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

// WiFi credentials
const char* ssid = "Wokwi-GUEST";
const char* password = "";

// MQTT broker
const char* mqtt_server = "test.mosquitto.org";

WiFiClient espClient;
PubSubClient client(espClient);

// JSON Database
StaticJsonDocument<300> db;

void setupDatabase() {
  db["users"][0]["name"] = "Deepak";
  db["users"][0]["debit_card"] = "1234567890123456";
  db["users"][0]["credit_card"] = "9876543210987654";
  db["users"][0]["upi"] = "deepak@upi";
  db["users"][0]["balance"] = 5000;
}

// Callback when message received
void callback(char* topic, byte* payload, unsigned int length) {

  StaticJsonDocument<200> doc;
  deserializeJson(doc, payload);

  const char* name = doc["name"];
  const char* method = doc["method"];
  int amount = doc["amount"];

  Serial.println("\n--- Payment Request Received ---");
  Serial.print("Name: "); Serial.println(name);
  Serial.print("Method: "); Serial.println(method);
  Serial.print("Amount: "); Serial.println(amount);

  const char* db_name = db["users"][0]["name"];
  int balance = db["users"][0]["balance"];

  // Validation
  if (strcmp(name, db_name) == 0 && amount <= balance) {

    Serial.println("Payment SUCCESS ✅");

    // Deduct balance
    db["users"][0]["balance"] = balance - amount;

    Serial.print("Remaining Balance: ");
    Serial.println((int)db["users"][0]["balance"]);

  } else {
    Serial.println("Payment FAILED ❌");
  }
}

// MQTT reconnect
void reconnect() {
  while (!client.connected()) {
    Serial.print("Connecting to MQTT...");
    if (client.connect("ESP32Subscriber")) {
      Serial.println("Connected!");
      client.subscribe("payment/request");
    } else {
      Serial.println("Retrying...");
      delay(2000);
    }
  }
}

void setup() {
  Serial.begin(115200);
  delay(2000); // important for serial

  Serial.println("Starting Subscriber...");

  // WiFi connection
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("\nWiFi Connected!");

  setupDatabase();

  client.setServer(mqtt_server, 1883);
  client.setCallback(callback);
}

void loop() {
  if (!client.connected()) {
    reconnect();
  }
  client.loop();
}