aqi_calculator.h

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#pragma once

#include "abstract_aqi_calculator.h"
// https://www.airnow.gov/sites/default/files/2020-05/aqi-technical-assistance-document-sept2018.pdf

namespace esphome {
namespace hm3301 {

class AQICalculator : public AbstractAQICalculator {
 public:
  uint16_t get_aqi(uint16_t pm2_5_value, uint16_t pm10_0_value) override {
    int pm2_5_index = calculate_index_(pm2_5_value, pm2_5_calculation_grid_);
    int pm10_0_index = calculate_index_(pm10_0_value, pm10_0_calculation_grid_);

    return (pm2_5_index < pm10_0_index) ? pm10_0_index : pm2_5_index;
  }

 protected:
  static const int AMOUNT_OF_LEVELS = 7;

  int index_grid_[AMOUNT_OF_LEVELS][2] = {{0, 50},    {51, 100},  {101, 150}, {151, 200},
                                          {201, 300}, {301, 400}, {401, 500}};

  int pm2_5_calculation_grid_[AMOUNT_OF_LEVELS][2] = {{0, 12},    {13, 35},   {36, 55},  {56, 150},
                                                      {151, 250}, {251, 350}, {351, 500}};

  int pm10_0_calculation_grid_[AMOUNT_OF_LEVELS][2] = {{0, 54},    {55, 154},  {155, 254}, {255, 354},
                                                       {355, 424}, {425, 504}, {505, 604}};

  int calculate_index_(uint16_t value, int array[AMOUNT_OF_LEVELS][2]) {
    int grid_index = get_grid_index_(value, array);
    int aqi_lo = index_grid_[grid_index][0];
    int aqi_hi = index_grid_[grid_index][1];
    int conc_lo = array[grid_index][0];
    int conc_hi = array[grid_index][1];

    return (value - conc_lo) * (aqi_hi - aqi_lo) / (conc_hi - conc_lo) + aqi_lo;
  }

  int get_grid_index_(uint16_t value, int array[AMOUNT_OF_LEVELS][2]) {
    for (int i = 0; i < AMOUNT_OF_LEVELS; i++) {
      if (value >= array[i][0] && value <= array[i][1]) {
        return i;
      }
    }
    return -1;
  }
};

}  // namespace hm3301
}  // namespace esphome