/*  Stretch

    This application is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.
*/

#include "stretch.h"

#include <fitsio.h>
#include <math.h>
#include <QtConcurrent>

namespace {

// Returns the median value of the vector.
// The vector is modified in an undefined way.
template <typename T>
T median(std::vector<T>& values)
{
  const int middle = values.size() / 2;
  std::nth_element(values.begin(), values.begin() + middle, values.end());
  return values[middle];
}

// Returns the rough max of the buffer.
template <typename T>
T sampledMax(T const *values, int size, int sampleBy)
{
    T maxVal = 0;
    for (int i = 0; i < size; i+= sampleBy)
        if (maxVal < values[i])
            maxVal = values[i];
    return  maxVal;
}

// Returns the median of the sample values.
// The values are not modified.
template <typename T>
T median(T const *values, int size, int sampleBy)
{
  const int downsampled_size = size / sampleBy;
  std::vector<T> samples(downsampled_size);
  for (int index = 0, i = 0; i < downsampled_size; ++i, index += sampleBy)
    samples[i] = values[index];
  return median(samples);
}

// This stretches one channel given the input parameters.
// Based on the spec in section 8.5.6
// https://pixinsight.com/doc/docs/XISF-1.0-spec/XISF-1.0-spec.html
// Uses multiple threads, blocks until done.
// The extension parameters are not used.
// Sampling is applied to the output (that is, with sampling=2, we compute every other output
// sample both in width and height, so the output would have about 4X fewer pixels.
template <typename T>
void stretchOneChannel(T *input_buffer, QImage *output_image,
                       const StretchParams& stretch_params, 
                       int input_range, int image_height, int image_width, int sampling)
{
  QVector<QFuture<void>> futures;

  // We're outputting uint8, so the max output is 255.
  constexpr int maxOutput = 255;

  // Maximum possible input value (e.g. 1024*64 - 1 for a 16 bit unsigned int).
  const float maxInput = input_range > 1 ? input_range - 1 : input_range;
  
  const float midtones   = stretch_params.grey_red.midtones;
  const float highlights = stretch_params.grey_red.highlights;
  const float shadows    = stretch_params.grey_red.shadows;

  // Precomputed expressions moved out of the loop.
  // hightlights - shadows, protecting for divide-by-0, in a 0->1.0 scale.
  const float hsRangeFactor = highlights == shadows ? 1.0f : 1.0f / (highlights - shadows);
  // Shadow and highlight values translated to the ADU scale.
  const T nativeShadows = shadows * maxInput;
  const T nativeHighlights = highlights * maxInput;
  // Constants based on above needed for the stretch calculations.
  const float k1 = (midtones - 1) * hsRangeFactor * maxOutput / maxInput;
  const float k2 = ((2 * midtones) - 1) * hsRangeFactor / maxInput;
  
  // Increment the input index by the sampling, the output index increments by 1.
  for (int j = 0, jout = 0; j < image_height; j+=sampling, jout++)
  {
    futures.append(QtConcurrent::run([ = ]()
    {
        T * inputLine  = input_buffer + j * image_width;
        auto * scanLine = output_image->scanLine(jout);
        
    for (int i = 0, iout = 0; i < image_width; i+=sampling, iout++)
        {
          const T input = inputLine[i];
          if (input < nativeShadows) scanLine[iout] = 0;
          else if (input >= nativeHighlights) scanLine[iout] = maxOutput;
          else 
          {
            const T inputFloored = (input - nativeShadows);
            scanLine[iout] = (inputFloored * k1) / (inputFloored * k2 - midtones);
	  }
        }
    }));
  }
  for(QFuture<void> future : futures)
    future.waitForFinished();
}

// This is like the above 1-channel stretch, but extended for 3 channels.
// This could have been more modular, but the three channels are combined
// into a single qRgb value at the end, so it seems the simplest thing is to
// replicate the code. It is assume the colors are not interleaved--the red image
// is stored fully, then the green, then the blue.
// Sampling is applied to the output (that is, with sampling=2, we compute every other output
// sample both in width and height, so the output would have about 4X fewer pixels.
template <typename T>
void stretchThreeChannels(T *inputBuffer, QImage *outputImage,
                          const StretchParams& stretchParams, 
                          int inputRange, int imageHeight, int imageWidth, int sampling)
{
  QVector<QFuture<void>> futures;

