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	- Project: # Smart Gateway
	- Version: 009
	- Source Code NOT compiled for: ESP32S3 Dev Module
	- Source Code created on: 2026-03-08 21:02:43

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/****** SYSTEM REQUIREMENTS *****/
/****** SYSTEM REQUIREMENT 1 *****/
	/* Inicijalizovati UART1 sa GPIO17(TX) i GPIO18(RX) */
	/* na 9600 baud za Modbus RTU komunikaciju. GPIO4 kao */
	/* RS485 DE kontrola. Slave ID=1, 8 releja (Coil */
	/* 0-7), CRC16 provjera, timeout zaštita. */
/****** SYSTEM REQUIREMENT 2 *****/
	/* Inicijalizovati LVGL display sa Waveshare 7" touch */
	/* LCD. Prikazati 8 touchscreen dugmadi za releje */
	/* (4+4 raspored), status LED, WiFi ikona, Modbus */
	/* status. Real-time ažuriranje stanja releja. */
/****** SYSTEM REQUIREMENT 3 *****/
	/* Pritiskom na relay dugme na displeju poslati */
	/* Modbus Write Single Coil (FC 0x05) komandu. */
	/* 0xFF00=ON, 0x0000=OFF. Log svaku komandu sa */
	/* vremenskom markom. Debounce 100ms. */
/****** SYSTEM REQUIREMENT 4 *****/
	/* WiFi pristup sa SSID i password (hardkod ili web */
	/* konfiguracija). Web server na portu 80 sa REST */
	/* API: GET /api/relay/status, POST */
	/* /api/relay/control, GET /api/logs. JSON format */
	/* odgovora. */
/****** SYSTEM REQUIREMENT 5 *****/
	/* Web dashboard sa HTML/CSS/JavaScript: prikaz svih */
	/* 8 releja, ON/OFF dugmadi, status Modbus konekcije, */
	/* log Modbus komunikacije, OTA update sekcija. Auto- */
	/* refresh svakih 500ms. */
/****** SYSTEM REQUIREMENT 6 *****/
	/* OTA (Over-The-Air) firmware update mogućnost. Web */
	/* upload interface za novi .bin fajl. ArduinoOTA */
	/* biblioteka, sigurna autentifikacija sa korisničkim */
	/* imenom i lozinkom. */
/****** SYSTEM REQUIREMENT 7 *****/
	/* Čuvanje Modbus komunikacijskih logova u */
	/* EEPROM/SPIFFS (max 1000 posljednjih komandi). */
	/* Prikaz logova na web interfejsu sa filtriranjem po */
	/* tipu, vremenu, statusu. CSV export mogućnost. */
/****** SYSTEM REQUIREMENT 8 *****/
	/* Web interfejs autentifikacija sa admin korisničkim */
	/* imenom i lozinkom. JWT token ili session-based */
	/* autentifikacija. Logovanje pokušaja pristupa. */
	/* Default user: admin/admin123 (promjena obavezna */
	/* pri prvom loginu). */
/****** END SYSTEM REQUIREMENTS *****/


/* START CODE */

#include <Arduino.h>
#include <HardwareSerial.h>
#include <WiFi.h>
#include <WebServer.h>
#include <ArduinoJson.h>
#include <Update.h>
#include <Preferences.h>
#include <time.h>
#include <vector>
#include <lvgl.h>
#include "waveshare_lcd_port.h"

// =====================================================================
// SYSTEM REQUIREMENTS - UART1 Configuration for Modbus RTU
// =====================================================================
// UART1 sa GPIO17(TX) i GPIO18(RX) na 9600 baud
#define UART1_TX_PIN 17
#define UART1_RX_PIN 18
#define MODBUS_BAUD 9600
#define UART_CHANNEL 1

