#include <Arduino.h>
#include <WiFi.h>
#include <WiFiUdp.h>
#include <coap-simple.h>   // hirotakaster/CoAP simple library

// ===== Wi-Fi creds =====
const char* WIFI_SSID = "UPB-Guest";
const char* WIFI_PASS = "";

// ===== CoAP server (Californium demo) =====
const char* COAP_HOST = "californium.eclipseprojects.io";
const uint16_t COAP_PORT = 5683;   // RFC 7252 default port

// UDP + CoAP objects
WiFiUDP udp;
Coap coap(udp);

// ----- Response callback: prints payload as text -----
void onCoapResponse(CoapPacket &packet, IPAddress ip, int port) {
  // Copy payload into a printable buffer
  const size_t n = packet.payloadlen;
  String from = ip.toString() + ":" + String(port);
  Serial.printf("[CoAP] Response from %s  code=%u (0x%02X)  len=%u\n",
                from.c_str(), (packet.code >> 5), packet.code, (unsigned)n);

  if (n > 0) {
    // Make it printable; not all payloads are ASCII
    size_t m = n;
    if (m > 1023) m = 1023;     // clamp for serial
    char buf[1024];
    memcpy(buf, packet.payload, m);
    buf[m] = '\0';
    Serial.println(F("[CoAP Payload]"));
    Serial.println(buf);
  }
}

// Re-resolves hostname and sends GET to "/"
bool coapGetRoot() {
  IPAddress remote;
  if (!WiFi.hostByName(COAP_HOST, remote)) {
    Serial.println(F("[CoAP] DNS failed"));
    return false;
  }
  Serial.printf("[CoAP] GET coap://%s:%u/\n", COAP_HOST, COAP_PORT);
  // Path is "" for "/", per library examples
  int msgid = coap.get(remote, COAP_PORT, "");
  (void)msgid; // not used further in this demo
  return true;
}

unsigned long lastGetMs = 0;
const unsigned long GET_PERIOD_MS = 10000;

void setup() {
  Serial.begin(115200);
  delay(200);
  Serial.println(F("\n== CoAP client (Californium demo) =="));

  // Wi-Fi
  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASS);
  Serial.print(F("Connecting"));
  while (WiFi.status() != WL_CONNECTED) { delay(300); Serial.print('.'); }
  Serial.println();
  Serial.print(F("Wi-Fi OK. IP: ")); Serial.println(WiFi.localIP());

  // Bind UDP so we can receive responses (use standard CoAP port or 0 for ephemeral)
  udp.begin(5683);

  // Register response handler and start CoAP
  coap.response(onCoapResponse);
  coap.start();

  // First GET right away
  coapGetRoot();
  lastGetMs = millis();
}

void loop() {
  // Let the library process incoming UDP (and fire onCoapResponse)
  coap.loop();

  // Periodic GET
  unsigned long now = millis();
  if (now - lastGetMs >= GET_PERIOD_MS) {
    lastGetMs = now;
    coapGetRoot();
  }
}