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 *                                                                                       *
 * OpenSpace                                                                             *
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 * Copyright (c) 2014-2025                                                               *
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#include <modules/multiresvolume/rendering/tfbrickselector.h>

#include <modules/multiresvolume/rendering/brickcover.h>
#include <modules/multiresvolume/rendering/errorhistogrammanager.h>
#include <modules/multiresvolume/rendering/tsp.h>
#include <openspace/rendering/transferfunction.h>
#include <openspace/util/histogram.h>
#include <ghoul/misc/assert.h>
#include <algorithm>
#include <cmath>

namespace {
    bool compareSplitPoints(const openspace::BrickSelection& a,
        const openspace::BrickSelection& b)
    {
        return a.splitPoints < b.splitPoints;
    }
} // namespace

namespace openspace {

TfBrickSelector::TfBrickSelector(TSP* tsp, ErrorHistogramManager* hm,
                                 TransferFunction* tf, int memoryBudget,
                                 int streamingBudget)
    : _tsp(tsp)
    , _histogramManager(hm)
    , _transferFunction(tf)
    , _memoryBudget(memoryBudget)
    , _streamingBudget(streamingBudget)
{}

bool TfBrickSelector::initialize() {
    return calculateBrickErrors();
}

void TfBrickSelector::setMemoryBudget(int memoryBudget) {
    _memoryBudget = memoryBudget;
}

void TfBrickSelector::setStreamingBudget(int streamingBudget) {
    _streamingBudget = streamingBudget;
}

void TfBrickSelector::selectBricks(int timestep, std::vector<int>& bricks) {
    int numTimeSteps = _tsp->header().numTimesteps;
    int numBricksPerDim = _tsp->header().xNumBricks;

    unsigned int rootNode = 0;
    BrickSelection::SplitType splitType;
    float rootSplitPoints = splitPoints(rootNode, splitType);

    BrickSelection brickSelection = BrickSelection(
        numBricksPerDim,
        numTimeSteps,
        splitType,
        rootSplitPoints
    );

    std::vector<BrickSelection> priorityQueue;
    std::vector<BrickSelection> leafSelections;
    std::vector<BrickSelection> temporalSplitQueue;
    std::vector<BrickSelection> deadEnds;

    if (splitType != BrickSelection::SplitType::None) {
        priorityQueue.push_back(brickSelection);
    }
    else {
        leafSelections.push_back(brickSelection);
    }

    int totalStreamingBudget = _streamingBudget * numTimeSteps;
    int nBricksInMemory = 1;
    int nStreamedBricks = 1;

    // First loop: While neither the memory nor the streaming budget is reached,
    // try to optimize for visual quality vs memory.

    while (nBricksInMemory <= _memoryBudget - 7 && priorityQueue.size() > 0) {
        std::pop_heap(priorityQueue.begin(), priorityQueue.end(), compareSplitPoints);

        BrickSelection bs = priorityQueue.back();
        unsigned int brickIndex = bs.brickIndex;
        priorityQueue.pop_back();

        // TODO: handle edge case when we can only afford temporal splits or no split
        //       (only 1 spot left)
        if (bs.splitType == BrickSelection::SplitType::Temporal) {
            unsigned int childBrickIndex;
            bool pickRightTimeChild = bs.timestepInRightChild(timestep);

            // On average on the whole time period, splitting this spatial brick in two
            // time steps would generate twice as much streaming. Current number of
            // streams of this spatial brick is 2^nTemporalSplits over the whole time
            // period.

            int newStreams = static_cast<int>(std::pow(2, bs.nTemporalSplits));
            //std::cout << "preparing for " << newStreams << " new streams" << std::endl;

            // Refining this one more step would require the double amount of streams
            if (nStreamedBricks + newStreams > totalStreamingBudget) {
                // Reached dead end (streaming budget would be exceeded)
                deadEnds.push_back(bs);
                break;
            }
            nStreamedBricks += newStreams;

            if (pickRightTimeChild) {
                childBrickIndex = _tsp->bstRight(brickIndex);
            }
            else {
                childBrickIndex = _tsp->bstLeft(brickIndex);
            }

            BrickSelection::SplitType childSplitType;
            float childSplitPoints = splitPoints(childBrickIndex, childSplitType);
            BrickSelection childSelection = bs.splitTemporally(
                pickRightTimeChild,
                childBrickIndex,
                childSplitType,
                childSplitPoints
            );
            if (childSplitType != BrickSelection::SplitType::None) {
                priorityQueue.push_back(childSelection);
                std::push_heap(
                    priorityQueue.begin(),
                    priorityQueue.end(),
                    compareSplitPoints
                );
            }
            else {
                leafSelections.push_back(childSelection);
            }
        }
        else if (bs.splitType == BrickSelection::SplitType::Spatial) {
            nBricksInMemory += 7; // Remove one and add eight.
            unsigned int firstChild = _tsp->firstOctreeChild(brickIndex);

