NFC Guard Checkpoint Logger

#include <Arduino.h>
#include <WiFi.h>
#include <HTTPClient.h>
#include <Wire.h>
#include <Adafruit_PN532.h>

// Replace these placeholders before pressing Deploy.

// Forward declarations
String uidToHex(const uint8_t *uid, uint8_t uidLength);
String jsonEscape(const String &value);
void connectWiFiIfNeeded();
bool sendCheckpointRecord(const String &cardUid);
void signalSuccess();
void signalFailure();

const char *WIFI_SSID = "YOUR_WIFI_NAME";
const char *WIFI_PASSWORD = "YOUR_WIFI_PASSWORD";
const char *CHECKPOINT_URL = "https://example.com/api/checkpoints";
const char *CHECKPOINT_ID = "CHECKPOINT_01";
// Leave empty when the server does not require an API key.
const char *API_KEY = "";
const char *API_KEY_HEADER = "X-API-Key";

constexpr uint8_t PN532_SDA_PIN = 21;
constexpr uint8_t PN532_SCL_PIN = 22;
constexpr uint8_t GREEN_LED_PIN = 25;
constexpr uint8_t RED_LED_PIN = 26;
constexpr uint8_t BUZZER_PIN = 27;
constexpr uint32_t WIFI_RETRY_MS = 10000;
constexpr uint32_t SAME_CARD_COOLDOWN_MS = 3000;

Adafruit_PN532 nfc(PN532_SDA_PIN, PN532_SCL_PIN);
String lastUid;
uint32_t lastScanAt = 0;
uint32_t lastWiFiAttemptAt = 0;

String uidToHex(const uint8_t *uid, uint8_t uidLength) {
  String text;
  for (uint8_t i = 0; i < uidLength; ++i) {
    if (uid[i] < 0x10) text += '0';
    text += String(uid[i], HEX);
  }
  text.toUpperCase();
  return text;
}

String jsonEscape(const String &value) {
  String escaped;
  for (size_t i = 0; i < value.length(); ++i) {
    const char c = value[i];
    if (c == '\\' || c == '"') escaped += '\\';
    escaped += c;
  }
  return escaped;
}

void signalSuccess() {
  digitalWrite(RED_LED_PIN, LOW);
  digitalWrite(GREEN_LED_PIN, HIGH);
  digitalWrite(BUZZER_PIN, HIGH);
  delay(120);
  digitalWrite(BUZZER_PIN, LOW);
  delay(880);
  digitalWrite(GREEN_LED_PIN, LOW);
}

void signalFailure() {
  digitalWrite(GREEN_LED_PIN, LOW);
  digitalWrite(RED_LED_PIN, HIGH);
  for (uint8_t i = 0; i < 2; ++i) {
    digitalWrite(BUZZER_PIN, HIGH);
    delay(120);
    digitalWrite(BUZZER_PIN, LOW);
    delay(120);
  }
  delay(760);
  digitalWrite(RED_LED_PIN, LOW);
}

void connectWiFiIfNeeded() {
  if (WiFi.status() == WL_CONNECTED) return;
  if (millis() - lastWiFiAttemptAt < WIFI_RETRY_MS) return;

  lastWiFiAttemptAt = millis();
  Serial.println("Connecting to Wi-Fi...");
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
}

bool sendCheckpointRecord(const String &cardUid) {
  if (WiFi.status() != WL_CONNECTED) {
    Serial.println("Record not sent: Wi-Fi is not connected.");
    return false;
  }

  HTTPClient http;
  http.setTimeout(10000);
  if (!http.begin(CHECKPOINT_URL)) {
    Serial.println("Record not sent: invalid server URL.");
    return false;
  }

  String body = "{\"card_uid\":\"" + jsonEscape(cardUid) +
                "\",\"checkpoint_id\":\"" + jsonEscape(CHECKPOINT_ID) +
                "\",\"device_id\":\"" + WiFi.macAddress() +
                "\",\"uptime_ms\":" + String(millis()) + "}";

  http.addHeader("Content-Type", "application/json");
  if (strlen(API_KEY) > 0) http.addHeader(API_KEY_HEADER, API_KEY);

  const int statusCode = http.POST(body);
  Serial.print("Server response: ");
  Serial.println(statusCode);
  http.end();
  return statusCode >= 200 && statusCode < 300;
}

void setup() {
  Serial.begin(115200);
  pinMode(GREEN_LED_PIN, OUTPUT);
  pinMode(RED_LED_PIN, OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);
  digitalWrite(GREEN_LED_PIN, LOW);
  digitalWrite(RED_LED_PIN, LOW);
  digitalWrite(BUZZER_PIN, LOW);
  Wire.begin(PN532_SDA_PIN, PN532_SCL_PIN);

  nfc.begin();
  const uint32_t version = nfc.getFirmwareVersion();
  if (!version) {
    Serial.println("PN532 was not found. Set both PN532 switches to I2C mode and check the four wires.");
  } else {
    nfc.SAMConfig();
    Serial.println("PN532 ready. Hold a card near the reader.");
  }

  WiFi.mode(WIFI_STA);
  connectWiFiIfNeeded();
}

void loop() {
  connectWiFiIfNeeded();

  uint8_t uid[7] = {0};
  uint8_t uidLength = 0;
  const bool found = nfc.readPassiveTargetID(PN532_MIFARE_ISO14443A, uid, &uidLength, 100);
  if (!found) return;

  const String cardUid = uidToHex(uid, uidLength);
  const uint32_t now = millis();
  if (cardUid == lastUid && now - lastScanAt < SAME_CARD_COOLDOWN_MS) return;

  lastUid = cardUid;
  lastScanAt = now;
  Serial.print("Card UID: ");
  Serial.println(cardUid);

  if (sendCheckpointRecord(cardUid)) {
    Serial.println("Checkpoint record delivered.");
    signalSuccess();
  } else {
    Serial.println("Checkpoint record was not delivered; scan the card again after Wi-Fi/server is available.");
    signalFailure();
  }

  delay(400);
}