/*
 * Copyright 2009 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;
using System.Collections.Generic;
using ZXing.Common;
using ZXing.QrCode.Internal;

namespace ZXing.Multi.QrCode.Internal
{
    /// <summary>
    /// <p>This class attempts to find finder patterns in a QR Code. Finder patterns are the square
    /// markers at three corners of a QR Code.</p>
    ///
    /// <p>This class is thread-safe but not reentrant. Each thread must allocate its own object.</p>
    ///
    /// <p>In contrast to <see cref="FinderPatternFinder" />, this class will return an array of all possible
    /// QR code locations in the image.</p>
    ///
    /// <p>Use the TRY_HARDER hint to ask for a more thorough detection.</p>
    ///
    /// <author>Sean Owen</author>
    /// <author>Hannes Erven</author>
    /// </summary>
    public sealed class MultiFinderPatternFinder : FinderPatternFinder
    {
        private static readonly FinderPatternInfo[] EMPTY_RESULT_ARRAY = new FinderPatternInfo[0];

        // TODO MIN_MODULE_COUNT and MAX_MODULE_COUNT would be great hints to ask the user for
        // since it limits the number of regions to decode

        // max. legal count of modules per QR code edge (177)
        private static float MAX_MODULE_COUNT_PER_EDGE = 180;

        // min. legal count per modules per QR code edge (11)
        private static float MIN_MODULE_COUNT_PER_EDGE = 9;

        /// <summary>
        /// More or less arbitrary cutoff point for determining if two finder patterns might belong
        /// to the same code if they differ less than DIFF_MODSIZE_CUTOFF_PERCENT percent in their
        /// estimated modules sizes.
        /// </summary>
        private static float DIFF_MODSIZE_CUTOFF_PERCENT = 0.05f;

        /// <summary>
        /// More or less arbitrary cutoff point for determining if two finder patterns might belong
        /// to the same code if they differ less than DIFF_MODSIZE_CUTOFF pixels/module in their
        /// estimated modules sizes.
        /// </summary>
        private const float DIFF_MODSIZE_CUTOFF = 0.5f;


        /// <summary>
        /// A comparator that orders FinderPatterns by their estimated module size.
        /// </summary>
        private sealed class ModuleSizeComparator : IComparer<FinderPattern>
        {
            public int Compare(FinderPattern center1, FinderPattern center2)
            {
                float value = center2.EstimatedModuleSize - center1.EstimatedModuleSize;
                return value < 0.0 ? -1 : value > 0.0 ? 1 : 0;
            }
        }

        /// <summary>
        /// <p>Creates a finder that will search the image for three finder patterns.</p>
        ///
        /// <param name="image">image to search</param>
        /// <param name="resultPointCallback">callback for result points</param>
        /// </summary>
        public MultiFinderPatternFinder(BitMatrix image, ResultPointCallback resultPointCallback)
            : base(image, resultPointCallback)
        {
        }

        /// <summary>
        /// </summary>
        /// <returns>the 3 best <see cref="FinderPattern" />s from our list of candidates. The "best" are
        ///         those that have been detected at least CENTER_QUORUM times, and whose module
        ///         size differs from the average among those patterns the least
        /// </returns>
        private FinderPattern[][] selectMultipleBestPatterns()
        {
            List<FinderPattern> possibleCenters = PossibleCenters;
            int size = possibleCenters.Count;

            if (size < 3)
            {
                // Couldn't find enough finder patterns
                return null;
            }

            /*
             * Begin HE modifications to safely detect multiple codes of equal size
             */
            if (size == 3)
            {
                return new FinderPattern[][]
                {
                    new FinderPattern[]
                    {
                        possibleCenters[0],
                        possibleCenters[1],
                        possibleCenters[2]
                    }
                };
            }

            // Sort by estimated module size to speed up the upcoming checks
            possibleCenters.Sort(new ModuleSizeComparator());

            /*
             * Now lets start: build a list of tuples of three finder locations that
             *  - feature similar module sizes
             *  - are placed in a distance so the estimated module count is within the QR specification
             *  - have similar distance between upper left/right and left top/bottom finder patterns
             *  - form a triangle with 90° angle (checked by comparing top right/bottom left distance
             *    with pythagoras)
             *
             * Note: we allow each point to be used for more than one code region: this might seem
             * counterintuitive at first, but the performance penalty is not that big. At this point,
             * we cannot make a good quality decision whether the three finders actually represent
             * a QR code, or are just by chance layouted so it looks like there might be a QR code there.
             * So, if the layout seems right, lets have the decoder try to decode.     
             */

            List<FinderPattern[]> results = new List<FinderPattern[]>(); // holder for the results

            for (int i1 = 0; i1 < (size - 2); i1++)
            {
                FinderPattern p1 = possibleCenters[i1];
                if (p1 == null)
                {
                    continue;
                }

                for (int i2 = i1 + 1; i2 < (size - 1); i2++)
                {
                    FinderPattern p2 = possibleCenters[i2];
                    if (p2 == null)
                    {
                        continue;
                    }

                    // Compare the expected module sizes; if they are really off, skip
                    float vModSize12 = (p1.EstimatedModuleSize - p2.EstimatedModuleSize) /
                                       Math.Min(p1.EstimatedModuleSize, p2.EstimatedModuleSize);
                    float vModSize12A = Math.Abs(p1.EstimatedModuleSize - p2.EstimatedModuleSize);
                    if (vModSize12A > DIFF_MODSIZE_CUTOFF && vModSize12 >= DIFF_MODSIZE_CUTOFF_PERCENT)
                    {
                        // break, since elements are ordered by the module size deviation there cannot be
                        // any more interesting elements for the given p1.
                        break;
                    }

                    for (int i3 = i2 + 1; i3 < size; i3++)
                    {
                        FinderPattern p3 = possibleCenters[i3];
                        if (p3 == null)
                        {
                            continue;
                        }

