#include <SPI.h> 
#include <MFRC522.h> 
#include <WiFi.h>
#include <PubSubClient.h>
#include <ArduinoJson.h>

// --- Pin Definitions ---
#define SS_PIN 5 
#define RST_PIN 22 
#define GREEN_LED 25 
#define RED_LED 26 
#define TRIG_PIN 14 
#define ECHO_PIN 12 

// --- Network & Shared MQTT Broker Configuration ---
const char* SSID = "Wokwi-GUEST";
const char* PASSWORD = "";
const char* MQTT_BROKER = "broker.hivemq.com";
const int MQTT_PORT = 1883;

// Global topic for all school terminals to clear active pass timers
const char* TOPIC_PASS_EVENTS = "school/hallway/pass/events";

WiFiClient espClient;
PubSubClient mqttClient(espClient);
MFRC522 rfid(SS_PIN, RST_PIN); 

// --- Recognized Card UIDs ---
const String FLOOR_INCHARGE_UID = "55667788"; 
const String TEACHER_CARD_UID   = "1234"; 
const String STUDENT_1_UID      = "11223344"; 

// --- State Variables ---
bool teacherPresent = false; 
unsigned long exitTimestamp = 0; 
bool studentOutUnscanned = false; 
bool alertActive = false; 
String activeStudentUID = "";

const int DOORWAY_TRIGGER_CM = 30; 
long lastDistance = 9999; 
const unsigned long GRACE_PERIOD_TEACHER_ABSENT = 7UL * 60UL * 1000UL;  // 7 minutes
const unsigned long ALERT_WINDOW_TEACHER_PRESENT = 2UL * 60UL * 1000UL; // 2 minutes

// --- Network Initialization ---
void connectWiFi() {
  Serial.print("Connecting to Wi-Fi...");
  WiFi.begin(SSID, PASSWORD);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println(" Connected!");
}

void connectMQTT() {
  while (!mqttClient.connected()) {
    Serial.print("Connecting to MQTT...");
    String clientId = "ESP32-Room101-" + String(random(0xffff), HEX);
    if (mqttClient.connect(clientId.c_str())) {
      Serial.println(" Connected!");
      // Subscribe to pass events so destination taps (Infirmary/Reception) auto-clear local timer
      mqttClient.subscribe(TOPIC_PASS_EVENTS);
    } else {
      Serial.print(" Failed, rc=");
      Serial.print(mqttClient.state());
      delay(2000);
    }
  }
}

// --- Multi-Terminal Incoming MQTT Listener ---
void mqttCallback(char* topic, byte* payload, unsigned int length) {
  StaticJsonDocument<384> doc;
  DeserializationError error = deserializeJson(doc, payload, length);

  if (error) {
    Serial.print("MQTT JSON parse error: ");
    Serial.println(error.f_str());
    return;
  }

  const char* eventType  = doc["eventType"];
  const char* studentUID = doc["studentId"];
  const char* terminal   = doc["terminal"];

  // If student tapped at another terminal (Infirmary/Reception), auto-clear local countdown
  if (studentOutUnscanned && String(studentUID) == activeStudentUID) {
    if (String(eventType) == "ARRIVED") {
      Serial.print("Pass cleared! Student ");
      Serial.print(studentUID);
      Serial.print(" checked in at destination: ");
      Serial.println(terminal);

      studentOutUnscanned = false;
      alertActive = false;
      activeStudentUID = "";
      exitTimestamp = 0;
    }
  }
}

// --- Helper Function to Publish JSON Payload ---
void publishEvent(String eventType, String detail, String studentId = "") {
  if (!mqttClient.connected()) connectMQTT();
  
  StaticJsonDocument<384> doc;
  doc["room"] = "ROOM 101";
  doc["terminal"] = "ROOM_101";
  doc["teacherPresent"] = teacherPresent;
  doc["studentOut"] = studentOutUnscanned;
  doc["alertActive"] = alertActive;
  doc["eventType"] = eventType;
  doc["detail"] = detail;
  doc["studentId"] = studentId.length() > 0 ? studentId : activeStudentUID;

  char buffer[384];
  serializeJson(doc, buffer);
  mqttClient.publish(TOPIC_PASS_EVENTS, buffer);
  Serial.print("Published MQTT: ");
  Serial.println(buffer);
}

