// Fnu Shoaib Ahmed, 652420658, fahme8
// Lab 8 - Interrupt Service Routines (ISR)

// Description - This code uses interrupts to handle button presses and toggles between two states on an LCD.
//               It displays elapsed time in the default state and scrolls a message when an interrupt is triggered.

// Assumptions - Buttons use pull-up resistors; pins 2 and 3 are used for interrupts as required by the lab.

// References - I used prelab links for understanding Interrupt Service Routines (ISR) and I used Lab 3 for scrolling functionality.

#include <LiquidCrystal.h>

// Pin definitions
const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 6, d7 = 7;
const int buttonPin1 = 2;  // Interrupt 0 (pin 2)
const int buttonPin2 = 3;  // Interrupt 1 (pin 3)
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

volatile int state = 0;
unsigned long startTime = 0;
unsigned long lastUpdateTime = 0; // For tracking the last display update
unsigned long scrollUpdateTime = 0; // For scrolling timing

void setup() {
  lcd.begin(16, 2);
  pinMode(buttonPin1, INPUT_PULLUP);
  pinMode(buttonPin2, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(buttonPin1), button1ISR, FALLING);
  attachInterrupt(digitalPinToInterrupt(buttonPin2), button2ISR, FALLING);
  startTime = millis();
}

void loop() {
  if (state == 0) {
    // Update every second to avoid unnecessary refreshing
    if (millis() - lastUpdateTime >= 1000) {
      lastUpdateTime = millis();
      lcd.clear();
      lcd.setCursor(0, 0);
      lcd.print("System on for: ");
      lcd.setCursor(0, 1);
      lcd.print((millis() - startTime) / 1000);
      lcd.print(" seconds");
    }
  } 
  else if (state == 1) {
    // Scroll the message in State 1
    if (millis() - scrollUpdateTime >= 500) {  // Adjust delay to control scroll speed
      scrollUpdateTime = millis();
      lcd.scrollDisplayLeft();
    }
  }
}

void button1ISR() {
  state = 1;
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("Interrupt received!");
  lcd.setCursor(0, 1);
  lcd.print("Press button 2 to continue");
  scrollUpdateTime = millis();  // Reset scroll timer
}

void button2ISR() {
  if (state == 1) {
    startTime = millis();  // Reset timer
    state = 0;
    lastUpdateTime = millis();  // Reset display update time
    lcd.clear();
  }
}