/*
* 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.
*/

using System;

namespace ZXing.QrCode.Internal
{

    /// <summary> <p>Encapsulates a QR Code's format information, including the data mask used and
    /// error correction level.</p>
    /// 
    /// </summary>
    /// <author>  Sean Owen
    /// </author>
    /// <author>www.Redivivus.in (suraj.supekar@redivivus.in) - Ported from ZXING Java Source 
    /// </author>
    /// <seealso cref="DataMask">
    /// </seealso>
    /// <seealso cref="ErrorCorrectionLevel">
    /// </seealso>
    sealed class FormatInformation
    {
        private const int FORMAT_INFO_MASK_QR = 0x5412;

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

        /// <summary> Offset i holds the number of 1 bits in the binary representation of i</summary>
        private static readonly int[] BITS_SET_IN_HALF_BYTE = new[]
           { 0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4 };

        private readonly ErrorCorrectionLevel errorCorrectionLevel;
        private readonly byte dataMask;

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

        internal 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[((int)((uint)a >> 4)) & 0x0F] +
               BITS_SET_IN_HALF_BYTE[((int)((uint)a >> 8)) & 0x0F] +
               BITS_SET_IN_HALF_BYTE[((int)((uint)a >> 12)) & 0x0F] +
               BITS_SET_IN_HALF_BYTE[((int)((uint)a >> 16)) & 0x0F] +
               BITS_SET_IN_HALF_BYTE[((int)((uint)a >> 20)) & 0x0F] +
               BITS_SET_IN_HALF_BYTE[((int)((uint)a >> 24)) & 0x0F] +
               BITS_SET_IN_HALF_BYTE[((int)((uint)a >> 28)) & 0x0F];
        }

        /// <summary>
        /// Decodes the format information.
        /// </summary>
        /// <param name="maskedFormatInfo1">format info indicator, with mask still applied</param>
        /// <param name="maskedFormatInfo2">The masked format info2.</param>
        /// <returns>
        /// information about the format it specifies, or <code>null</code>
        /// if doesn't seem to match any known pattern
        /// </returns>
        internal 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 = Int32.MaxValue;
            int bestFormatInfo = 0;
            foreach (var decodeInfo in 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;
        }

        internal ErrorCorrectionLevel ErrorCorrectionLevel
        {
            get
            {
                return errorCorrectionLevel;
            }
        }

        internal byte DataMask
        {
            get
            {
                return dataMask;
            }
        }

        public override int GetHashCode()
        {
            return (errorCorrectionLevel.ordinal() << 3) | dataMask;
        }

        public override bool Equals(Object o)
        {
            if (!(o is FormatInformation))
            {
                return false;
            }
            var other = (FormatInformation)o;
            return errorCorrectionLevel == other.errorCorrectionLevel && dataMask == other.dataMask;
        }
    }
}