/*
  Session 4 — Autonomous field node: SD card CSV logging + deep sleep (ESP32)
  SD module (SPI): CS->5, SCK->18, MISO->19, MOSI->23, VCC 3.3V/5V (check your module), GND
  DHT22 -> GPIO 4, soil -> GPIO 34, battery divider (100k/100k) -> GPIO 33
  Wakes every 15 minutes, logs one CSV line, sleeps (~10 µA on a bare ESP32 module).
  Power budget example: 2000 mAh Li-ion, awake 3 s @ 80 mA, sleep @ 0.15 mA (DevKit LDO) -> ~26 days.
*/
#include <SD.h>
#include <SPI.h>
#include <DHT.h>

#define SD_CS 5
#define DHT_PIN 4
#define SOIL_PIN 34
#define BAT_PIN 33
#define SLEEP_MINUTES 15

DHT dht(DHT_PIN, DHT22);
RTC_DATA_ATTR uint32_t bootCount = 0;     // survives deep sleep (RTC memory)

void goToSleep() {
  esp_sleep_enable_timer_wakeup((uint64_t)SLEEP_MINUTES * 60ULL * 1000000ULL);
  Serial.flush();
  esp_deep_sleep_start();
}

void setup() {
  Serial.begin(115200);
  bootCount++;
  dht.begin();
  delay(2000);                              // DHT22 warm-up
  float t = dht.readTemperature(), h = dht.readHumidity();
  int soil = analogRead(SOIL_PIN);
  float bat = analogReadMilliVolts(BAT_PIN) * 2 / 1000.0;

  if (!SD.begin(SD_CS)) {
    Serial.println("SD init failed — check wiring / FAT32 format");
    goToSleep();
  }
  bool newFile = !SD.exists("/farmlog.csv");
  File f = SD.open("/farmlog.csv", FILE_APPEND);
  if (f) {
    if (newFile) f.println("boot,uptime_min,air_temp_c,air_hum_pct,soil_raw,battery_v");
    f.printf("%lu,%lu,%.1f,%.1f,%d,%.2f\n", bootCount, bootCount * SLEEP_MINUTES, t, h, soil, bat);
    f.close();
    Serial.printf("logged boot #%lu  t=%.1f h=%.1f soil=%d bat=%.2fV\n", bootCount, t, h, soil, bat);
  }
  if (bat > 0.5 && bat < 3.3) {
    Serial.println("battery critical -> sleeping 4x longer");
    esp_sleep_enable_timer_wakeup((uint64_t)SLEEP_MINUTES * 4 * 60ULL * 1000000ULL);
    esp_deep_sleep_start();
  }
  goToSleep();
}

void loop() {}   // never reached — every wake-up starts again from setup()