// =====================================================================
// RS485 Control and Modbus Configuration
// =====================================================================
#define RS485_DE_PIN 4              // RS485 Driver Enable pin
#define MODBUS_SLAVE_ADDR 1         // Slave address for Modbus commands
#define NUM_RELAYS 8                // Number of relays (0-7)
#define MODBUS_TIMEOUT 1000         // milliseconds
#define MODBUS_MAX_RETRIES 3
#define MODBUS_CRC_POLY 0xA001

// =====================================================================
// Web Server Configuration
// =====================================================================
#define WEB_SERVER_PORT 80
#define WEB_DASHBOARD_REFRESH_MS 500

// =====================================================================
// EEPROM/SPIFFS Configuration
// =====================================================================
#define MAX_LOG_ENTRIES 1000
#define LOG_ENTRY_SIZE 128

// =====================================================================
// WiFi Configuration
// =====================================================================
#define WIFI_SSID "YourSSID"
#define WIFI_PASSWORD "YourPassword"
#define WIFI_TIMEOUT 20000

// =====================================================================
// JWT/Session Configuration
// =====================================================================
#define JWT_SECRET "your-secret-key-change-this"
#define DEFAULT_USERNAME "admin"
#define DEFAULT_PASSWORD "admin123"

// =====================================================================
// Display Configuration
// =====================================================================
#define DISPLAY_WIDTH 800
#define DISPLAY_HEIGHT 480
#define BUTTON_ROWS 2
#define BUTTONS_PER_ROW 4
#define TOTAL_BUTTONS 8

// =====================================================================
// LVGL Configuration
// =====================================================================
#define LVGL_TICK_PERIOD 5
#define LVGL_BUFFER_SIZE (DISPLAY_WIDTH * DISPLAY_HEIGHT / 10)

// =====================================================================
// Global Variables
// =====================================================================
HardwareSerial ModbusSerial(UART_CHANNEL);
WebServer webServer(WEB_SERVER_PORT);
Preferences prefs;

// Relay states: 0 = OFF, 1 = ON
uint8_t relayStates[NUM_RELAYS] = {0};

// UI state
bool wifiConnected = false;
bool modbusConnected = false;
uint32_t lastUIRefresh = 0;
uint32_t lastHealthCheck = 0;

// Authentication
String currentSessionToken = "";
uint32_t sessionExpire = 0;
const uint32_t SESSION_TIMEOUT = 3600000; // 1 hour in milliseconds

// LVGL objects
static lv_obj_t *screen_main = NULL;
static lv_obj_t *relay_buttons[NUM_RELAYS];
static lv_obj_t *wifi_label = NULL;
static lv_obj_t *modbus_label = NULL;
static lv_obj_t *status_container = NULL;

// =====================================================================
// Log Entry Structure
// =====================================================================
struct LogEntry {
    uint32_t timestamp;
    uint8_t type;           // 0=Modbus Send, 1=Modbus Response, 2=Error, 3=Access
    uint8_t relayIndex;
    bool value;
    bool success;
    char details[64];
};

// =====================================================================
// Global Log Buffer
// =====================================================================
std::vector<LogEntry> modbusLog;

// =====================================================================
// LVGL Display Buffer
// =====================================================================
static lv_disp_buf_t disp_buf;
static lv_color_t buf[LVGL_BUFFER_SIZE];

// =====================================================================
// FUNCTION: LVGL Flush Callback
// =====================================================================
void lv_flush_cb(lv_disp_drv_t *disp_drv, const lv_area_t *area, lv_color_t *color_p)
{
    esp_panel::drivers::LCD *lcd = waveshare_lcd_get();
    if (!lcd) return;

    uint32_t w = (area->x2 - area->x1 + 1);
    uint32_t h = (area->y2 - area->y1 + 1);
    
    lcd->drawBitmap(area->x1, area->y1, w, h, (uint16_t *)color_p);
    
    lv_disp_flush_ready(disp_drv);
}

// =====================================================================
// FUNCTION: LVGL Timer Callback
// =====================================================================
static void lv_tick_task(void *arg)
{
    lv_tick_inc(LVGL_TICK_PERIOD);
}

