/*
  Session 6 — ESP-NOW gateway (center of the star) — receives all field nodes and prints JSON lines.
  Connect it by USB to the farm laptop:  python serial_to_api.py  forwards each line to the Flask API,
  or extend it to publish over MQTT (session 7). Detects lost packets with the sequence number and
  marks a node offline when nothing arrives for 3 minutes.
  ESP32 Arduino core 3.x callback signature (core 2.x: void onRecv(const uint8_t *mac, const uint8_t *data, int len)).
*/
#include <WiFi.h>
#include <esp_now.h>
#include <esp_wifi.h>

const uint8_t CHANNEL = 6;
typedef struct __attribute__((packed)) {
  uint8_t node; uint32_t seq; float temp; float hum; uint16_t soilRaw; float battery;
} Reading;

uint32_t lastSeq[21] = {0};
unsigned long lastSeen[21] = {0};
uint32_t lost[21] = {0};

void onRecv(const esp_now_recv_info_t *info, const uint8_t *data, int len) {
  if (len != sizeof(Reading)) return;
  Reading r; memcpy(&r, data, sizeof(r));
  if (r.node > 20) return;
  if (lastSeq[r.node] && r.seq > lastSeq[r.node] + 1) lost[r.node] += r.seq - lastSeq[r.node] - 1;
  lastSeq[r.node] = r.seq;
  lastSeen[r.node] = millis();
  Serial.printf("{\"node_id\":\"node_%02d\",\"seq\":%lu,\"air_temp_c\":%.1f,\"air_humidity_pct\":%.1f,"
                "\"soil_raw\":%u,\"battery_v\":%.2f,\"rssi\":%d,\"lost\":%lu}\n",
                r.node, r.seq, r.temp, r.hum, r.soilRaw, r.battery, info->rx_ctrl->rssi, lost[r.node]);
}

void setup() {
  Serial.begin(115200);
  WiFi.mode(WIFI_STA);
  esp_wifi_set_channel(CHANNEL, WIFI_SECOND_CHAN_NONE);
  esp_now_init();
  esp_now_register_recv_cb(onRecv);
  Serial.print("# gateway MAC (copy into the nodes): "); Serial.println(WiFi.macAddress());
}

void loop() {
  static unsigned long check = 0;
  if (millis() - check > 30000) {
    check = millis();
    for (int n = 1; n <= 20; n++)
      if (lastSeen[n] && millis() - lastSeen[n] > 180000) Serial.printf("# node_%02d OFFLINE\n", n);
  }
}