Air Humidity Display

#include <Arduino.h>
#include <Wire.h>
#include <WiFi.h>
#include <HTTPClient.h>
#include <WiFiClientSecure.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <DHT.h>


// Forward declarations
void showMessage(const char *line1, const char *line2);
void showValues(float airHumidity, int gasOne, int gasTwo);
void updateSimulatedGasValues();
void startWifi();
bool uploadToGoogleSheets();

constexpr int DHT_PIN = 27;
constexpr int OLED_SDA_PIN = 21;
constexpr int OLED_SCL_PIN = 22;
constexpr uint8_t SCREEN_WIDTH = 128;
constexpr uint8_t SCREEN_HEIGHT = 64;
constexpr uint8_t OLED_ADDRESS = 0x3C;
constexpr unsigned long READ_INTERVAL_MS = 2000;
constexpr unsigned long UPLOAD_INTERVAL_MS = 20000;
constexpr unsigned long WIFI_RETRY_INTERVAL_MS = 30000;

const char *WIFI_SSID = "BNG Tech";
const char *WIFI_PASS = "bng@2025";
const char *SHEETS_WEB_APP_URL =
    "https://script.google.com/macros/s/AKfycbwAvTXGWs5MF2O78SfbQrMTWB6zNAO9GuU6QILcq1QRVG6JKoO9BD66O-5ZTwfVUG-f/exec";

DHT dht(DHT_PIN, DHT11);
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

float humidity = NAN;
int gas1 = 0;
int gas2 = 0;
float shownHumidity = NAN;
int shownGas1 = -1;
int shownGas2 = -1;
unsigned long lastReadMs = 0;
unsigned long lastUploadMs = 0;
unsigned long lastWifiRetryMs = 0;

void showMessage(const char *line1, const char *line2) {
  display.clearDisplay();
  display.setTextColor(SSD1306_WHITE);
  display.setTextSize(1);
  display.setCursor(0, 10);
  display.println(line1);
  display.setCursor(0, 30);
  display.println(line2);
  display.display();
}

void showValues(float airHumidity, int gasOne, int gasTwo) {
  display.clearDisplay();
  display.setTextColor(SSD1306_WHITE);
  display.setTextSize(1);
  display.setCursor(0, 4);
  display.print("Do am: ");
  display.print(airHumidity, 0);
  display.println(" %");
  display.setCursor(0, 25);
  display.print("Gas 1: ");
  display.println(gasOne);
  display.setCursor(0, 46);
  display.print("Gas 2: ");
  display.println(gasTwo);
  display.display();
}

void updateSimulatedGasValues() {
  const unsigned long seconds = millis() / 1000UL;
  gas1 = 120 + static_cast<int>((seconds * 7UL) % 181UL);
  gas2 = 180 + static_cast<int>((seconds * 11UL) % 221UL);
}

void startWifi() {
  WiFi.mode(WIFI_STA);
  WiFi.disconnect(false, false);
  delay(100);
  Serial.println("Dang ket noi WiFi");
  WiFi.begin(WIFI_SSID, WIFI_PASS);
  lastWifiRetryMs = millis();
}

bool uploadToGoogleSheets() {
  WiFiClientSecure client;
  client.setInsecure();
  HTTPClient http;

  if (!http.begin(client, SHEETS_WEB_APP_URL)) {
    Serial.println("Khong mo duoc ket noi Google Sheets");
    return false;
  }

  // Google Apps Script redirects the /exec address to its receiving service.
  http.setFollowRedirects(HTTPC_STRICT_FOLLOW_REDIRECTS);
  http.setTimeout(15000);
  http.addHeader("Content-Type", "application/x-www-form-urlencoded");
  const String body = "humidity=" + String(humidity, 1) +
                      "&gas1=" + String(gas1) +
                      "&gas2=" + String(gas2);
  const int statusCode = http.POST(body);
  const String response = statusCode > 0 ? http.getString() : "";
  http.end();

  Serial.print("Gui Google Sheets: HTTP ");
  Serial.print(statusCode);
  if (response.length() > 0) {
    Serial.print(" | Phan hoi: ");
    Serial.println(response);
  } else {
    Serial.println();
  }
  return statusCode >= 200 && statusCode < 300;
}

void setup() {
  Serial.begin(115200);
  Wire.begin(OLED_SDA_PIN, OLED_SCL_PIN);
  if (!display.begin(SSD1306_SWITCHCAPVCC, OLED_ADDRESS)) {
    Serial.println("Khong tim thay OLED o dia chi 0x3C");
    while (true) {
      delay(1000);
    }
  }

  dht.begin();
  showMessage("Dang khoi dong...", "Ket noi WiFi");
  startWifi();
}

void loop() {
  const unsigned long now = millis();
  static bool wifiWasConnected = false;
  const bool wifiConnected = WiFi.status() == WL_CONNECTED;

  if (wifiConnected && !wifiWasConnected) {
    Serial.print("WiFi da ket noi. IP: ");
    Serial.println(WiFi.localIP());
  }
  wifiWasConnected = wifiConnected;

  if (!wifiConnected && now - lastWifiRetryMs >= WIFI_RETRY_INTERVAL_MS) {
    startWifi();
  }

  if (now - lastReadMs >= READ_INTERVAL_MS) {
    lastReadMs = now;
    const float reading = dht.readHumidity();
    if (isnan(reading)) {
      Serial.println("Doc DHT11 that bai");
      showMessage("Khong doc duoc DHT11", "Kiem tra day DATA");
    } else {
      humidity = reading;
      updateSimulatedGasValues();
      if (humidity != shownHumidity || gas1 != shownGas1 || gas2 != shownGas2) {
        showValues(humidity, gas1, gas2);
        shownHumidity = humidity;
        shownGas1 = gas1;
        shownGas2 = gas2;
      }
    }
  }

  if (!isnan(humidity) && wifiConnected && now - lastUploadMs >= UPLOAD_INTERVAL_MS) {
    lastUploadMs = now;
    uploadToGoogleSheets();
  }
}