// =====================================================================
// FUNCTION: Initialize LVGL Display
// =====================================================================
void initializeLVGL()
{
    Serial.println("Initializing LVGL display...");
    
    // Initialize LVGL
    lv_init();
    
    // Initialize display buffer
    lv_disp_buf_init(&disp_buf, buf, NULL, LVGL_BUFFER_SIZE);
    
    // Initialize display driver
    lv_disp_drv_t disp_drv;
    lv_disp_drv_init(&disp_drv);
    
    disp_drv.buffer = &disp_buf;
    disp_drv.hor_res = DISPLAY_WIDTH;
    disp_drv.ver_res = DISPLAY_HEIGHT;
    disp_drv.flush_cb = lv_flush_cb;
    
    lv_disp_drv_register(&disp_drv);
    
    // Create main screen
    screen_main = lv_scr_act();
    lv_obj_set_style_local_bg_color(screen_main, LV_OBJ_PART_MAIN, LV_STATE_DEFAULT, LV_COLOR_WHITE);
    
    Serial.println("LVGL initialized successfully");
}

// =====================================================================
// FUNCTION: Create GUI Relay Control Panel
// =====================================================================
void createRelayPanel()
{
    Serial.println("Creating relay control panel...");
    
    // Create container for relay buttons
    lv_obj_t *relay_container = lv_cont_create(screen_main, NULL);
    lv_obj_set_auto_realign(relay_container, true);
    lv_obj_align(relay_container, NULL, LV_ALIGN_IN_TOP_MID, 0, 10);
    lv_cont_set_fit2(relay_container, LV_FIT_MAX, LV_FIT_MAX);
    lv_cont_set_layout(relay_container, LV_LAYOUT_GRID);
    
    // Set grid spacing
    lv_obj_set_style_local_pad_all(relay_container, LV_OBJ_PART_MAIN, LV_STATE_DEFAULT, 10);
    lv_obj_set_style_local_pad_inner(relay_container, LV_OBJ_PART_MAIN, LV_STATE_DEFAULT, 10);
    
    // Create relay buttons in 4x2 grid
    for (uint8_t i = 0; i < NUM_RELAYS; i++)
    {
        relay_buttons[i] = lv_btn_create(relay_container, NULL);
        lv_obj_set_width(relay_buttons[i], 150);
        lv_obj_set_height(relay_buttons[i], 100);
        
        // Update button appearance based on state
        if (relayStates[i])
        {
            lv_obj_set_style_local_bg_color(relay_buttons[i], LV_BTN_PART_MAIN, LV_STATE_DEFAULT, LV_COLOR_GREEN);
        }
        else
        {
            lv_obj_set_style_local_bg_color(relay_buttons[i], LV_BTN_PART_MAIN, LV_STATE_DEFAULT, LV_COLOR_RED);
        }
        
        // Add label to button
        lv_obj_t *label = lv_label_create(relay_buttons[i], NULL);
        char btn_text[16];
        snprintf(btn_text, sizeof(btn_text), "Relay %d\n%s", i, relayStates[i] ? "ON" : "OFF");
        lv_label_set_text(label, btn_text);
        lv_obj_set_style_local_text_color(label, LV_LABEL_PART_MAIN, LV_STATE_DEFAULT, LV_COLOR_WHITE);
    }
    
    Serial.println("Relay panel created successfully");
}

// =====================================================================
// FUNCTION: Create Status Display
// =====================================================================
void createStatusDisplay()
{
    Serial.println("Creating status display...");
    
    // Create status container at bottom
    status_container = lv_cont_create(screen_main, NULL);
    lv_obj_set_width(status_container, DISPLAY_WIDTH);
    lv_obj_set_height(status_container, 80);
    lv_obj_align(status_container, NULL, LV_ALIGN_IN_BOTTOM_MID, 0, 0);
    lv_obj_set_style_local_bg_color(status_container, LV_OBJ_PART_MAIN, LV_STATE_DEFAULT, LV_COLOR_GRAY);
    
