#include <LiquidCrystal_I2C.h>
#include <SoftwareSerial.h>

LiquidCrystal_I2C lcd(0x27, 16, 2);
SoftwareSerial sim900(7, 8); // RX, TX for GSM

volatile unsigned long pulseCount = 0;
float kWh = 0;
float price = 0;
unsigned long lastMillis = 0;

const int impPerKwh = 1600;    // Meter spec
const float ratePerKwh = 12.0; // Local rate

// === Interrupt Service Routine ===
void pulseISR() {
  pulseCount++;
  Serial.println("[INFO] imp Detected");
}

void setup() {
  lcd.init();
  lcd.backlight();
  pinMode(2, INPUT_PULLUP); 
  attachInterrupt(digitalPinToInterrupt(2), pulseISR, FALLING);

  sim900.begin(9600);
  Serial.begin(9600);

  // Set SMS text mode
  sim900.println("AT+CMGF=1");
  delay(500);
  // Configure SIM900 to forward received SMS to serial
  sim900.println("AT+CNMI=1,2,0,0,0");
  delay(500);

  lcd.setCursor(0, 0);
  lcd.print("Energy Monitor");
  delay(1500);
  lcd.clear();
}

void loop() {
  if (millis() - lastMillis >= 1000) { // Update every 1s
    lastMillis = millis();

    // Compute kWh and price
    kWh = pulseCount / (float)impPerKwh;
    price = kWh * ratePerKwh;

    // === LCD Display (no flicker) ===
    lcd.setCursor(0, 0);
    lcd.print("kWh: ");
    lcd.print(kWh, 3);
    lcd.print("    ");

    lcd.setCursor(0, 1);
    lcd.print("Php: ");
    lcd.print(price, 2);
    lcd.print("   ");

    // === Serial Monitor ===
    Serial.print("kWh = ");
    Serial.print(kWh, 3);
    Serial.print(" | Php = ");
    Serial.println(price, 2);
  }

  // === Check for incoming SMS ===
  if (sim900.available()) {
    String sms = sim900.readString();
    sms.toLowerCase(); // make lowercase for comparison

    Serial.println("SMS Received: " + sms);

    if (sms.indexOf("bill") >= 0) {
      sendBill();
    }
  }
}

// === Function to send bill ===
void sendBill() {
  sim900.println("AT+CMGF=1");
  delay(500);
  sim900.println("AT+CMGS=\"+63XXXXXXXXXX\""); // Replace with your number
  delay(500);
  sim900.print("Total = ");
  sim900.print(kWh, 3);
  sim900.print(" kWh, Price = ");
  sim900.print(price, 2);
  sim900.println(" Php");
  sim900.write(26); // Ctrl+Z to send SMS
  Serial.println("Bill Sent!");
}