#include <Servo.h> // include Servo library

unsigned long previousMillis = 0;
const long interval = 1000; // serial print interval

Servo horizontal; // horizontal servo (LEFT <-> RIGHT)
int servoh = 90;   // 90;     // stand horizontal servo
int servohLimitHigh = 175; // this value needs to be checked prior to first start up
int servohLimitLow = 5; // this value needs to be checked prior to first start up

Servo vertical;   // vertical servo (UP <-> DOWN)
int servov = 35;    //   35;     // stand vertical servo
int servovLimitHigh = 70; // this value needs to be checked prior to first start up
int servovLimitLow = 0; // this value needs to be checked prior to first start up

/*brown = GND
 * red = VCC
 * orange = Signal
 */

// LDR pin connections
//  name  = analogpin;
int ldrtl = 0; //LDR top left
int ldrtr = 1; //LDR top right
int ldrbl = 2; //LDR bottom left
int ldrbr = 3; //LDR bottom right

void setup() {
  Serial.begin(9600);
  horizontal.attach(10);
  vertical.attach(11);
  horizontal.write(180); // horizontal start up angle: 180° => east, 0° => west
  vertical.write(35); // vertical start up angle: 45° => mid angle between high noon and sunset
  delay(2000);
}

void loop() {
  int tl = analogRead(ldrtl); // top left
  int tr = analogRead(ldrtr); // top right
  int bl = analogRead(ldrbl); // bottom left
  int br = analogRead(ldrbr); // bottom rigt
  // the more sunlight the lower the resistance the lower the analog reading the lower the voltage (example: direct sunlight => 100 lux, 79 Ohm, 0.04 Volt, 8)

  // int dtime = analogRead(4)/20; // read potentiometers
  // int tol = analogRead(5)/4;
  int dtime = 100; // determines the interval between each run through and therefore the speed of movement
  int tol = 20; // determines the adjustment tolerance

  int avt = (tl + tr) / 2; // average value top (top left vs. top right)
  int avb = (bl + br) / 2; // average value bottom (down left vs. down right)
  int dvert = avt - avb; // difference TOP vs. BOTTOM

  int avl = (tl + bl) / 2; // average value left (top left vs. down left)
  int avr = (tr + br) / 2; // average value right (top right vs. down right)
  int dhoriz = avl - avr;//  difference LEFT vs. RIGHT

  unsigned long currentMillis = millis();
  if (currentMillis - previousMillis >= interval) {
    previousMillis = currentMillis;
    Serial.print("avt:");
    Serial.print(avt);
    Serial.print(" avb:");
    Serial.print(avb);
    Serial.print(" avl:");
    Serial.print(avl);
    Serial.print(" avr:");
    Serial.print(avr);
    Serial.print(" dhoriz:");
    Serial.print(dhoriz);
    Serial.print(" dvert:");
    Serial.print(dvert);
    /*Serial.print(" dtime:");
      Serial.print(dtime);
      Serial.print(" tol:");
      Serial.print(tol);*/
    Serial.print(" servoh:");
    Serial.print(servoh);
    Serial.print(" servov:");
    Serial.print(servov);
    Serial.println();
  }

  //----------------- VERTICAL (UP/DOWN) ---------------------------
  if (dvert < -1 * tol || dvert > tol) { // if TOP/DOWN difference is smaller than tolerance OR TOP/DOWN difference is higher than tolerance
    if (avt > avb) { // if TOP is brigher than BOTTOM
      servov = ++servov; // then move panel upwards
      if (servov > servovLimitHigh) { // if panel reaches TOP limit stop there
        servov = servovLimitHigh;
      }
    }
    else if (avt < avb) { // if top is darker than bottom
      servov = --servov; // then move panel downwards
      if (servov < servovLimitLow) { // if panel reaches bottom limit stop there
        servov = servovLimitLow;
      }
    }
    vertical.write(servov);
  }

  //----------------- HORIZONTAL (LEFT/RIGHT) ---------------------------
  if (dhoriz < -1 * tol || dhoriz > tol) { // if LEFT/RIGHT difference is smaller than tolerance OR LEFT/RIGHT difference is higher than tolerance
    if (avl > avr) { // if LEFT is brighter than RIGHT
      servoh = --servoh; // then move panel to LEFT
      if (servoh < servohLimitLow) { // if panel reaches LEFT limit stop there
        servoh = servohLimitLow;
      }
    }
    else if (avl < avr) { // if LEFT is darker than RIGHT
      servoh = ++servoh; // then move panel to RIGHT
      if (servoh > servohLimitHigh) { // if panel reaches RIGHT limit stop there
        servoh = servohLimitHigh;
      }
    }
    else if (avl = avr) {
      // nothing
    }
    horizontal.write(servoh);
  }
  delay(dtime); // delay between every run through
}