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

// Define OLED width and height
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

// Define Thresholds
#define TEMP_HOT_THRESHOLD 25.0 //To detect hotness
#define TEMP_COLD_THRESHOLD 10.0 //To detect Coldness
#define DIST_THRESHOLD 10

// Define SSD1306 OLED display object
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

// Define pin connections for sensors and LEDs as constants for safety
const int TEMP_PIN = A0;
const int PIR_PIN = 4;
const int TRIG_PIN = 6;
const int ECHO_PIN = 7;
const int TEMP_LED = 3;
const int PIR_LED = 5;
const int DIST_LED = 8;

// Constants for the thermistor calculation
const float BETA = 3950; // Beta coefficient for thermistor
const int SERIES_RESISTOR = 10000; // 10kΩ resistor

void setup() {
  // Initialize Serial Monitor
  Serial.begin(9600);

  // Initialize pins
  pinMode(TEMP_LED, OUTPUT);
  pinMode(PIR_LED, OUTPUT);
  pinMode(DIST_LED, OUTPUT);
  pinMode(PIR_PIN, INPUT);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);

  // Initialize the display with address 0x3C for I2C
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("SSD1306 allocation failed"));
    for (;;); // Infinite loop to stop execution if display fails
  }

  // Display a welcome message
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(0, 10);
  display.println("Welcome to Smart Home");
  display.display();
  delay(2000); // Pause for 2 seconds
  // Read and display the initial temperature value
  readTemperature();
  display.clearDisplay();
}

void loop() {
  readTemperature();   // Modular function for temperature reading
  checkMotion();       // Modular function for PIR sensor logic
  measureDistance();   // Modular function for ultrasonic sensor
  display.display();   // Update the display once after all measurements
  delay(5000);         // Pause for 5 second before next loop
}

// Modular function for temperature sensor reading using Beta coefficient method
void readTemperature() {
  int tempValue = analogRead(TEMP_PIN);
  // Guard against divide-by-zero error
  if (tempValue == 0) {
    Serial.println("Error: Temperature sensor read value 0. Skipping temperature reading.");
    return; // Skip temperature processing if invalid reading
  }

  float resistance = (1023.0 / tempValue) - 1.0;
  resistance = SERIES_RESISTOR / resistance;

  // Calculate temperature using Beta coefficient
  float temperatureC = 1 / (log(resistance / SERIES_RESISTOR) / BETA + 1.0 / 298.15) - 273.15;

  // Display temperature on Serial Monitor and OLED Display
  Serial.print("Temperature: ");
  Serial.print(temperatureC);
  Serial.println(" °C");

  display.clearDisplay();
  display.setTextSize(1);
  display.setCursor(0, 0);
  display.print("Temperature: ");
  display.print(temperatureC);
  display.println(" C");

  // Temperature LED logic
  if (temperatureC > TEMP_HOT_THRESHOLD || temperatureC < TEMP_COLD_THRESHOLD) {
    digitalWrite(TEMP_LED, HIGH);
  } else {
    digitalWrite(TEMP_LED, LOW);
  }
}

// Updated modular function for PIR motion sensor logic
void checkMotion() {
  static int pirState = LOW; // Maintain state across function calls
  int val = digitalRead(PIR_PIN); // Read the input value from the PIR sensor

  if (val == HIGH) { // Check if the input is HIGH (motion detected)
    digitalWrite(PIR_LED, HIGH); // Turn LED ON
    if (pirState == LOW) {
      // Motion has just been detected
      Serial.println("Motion detected!");
      display.setCursor(0, 20); // Set the cursor position on the display
      display.println("Motion Detected!");
      pirState = HIGH; // Update state
    }
  } else {
    digitalWrite(PIR_LED, LOW); // Turn LED OFF
    if (pirState == HIGH) {
      // Motion has just ended
      Serial.println("Motion ended!");
      pirState = LOW; // Update state
    }
  }
}

// Modular function for ultrasonic distance measurement using HC-SR04
void measureDistance() {
  // Start a new measurement:
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2); // Ensure the TRIG pin is low for a stable pulse
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10); // Keep TRIG pin high for 10 microseconds
  digitalWrite(TRIG_PIN, LOW);

  // Read the duration from the ECHO pin
  long duration = pulseIn(ECHO_PIN, HIGH);

  // Calculate distance in centimeters
  int distance_cm = duration / 58;

  // Display distance on Serial Monitor and OLED Display
  Serial.print("Distance in CM: ");
  Serial.println(distance_cm);

  display.setCursor(0, 40);
  display.print("Distance: ");
  display.print(distance_cm);
  display.println(" cm");

  // Distance LED logic
  if (distance_cm < DIST_THRESHOLD) {
    digitalWrite(DIST_LED, HIGH);
  } else {
    digitalWrite(DIST_LED, LOW);
  }
}