/*

    This file is part of the iText (R) project.
    Copyright (c) 1998-2020 iText Group NV
    Authors: Bruno Lowagie, Paulo Soares, et al.

    This program is free software; you can redistribute it and/or modify
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    following permission added to Section 15 as permitted in Section 7(a):
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 */
package com.itextpdf.barcodes.qrcode;

/**
 * Encapsulates a QR Code's format information, including the data mask used and
 * error correction level.
 *
 * @author Sean Owen
 * @see ErrorCorrectionLevel
 */
final class FormatInformation {

    private static final int FORMAT_INFO_MASK_QR = 0x5412;

    /**
     * See ISO 18004:2006, Annex C, Table C.1
     */
    private static final int[][] FORMAT_INFO_DECODE_LOOKUP = {
            {0x5412, 0x00},
            {0x5125, 0x01},
            {0x5E7C, 0x02},
            {0x5B4B, 0x03},
            {0x45F9, 0x04},
            {0x40CE, 0x05},
            {0x4F97, 0x06},
            {0x4AA0, 0x07},
            {0x77C4, 0x08},
            {0x72F3, 0x09},
            {0x7DAA, 0x0A},
            {0x789D, 0x0B},
            {0x662F, 0x0C},
            {0x6318, 0x0D},
            {0x6C41, 0x0E},
            {0x6976, 0x0F},
            {0x1689, 0x10},
            {0x13BE, 0x11},
            {0x1CE7, 0x12},
            {0x19D0, 0x13},
            {0x0762, 0x14},
            {0x0255, 0x15},
            {0x0D0C, 0x16},
            {0x083B, 0x17},
            {0x355F, 0x18},
            {0x3068, 0x19},
            {0x3F31, 0x1A},
            {0x3A06, 0x1B},
            {0x24B4, 0x1C},
            {0x2183, 0x1D},
            {0x2EDA, 0x1E},
            {0x2BED, 0x1F},
    };

    /**
     * Offset i holds the number of 1 bits in the binary representation of i
     */
    private static final int[] BITS_SET_IN_HALF_BYTE =
            {0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4};

    private final ErrorCorrectionLevel errorCorrectionLevel;
    private final byte dataMask;

    private FormatInformation(int formatInfo) {
        // Bits 3,4
        errorCorrectionLevel = ErrorCorrectionLevel.forBits((formatInfo >> 3) & 0x03);
        // Bottom 3 bits
        dataMask = (byte) (formatInfo & 0x07);
    }

    static int numBitsDiffering(int a, int b) {

        // a now has a 1 bit exactly where its bit differs with b's
        a ^= b;

        // Count bits set quickly with a series of lookups:
        return BITS_SET_IN_HALF_BYTE[a & 0x0F] +
                BITS_SET_IN_HALF_BYTE[(a >>> 4 & 0x0F)] +
                BITS_SET_IN_HALF_BYTE[(a >>> 8 & 0x0F)] +
                BITS_SET_IN_HALF_BYTE[(a >>> 12 & 0x0F)] +
                BITS_SET_IN_HALF_BYTE[(a >>> 16 & 0x0F)] +
                BITS_SET_IN_HALF_BYTE[(a >>> 20 & 0x0F)] +
                BITS_SET_IN_HALF_BYTE[(a >>> 24 & 0x0F)] +
                BITS_SET_IN_HALF_BYTE[(a >>> 28 & 0x0F)];
    }

    /**
     * @param maskedFormatInfo1 format info indicator, with mask still applied
     * @param maskedFormatInfo2 second copy of same info; both are checked at the same time
     *  to establish best match
     * @return information about the format it specifies, or <code>null</code>
     *  if doesn't seem to match any known pattern
     */
    static FormatInformation decodeFormatInformation(int maskedFormatInfo1, int maskedFormatInfo2) {
        FormatInformation formatInfo = doDecodeFormatInformation(maskedFormatInfo1, maskedFormatInfo2);
        if (formatInfo != null) {
            return formatInfo;
        }
        // Should return null, but, some QR codes apparently
        // do not mask this info. Try again by actually masking the pattern
        // first
        return doDecodeFormatInformation(maskedFormatInfo1 ^ FORMAT_INFO_MASK_QR,
                maskedFormatInfo2 ^ FORMAT_INFO_MASK_QR);
    }

    private static FormatInformation doDecodeFormatInformation(int maskedFormatInfo1, int maskedFormatInfo2) {
        // Find the int in FORMAT_INFO_DECODE_LOOKUP with fewest bits differing
        int bestDifference = Integer.MAX_VALUE;
        int bestFormatInfo = 0;
        for (int i = 0; i < FORMAT_INFO_DECODE_LOOKUP.length; i++) {
            int[] decodeInfo = FORMAT_INFO_DECODE_LOOKUP[i];
            int targetInfo = decodeInfo[0];
            if (targetInfo == maskedFormatInfo1 || targetInfo == maskedFormatInfo2) {
                // Found an exact match
                return new FormatInformation(decodeInfo[1]);
            }
            int bitsDifference = numBitsDiffering(maskedFormatInfo1, targetInfo);
            if (bitsDifference < bestDifference) {
                bestFormatInfo = decodeInfo[1];
                bestDifference = bitsDifference;
            }
            if (maskedFormatInfo1 != maskedFormatInfo2) {
                // also try the other option
                bitsDifference = numBitsDiffering(maskedFormatInfo2, targetInfo);
                if (bitsDifference < bestDifference) {
                    bestFormatInfo = decodeInfo[1];
                    bestDifference = bitsDifference;
                }
            }
        }
        // Hamming distance of the 32 masked codes is 7, by construction, so <= 3 bits
        // differing means we found a match
        if (bestDifference <= 3) {
            return new FormatInformation(bestFormatInfo);
        }
        return null;
    }

    ErrorCorrectionLevel getErrorCorrectionLevel() {
        return errorCorrectionLevel;
    }

    /**
     * @return The datamask in byte-format
     */
    byte getDataMask() {
        return dataMask;
    }

    /**
     * @return the hashcode of the QR-code format information
     */
    public int hashCode() {
        return (errorCorrectionLevel.ordinal() << 3) | (int) dataMask;
    }

    /**
     * Compares the Format Information of this and o
     * @param o object to compare to
     * @return True if o is a FormatInformationObject and the error-correction level and the datamask are equal, false otherwise
     */
    public boolean equals(Object o) {
        if (!(o instanceof FormatInformation)) {
            return false;
        }
        FormatInformation other = (FormatInformation) o;
        return this.errorCorrectionLevel == other.errorCorrectionLevel &&
                this.dataMask == other.dataMask;
    }

}

