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

// GPIO pin assignments
#define INCREASE_BUTTON 17
#define DECREASE_BUTTON 16
#define START_STOP_BUTTON 15
#define BUZZER_PIN 4

// OLED dimensions
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

// Timer variables
int sessionMinutes = 0;   // Total session duration in minutes
int studyMinutes = 0;     // Study time in minutes
bool timerRunning = false; // Timer state: running or stopped
unsigned long startTime;   // Timer start time (in milliseconds)
unsigned long elapsedTime; // Elapsed time since start

void setup() {
  // Initialize Serial Monitor
  Serial.begin(115200);

  // Initialize buttons
  pinMode(INCREASE_BUTTON, INPUT_PULLDOWN);
  pinMode(DECREASE_BUTTON, INPUT_PULLDOWN);
  pinMode(START_STOP_BUTTON, INPUT_PULLDOWN);

  // Initialize buzzer
  pinMode(BUZZER_PIN, OUTPUT);

  // Initialize OLED display
  if (!display.begin(0x3C, -1)) {
    Serial.println("OLED initialization failed!");
    while (true);
  }
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(0, 0);
  display.println("Welcome!");
  display.display();
  delay(2000); // Show welcome message for 2 seconds

  // Initial display update
  updateDisplay();
}


void loop() {
  // Check Increase Button
  if (digitalRead(INCREASE_BUTTON) == HIGH) {
    sessionMinutes += 5; // Increment session time by 5 minutes
    updateDisplay();
    delay(200); // Debounce delay
  }

  // Check Decrease Button
  if (digitalRead(DECREASE_BUTTON) == HIGH) {
    if (sessionMinutes > 0) sessionMinutes -= 5; // Decrement session time
    updateDisplay();
    delay(200); // Debounce delay
  }

  // Check Start/Stop Button
  if (digitalRead(START_STOP_BUTTON) == HIGH) {
    timerRunning = !timerRunning; // Toggle the timer state
    playBuzzer(timerRunning);    // Play buzzer sound
    startTime = millis();        // Record start time
    updateDisplay();
    delay(500); // Debounce delay
  }

  // Timer logic
  if (timerRunning) {
    elapsedTime = millis() - startTime;
    int elapsedMinutes = elapsedTime / 60000; // Convert ms to minutes
    if (elapsedMinutes >= sessionMinutes) {
      // Timer completed
      timerRunning = false;
      playBuzzer(false); // End buzzer
      sessionMinutes = 0; // Reset session time
      updateDisplay();
    }
  }
}

void updateDisplay() {
  display.clearDisplay();
  display.setTextSize(1);
  display.setCursor(0, 0);

  // Display timer settings
  display.println("Timer Settings:");
  display.setCursor(0, 15);
  display.print("Session: ");
  display.print(sessionMinutes);
  display.println(" mins");
  display.setCursor(0, 30);
  display.print("Study: ");
  display.print(studyMinutes);
  display.println(" mins");

  // Display timer state
  if (timerRunning) {
    display.setCursor(0, 45);
    display.println("Timer: RUNNING");
  } else {
    display.setCursor(0, 45);
    display.println("Timer: STOPPED");
  }

  display.display();
}

void playBuzzer(bool start) {
  if (start) {
    digitalWrite(BUZZER_PIN, HIGH);
    delay(200);
    digitalWrite(BUZZER_PIN, LOW);
  } else {
    for (int i = 0; i < 3; i++) {
      digitalWrite(BUZZER_PIN, HIGH);
      delay(200);
      digitalWrite(BUZZER_PIN, LOW);
      delay(200);
    }
  }
}