                        // Compare the expected module sizes; if they are really off, skip
                        float vModSize23 = (p2.EstimatedModuleSize - p3.EstimatedModuleSize) /
                                           Math.Min(p2.EstimatedModuleSize, p3.EstimatedModuleSize);
                        float vModSize23A = Math.Abs(p2.EstimatedModuleSize - p3.EstimatedModuleSize);
                        if (vModSize23A > DIFF_MODSIZE_CUTOFF && vModSize23 >= DIFF_MODSIZE_CUTOFF_PERCENT)
                        {
                            // break, since elements are ordered by the module size deviation there cannot be
                            // any more interesting elements for the given p1.
                            break;
                        }

                        FinderPattern[] test = {p1, p2, p3};
                        ResultPoint.orderBestPatterns(test);

                        // Calculate the distances: a = topleft-bottomleft, b=topleft-topright, c = diagonal
                        FinderPatternInfo info = new FinderPatternInfo(test);
                        float dA = ResultPoint.distance(info.TopLeft, info.BottomLeft);
                        float dC = ResultPoint.distance(info.TopRight, info.BottomLeft);
                        float dB = ResultPoint.distance(info.TopLeft, info.TopRight);

                        // Check the sizes
                        float estimatedModuleCount = (dA + dB) / (p1.EstimatedModuleSize * 2.0f);
                        if (estimatedModuleCount > MAX_MODULE_COUNT_PER_EDGE ||
                            estimatedModuleCount < MIN_MODULE_COUNT_PER_EDGE)
                        {
                            continue;
                        }

                        // Calculate the difference of the edge lengths in percent
                        float vABBC = Math.Abs((dA - dB) / Math.Min(dA, dB));
                        if (vABBC >= 0.1f)
                        {
                            continue;
                        }

                        // Calculate the diagonal length by assuming a 90° angle at topleft
                        float dCpy = (float) Math.Sqrt((double) dA * dA + (double) dB * dB);
                        // Compare to the real distance in %
                        float vPyC = Math.Abs((dC - dCpy) / Math.Min(dC, dCpy));

                        if (vPyC >= 0.1f)
                        {
                            continue;
                        }

                        // All tests passed!
                        results.Add(test);
                    } // end iterate p3
                } // end iterate p2
            } // end iterate p1

            if (results.Count != 0)
            {
                return results.ToArray();
            }

            // Nothing found!
            return null;
        }

        public FinderPatternInfo[] findMulti(IDictionary<DecodeHintType, object> hints)
        {
            bool tryHarder = hints != null && hints.ContainsKey(DecodeHintType.TRY_HARDER);
            BitMatrix image = Image;
            int maxI = image.Height;
            int maxJ = image.Width;
            // We are looking for black/white/black/white/black modules in
            // 1:1:3:1:1 ratio; this tracks the number of such modules seen so far

            // Let's assume that the maximum version QR Code we support takes up 1/4 the height of the
            // image, and then account for the center being 3 modules in size. This gives the smallest
            // number of pixels the center could be, so skip this often. When trying harder, look for all
            // QR versions regardless of how dense they are.
            int iSkip = (3 * maxI) / (4 * MAX_MODULES);
            if (iSkip < MIN_SKIP || tryHarder)
            {
                iSkip = MIN_SKIP;
            }

            int[] stateCount = new int[5];
            for (int i = iSkip - 1; i < maxI; i += iSkip)
            {
                // Get a row of black/white values
                doClearCounts(stateCount);
                int currentState = 0;
                for (int j = 0; j < maxJ; j++)
                {
                    if (image[j, i])
                    {
                        // Black pixel
                        if ((currentState & 1) == 1)
                        {
                            // Counting white pixels
                            currentState++;
                        }
                        stateCount[currentState]++;
                    }
                    else
                    {
                        // White pixel
                        if ((currentState & 1) == 0)
                        {
                            // Counting black pixels
                            if (currentState == 4)
                            {
                                // A winner?
                                if (foundPatternCross(stateCount) && handlePossibleCenter(stateCount, i, j))
                                {
                                    // Yes
                                    // Clear state to start looking again
                                    currentState = 0;
                                    doClearCounts(stateCount);
                                }
                                else
                                {
                                    // No, shift counts back by two
                                    doShiftCounts2(stateCount);
                                    currentState = 3;
                                }
                            }
                            else
                            {
                                stateCount[++currentState]++;
                            }
                        }
                        else
                        {
                            // Counting white pixels
                            stateCount[currentState]++;
                        }
                    }
                } // for j=...

                if (foundPatternCross(stateCount))
                {
                    handlePossibleCenter(stateCount, i, maxJ);
                } // end if foundPatternCross
            } // for i=iSkip-1 ...
            FinderPattern[][] patternInfo = selectMultipleBestPatterns();
            if (patternInfo == null)
                return EMPTY_RESULT_ARRAY;
            List<FinderPatternInfo> result = new List<FinderPatternInfo>();
            foreach (FinderPattern[] pattern in patternInfo)
            {
                ResultPoint.orderBestPatterns(pattern);
                result.Add(new FinderPatternInfo(pattern));
            }

            if (result.Count == 0)
            {
                return EMPTY_RESULT_ARRAY;
            }
            else
            {
                return result.ToArray();
            }
        }
    }
}