#include <Wire.h>
#include <LiquidCrystal_I2C.h>

// ============================================================
//  SMART CLASSROOM ENERGY MANAGEMENT SYSTEM
//  Occupancy-based lighting control with IR + PIR sensing
// ============================================================

LiquidCrystal_I2C lcd(0x27, 16, 2);

// --- Pin Definitions ---
const int IR1_PIN  = 4;
const int IR2_PIN  = 5;
const int PIR_PIN  = 27;

const int LED_LOW  = 25;
const int LED_MED  = 26;
const int LED_HIGH = 18;

// --- Timing Constants ---
const int           DEBOUNCE_MS   = 200;
const unsigned long SEQ_WINDOW_MS = 1200;
const unsigned long PIR_HOLD_MS   = 5000;
const unsigned long FLASH_MS      = 1500;
const unsigned long LCD_UPDATE_MS = 200;

// --- Occupancy & Sensor State ---
int  occupancy   = 0;
int  pendingSensor  = 0;
unsigned long pendingTime   = 0;
unsigned long lastMotionTime = 0;

bool lastIR1 = HIGH;
bool lastIR2 = HIGH;
bool lastPIR = LOW;

unsigned long lastIR1Trigger = 0;
unsigned long lastIR2Trigger = 0;
unsigned long lastLCDUpdate  = 0;

// --- LCD Flash State ---
bool          flashActive = false;
unsigned long flashStart  = 0;
String        flashLine1  = "";
String        flashLine2  = "";

// ============================================================
//  LIGHTING CONTROL
// ============================================================

void setLights(int mode) {
  digitalWrite(LED_LOW,  mode >= 1 ? HIGH : LOW);
  digitalWrite(LED_MED,  mode >= 2 ? HIGH : LOW);
  digitalWrite(LED_HIGH, mode >= 3 ? HIGH : LOW);
}

// ============================================================
//  MODE HELPERS
// ============================================================

String getModeName(int mode) {
  switch (mode) {
    case 0: return "OFF ";
    case 1: return "LOW ";
    case 2: return "MED ";
    default: return "HIGH";
  }
}

int calculateMode() {
  if (occupancy == 0) {
    return (millis() - lastMotionTime < PIR_HOLD_MS) ? 1 : 0;
  }
  if (occupancy <= 2) return 1;
  if (occupancy <= 4) return 2;
  return 3;
}

// ============================================================
//  LCD DISPLAY
// ============================================================

// Pads a string to exactly 16 chars to avoid stale characters
String padTo16(String s) {
  while (s.length() < 16) s += " ";
  return s;
}

void triggerFlash(String line1, String line2) {
  flashLine1  = padTo16(line1);
  flashLine2  = padTo16(line2);
  flashActive = true;
  flashStart  = millis();
}

void updateLCD(int mode, bool pirState) {

  // --- Flash screen for ENTRY / EXIT ---
  if (flashActive) {
    if (millis() - flashStart < FLASH_MS) {
      lcd.setCursor(0, 0);
      lcd.print(flashLine1);
      lcd.setCursor(0, 1);
      lcd.print(flashLine2);
      return;
    }
    flashActive = false;
    lcd.clear();   // clean slate after flash ends
  }

  // --- Throttle normal LCD updates to avoid flicker ---
  if (millis() - lastLCDUpdate < LCD_UPDATE_MS) return;
  lastLCDUpdate = millis();

  // Row 0:  "Occ:5   Mode:HIGH"
  String row0 = "Occ:" + String(occupancy) + "   Mode:" + getModeName(mode);
  // Row 1:  "Motion: YES"
  String row1 = "Motion: " + String(pirState ? "YES" : "NO ");

  lcd.setCursor(0, 0);
  lcd.print(padTo16(row0));
  lcd.setCursor(0, 1);
  lcd.print(padTo16(row1));
}

// ============================================================
//  ENTRY / EXIT LOGIC
// ============================================================

void handleIR(int sensor) {
  unsigned long now = millis();

  if (pendingSensor != 0 && (now - pendingTime) <= SEQ_WINDOW_MS) {

    if (pendingSensor == 1 && sensor == 2) {
      occupancy++;
      Serial.println("[EVENT] ENTRY detected | Occupancy: " + String(occupancy));
      triggerFlash("  >> ENTRY <<   ", "  Occupancy: " + String(occupancy));
    }

    else if (pendingSensor == 2 && sensor == 1) {
      if (occupancy > 0) occupancy--;
      Serial.println("[EVENT] EXIT detected  | Occupancy: " + String(occupancy));
      triggerFlash("  >> EXIT <<    ", "  Occupancy: " + String(occupancy));
    }

    pendingSensor = 0;

  } else {
    pendingSensor = sensor;
    pendingTime   = now;
  }
}

// ============================================================
//  SETUP
// ============================================================

void setup() {
  Serial.begin(115200);
  Serial.println("============================================");
  Serial.println("  Smart Classroom Energy Management System ");
  Serial.println("============================================");

  pinMode(IR1_PIN,  INPUT_PULLUP);
  pinMode(IR2_PIN,  INPUT_PULLUP);
  pinMode(PIR_PIN,  INPUT_PULLDOWN);

  pinMode(LED_LOW,  OUTPUT);
  pinMode(LED_MED,  OUTPUT);
  pinMode(LED_HIGH, OUTPUT);

  lcd.init();
  lcd.backlight();

  // Boot message
  lcd.setCursor(0, 0);
  lcd.print("  Smart Class   ");
  lcd.setCursor(0, 1);
  lcd.print(" Energy System  ");
  delay(2000);
  lcd.clear();

  Serial.println("[SYSTEM] Initialisation complete. Ready.");
}

// ============================================================
//  MAIN LOOP
// ============================================================

void loop() {

  bool ir1 = digitalRead(IR1_PIN);
  bool ir2 = digitalRead(IR2_PIN);
  bool pir = digitalRead(PIR_PIN);

  // --- IR Sensor 1 ---
  if (lastIR1 == HIGH && ir1 == LOW && (millis() - lastIR1Trigger > DEBOUNCE_MS)) {
    lastIR1Trigger = millis();
    handleIR(1);
  }

  // --- IR Sensor 2 ---
  if (lastIR2 == HIGH && ir2 == LOW && (millis() - lastIR2Trigger > DEBOUNCE_MS)) {
    lastIR2Trigger = millis();
    handleIR(2);
  }

  // --- PIR Sensor ---
  if (lastPIR == LOW && pir == HIGH) {
    lastMotionTime = millis();
    Serial.println("[EVENT] PIR motion detected");
  }

  // --- Reset incomplete IR sequence ---
  if (pendingSensor != 0 && (millis() - pendingTime > SEQ_WINDOW_MS)) {
    pendingSensor = 0;
  }

  // --- Update outputs ---
  int mode = calculateMode();
  setLights(mode);
  updateLCD(mode, pir);

  // --- Serial status (every loop) ---
  Serial.print("[STATUS] Occ:");
  Serial.print(occupancy);
  Serial.print(" | Mode:");
  Serial.print(getModeName(mode));
  Serial.print(" | Motion:");
  Serial.println(pir ? "YES" : "NO");

  lastIR1 = ir1;
  lastIR2 = ir2;
  lastPIR = pir;

  delay(100);
}