Offline Classroom Controller

#include <Arduino.h>
#include <Wire.h>
#include <SPI.h>
#include <SoftwareSerial.h>
#include <U8g2lib.h>
#include <qrcode.h>

const uint8_t NAV_PIN = 2;
const uint8_t SELECT_PIN = 3;
const uint8_t BACK_PIN = 4;
const uint8_t SESSION_PIN = 5;
const uint8_t GREEN_LED_PIN = 6;
const uint8_t YELLOW_LED_PIN = 7;
const uint8_t RED_LED_PIN = 8;
const uint8_t BUZZER_PIN = 9;
const uint8_t SD_CS_PIN = 10;
const uint8_t NODE_RX_PIN = A1;
const uint8_t NODE_TX_PIN = A0;
const uint8_t OLED_SDA_PIN = A4;
const uint8_t OLED_SCL_PIN = A5;

U8G2_SSD1327_MIDAS_128X128_1_HW_I2C display(U8G2_R0, U8X8_PIN_NONE);
SoftwareSerial nodeSerial(NODE_RX_PIN, NODE_TX_PIN);

enum Screen { IDLE, CREATE, CONFIGURE, QR_READY, READY, ACTIVE, END_SCREEN };
Screen screen = IDLE;
uint8_t configItem = 0;
uint16_t attendance = 0;
unsigned long sessionStarted = 0;
unsigned long lastDraw = 0;
unsigned long lastButton = 0;
bool sdAvailable = false;

bool pressed(uint8_t pin) {
  if (digitalRead(pin) == LOW && millis() - lastButton > 180) {
    lastButton = millis();
    return true;
  }
  return false;
}

void setIndicators() {
  digitalWrite(GREEN_LED_PIN, (screen == READY || screen == ACTIVE) ? HIGH : LOW);
  digitalWrite(YELLOW_LED_PIN, (screen == CREATE || screen == CONFIGURE || screen == QR_READY) ? HIGH : LOW);
  digitalWrite(RED_LED_PIN, screen == END_SCREEN ? HIGH : LOW);
}

void title(const char *text) {
  display.setFont(u8g2_font_6x10_tf);
  display.drawStr(5, 11, text);
  display.drawHLine(5, 14, 118);
}

void drawFace() {
  unsigned long phase = millis() % 6000UL;
  bool blink = phase > 4800 && phase < 4990;
  int8_t glance = (phase > 2400 && phase < 3800) ? 2 : 0;
  if (blink) {
    display.drawHLine(41 + glance, 57, 9);
    display.drawHLine(78 + glance, 57, 9);
  } else {
    display.drawDisc(45 + glance, 57, 3);
    display.drawDisc(82 + glance, 57, 3);
  }
  display.drawLine(54, 78, 61, 79);
  display.drawLine(61, 79, 68, 79);
  display.drawLine(68, 79, 74, 77);
}

void drawQr() {
  QRCode qr;
  uint8_t qrData[qrcode_getBufferSize(2)];
  qrcode_initText(&qr, qrData, 2, 0, "SNTCH:K7M4");
  const uint8_t scale = 4;
  const uint8_t x0 = 22;
  const uint8_t y0 = 20;
  for (uint8_t y = 0; y < qr.size; y++) {
    for (uint8_t x = 0; x < qr.size; x++) {
      if (qrcode_getModule(&qr, x, y)) {
        display.drawBox(x0 + x * scale, y0 + y * scale, scale, scale);
      }
    }
  }
}

