#include <WiFi.h>
#include <PubSubClient.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <ArduinoJson.h>

// ================= NETWORK =================
const char* ssid = "Wokwi-GUEST";
const char* password = "";
const char* mqtt_server = "broker.emqx.io"; // Switched to a more stable public broker

// Unique topic to prevent interference from others
const char* topic_req = "wokwibank/atm999_secure/request";
const char* topic_res = "wokwibank/atm999_secure/response";

WiFiClient espClient;
PubSubClient mqtt(espClient);
LiquidCrystal_I2C lcd(0x27, 20, 4);

// ================= DATABASE =================
StaticJsonDocument<1024> db;
unsigned long lastActivityTime = 0;
bool showingActivity = false;

void initDatabase() {
  db["atm_host"]["id"] = "ATM001";
  db["atm_host"]["cash_available"] = 10000;

  JsonArray accounts = db.createNestedArray("accounts");

  JsonObject acc1 = accounts.createNestedObject();
  acc1["acc_no"] = "1234";
  acc1["pin"] = "0000";
  acc1["balance"] = 5000; // Fixed: Gave the account money to withdraw!

  JsonObject acc2 = accounts.createNestedObject();
  acc2["acc_no"] = "9876";
  acc2["pin"] = "1111";
  acc2["balance"] = 200;
}

// ================= LCD =================
void displayIdle() {
  lcd.clear();
  lcd.setCursor(0, 0); lcd.print("--- SERVER ONLINE ---");
  lcd.setCursor(0, 1); lcd.print("Listening on:");
  lcd.setCursor(0, 2); lcd.print("atm999_secure/req");
  showingActivity = false;
}

// ================= MQTT CALLBACK =================
void callback(char* topic, byte* payload, unsigned int length) {
  if (String(topic) != topic_req) return;

  StaticJsonDocument<512> req;
  DeserializationError error = deserializeJson(req, payload, length);
  
  if (error) {
    Serial.println("Invalid JSON Received!");
    return;
  }

  String accNo = req["acc"].as<String>();
  String pin = req["pin"].as<String>();
  String type = req["type"].as<String>();
  int amount = req["amount"] | 0;

  lcd.clear();
  lcd.setCursor(0, 0); lcd.print("Incoming Request");
  lcd.setCursor(0, 1); lcd.print("Acc:" + accNo);
  lcd.setCursor(0, 2); lcd.print("Type:" + type + " Amt:" + String(amount));

  StaticJsonDocument<256> res;
  res["status"] = "error";
  res["msg"] = "Invalid Account/PIN";
  res["balance"] = 0;

  for (JsonObject acc : db["accounts"].as<JsonArray>()) {
    if (acc["acc_no"] == accNo && acc["pin"] == pin) {
      int bal = acc["balance"];
      int atmCash = db["atm_host"]["cash_available"];

      if (type == "B") {
        res["status"] = "success";
        res["msg"] = "Balance OK";
        res["balance"] = bal;
      }
      else if (type == "W") {
        if (atmCash < amount) {
          res["msg"] = "ATM Out of Cash";
        }
        else if (bal < amount) {
          res["msg"] = "Insufficient Funds";
        }
        else {
          acc["balance"] = bal - amount;
          db["atm_host"]["cash_available"] = atmCash - amount;
          res["status"] = "success";
          res["msg"] = "Take Cash";
          res["balance"] = acc["balance"];
        }
      }
      else if (type == "D") {
        acc["balance"] = bal + amount;
        db["atm_host"]["cash_available"] = atmCash + amount;
        res["status"] = "success";
        res["msg"] = "Deposit OK";
        res["balance"] = acc["balance"];
      }
      break;
    }
  }

  char buffer[256];
  serializeJson(res, buffer);
  
  Serial.println("Sending Response: ");
  Serial.println(buffer);
  
  mqtt.publish(topic_res, buffer);

  lcd.setCursor(0, 3);
  lcd.print("Response Sent");

  lastActivityTime = millis();
  showingActivity = true;
}

// ================= MQTT =================
void reconnect() {
  while (!mqtt.connected()) {
    lcd.clear();
    lcd.setCursor(0, 0); lcd.print("Connecting MQTT...");

    // Better randomness to prevent boot collisions
    String clientId = "ATM_Server_" + String(random(0xffffff), HEX);
    if (mqtt.connect(clientId.c_str())) {
      Serial.println("MQTT Connected");
      mqtt.subscribe(topic_req);
      displayIdle();
    } else {
      lcd.setCursor(0, 2); lcd.print("Retrying...");
      delay(1000);
    }
  }
}

// ================= SETUP =================
void setup() {
  Serial.begin(115200);
  lcd.init();
  lcd.backlight();
  lcd.setCursor(0, 0); lcd.print("Booting Server...");

  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) { delay(500); }

  mqtt.setServer(mqtt_server, 1883);
  mqtt.setCallback(callback);
  mqtt.setBufferSize(512); // Give it plenty of breathing room

  initDatabase();
  
  // Seed random using analog noise to prevent duplicate Client IDs
  randomSeed(analogRead(34) + micros());
  reconnect();
}

// ================= LOOP =================
void loop() {
  if (!mqtt.connected()) reconnect();
  mqtt.loop();

  if (showingActivity && (millis() - lastActivityTime > 2500)) {
    displayIdle();
  }
}