    // WiFi status label
    wifi_label = lv_label_create(status_container, NULL);
    lv_label_set_text(wifi_label, "WiFi: Connecting...");
    lv_obj_align(wifi_label, NULL, LV_ALIGN_IN_TOP_LEFT, 10, 10);
    
    // Modbus status label
    modbus_label = lv_label_create(status_container, NULL);
    lv_label_set_text(modbus_label, "Modbus: Ready");
    lv_obj_align(modbus_label, wifi_label, LV_ALIGN_OUT_BOTTOM_LEFT, 0, 5);
    
    Serial.println("Status display created successfully");
}

// =====================================================================
// FUNCTION: Update GUI Display
// =====================================================================
void updateGUIDisplay()
{
    // Update WiFi status
    if (wifi_label)
    {
        if (wifiConnected)
        {
            lv_label_set_text(wifi_label, "WiFi: Connected");
            lv_obj_set_style_local_text_color(wifi_label, LV_LABEL_PART_MAIN, LV_STATE_DEFAULT, LV_COLOR_GREEN);
        }
        else
        {
            lv_label_set_text(wifi_label, "WiFi: Disconnected");
            lv_obj_set_style_local_text_color(wifi_label, LV_LABEL_PART_MAIN, LV_STATE_DEFAULT, LV_COLOR_RED);
        }
    }
    
    // Update Modbus status
    if (modbus_label)
    {
        if (modbusConnected)
        {
            lv_label_set_text(modbus_label, "Modbus: Connected");
            lv_obj_set_style_local_text_color(modbus_label, LV_LABEL_PART_MAIN, LV_STATE_DEFAULT, LV_COLOR_GREEN);
        }
        else
        {
            lv_label_set_text(modbus_label, "Modbus: Offline");
            lv_obj_set_style_local_text_color(modbus_label, LV_LABEL_PART_MAIN, LV_STATE_DEFAULT, LV_COLOR_RED);
        }
    }
    
    // Update relay button states
    for (uint8_t i = 0; i < NUM_RELAYS; i++)
    {
        if (relay_buttons[i])
        {
            if (relayStates[i])
            {
                lv_obj_set_style_local_bg_color(relay_buttons[i], LV_BTN_PART_MAIN, LV_STATE_DEFAULT, LV_COLOR_GREEN);
            }
            else
            {
                lv_obj_set_style_local_bg_color(relay_buttons[i], LV_BTN_PART_MAIN, LV_STATE_DEFAULT, LV_COLOR_RED);
            }
        }
    }
    
    // Refresh LVGL
    lv_task_handler();
}

// =====================================================================
// FUNCTION: Initialize Preferences/NVS Storage
// =====================================================================
void initializeStorage()
{
    if (!prefs.begin("modbus_esp32", false))
    {
        Serial.println("Failed to initialize Preferences");
        return;
    }
    
    Serial.println("Storage initialized");
}

// =====================================================================
// FUNCTION: Add Log Entry
// =====================================================================
void addLogEntry(uint8_t type, uint8_t relayIndex, bool value, bool success, const char* details)
{
    LogEntry entry;
    entry.timestamp = millis() / 1000;
    entry.type = type;
    entry.relayIndex = relayIndex;
    entry.value = value;
    entry.success = success;
    strncpy(entry.details, details, sizeof(entry.details) - 1);
    entry.details[sizeof(entry.details) - 1] = '\0';
    
    modbusLog.push_back(entry);
    
    // Maintain max log size
    if (modbusLog.size() > MAX_LOG_ENTRIES)
    {
        modbusLog.erase(modbusLog.begin());
    }
}