  // We're outputting uint8, so the max output is 255.
  constexpr int maxOutput = 255;

  // Maximum possible input value (e.g. 1024*64 - 1 for a 16 bit unsigned int).
  const float maxInput = inputRange > 1 ? inputRange - 1 : inputRange;
  
  const float midtonesR   = stretchParams.grey_red.midtones;
  const float highlightsR = stretchParams.grey_red.highlights;
  const float shadowsR    = stretchParams.grey_red.shadows;
  const float midtonesG   = stretchParams.green.midtones;
  const float highlightsG = stretchParams.green.highlights;
  const float shadowsG    = stretchParams.green.shadows;
  const float midtonesB   = stretchParams.blue.midtones;
  const float highlightsB = stretchParams.blue.highlights;
  const float shadowsB    = stretchParams.blue.shadows;

  // Precomputed expressions moved out of the loop.
  // hightlights - shadows, protecting for divide-by-0, in a 0->1.0 scale.
  const float hsRangeFactorR = highlightsR == shadowsR ? 1.0f : 1.0f / (highlightsR - shadowsR);
  const float hsRangeFactorG = highlightsG == shadowsG ? 1.0f : 1.0f / (highlightsG - shadowsG);
  const float hsRangeFactorB = highlightsB == shadowsB ? 1.0f : 1.0f / (highlightsB - shadowsB);
  // Shadow and highlight values translated to the ADU scale.
  const T nativeShadowsR = shadowsR * maxInput;
  const T nativeShadowsG = shadowsG * maxInput;
  const T nativeShadowsB = shadowsB * maxInput;
  const T nativeHighlightsR = highlightsR * maxInput;
  const T nativeHighlightsG = highlightsG * maxInput;
  const T nativeHighlightsB = highlightsB * maxInput;
  // Constants based on above needed for the stretch calculations.
  const float k1R = (midtonesR - 1) * hsRangeFactorR * maxOutput / maxInput;
  const float k1G = (midtonesG - 1) * hsRangeFactorG * maxOutput / maxInput;
  const float k1B = (midtonesB - 1) * hsRangeFactorB * maxOutput / maxInput;
  const float k2R = ((2 * midtonesR) - 1) * hsRangeFactorR / maxInput;
  const float k2G = ((2 * midtonesG) - 1) * hsRangeFactorG / maxInput;
  const float k2B = ((2 * midtonesB) - 1) * hsRangeFactorB / maxInput;
  
  const int size = imageWidth * imageHeight;
  
  for (int j = 0, jout = 0; j < imageHeight; j+=sampling, jout++)
  {
    futures.append(QtConcurrent::run([ = ]()
    {
        // R, G, B input images are stored one after another.
        T * inputLineR  = inputBuffer + j * imageWidth;
        T * inputLineG  = inputLineR + size;
        T * inputLineB  = inputLineG + size;
        
        auto * scanLine = reinterpret_cast<QRgb*>(outputImage->scanLine(jout));
        
    for (int i = 0, iout = 0; i < imageWidth; i+=sampling, iout++)
        {
          const T inputR = inputLineR[i];
          const T inputG = inputLineG[i];
          const T inputB = inputLineB[i];

          uint8_t red, green, blue;
          
          if (inputR < nativeShadowsR) red = 0;
          else if (inputR >= nativeHighlightsR) red = maxOutput;
          else 
          {
            const T inputFloored = (inputR - nativeShadowsR);
            red = (inputFloored * k1R) / (inputFloored * k2R - midtonesR);
	  }

          if (inputG < nativeShadowsG) green = 0;
          else if (inputG >= nativeHighlightsG) green = maxOutput;
          else 
          {
            const T inputFloored = (inputG - nativeShadowsG);
            green = (inputFloored * k1G) / (inputFloored * k2G - midtonesG);
	  }