// --- Sensor & RFID Logic ---
long readDistanceCM() { 
  digitalWrite(TRIG_PIN, LOW); 
  delayMicroseconds(2); 
  digitalWrite(TRIG_PIN, HIGH); 
  delayMicroseconds(10); 
  digitalWrite(TRIG_PIN, LOW); 
  
  long duration = pulseIn(ECHO_PIN, HIGH, 30000); 
  if (duration == 0) return 9999; 
  return duration * 0.0343 / 2; 
} 

void checkCardTap() { 
  if (!rfid.PICC_IsNewCardPresent() || !rfid.PICC_ReadCardSerial()) { 
    return; 
  } 
  
  String cardUID = ""; 
  for (byte i = 0; i < rfid.uid.size; i++) { 
    cardUID += String(rfid.uid.uidByte[i], HEX); 
  } 
  cardUID.toUpperCase(); 
  
  if (cardUID == FLOOR_INCHARGE_UID) { 
    if (studentOutUnscanned) { 
      studentOutUnscanned = false; 
      alertActive = false; 
      activeStudentUID = "";
      publishEvent("ADMIN_OVERRIDE", "Floor Incharge cleared active room alert.", cardUID);
    } 
  } 
  else if (cardUID == TEACHER_CARD_UID) { 
    teacherPresent = !teacherPresent; 
    digitalWrite(RED_LED, teacherPresent ? LOW : HIGH); 
    digitalWrite(GREEN_LED, teacherPresent ? HIGH : LOW); 
    publishEvent("TEACHER_TOGGLE", teacherPresent ? "ACTIVE CLASS" : "CLASS ENDED", cardUID);
  } 
  else if (cardUID == STUDENT_1_UID) { 
    if (teacherPresent) { 
      activeStudentUID = cardUID;
      publishEvent("STUDENT_PASS", "Pass Approved for UID: " + cardUID, cardUID);
    } else { 
      publishEvent("DENIED", "Room locked. Teacher must unlock room first.", cardUID);
    } 
  } 
  else { 
    publishEvent("DENIED", "Unregistered Card UID: " + cardUID, cardUID);
  } 
  
  rfid.PICC_HaltA(); 
  rfid.PCD_StopCrypto1(); 
} 

void checkDoorwaySensor() { 
  long distance = readDistanceCM(); 
  bool passageDetected = (distance < DOORWAY_TRIGGER_CM && lastDistance >= DOORWAY_TRIGGER_CM); 
  lastDistance = distance; 
  
  if (!passageDetected) return; 
  
  if (!teacherPresent && !studentOutUnscanned) { 
    studentOutUnscanned = true; 
    exitTimestamp = millis(); 
    if (activeStudentUID == "") activeStudentUID = STUDENT_1_UID; // Default active student context
    publishEvent("UNSCANNED_EXIT", "Teacher Absent - 7-min grace started");
  } 
  else if (!teacherPresent && studentOutUnscanned) { 
    studentOutUnscanned = false; 
    alertActive = false; 
    publishEvent("RE_ENTRY", "Student re-entry detected. Grace timer cleared.");
    activeStudentUID = "";
  } 
  else if (teacherPresent) { 
    studentOutUnscanned = true; 
    exitTimestamp = millis(); 
    if (activeStudentUID == "") activeStudentUID = STUDENT_1_UID;
    publishEvent("UNSCANNED_EXIT", "Active Class - 2-min alert timer started");
  } 
} 

void checkGraceTimerExpiry() { 
  if (!studentOutUnscanned || alertActive) return; 
  
  unsigned long elapsed = millis() - exitTimestamp; 
  unsigned long limit = teacherPresent ? ALERT_WINDOW_TEACHER_PRESENT : GRACE_PERIOD_TEACHER_ABSENT; 
  
  if (elapsed >= limit) { 
    alertActive = true; 
    publishEvent("ALERT_TIMEOUT", "Unaccounted exit timed out!");
  } 
}

// --- Arduino Core Routines ---
void setup() { 
  Serial.begin(115200); 
  SPI.begin(); 
  rfid.PCD_Init(); 
  
  pinMode(GREEN_LED, OUTPUT); 
  pinMode(RED_LED, OUTPUT); 
  pinMode(TRIG_PIN, OUTPUT); 
  pinMode(ECHO_PIN, INPUT); 
  
  digitalWrite(RED_LED, HIGH); 
  digitalWrite(GREEN_LED, LOW); 
  
  connectWiFi();
  mqttClient.setServer(MQTT_BROKER, MQTT_PORT);
  mqttClient.setCallback(mqttCallback);
} 

void loop() { 
  if (!mqttClient.connected()) connectMQTT();
  mqttClient.loop();

  checkCardTap(); 
  checkDoorwaySensor(); 
  checkGraceTimerExpiry(); 
  delay(50); 
}