/* Calibration of LDR values of Ohms to LUX values using a LUXmeter.
In this sketch, the calibration of LDR values to 
*/


#include <Adafruit_Sensor.h>


int light = 0; //LDR readings taken and stored at pin A0.
int lightCal = 0; //creating variable to store calibrated LUX values values and be called later in the loop.

int LEDPIN_1 = 27;  //LED pins used to react to light value differences.
int LEDPIN_2 = 14;

//LDR Calibration Parameters
#define SNS_LIGHT_PIN 0
int sns_light_raw = 0; // the raw light value is taken from the input pin of the LDR
float SNS_LIGHT_SLOPE = 0; //variable to store value relating to  (assumed) linear relationship between LUX and Ohmsreadings 
float SNS_LIGHT_OFFSET = 0;

int light_sensor_mean(int sensor_pin, int iterations=10) { //Creating an initial reading to measure against iterations.
  int reading = 0;
  Serial.println("Calculationg mean of readings... ");
  Serial.println("\nReading raw value...");
  Serial.print("Iterations: ");
  Serial.println(iterations);
  
  int temporary_value = 0; //temporary value collected of raw light reading.
  for (int i=0; i<iterations; i++){
    reading = analogRead(sensor_pin);
    Serial.println(reading);
    temporary_value = temporary_value + reading; //saving the raw LDR sensor readings into a temporay value folder for further manipulation.
    delay (10);
  
  }
  
  Serial.print("/nMean of raw values: "); 
  int mean = temporary_value/iterations; //calculating the mean value of raw readings using the number of trials(iterations) it passed through.
  Serial.println(mean);
  return mean;
}

void light_sensor_calibration( int sensor_pin, int iterations=10){ 
  Serial.println("==========================");
  Serial.println("Light Sensor Calibration");
  Serial.println("==========================");
  
  int x1 = light_sensor_mean(sensor_pin, iterations);  //calibration at this stage takes place in teh serial monitor. Corresponding values on the LUX meter and given in.
  Serial.print("x1 from reading: ");
  Serial.println(x1);
  
  Serial.println("Enter LUX value from luxmeter (y1): ");
  delay(100);
  while(Serial.available() == 0){} //Wait for user input
  int y1 = Serial.parseInt(); // Lux value
  Serial.read(); // Drop "/n" character from partInt()
  Serial.print("Lux value registed: ");
  Serial.println(y1);
  
  int x2 = light_sensor_mean(SNS_LIGHT_PIN, 10);  // several x values are taking to better map the relationship between LUX from the meter and digital to analog range (0-4096) from the LDR.
  Serial.print("x2 from reading: ");
  Serial.println(x2);

  Serial.println("Enter LUX value from luxmeter (y2): ");
  delay(100);
  while(Serial.available() == 0){} //Wait for user input
  int y2 = Serial.parseInt(); // Lux value
  Serial.read(); // Drop "/n" character from partInt()
  Serial.print("Lux value registed: ");
  Serial.println(y2);
  
  SNS_LIGHT_SLOPE = get_slope(x1,x2,y1,y2);  // 
  Serial.print("Calculated Slope: ");
  Serial.println(SNS_LIGHT_SLOPE);
  Serial.println("Save this value in variable SNS_LIGHT_SLOPE");
  
  SNS_LIGHT_OFFSET = get_offset(x1,x2,y1,y2);
  Serial.print("Calculated Offset: ");
  Serial.println(SNS_LIGHT_OFFSET);
  Serial.println("Save this value in variable SNS_LIGHT_OFFSET");

  Serial.println("======================");
  Serial.println("Calibration complete!");
  Serial.println("======================");
  
}

void light_sensor_test(int sensor_pin){
  Serial.print("Light sensor reading raw: ");
  Serial.println(light_sensor_value_raw(sensor_pin));
  Serial.print("Light sensor reading lux: ");
  Serial.println(light_sensor_value_lux(sensor_pin));
}

int light_sensor_value_raw(int sensor_pin){
  /*
   * Return Light sensor raw value
   */
  return analogRead(sensor_pin);
}

int light_sensor_value_lux(int sensor_pin){
  /*
   * Return Light sensor in lux
   */
  int raw = light_sensor_value_raw(sensor_pin);
  return (SNS_LIGHT_SLOPE*raw) + SNS_LIGHT_OFFSET;
}

int get_slope(int x1, int x2, int y1, int y2){
  /*
   * Return slope (m) from linear function ADC
   * 
   * Linear function y=mx+b
   * m = (y2-y1)/(x2-x1)
   * reference: https://keisan.casio.com/exec/system/1223508685
   */

  return (y2-y1)/(x2-x1);
}

int get_offset(int x1, int x2, int y1, int y2){
  /*
   * Linear function y=mx+b
   * b = (x2y1-x1y2)/(x2-x1)
   * reference: https://keisan.casio.com/exec/system/1223508685
   */
   
  return (x2*y1-x1*y2)/(x2-x1);
}


void setup() {
  pinMode(LEDPIN_1, OUTPUT);
   pinMode(LEDPIN_2, OUTPUT);
  delay(100);  //100ms delay
  lightCal = analogRead(SNS_LIGHT_PIN); //take a single reading and store it in lightCal variable.
  // This gives us preleminary value to compare and set the standard in the loop.



  light_sensor_calibration(SNS_LIGHT_PIN);
}

void loop() {
  // || PHOTORESISTOR ||
  // Take reading using analogRead() on sensor pin and store it in lightcal
  lightCal = analogRead(SNS_LIGHT_PIN);

  //set threshold reactions based on lightcalibrated value
  if (lightCal < 2000) {  // when its bright (i.e greater than 450Ohms), both LEDs will be off to save eergy)
    Serial.println("It very bright, lots of natural light");
    digitalWrite(LEDPIN_1, LOW);
    digitalWrite(LEDPIN_2, LOW); 
  }

  else if (lightCal > 1000 && light < 2000) { //medium amount of light to show one LED at a time).
    Serial.println("moderate light quantity, quite cloudy");
    digitalWrite(LEDPIN_1, HIGH);
    digitalWrite(LEDPIN_2,LOW);
  }
  else { // both LEDs turn on when the surroundings are dark.
    Serial.println("It very dark, extremely overcast or night time");
    digitalWrite(LEDPIN_1, HIGH);
    digitalWrite(LEDPIN_2, HIGH);
  }
 delay(750); //750ms delay between sensor readings.
}