void drawScreen() {
  display.firstPage();
  do {
    display.setDrawColor(1);
    if (screen == IDLE) {
      title("SNTCH  OFFLINE");
      drawFace();
      display.setFont(u8g2_font_5x8_tf);
      display.drawStr(22, 106, "Press SESSION");
      display.drawStr(31, 117, "to create");
    } else if (screen == CREATE) {
      title("CREATE SESSION");
      display.setFont(u8g2_font_6x10_tf);
      display.drawStr(13, 43, "New class session");
      display.drawStr(13, 64, "SESSION to configure");
    } else if (screen == CONFIGURE) {
      title("CONFIGURE");
      display.setFont(u8g2_font_6x10_tf);
      display.drawStr(12, 40, configItem == 0 ? "> Class: Room 12" : "  Class: Room 12");
      display.drawStr(12, 59, configItem == 1 ? "> Join: QR + code" : "  Join: QR + code");
      display.drawStr(12, 78, configItem == 2 ? "> Duration: 45m" : "  Duration: 45m");
      display.setFont(u8g2_font_5x8_tf);
      display.drawStr(10, 111, "NAV move  SELECT change");
    } else if (screen == QR_READY) {
      title("JOIN SESSION");
      drawQr();
      display.setFont(u8g2_font_5x8_tf);
      display.drawStr(17, 117, "ID SNTCH-042  K7M4");
    } else if (screen == READY) {
      title("READY");
      display.setFont(u8g2_font_6x10_tf);
      display.drawStr(29, 45, "LOCAL Wi-Fi");
      display.drawStr(22, 65, "0 students joined");
      display.drawStr(18, 99, "SESSION to start");
    } else if (screen == ACTIVE) {
      title("ACTIVE SESSION");
      unsigned long elapsed = (millis() - sessionStarted) / 1000UL;
      char line[22];
      snprintf(line, sizeof(line), "Time  %02lu:%02lu", elapsed / 60UL, elapsed % 60UL);
      display.setFont(u8g2_font_6x10_tf);
      display.drawStr(22, 46, line);
      snprintf(line, sizeof(line), "Present  %u", attendance);
      display.drawStr(22, 67, line);
      display.setFont(u8g2_font_5x8_tf);
      display.drawStr(25, 107, "SESSION to end");
    } else {
      title("SESSION ENDED");
      display.setFont(u8g2_font_6x10_tf);
      display.drawStr(27, 48, "Attendance saved");
      display.drawStr(34, 70, "Thank you");
      display.setFont(u8g2_font_5x8_tf);
      display.drawStr(24, 108, "BACK returns home");
    }
  } while (display.nextPage());
}

void handleInput() {
  if (pressed(BACK_PIN)) {
    if (screen == END_SCREEN) screen = IDLE;
    else if (screen != IDLE) screen = (screen == CONFIGURE) ? CREATE : IDLE;
    tone(BUZZER_PIN, 1100, 40);
  }
  if (pressed(NAV_PIN) && screen == CONFIGURE) {
    configItem = (configItem + 1) % 3;
    tone(BUZZER_PIN, 1200, 30);
  }
  if (pressed(SELECT_PIN) && screen == CONFIGURE) {
    tone(BUZZER_PIN, 1500, 45);
  }
  if (pressed(SESSION_PIN)) {
    if (screen == IDLE) screen = CREATE;
    else if (screen == CREATE || screen == CONFIGURE) screen = (screen == CONFIGURE) ? QR_READY : CONFIGURE;
    else if (screen == QR_READY) screen = READY;
    else if (screen == READY) { screen = ACTIVE; sessionStarted = millis(); attendance = 0; }
    else if (screen == ACTIVE) screen = END_SCREEN;
    tone(BUZZER_PIN, 1800, 70);
  }
}

void setup() {
  pinMode(NAV_PIN, INPUT_PULLUP);
  pinMode(SELECT_PIN, INPUT_PULLUP);
  pinMode(BACK_PIN, INPUT_PULLUP);
  pinMode(SESSION_PIN, INPUT_PULLUP);
  pinMode(GREEN_LED_PIN, OUTPUT);
  pinMode(YELLOW_LED_PIN, OUTPUT);
  pinMode(RED_LED_PIN, OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);
  Wire.begin();
  display.begin();
  display.setContrast(190);
  nodeSerial.begin(9600);
  nodeSerial.println("SNTCH_BOOT");
  drawScreen();
}

void loop() {
  handleInput();
  if (screen == ACTIVE && nodeSerial.available()) {
    char c = nodeSerial.read();
    if (c == '+') attendance++;
  }
  setIndicators();
  unsigned long interval = (screen == IDLE || screen == ACTIVE) ? 100UL : 250UL;
  if (millis() - lastDraw >= interval) {
    lastDraw = millis();
    drawScreen();
  }
}