            // On average on the whole time period, splitting this spatial brick into
            // eight spatial bricks would generate eight times as much streaming. Current
            // number of streams of this spatial brick is 2^nTemporalStreams over the
            // whole time period.
            int newStreams = 7 * static_cast<int>(std::pow(2, bs.nTemporalSplits));

            if (nStreamedBricks + newStreams > totalStreamingBudget) {
                // Reached dead end (streaming budget would be exceeded)
                // However, temporal split might be possible
                if (bs.splitType != BrickSelection::SplitType::Temporal) {
                    bs.splitType = BrickSelection::SplitType::Temporal;
                    bs.splitPoints = temporalSplitPoints(bs.brickIndex);
                }
                if (bs.splitPoints > -1) {
                    temporalSplitQueue.push_back(bs);
                }
                else {
                    deadEnds.push_back(bs);
                }
                break;
            }
            nStreamedBricks += newStreams;

            for (unsigned int i = 0; i < 8; i++) {
                unsigned int childBrickIndex = firstChild + i;

                BrickSelection::SplitType childSplitType;
                float childSplitPoints = splitPoints(childBrickIndex, childSplitType);
                //std::cout << "Splitting spatially" << std::endl;
                BrickSelection childSelection = bs.splitSpatially(
                    i % 2 != 0,
                    (i / 2) % 2 != 0, // abock: isn't this always 0?
                    i / 4 != 0,
                    childBrickIndex,
                    childSplitType,
                    childSplitPoints
                );

                if (childSplitType != BrickSelection::SplitType::None) {
                    priorityQueue.push_back(childSelection);
                    std::push_heap(
                        priorityQueue.begin(),
                        priorityQueue.end(),
                        compareSplitPoints
                    );
                }
                else {
                    leafSelections.push_back(childSelection);
                }
            }
        }
    }

    if (nBricksInMemory <= _memoryBudget - 7) {
        // std::cout << "memory budget not reached. " << nBricksInMemory << " out of " <<
        // memoryBudget << std::endl;
    }

    // Is it possible that we may stream more bricks?
    if (nStreamedBricks < totalStreamingBudget - 1) {
        while (priorityQueue.size() > 0) {
            BrickSelection bs = priorityQueue.back();
            if (bs.splitType != BrickSelection::SplitType::Temporal) {
                bs.splitType = BrickSelection::SplitType::Temporal;
                bs.splitPoints = temporalSplitPoints(bs.brickIndex);
            }
            priorityQueue.pop_back();
            if (bs.splitPoints > -1) {
                temporalSplitQueue.push_back(bs);
                std::push_heap(
                    temporalSplitQueue.begin(),
                    temporalSplitQueue.end(),
                    compareSplitPoints
                );
            }
            else {
                deadEnds.push_back(bs);
            }
        }

        // Keep splitting until it's not possible anymore
        while (nStreamedBricks < totalStreamingBudget - 1 &&
               temporalSplitQueue.size() > 0)
        {
            std::pop_heap(
                temporalSplitQueue.begin(),
                temporalSplitQueue.end(),
                compareSplitPoints
            );
            BrickSelection bs = temporalSplitQueue.back();
            temporalSplitQueue.pop_back();

            unsigned int brickIndex = bs.brickIndex;
            int newStreams = static_cast<int>(std::pow(2, bs.nTemporalSplits));
            if (nStreamedBricks + newStreams > totalStreamingBudget) {
                // The current best choice would make us exceed the streaming budget,
                // try next instead.
                deadEnds.push_back(bs);
                continue;
            }

            nStreamedBricks += newStreams;
            ;
            bool pickRightTimeChild = bs.timestepInRightChild(timestep);

            unsigned int childBrickIndex = pickRightTimeChild ?
                _tsp->bstRight(brickIndex) :
                _tsp->bstLeft(brickIndex);

            float childSplitPoints = temporalSplitPoints(childBrickIndex);

            if (childSplitPoints > -1) {
                BrickSelection childSelection = bs.splitTemporally(
                    pickRightTimeChild,
                    childBrickIndex,
                    BrickSelection::SplitType::Temporal,
                    childSplitPoints
                );
                temporalSplitQueue.push_back(childSelection);
                std::push_heap(
                    temporalSplitQueue.begin(),
                    temporalSplitQueue.end(),
                    compareSplitPoints
                );
            }
            else {
                BrickSelection childSelection = bs.splitTemporally(
                    pickRightTimeChild,
                    childBrickIndex,
                    BrickSelection::SplitType::None,
                    -1
                );
                deadEnds.push_back(childSelection);
            }
        }
    }
    else {
        // Write selected inner nodes to brickSelection vector
        //std::cout << "priority queue: " << priorityQueue.size() << std::endl;
        for (const BrickSelection& bs : priorityQueue) {
            writeSelection(bs, bricks);
        }
    }

