#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

// PID constants
float Kp = 2.0;
float Ki = 0.5;
float Kd = 1.0;

// PID variables
float setPoint = 25.0;  // Desired temperature in Celsius
float currentTemp = 0;
float error, previousError = 0;
float integral = 0;
float derivative;
float output;

// Pin definitions
const int tempSensorPin = A0;   // Mock input using potentiometer
const int heaterPin = 9;        // PWM output to LED

// OLED display setup
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

void setup() {
  Serial.begin(9600);
  pinMode(heaterPin, OUTPUT);

  // Initialize OLED
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("SSD1306 allocation failed"));
    while (true); // Halt if OLED init fails
  }
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
}

void loop() {
  // Read analog input and map to temperature (0–50 °C)
  int analogValue = analogRead(tempSensorPin);
  currentTemp = map(analogValue, 0, 1023, 0, 50);

  // Compute PID
  error = setPoint - currentTemp;
  integral += error;
  derivative = error - previousError;
  output = Kp * error + Ki * integral + Kd * derivative;
  output = constrain(output, 0, 255);  // Clamp for PWM range

  // Apply output to heater (LED)
  analogWrite(heaterPin, output);

  // Serial output for debugging
  Serial.print("Temp: ");
  Serial.print(currentTemp);
  Serial.print(" °C | Output: ");
  Serial.println(output);

  // OLED display update
  display.clearDisplay();
  display.setCursor(0, 0);
  display.print("Temp: ");
  display.print(currentTemp);
  display.print(" C");

  display.setCursor(0, 16);
  display.print("Set: ");
  display.print(setPoint);
  display.print(" C");

  display.setCursor(0, 32);
  display.print("Output: ");
  display.print((int)output);

  display.display();

  // Store previous error and wait
  previousError = error;
  delay(200);
}