/*=========================================================================

   Library: iMSTK

   Copyright (c) Kitware, Inc. & Center for Modeling, Simulation,
   & Imaging in Medicine, Rensselaer Polytechnic Institute.

   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.txt

   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.

=========================================================================*/

#include "imstkFastMarch.h"
#include "imstkLogger.h"
#include "imstkVecDataArray.h"

namespace imstk
{
void
FastMarch::solve()
{
    // Get the scalars (ensure they're single component doubles)
    std::shared_ptr<AbstractDataArray> abstractScalars = m_imageData->getScalars();
    if (abstractScalars->getScalarType() != IMSTK_DOUBLE || abstractScalars->getNumberOfComponents() != 1)
    {
        LOG(WARNING) << "fastMarch only works with single component double images";
        return;
    }
    auto    scalars = std::dynamic_pointer_cast<DataArray<double>>(abstractScalars);
    double* imgPtr  = scalars->getPointer();
    m_dim        = m_imageData->getDimensions();
    m_spacing    = m_imageData->getSpacing();
    m_indexShift = m_dim[0] * m_dim[1];

    // We maintain a solution in maps, to keep things sparse

    // Sparse container for which nodes are marked visited
    m_visited = std::unordered_set<int>();
    // Sparse container for nodal distances
    m_distances = std::unordered_map<int, double>();   // Solved distances

    m_queue = std::priority_queue<Node, std::vector<Node>, NodeComparator>();

    // Add the initial seeds to the queue
    for (size_t i = 0; i < m_seedVoxels.size(); i++)
    {
        const Vec3i& coord = m_seedVoxels[i];
        if (coord[0] < 0 || coord[0] >= m_dim[0]
            || coord[1] < 0 || coord[1] >= m_dim[1]
            || coord[2] < 0 || coord[2] >= m_dim[2])
        {
            continue;
        }
        const int index = static_cast<int>(m_imageData->getScalarIndex(coord));
        m_distances[index] = imgPtr[m_imageData->getScalarIndex(coord)];
        m_queue.push(Node(index, 0.0, coord));
    }

    // Process every node in order of minimum distance
    while (!m_queue.empty())
    {
        Node node = m_queue.top();
        m_queue.pop();

        const Vec3i& coord  = node.m_coord;
        const int&   nodeId = node.m_nodeId;

        // Termination conditions
        if (isVisited(nodeId)
            || getDistance(nodeId) >= m_distThreshold)
        {
            continue;
        }

        // Mark node as visited (to avoid readdition)
        m_visited.insert(nodeId);

        // Update all its neighbor cells (diagonals not considered neighbors)
        // Right +x
        int   neighborId    = nodeId + 1;
        Vec3i neighborCoord = coord + Vec3i(1, 0, 0);
        if (neighborCoord[0] < m_dim[0] && !isVisited(neighborId))
        {
            solveNode(neighborCoord, neighborId);
        }
        // Left -x
        neighborId    = nodeId - 1;
        neighborCoord = coord - Vec3i(1, 0, 0);
        if (neighborCoord[0] >= 0 && !isVisited(neighborId))
        {
            solveNode(neighborCoord, neighborId);
        }

        // Up +y
        neighborId    = nodeId + m_dim[0];
        neighborCoord = coord + Vec3i(0, 1, 0);
        if (neighborCoord[1] < m_dim[1] && !isVisited(neighborId))
        {
            solveNode(neighborCoord, neighborId);
        }
        // Down -y
        neighborId    = nodeId - m_dim[0];
        neighborCoord = coord - Vec3i(0, 1, 0);
        if (neighborCoord[1] >= 0 && !isVisited(neighborId))
        {
            solveNode(neighborCoord, neighborId);
        }

        // Forward +z
        neighborId    = nodeId + m_indexShift;
        neighborCoord = coord + Vec3i(0, 0, 1);
        if (neighborCoord[2] < m_dim[2] && !isVisited(neighborId))
        {
            solveNode(neighborCoord, neighborId);
        }
        // Backward -z
        neighborId    = nodeId - m_indexShift;
        neighborCoord = coord - Vec3i(0, 0, 1);
        if (neighborCoord[2] >= 0 && !isVisited(neighborId))
        {
            solveNode(neighborCoord, neighborId);
        }
    }

    // Write the sparse distances to the image
    for (auto i : m_distances)
    {
        imgPtr[i.first] = i.second;
    }
}

void
FastMarch::solveNode(Vec3i coord, int index)
{
    // Compute the min distance in each axes
    const double dists[6] =
    {
        coord[0] - 1 >= 0 ? getDistance(index - 1) : IMSTK_DOUBLE_MAX,
        coord[0] + 1 < m_dim[0] ? getDistance(index + 1) : IMSTK_DOUBLE_MAX,
        coord[1] - 1 >= 0 ? getDistance(index - m_dim[0]) : IMSTK_DOUBLE_MAX,
        coord[1] + 1 < m_dim[1] ? getDistance(index + m_dim[0]) : IMSTK_DOUBLE_MAX,
        coord[2] - 1 >= 0 ? getDistance(index - m_indexShift) : IMSTK_DOUBLE_MAX,
        coord[2] + 1 < m_dim[2] ? getDistance(index + m_indexShift) : IMSTK_DOUBLE_MAX
    };
    const double minDist[3] =
    {
        std::min(dists[0], dists[1]),
        std::min(dists[2], dists[3]),
        std::min(dists[4], dists[5])
    };

    // Sort so that the min of minDist is first
    int dimReorder[3] = { 0, 1, 2 };
    for (int i = 0; i < 3; i++)
    {
        for (int j = i + 1; j < 3; j++)
        {
            const int dim1 = dimReorder[i];
            const int dim2 = dimReorder[j];
            if (minDist[dim1] > minDist[dim2])
            {
                std::swap(dimReorder[i], dimReorder[j]);
            }
        }
    }

    double aa = 0.0;
    double bb = 0.0;
    double cc = -1.0;

    // For every dimension
    double solution = IMSTK_DOUBLE_MAX;
    double discrim  = 0.0;
    // todo: Sort dimensions by minDist, start with smallest (break faster)
    for (unsigned int i = 0; i < 3; i++)
    {
        const double value = minDist[dimReorder[i]];
        if (solution >= value)
        {
            const double spaceFactor = std::sqrt(1.0 / m_spacing[dimReorder[i]]);
            aa += spaceFactor;
            bb += value * spaceFactor;
            cc += value * value * spaceFactor;

            discrim = bb * bb - aa * cc;
            if (discrim < 0.0)
            {
                // Whoops
                return;
            }

            solution = (std::sqrt(discrim) + bb) / aa;
        }
        else
        {
            break;
        }
    }

    if (solution < IMSTK_DOUBLE_MAX)
    {
        // Accept it as the new distance
        m_distances[index] = solution;
        m_queue.push(Node(index, solution, coord));
    }
}
}