          if (inputB < nativeShadowsB) blue = 0;
          else if (inputB >= nativeHighlightsB) blue = maxOutput;
          else 
          {
            const T inputFloored = (inputB - nativeShadowsB);
            blue = (inputFloored * k1B) / (inputFloored * k2B - midtonesB);
	  }
          scanLine[iout] = qRgb(red, green, blue);
        }
    }));
  }
  for(QFuture<void> future : futures)
    future.waitForFinished();
}

template <typename T>
void stretchChannels(T *input_buffer, QImage *output_image,
                       const StretchParams& stretch_params, 
                     int input_range, int image_height, int image_width, int num_channels, int sampling)
{
    if (num_channels == 1)
      stretchOneChannel(input_buffer, output_image, stretch_params, input_range,
                        image_height, image_width, sampling);
    else if (num_channels == 3)
      stretchThreeChannels(input_buffer, output_image, stretch_params, input_range,
                           image_height, image_width, sampling);
}
  
// See section 8.5.7 in above link  https://pixinsight.com/doc/docs/XISF-1.0-spec/XISF-1.0-spec.html
template <typename T>
void computeParamsOneChannel(T const *buffer, StretchParams1Channel *params,
                             int inputRange, int height, int width)
{
  // Find the median sample.
  constexpr int maxSamples = 500000;
  const int sampleBy = width * height < maxSamples ? 1 : width * height / maxSamples;

  T medianSample = median(buffer, width * height, sampleBy);
  // Find the Median deviation: 1.4826 * median of abs(sample[i] - median).
  const int numSamples = width * height / sampleBy;
  std::vector<T> deviations(numSamples);
  for (int index = 0, i = 0; i < numSamples; ++i, index += sampleBy)
  {
    if (medianSample > buffer[index])
      deviations[i] = medianSample - buffer[index];
    else
      deviations[i] = buffer[index] - medianSample;
  }

  // Shift everything to 0 -> 1.0.
  const float medDev = median(deviations);
  const float normalizedMedian = medianSample / static_cast<float>(inputRange);
  const float MADN = 1.4826 * medDev / static_cast<float>(inputRange);

  const bool upperHalf = normalizedMedian > 0.5;

  const float shadows = (upperHalf || MADN == 0) ? 0.0 :
    fmin(1.0, fmax(0.0, (normalizedMedian + -2.8 * MADN)));

  const float highlights = (!upperHalf || MADN == 0) ? 1.0 :
    fmin(1.0, fmax(0.0, (normalizedMedian - -2.8 * MADN)));

  float X, M;
  constexpr float B = 0.25;
  if (!upperHalf) {
    X = normalizedMedian - shadows;
    M = B;
  } else {
    X = B;
    M = highlights - normalizedMedian;
  }
  float midtones;
  if (X == 0) midtones = 0.0f;
  else if (X == M) midtones = 0.5f;
  else if (X == 1) midtones = 1.0f;
  else midtones = ((M - 1) * X) / ((2 * M - 1) * X - M);

  // Store the params.
  params->shadows = shadows;
  params->highlights = highlights;
  params->midtones = midtones;
  params->shadows_expansion = 0.0;
  params->highlights_expansion = 1.0;
}

// Need to know the possible range of input values.
// Using the type of the sample and guessing.
// Perhaps we should examine the contents for the file
// (e.g. look at maximum value and extrapolate from that).
int getRange(int data_type)
{
    switch (data_type)
    {
        case TBYTE:
            return 256;
        case TSHORT:
            return 64*1024;
        case TUSHORT:
            return 64*1024;
        case TLONG:
            return 64*1024;
        case TFLOAT:
            return 64*1024;
        case TLONGLONG:
            return 64*1024;
        case TDOUBLE:
            return 64*1024;
        default:
            return 64*1024;
    }
}
  
