#include <PID_v1.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

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

// Pin Configuration
const int tempPin = A0;        // LM35 sensor
const int heaterPin = 9;       // PWM output for heating element
const int upButton = 2;        // Setpoint increase
const int downButton = 3;      // Setpoint decrease

// PID Variables
double Setpoint = 30.0;        // Initial target temperature
double Input, Output;
double Kp = 500, Ki = 1, Kd = 0.1;
PID myPID(&Input, &Output, &Setpoint, Kp, Ki, Kd, DIRECT);

// Temperature Reading
float temperature = 0;
unsigned long lastUpdate = 0;

// Button Handling
unsigned long lastDebounceTime = 0;
const int debounceDelay = 50;

void setup() {
  Serial.begin(9600);
  
  // Initialize OLED
  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("OLED failed"));
    while(1);
  }
  display.clearDisplay();
  
  // Initialize PID
  myPID.SetOutputLimits(0, 255);
  myPID.SetSampleTime(1000);
  myPID.SetMode(AUTOMATIC);

  // Initialize Pins
  pinMode(heaterPin, OUTPUT);
  pinMode(upButton, INPUT_PULLUP);
  pinMode(downButton, INPUT_PULLUP);

  // Initial display update
  updateDisplay();
}

void loop() {
  // Update temperature every second
  if(millis() - lastUpdate >= 1000) {
    temperature = readTemperature();
    Input = temperature;
    myPID.Compute();
    lastUpdate = millis();
  }

  handleButtons();
  analogWrite(heaterPin, Output);
  updateDisplay();
}

float readTemperature() {
  int raw = analogRead(tempPin);
  return (raw * 500.0) / 1024.0;  // Convert to Celsius
}

void handleButtons() {
  // Debounce check
  if((millis() - lastDebounceTime) < debounceDelay) return;
  
  // Up button pressed
  if(digitalRead(upButton) == LOW) {
    Setpoint += 0.5;
    lastDebounceTime = millis();
  }
  
  // Down button pressed
  if(digitalRead(downButton) == LOW) {
    Setpoint -= 0.5;
    lastDebounceTime = millis();
  }
  
  // Constrain setpoint between 0-100°C
  Setpoint = constrain(Setpoint, 0, 100);
}

void updateDisplay() {
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);

  // Current Temperature
  display.setCursor(0, 0);
  display.print("Actual: ");
  display.print(temperature, 1);
  display.print("C");

  // Setpoint
  display.setCursor(0, 20);
  display.print("Target: ");
  display.print(Setpoint, 1);
  display.print("C");

  // PID Output
  display.setCursor(0, 40);
  display.print("Power: ");
  display.print((Output/255)*100, 0);
  display.print("%");

  // PID Parameters
  display.setCursor(0, 55);
  display.print("PID: ");
  display.print(Kp, 0);
  display.print("/");
  display.print(Ki, 1);
  display.print("/");
  display.print(Kd, 1);

  display.display();
}