/*
 * 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 org.akvo.caddisfly.sensor.striptest.qrdetector;

/**
 * <p>Encapsulates a QR Code's format information, including the data mask used and
 * error correction level.</p>
 *
 * @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 ^= b; // a now has a 1 bit exactly where its bit differs with b's
        // 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}
     * 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[] decodeInfo : FORMAT_INFO_DECODE_LOOKUP) {
            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;
    }

    byte getDataMask() {
        return dataMask;
    }

    @Override
    public int hashCode() {
        return (errorCorrectionLevel.ordinal() << 3) | (int) dataMask;
    }

    @Override
    public boolean equals(Object o) {
        if (!(o instanceof FormatInformation)) {
            return false;
        }
        FormatInformation other = (FormatInformation) o;
        return this.errorCorrectionLevel == other.errorCorrectionLevel &&
                this.dataMask == other.dataMask;
    }

}
