#pragma once

#include <glm/ext.hpp>
#include <glm/glm.hpp>

enum ToneMappingMode {
  ToneMapping_None       = 0,
  ToneMapping_Reinhard   = 1,
  ToneMapping_Uchimura   = 2,
  ToneMapping_KhronosPBR = 3,
};

// Uchimura 2017, "HDR theory and practice"
// Math: https://www.desmos.com/calculator/gslcdxvipg
// Source: https://www.slideshare.net/nikuque/hdr-theory-and-practicce-jp
float uchimura(float x, float P, float a, float m, float l, float c, float b)
{
  float l0 = ((P - m) * l) / a;
  float L0 = m - m / a;
  float L1 = m + (1.0f - m) / a;
  float S0 = m + l0;
  float S1 = m + a * l0;
  float C2 = (a * P) / (P - S1);
  float CP = -C2 / P;

  float w0 = float(1.0f - glm::smoothstep(0.0f, m, x));
  float w2 = float(glm::step(m + l0, x));
  float w1 = float(1.0f - w0 - w2);

  float T = float(m * pow(x / m, float(c)) + b);
  float S = float(P - (P - S1) * exp(CP * (x - S0)));
  float L = float(m + a * (x - m));

  return T * w0 + L * w1 + S * w2;
}

float reinhard2(float v, float maxWhite)
{
  return v * (1.0f + (v / (maxWhite * maxWhite))) / (1.0f + v);
}

// Khronos PBR Neutral Tone Mapper
// https://github.com/KhronosGroup/ToneMapping/blob/main/PBR_Neutral/README.md#pbr-neutral-specification
// https://github.com/KhronosGroup/ToneMapping/blob/main/PBR_Neutral/pbrNeutral.glsl
float PBRNeutralToneMapping(float color, float startCompression, float desaturation)
{
  startCompression -= 0.04f;

  float x      = color;
  float offset = x < 0.08f ? x - 6.25f * x * x : 0.04f;
  color -= offset;

  float peak = color;
  if (peak < startCompression)
    return color;

  const float d = 1. - startCompression;
  float newPeak = 1. - d * d / (peak + d - startCompression);
  color *= newPeak / peak;

  float g = 1.0f - 1.0f / (desaturation * (peak - newPeak) + 1.0f);
  return glm::mix(color, newPeak, g);
}