com.google.zxing.common.CharacterSetECI;
import com.google.zxing.common.DecoderResult;
import com.google.zxing.common.StringUtils;

/**
 * <p>
 * QR Codes can encode text as bits in one of several modes, and can use
 * multiple modes in one QR Code. This class decodes the bits back into text.
 * </p>
 * 
 * <p>
 * See ISO 18004:2006, 6.4.3 - 6.4.7
 * </p>
 * 
 * @author Sean Owen
 */
final class DecodedBitStreamParser {

    /**
     * See ISO 18004:2006, 6.4.4 Table 5
     */
    private static final char[] ALPHANUMERIC_CHARS = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K',
            'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', ' ', '$', '%', '*', '+', '-', '.', '/', ':' };
    private static final int GB2312_SUBSET = 1;

    private DecodedBitStreamParser() {
    }

    static DecoderResult decode(byte[] bytes, Version version, ErrorCorrectionLevel ecLevel, Map<DecodeHintType, ?> hints) throws FormatException {
        BitSource bits = new BitSource(bytes);
        StringBuilder result = new StringBuilder(50);
        CharacterSetECI currentCharacterSetECI = null;
        boolean fc1InEffect = false;
        List<byte[]> byteSegments = new ArrayList<byte[]>(1);
        Mode mode;
        do {
            // While still another segment to read...
            if (bits.available() < 4) {
                // OK, assume we're done. Really, a TERMINATOR mode should have
                // been recorded here
                mode = Mode.TERMINATOR;
            } else {
                try {
                    mode = Mode.forBits(bits.readBits(4)); // mode is encoded by
                                                           // 4 bits
                } catch (IllegalArgumentException iae) {
                    throw FormatException.getFormatInstance();
                }
            }
            if (mode != Mode.TERMINATOR) {
                if (mode == Mode.FNC1_FIRST_POSITION || mode == Mode.FNC1_SECOND_POSITION) {
                    // We do little with FNC1 except alter the parsed result a
                    // bit according to the
                    // spec
                    fc1InEffect = true;
                } else if (mode == Mode.STRUCTURED_APPEND) {
                    // not really supported; all we do is ignore it
                    // Read next 8 bits (symbol sequence #) and 8 bits (parity
                    // data), then continue
                    bits.readBits(16);
                } else if (mode == Mode.ECI) {
                    // Count doesn't apply to ECI
                    int value = parseECIValue(bits);
                    currentCharacterSetECI = CharacterSetECI.getCharacterSetECIByValue(value);
                    if (currentCharacterSetECI == null) {
                        throw FormatException.getFormatInstance();
                    }
                } else {
                    // First handle Hanzi mode which does not start with
                    // character count
                    if (mode == Mode.HANZI) {
                        // chinese mode contains a sub set indicator right after
                        // mode indicator
                        int subset = bits.readBits(4);
                        int countHanzi = bits.readBits(mode.getCharacterCountBits(version));
                        if (subset == GB2312_SUBSET) {
                            decodeHanziSegment(bits, result, countHanzi);
                        }
                    } else {
                        // "Normal" QR code modes:
                        // How many characters will follow, encoded in this
                        // mode?
                        int count = bits.readBits(mode.getCharacterCountBits(version));
                        if (mode == Mode.NUMERIC) {
                            decodeNumericSegment(bits, result, count);
                        } else if (mode == Mode.ALPHANUMERIC) {
                            decodeAlphanumericSegment(bits, result, count, fc1InEffect);
                        } else if (mode == Mode.BYTE) {
                            decodeByteSegment(bits, result, count, currentCharacterSetECI, byteSegments, hints);
                        } else if (mode == Mode.KANJI) {
                            decodeKanjiSegment(bits, result, count);
                        } else {
                            throw FormatException.getFormatInstance();
                        }
                    }
                }
            }
        } while (mode != Mode.TERMINATOR);

        return new DecoderResult(bytes, result.toString(), byteSegments.isEmpty() ? null : byteSegments, ecLevel == null ? null : ecLevel.toString());
    }

    /**
     * See specification GBT 18284-2000
     */
    private static void decodeHanziSegment(BitSource bits, StringBuilder result, int count) throws FormatException {
        // Don't crash trying to read more bits than we have available.
        if (count * 13 > bits.available()) {
            throw FormatException.getFormatInstance();
        }

        // Each character will require 2 bytes. Read the characters as 2-byte
        // pairs
        // and decode as GB2312 afterwards
        byte[] buffer = new byte[2 * count];
        int offset = 0;
        while (count > 0) {
            // Each 13 bits encodes a 2-byte character
            int twoBytes = bits.readBits(13);
            int assembledTwoBytes = ((twoBytes / 0x060) << 8) | (twoBytes % 0x060);
            if (assembledTwoBytes < 0x003BF) {
                // In the 0xA1A1 to 0xAAFE range
                assembledTwoBytes += 0x0A1A1;
            } else {
                // In the 0xB0A1 to 0xFAFE range
                assembledTwoBytes += 0x0A6A1;
            }
            buffer[offset] = (byte) ((assembledTwoBytes >> 8) & 0xFF);
            buffer[offset + 1] = (byte) (assembledTwoBytes & 0xFF);
            offset += 2;
            count--;
        }

        try {
            result.append(new String(buffer, StringUtils.GB2312));
        } catch (UnsupportedEncodingException uee) {
            throw FormatException.getFormatInstance();
        }
    }

    private static void decodeKanjiSegment(BitSource bits, StringBuilder result, int count) throws FormatException {
        // Don't crash trying to read more bits than we have available.
        if (count * 13 > bits.available()) {
            throw FormatException.getFormatInstance();
        }

