// Install from the Library Manager:
// "LiquidCrystal I2C"
// Board: "ESP32 Dev Module"
#include <WiFi.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

// The ESP32's I2C pins
const int SDA_PIN = 21;
const int SCL_PIN = 22;
// How long each network stays on (ms)
const unsigned long SHOW_EACH = 3000;
// At most this many networks are listed
const int MAX_NETWORKS = 40;
// A network that hides its name
const char* HIDDEN = "(hidden)";

// I2C address: mostly 0x27, some 0x3F
LiquidCrystal_I2C lcd(0x27, 16, 2);
// Networks found, strongest first
int order[MAX_NETWORKS];
int found = 0;
// The next network to show
int next = 0;
unsigned long shownAt = 0;

// Signal strength (dBm) as 0-4 bars
int bars(int rssi) {
  if (rssi >= -55) return 4;
  if (rssi >= -67) return 3;
  if (rssi >= -75) return 2;
  if (rssi >= -85) return 1;
  return 0;
}

// The encryption's short name
const char* security(wifi_auth_mode_t mode) {
  switch (mode) {
    case WIFI_AUTH_OPEN: return "Open";
    case WIFI_AUTH_WEP: return "WEP";
    case WIFI_AUTH_WPA_PSK: return "WPA";
    case WIFI_AUTH_WPA2_PSK: return "WPA2";
    case WIFI_AUTH_WPA_WPA2_PSK: return "WPA/WPA2";
    case WIFI_AUTH_WPA3_PSK: return "WPA3";
    case WIFI_AUTH_WPA2_WPA3_PSK: return "WPA2/WPA3";
    default: return "Other";
  }
}

// The network's name, or HIDDEN
String networkName(int k) {
  String name = WiFi.SSID(k);
  if (name.length() == 0) name = HIDDEN;
  return name;
}

// Scans, then sorts strongest first
void scan() {
  lcd.clear();
  lcd.print("Scanning...");
  Serial.println("Scanning...");
  int count = WiFi.scanNetworks();
  found = constrain(count, 0, MAX_NETWORKS);
  for (int i = 0; i < found; i++) {
    order[i] = i;
  }
  // Sorting: each network moves ahead of
  // the weaker ones before it
  for (int i = 1; i < found; i++) {
    int k = order[i];
    int j = i - 1;
    while (j >= 0 &&
           WiFi.RSSI(order[j]) < WiFi.RSSI(k)) {
      order[j + 1] = order[j];
      j--;
    }
    order[j + 1] = k;
  }

  Serial.print(found);
  Serial.println(" networks found");
  for (int i = 0; i < found; i++) {
    int k = order[i];
    Serial.printf("%2d. %4d dBm  channel %2d  %s (%s)\n",
                  i + 1, WiFi.RSSI(k), WiFi.channel(k),
                  networkName(k).c_str(),
                  security(WiFi.encryptionType(k)));
  }
  next = 0;
  shownAt = millis();
}

// Writes one network: its name on top;
// rank, strength, bars and lock (*) below
void show(int i) {
  int k = order[i];
  int rssi = WiFi.RSSI(k);
  char barText[] = "    ";
  for (int b = 0; b < bars(rssi); b++) {
    barText[b] = '#';
  }
  bool locked =
      WiFi.encryptionType(k) != WIFI_AUTH_OPEN;
  char line[17];
  snprintf(line, sizeof line, "%2d/%-2d%4d %s %c",
           i + 1, found, rssi, barText,
           locked ? '*' : ' ');

  lcd.clear();
  lcd.print(networkName(k).substring(0, 16));
  lcd.setCursor(0, 1);
  lcd.print(line);
}

void setup() {
  Serial.begin(115200);
  Wire.begin(SDA_PIN, SCL_PIN);
  lcd.init();
  lcd.backlight();
  // Only listens; joins no network
  WiFi.mode(WIFI_STA);
  WiFi.disconnect();
  delay(100);
  scan();
}

void loop() {
  if (found == 0) {
    lcd.setCursor(0, 1);
    lcd.print("None found");
    delay(SHOW_EACH);
    scan();
    return;
  }
  // The first one at once, then in turn
  if (next > 0 && millis() - shownAt < SHOW_EACH) {
    return;
  }
  // All shown: scan again
  if (next >= found) {
    scan();
    return;
  }
  show(next);
  next++;
  shownAt = millis();
}