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/*
 * Copyright (c) 2011-2018 Isode Limited.
 * All rights reserved.
 * See the COPYING file for more information.
 */

#pragma once

#include <vector>

#include <boost/numeric/conversion/cast.hpp>

namespace Swift {
    using std::equal_to;

    namespace Detail {
        template<typename XIt, typename YIt, typename Length, typename Predicate>
        void computeLeastCommonSubsequenceMatrix(XIt xBegin, XIt xEnd, YIt yBegin, YIt yEnd, std::vector<Length>& result) {
            size_t width = static_cast<size_t>(std::distance(xBegin, xEnd) + 1);
            size_t height = static_cast<size_t>(std::distance(yBegin, yEnd)  + 1);
            result.resize(width * height);

            // Initialize first row & column
            for (size_t i = 0; i < width; ++i) {
                result[i] = 0;
            }
            for (size_t j = 0; j < height; ++j) {
                result[j*width] = 0;
            }

            // Compute the LCS lengths for subsets
            Predicate predicate;
            for (size_t i = 1; i < width; ++i) {
                for (size_t j = 1; j < height; ++j) {
                    result[i + j*width] = predicate(*(xBegin + static_cast<long long>(i)-1), *(yBegin + static_cast<long long>(j)-1)) ? result[(i-1) + (j-1)*width] + 1 : std::max(result[i + (j-1)*width], result[i-1 + (j*width)]);
                }
            }
        }
    }

    template<typename X, typename InsertRemovePredicate, typename UpdatePredicate>
    void computeIndexDiff(const std::vector<X>& x, const std::vector<X>& y, std::vector<size_t>& updates, std::vector<size_t>& postUpdates, std::vector<size_t>& removes, std::vector<size_t>& inserts) {
        InsertRemovePredicate insertRemovePredicate;
        UpdatePredicate updatePredicate;

        // Find & handle common prefix (Optimization to reduce LCS matrix size)
        typename std::vector<X>::const_iterator xBegin = x.begin();
        typename std::vector<X>::const_iterator yBegin = y.begin();
        while (xBegin < x.end() && yBegin < y.end() && insertRemovePredicate(*xBegin, *yBegin)) {
            if (updatePredicate(*xBegin, *yBegin)) {
                updates.push_back(static_cast<size_t>(std::distance(x.begin(), xBegin)));
                postUpdates.push_back(static_cast<size_t>(std::distance(y.begin(), yBegin)));
            }
            ++xBegin;
            ++yBegin;
        }
        size_t prefixLength = static_cast<size_t>(std::distance(x.begin(), xBegin));

        // Find & handle common suffix (Optimization to reduce LCS matrix size)
        typename std::vector<X>::const_reverse_iterator xEnd = x.rbegin();
        typename std::vector<X>::const_reverse_iterator yEnd = y.rbegin();
        while (xEnd.base() > xBegin && yEnd.base() > yBegin && insertRemovePredicate(*xEnd, *yEnd)) {
            if (updatePredicate(*xEnd, *yEnd)) {
                updates.push_back(static_cast<size_t>(std::distance(x.begin(), xEnd.base()) - 1));
                postUpdates.push_back(static_cast<size_t>(std::distance(y.begin(), yEnd.base()) - 1));
            }
            ++xEnd;
            ++yEnd;
        }

        // Compute lengths
        size_t xLength = static_cast<size_t>(std::distance(xBegin, xEnd.base()));
        size_t yLength = static_cast<size_t>(std::distance(yBegin, yEnd.base()));

        // Compute LCS matrix
        std::vector<unsigned int> lcs;
        Detail::computeLeastCommonSubsequenceMatrix<typename std::vector<X>::const_iterator, typename std::vector<X>::const_iterator, unsigned int, InsertRemovePredicate>(xBegin, xEnd.base(), yBegin, yEnd.base(), lcs);

        // Process LCS matrix
        size_t i = xLength;
        size_t j = yLength;
        size_t width = xLength + 1;
        while (true) {
            if (i > 0 && j > 0 && insertRemovePredicate(x[prefixLength + i-1], y[prefixLength + j-1])) {
                // x[i-1] same
                if (updatePredicate(x[prefixLength + i - 1], y[prefixLength + j - 1])) {
                    updates.push_back(prefixLength + i-1);
                    postUpdates.push_back(prefixLength + j-1);
                }
                i -= 1;
                j -= 1;
            }
            else if (j > 0 && (i == 0 || lcs[i + (j-1)*width] >= lcs[i-1 + j*width])) {
                // y[j-1] added
                inserts.push_back(prefixLength + j-1);
                j -= 1;
            }
            else if (i > 0 && (j == 0 || lcs[i + (j-1)*width] < lcs[i-1 + j*width])) {
                // x[i-1] removed
                removes.push_back(prefixLength + i-1);
                i -= 1;
            }
            else {
                break;
            }
        }
    }
}