        // Each character will require 2 bytes. Read the characters as 2-byte
        // pairs
        // and decode as Shift_JIS afterwards
        byte[] buffer = new byte[2 * count];
        int offset = 0;
        while (count > 0) {
            // Each 13 bits encodes a 2-byte character
            int twoBytes = bits.readBits(13);
            int assembledTwoBytes = ((twoBytes / 0x0C0) << 8) | (twoBytes % 0x0C0);
            if (assembledTwoBytes < 0x01F00) {
                // In the 0x8140 to 0x9FFC range
                assembledTwoBytes += 0x08140;
            } else {
                // In the 0xE040 to 0xEBBF range
                assembledTwoBytes += 0x0C140;
            }
            buffer[offset] = (byte) (assembledTwoBytes >> 8);
            buffer[offset + 1] = (byte) assembledTwoBytes;
            offset += 2;
            count--;
        }
        // Shift_JIS may not be supported in some environments:
        try {
            result.append(new String(buffer, StringUtils.SHIFT_JIS));
        } catch (UnsupportedEncodingException uee) {
            throw FormatException.getFormatInstance();
        }
    }

    private static void decodeByteSegment(BitSource bits, StringBuilder result, int count, CharacterSetECI currentCharacterSetECI,
            Collection<byte[]> byteSegments, Map<DecodeHintType, ?> hints) throws FormatException {
        // Don't crash trying to read more bits than we have available.
        if (count << 3 > bits.available()) {
            throw FormatException.getFormatInstance();
        }

        byte[] readBytes = new byte[count];
        for (int i = 0; i < count; i++) {
            readBytes[i] = (byte) bits.readBits(8);
        }
        String encoding;
        if (currentCharacterSetECI == null) {
            // The spec isn't clear on this mode; see
            // section 6.4.5: t does not say which encoding to assuming
            // upon decoding. I have seen ISO-8859-1 used as well as
            // Shift_JIS -- without anything like an ECI designator to
            // give a hint.
            encoding = StringUtils.guessEncoding(readBytes, hints);
        } else {
            encoding = currentCharacterSetECI.name();
        }
        try {
            result.append(new String(readBytes, encoding));
        } catch (UnsupportedEncodingException uce) {
            throw FormatException.getFormatInstance();
        }
        byteSegments.add(readBytes);
    }

    private static char toAlphaNumericChar(int value) throws FormatException {
        if (value >= ALPHANUMERIC_CHARS.length) {
            throw FormatException.getFormatInstance();
        }
        return ALPHANUMERIC_CHARS[value];
    }

    private static void decodeAlphanumericSegment(BitSource bits, StringBuilder result, int count, boolean fc1InEffect) throws FormatException {
        // Read two characters at a time
        int start = result.length();
        while (count > 1) {
            int nextTwoCharsBits = bits.readBits(11);
            result.append(toAlphaNumericChar(nextTwoCharsBits / 45));
            result.append(toAlphaNumericChar(nextTwoCharsBits % 45));
            count -= 2;
        }
        if (count == 1) {
            // special case: one character left
            result.append(toAlphaNumericChar(bits.readBits(6)));
        }
        // See section 6.4.8.1, 6.4.8.2
        if (fc1InEffect) {
            // We need to massage the result a bit if in an FNC1 mode:
            for (int i = start; i < result.length(); i++) {
                if (result.charAt(i) == '%') {
                    if (i < result.length() - 1 && result.charAt(i + 1) == '%') {
                        // %% is rendered as %
                        result.deleteCharAt(i + 1);
                    } else {
                        // In alpha mode, % should be converted to FNC1
                        // separator 0x1D
                        result.setCharAt(i, (char) 0x1D);
                    }
                }
            }
        }
    }

    private static void decodeNumericSegment(BitSource bits, StringBuilder result, int count) throws FormatException {
        // Read three digits at a time
        while (count >= 3) {
            // Each 10 bits encodes three digits
            if (bits.available() < 10) {
                throw FormatException.getFormatInstance();
            }
            int threeDigitsBits = bits.readBits(10);
            if (threeDigitsBits >= 1000) {
                throw FormatException.getFormatInstance();
            }
            result.append(toAlphaNumericChar(threeDigitsBits / 100));
            result.append(toAlphaNumericChar((threeDigitsBits / 10) % 10));
            result.append(toAlphaNumericChar(threeDigitsBits % 10));
            count -= 3;
        }
        if (count == 2) {
            // Two digits left over to read, encoded in 7 bits
            if (bits.available() < 7) {
                throw FormatException.getFormatInstance();
            }
            int twoDigitsBits = bits.readBits(7);
            if (twoDigitsBits >= 100) {
                throw FormatException.getFormatInstance();
            }
            result.append(toAlphaNumericChar(twoDigitsBits / 10));
            result.append(toAlphaNumericChar(twoDigitsBits % 10));
        } else if (count == 1) {
            // One digit left over to read
            if (bits.available() < 4) {
                throw FormatException.getFormatInstance();
            }
            int digitBits = bits.readBits(4);
            if (digitBits >= 10) {
                throw FormatException.getFormatInstance();
            }
            result.append(toAlphaNumericChar(digitBits));
        }
    }

    private static int parseECIValue(BitSource bits) {
        int firstByte = bits.readBits(8);
        if ((firstByte & 0x80) == 0) {
            // just one byte
            return firstByte & 0x7F;
        }
        if ((firstByte & 0xC0) == 0x80) {
            // two bytes
            int secondByte = bits.readBits(8);
            return ((firstByte & 0x3F) << 8) | secondByte;
        }
        if ((firstByte & 0xE0) == 0xC0) {
            // three bytes
            int secondThirdBytes = bits.readBits(16);
            return ((firstByte & 0x1F) << 16) | secondThirdBytes;
        }
        throw new IllegalArgumentException("Bad ECI bits starting with byte " + firstByte);
    }

}