// =====================================================================
// FUNCTION: Calculate Modbus CRC16
// =====================================================================
uint16_t calculateModbusCRC(uint8_t *data, uint8_t length)
{
    uint16_t crc = 0xFFFF;
    
    for(uint8_t i = 0; i < length; i++)
    {
        crc ^= data[i];
        
        for(uint8_t j = 0; j < 8; j++)
        {
            if(crc & 1)
                crc = (crc >> 1) ^ MODBUS_CRC_POLY;
            else
                crc >>= 1;
        }
    }
    
    return crc;
}

// =====================================================================
// FUNCTION: Set RS485 to TX mode
// =====================================================================
inline void rs485_tx()
{
    digitalWrite(RS485_DE_PIN, HIGH);
}

// =====================================================================
// FUNCTION: Set RS485 to RX mode
// =====================================================================
inline void rs485_rx()
{
    digitalWrite(RS485_DE_PIN, LOW);
}

// =====================================================================
// SYSTEM REQUIREMENT 3: Modbus Write Single Coil
// =====================================================================
// FC 0x05: Write Single Coil
bool modbusWriteCoil(uint8_t relayIndex, bool on)
{
    if (relayIndex >= NUM_RELAYS)
    {
        addLogEntry(2, relayIndex, on, false, "Invalid relay index");
        return false;
    }
    
    uint8_t txBuffer[8];
    
    // Build Modbus frame
    txBuffer[0] = MODBUS_SLAVE_ADDR;    // Slave address
    txBuffer[1] = 0x05;                 // Function code: Write Single Coil
    txBuffer[2] = 0x00;                 // Coil address high byte
    txBuffer[3] = relayIndex;           // Coil address low byte (Coil 0-7)
    txBuffer[4] = on ? 0xFF : 0x00;     // Value high byte (0xFF00 for ON, 0x0000 for OFF)
    txBuffer[5] = 0x00;                 // Value low byte
    
    // Calculate and append CRC16
    uint16_t crc = calculateModbusCRC(txBuffer, 6);
    txBuffer[6] = crc & 0xFF;
    txBuffer[7] = crc >> 8;
    
    // Clear any pending data in receive buffer
    while(ModbusSerial.available())
        ModbusSerial.read();
    
    // Switch RS485 to TX mode
    rs485_tx();
    delayMicroseconds(100);
    
    // Send Modbus frame
    ModbusSerial.write(txBuffer, 8);
    ModbusSerial.flush();
    
    // Wait for transmission to complete
    delayMicroseconds(200);
    
    // Switch RS485 to RX mode
    rs485_rx();
    
    // Read response with timeout
    uint8_t rxBuffer[8];
    uint8_t bytesRead = 0;
    uint32_t startTime = millis();
    
    while(ModbusSerial.available() && bytesRead < 8)
    {
        if(millis() - startTime > MODBUS_TIMEOUT)
        {
            addLogEntry(2, relayIndex, on, false, "Modbus timeout");
            modbusConnected = false;
            return false;
        }
        
        rxBuffer[bytesRead] = ModbusSerial.read();
        bytesRead++;
        delayMicroseconds(100);
    }
    
    // Verify response
    bool success = false;
    if(bytesRead >= 8)
    {
        // Extract CRC from response
        uint16_t receivedCRC = (rxBuffer[7] << 8) | rxBuffer[6];
        
        // Calculate CRC of received data (excluding CRC bytes)
        uint16_t calculatedCRC = calculateModbusCRC(rxBuffer, 6);
        
        if(receivedCRC == calculatedCRC)
        {
            success = true;
            relayStates[relayIndex] = on ? 1 : 0;
            addLogEntry(1, relayIndex, on, true, "CRC verified");
            modbusConnected = true;
            
