ESP32 RFID Inventory Tracker

// ESP32 RFID Inventory - Advanced (REST API + LittleFS JSON DB + MQTT)
#include <SPI.h>
#include <MFRC522.h>
#include <WiFi.h>
#include <ESPAsyncWebServer.h>
#include <AsyncTCP.h>
#include <PubSubClient.h>
#include <ArduinoJson.h>
#include <LittleFS.h>
#include <time.h>

MFRC522 rfid(5,22);
AsyncWebServer server(80);
WiFiClient wc; PubSubClient mqtt(wc);
const char* SSID="YourSSID", *PASS="YourPass";
const char* MQTT_HOST="192.168.1.100";

struct Asset { String uid,name; bool in; time_t last; int outCount; };
const int MAX_A=50; Asset assets[MAX_A]; int aCount=0;

void saveDB(){
  DynamicJsonDocument doc(8192);
  JsonArray arr=doc.createNestedArray("assets");
  for(int i=0;i<aCount;i++){
    JsonObject o=arr.createNestedObject();
    o["uid"]=assets[i].uid; o["name"]=assets[i].name;
    o["in"]=assets[i].in; o["last"]=(long)assets[i].last;
    o["out"]=assets[i].outCount;
  }
  File f=LittleFS.open("/db.json","w");
  serializeJson(doc,f); f.close();
}

void loadDB(){
  if(!LittleFS.exists("/db.json")) return;
  File f=LittleFS.open("/db.json","r");
  DynamicJsonDocument doc(8192);
  deserializeJson(doc,f); f.close();
  JsonArray arr=doc["assets"];
  for(JsonObject o:arr){
    if(aCount>=MAX_A) break;
    assets[aCount]={o["uid"].as<String>(),o["name"].as<String>(),
      o["in"]|true,(time_t)(o["last"]|0),(int)(o["out"]|0)};
    aCount++;
  }
}

String uidStr(MFRC522::Uid *u){
  String s="";
  for(byte i=0;i<u->size;i++){if(u->uidByte[i]<0x10)s+="0";s+=String(u->uidByte[i],HEX);}
  s.toUpperCase(); return s;
}

void mqttEvent(const String &uid, const String &name, bool in){
  StaticJsonDocument<128> doc;
  doc["uid"]=uid; doc["name"]=name; doc["in"]=in; doc["ts"]=(long)time(nullptr);
  char buf[128]; serializeJson(doc,buf);
  mqtt.publish("inventory/scan",buf);
}

void setup(){
  Serial.begin(115200); SPI.begin(); rfid.PCD_Init();
  LittleFS.begin(true);
  loadDB();
  WiFi.begin(SSID,PASS); while(WiFi.status()!=WL_CONNECTED) delay(500);
  configTime(0,0,"pool.ntp.org");
  mqtt.setServer(MQTT_HOST,1883);

  // Serve React SPA from LittleFS /www/index.html
  server.serveStatic("/",LittleFS,"/www/").setDefaultFile("index.html");

  server.on("/api/assets",HTTP_GET,[](AsyncWebServerRequest *r){
    DynamicJsonDocument doc(4096); JsonArray arr=doc.createNestedArray("assets");
    for(int i=0;i<aCount;i++){
      JsonObject o=arr.createNestedObject();
      o["uid"]=assets[i].uid; o["name"]=assets[i].name;
      o["in"]=assets[i].in; o["out"]=assets[i].outCount;
    }
    String out; serializeJson(doc,out);
    r->send(200,"application/json",out);
  });

  server.on("/api/add",HTTP_POST,[](AsyncWebServerRequest *r){
    if(!r->hasParam("uid",true)||!r->hasParam("name",true)){r->send(400); return;}
    String uid=r->getParam("uid",true)->value();
    String name=r->getParam("name",true)->value();
    if(aCount<MAX_A){ assets[aCount++]={uid,name,true,time(nullptr),0}; saveDB(); }
    r->send(200,"text/plain","OK");
  });

  server.begin();
  Serial.printf("Inventory API: http://%s/n",WiFi.localIP().toString().c_str());
}

void loop(){
  if(!mqtt.connected()) mqtt.connect("RFID");
  mqtt.loop();
  if(!rfid.PICC_IsNewCardPresent()||!rfid.PICC_ReadCardSerial()) return;
  String uid=uidStr(&rfid.uid);
  for(int i=0;i<aCount;i++){
    if(assets[i].uid==uid){
      assets[i].in=!assets[i].in;
      assets[i].last=time(nullptr);
      if(!assets[i].in) assets[i].outCount++;
      saveDB();
      mqttEvent(uid,assets[i].name,assets[i].in);
      Serial.printf("%s -> %sn",assets[i].name.c_str(),assets[i].in?"IN":"OUT");
      break;
    }
  }
  rfid.PICC_HaltA(); rfid.PCD_StopCrypto1();
  delay(1000);
}