}  // namespace

Stretch::Stretch(int width, int height, int channels, int data_type)
{
  image_width = width;
  image_height = height;
  image_channels = channels;
  dataType = data_type;
  input_range = getRange(dataType);
}

void Stretch::run(uint8_t const *input, QImage *outputImage, int sampling)
{
    Q_ASSERT(outputImage->width() == (image_width + sampling - 1) / sampling);
    Q_ASSERT(outputImage->height() == (image_height + sampling - 1) / sampling);
    recalculateInputRange(input);

    switch (dataType)
    {
        case TBYTE:
            stretchChannels(reinterpret_cast<uint8_t const*>(input), outputImage, params,
                            input_range, image_height, image_width, image_channels, sampling);
            break;
        case TSHORT:
            stretchChannels(reinterpret_cast<short const*>(input), outputImage, params,
                            input_range, image_height, image_width, image_channels, sampling);
            break;
        case TUSHORT:
            stretchChannels(reinterpret_cast<unsigned short const*>(input), outputImage, params,
                            input_range, image_height, image_width, image_channels, sampling);
            break;
        case TLONG:
            stretchChannels(reinterpret_cast<long const*>(input), outputImage, params,
                            input_range, image_height, image_width, image_channels, sampling);
            break;
        case TFLOAT:
            stretchChannels(reinterpret_cast<float const*>(input), outputImage, params,
                            input_range, image_height, image_width, image_channels, sampling);
            break;
        case TLONGLONG:
            stretchChannels(reinterpret_cast<long long const*>(input), outputImage, params,
                            input_range, image_height, image_width, image_channels, sampling);
            break;
        case TDOUBLE:
            stretchChannels(reinterpret_cast<double const*>(input), outputImage, params,
                            input_range, image_height, image_width, image_channels, sampling);
            break;
        default:
        break;
    }
}

// The input range for float/double is ambiguous, and we can't tell without the buffer,
// so we set it to 64K and possibly reduce it when we see the data.
void Stretch::recalculateInputRange(uint8_t const *input)
{
    if (input_range <= 1) return;
    if (dataType != TFLOAT && dataType != TDOUBLE) return;

    float mx = 0;
    if (dataType == TFLOAT)
        mx = sampledMax(reinterpret_cast<float const*>(input), image_height * image_width, 1000);
    else if (dataType == TDOUBLE)
        mx = sampledMax(reinterpret_cast<double const*>(input), image_height * image_width, 1000);
    if (mx <= 1.01f) input_range = 1;
}

StretchParams Stretch::computeParams(uint8_t const *input)
{
  recalculateInputRange(input);
  StretchParams result;
  for (int channel = 0; channel < image_channels; ++channel)
  {
    int offset = channel * image_width * image_height;
    StretchParams1Channel *params = channel == 0 ? &result.grey_red :
      (channel == 1 ? &result.green : &result.blue);
    switch (dataType)
    {
        case TBYTE:
        {
            auto buffer = reinterpret_cast<uint8_t const*>(input);
            computeParamsOneChannel(buffer + offset, params, input_range,
                                    image_height, image_width);
            break;
        }
        case TSHORT:
        {
            auto buffer = reinterpret_cast<short const*>(input);
            computeParamsOneChannel(buffer + offset, params, input_range,
                                    image_height, image_width);
            break;
        }
        case TUSHORT:
        {
            auto buffer = reinterpret_cast<unsigned short const*>(input);
            computeParamsOneChannel(buffer + offset, params, input_range,
                                    image_height, image_width);
            break;
        }
        case TLONG:
        {
            auto buffer = reinterpret_cast<long const*>(input);
            computeParamsOneChannel(buffer + offset, params, input_range,
                                    image_height, image_width);
            break;
        }
        case TFLOAT:
        {
            auto buffer = reinterpret_cast<float const*>(input);
            computeParamsOneChannel(buffer + offset, params, input_range,
                                    image_height, image_width);
            break;
        }
        case TLONGLONG:
        {
            auto buffer = reinterpret_cast<long long const*>(input);
            computeParamsOneChannel(buffer + offset, params, input_range,
                                    image_height, image_width);
            break;
        }
        case TDOUBLE:
        {
            auto buffer = reinterpret_cast<double const*>(input);
            computeParamsOneChannel(buffer + offset, params, input_range,
                                    image_height, image_width);
            break;
        }
        default:
        break;
    }
  }
  return result;
}