    //std::cout << "temporal split queue: " << temporalSplitQueue.size() << std::endl;
    // Write selected inner nodes to brickSelection vector
    for (const BrickSelection& bs : temporalSplitQueue) {
        writeSelection(bs, bricks);
    }
    //std::cout << "dead ends: " << deadEnds.size() << std::endl;
    for (const BrickSelection& bs : deadEnds) {
        writeSelection(bs, bricks);
    }
    // Write selected leaf nodes to brickSelection vector
    //std::cout << "leaf selections: " << leafSelections.size() << std::endl;
    for (const BrickSelection& bs : leafSelections) {
        writeSelection(bs, bricks);
    }
}

float TfBrickSelector::temporalSplitPoints(unsigned int brickIndex) {
    if (_tsp->isBstLeaf(brickIndex)) {
        return -1.f;
    }

    const unsigned int leftChild = _tsp->bstLeft(brickIndex);
    const unsigned int rightChild = _tsp->bstRight(brickIndex);

    const float currentError = _brickErrors[brickIndex];
    const float splitError = _brickErrors[leftChild] + _brickErrors[rightChild];

    float diff = currentError - splitError;
    if (diff < 0.f) {
        diff = -diff;
    }
    return diff * 0.5f;
}

float TfBrickSelector::spatialSplitPoints(unsigned int brickIndex) {
    if (_tsp->isOctreeLeaf(brickIndex)) {
        return -1.f;
    }

    float currentError = _brickErrors[brickIndex];
    float splitError = 0;

    unsigned int firstChild = _tsp->firstOctreeChild(brickIndex);
    for (unsigned int i = 0; i < 8; i++) {
        unsigned int child = firstChild + i;
        splitError += _brickErrors[child];
    }

    float diff = currentError - splitError;
    if (diff < 0.0) {
        diff = -diff;
    }

    return diff * 0.125f;
}

float TfBrickSelector::splitPoints(unsigned int brickIndex,
                                   BrickSelection::SplitType& splitType)
{
    const float temporalPoints = temporalSplitPoints(brickIndex);
    const float spatialPoints = spatialSplitPoints(brickIndex);
    float splitPoints;

    if (spatialPoints > 0 && spatialPoints > temporalPoints) {
        splitPoints = spatialPoints;
        splitType = BrickSelection::SplitType::Spatial;
    }
    else if (temporalPoints > 0) {
        splitPoints = temporalPoints;
        splitType = BrickSelection::SplitType::Temporal;
    }
    else {
        splitPoints = -1;
        splitType = BrickSelection::SplitType::None;
    }
    return splitPoints;
}


bool TfBrickSelector::calculateBrickErrors() {
    TransferFunction *tf = _transferFunction;
    if (!tf) {
        return false;
    }

    size_t tfWidth = tf->width();
    if (tfWidth <= 0) {
        return false;
    }

    std::vector<float> gradients(tfWidth - 1);
    for (size_t offset = 0; offset < tfWidth - 1; offset++) {
        glm::vec4 prevRgba = tf->sample(offset);
        glm::vec4 nextRgba = tf->sample(offset + 1);

        float colorDifference = glm::distance(prevRgba, nextRgba);
        float alpha = (prevRgba.w + nextRgba.w) * 0.5f;

        gradients[offset] = colorDifference*alpha;
    }

    unsigned int nHistograms = _tsp->numTotalNodes();
    _brickErrors = std::vector<float>(nHistograms);

    for (unsigned int brickIndex = 0; brickIndex < nHistograms; brickIndex++) {
        if (_tsp->isBstLeaf(brickIndex) && _tsp->isOctreeLeaf(brickIndex)) {
            _brickErrors[brickIndex] = 0;
        }
        else {
            const Histogram* histogram = _histogramManager->histogram(brickIndex);
            float error = 0;
            for (size_t i = 0; i < gradients.size(); i++) {
                float x = (i + 0.5f) / tfWidth;
                float sample = histogram->interpolate(x);
                ghoul_assert(sample >= 0, "@MISSING");
                ghoul_assert(gradients[i] >= 0, "@MISSING");
                error += sample * gradients[i];
            }
            _brickErrors[brickIndex] = error;
        }
    }

    return true;
}

int TfBrickSelector::linearCoords(int x, int y, int z) const {
    const TSP::Header &header = _tsp->header();
    return x + (header.xNumBricks * y) + (header.xNumBricks * header.yNumBricks * z);
}

void TfBrickSelector::writeSelection(BrickSelection brickSelection,
                                     std::vector<int>& bricks) const
{
    BrickCover coveredBricks = brickSelection.cover;
    for (int z = coveredBricks.lowZ; z < coveredBricks.highZ; z++) {
        for (int y = coveredBricks.lowY; y < coveredBricks.highY; y++) {
            for (int x = coveredBricks.lowX; x < coveredBricks.highX; x++) {
                bricks[linearCoords(x, y, z)] = brickSelection.brickIndex;
            }
        }
    }
}

} // namespace openspace