            Serial.print("Modbus Write Success: Relay ");
            Serial.print(relayIndex);
            Serial.print(" -> ");
            Serial.println(on ? "ON" : "OFF");
        }
        else
        {
            addLogEntry(2, relayIndex, on, false, "CRC mismatch");
            Serial.println("Modbus Response: CRC mismatch!");
            modbusConnected = false;
        }
    }
    else
    {
        addLogEntry(2, relayIndex, on, false, "No response");
        Serial.println("Modbus Write: No response from slave");
        modbusConnected = false;
    }
    
    return success;
}

// =====================================================================
// FUNCTION: Read Modbus Coil Status (Function Code 0x01)
// =====================================================================
bool modbusReadCoils(uint8_t startCoil, uint8_t count, uint8_t* values)
{
    if (startCoil + count > NUM_RELAYS)
    {
        addLogEntry(2, startCoil, false, false, "Invalid coil range");
        return false;
    }
    
    uint8_t txBuffer[12];
    
    // Build read coils frame
    txBuffer[0] = MODBUS_SLAVE_ADDR;
    txBuffer[1] = 0x01;                 // Function code: Read Coils
    txBuffer[2] = 0x00;
    txBuffer[3] = startCoil;
    txBuffer[4] = 0x00;
    txBuffer[5] = count;
    
    uint16_t crc = calculateModbusCRC(txBuffer, 6);
    txBuffer[6] = crc & 0xFF;
    txBuffer[7] = crc >> 8;
    
    // Clear receive buffer
    while(ModbusSerial.available())
        ModbusSerial.read();
    
    // Send request
    rs485_tx();
    delayMicroseconds(100);
    ModbusSerial.write(txBuffer, 8);
    ModbusSerial.flush();
    delayMicroseconds(200);
    rs485_rx();
    
    // Read response
    uint8_t rxBuffer[32];
    uint8_t bytesRead = 0;
    uint32_t startTime = millis();
    
    while(ModbusSerial.available() && bytesRead < 32)
    {
        if(millis() - startTime > MODBUS_TIMEOUT)
        {
            addLogEntry(2, startCoil, false, false, "Read timeout");
            return false;
        }
        
        rxBuffer[bytesRead] = ModbusSerial.read();
        bytesRead++;
        delayMicroseconds(100);
    }
    
    // Verify response
    if(bytesRead >= 5)
    {
        uint16_t receivedCRC = (rxBuffer[bytesRead - 1] << 8) | rxBuffer[bytesRead - 2];
        uint16_t calculatedCRC = calculateModbusCRC(rxBuffer, bytesRead - 2);
        
        if(receivedCRC == calculatedCRC)
        {
            // Parse coil values
            uint8_t byteCount = rxBuffer[2];
            for(uint8_t i = 0; i < count && i < byteCount; i++)
            {
                values[i] = (rxBuffer[3 + (i / 8)] >> (i % 8)) & 1;
            }
            addLogEntry(1, startCoil, false, true, "Read coils OK");
            modbusConnected = true;
            return true;
        }
        else
        {
            addLogEntry(2, startCoil, false, false, "Read CRC error");
        }
    }
    else
    {
        addLogEntry(2, startCoil, false, false, "Read no response");
    }
    
    modbusConnected = false;
    return false;
}

// =====================================================================
// FUNCTION: Initialize UART1 for Modbus RTU
// =====================================================================
void initializeModbusUART()
{
    // Configure RS485 control pin
    pinMode(RS485_DE_PIN, OUTPUT);
    digitalWrite(RS485_DE_PIN, LOW);  // Start in RX mode
    
    // Initialize UART1 with specified pins and baud rate
    ModbusSerial.begin(
        MODBUS_BAUD,           // 9600 baud
        SERIAL_8N1,            // 8 data bits, no parity, 1 stop bit
        UART1_RX_PIN,          // RX on GPIO18
        UART1_TX_PIN           // TX on GPIO17
    );
    
    Serial.println("Modbus UART1 initialized");
    Serial.println("TX: GPIO17, RX: GPIO18, Baud: 9600");
}

// =====================================================================
// FUNCTION: Initialize WiFi Connection
// =====================================================================
void initializeWiFi()
{
    Serial.println("\nStarting WiFi connection...");
    WiFi.mode(WIFI_STA);
    WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
    
    uint32_t startTime = millis();
    while(WiFi.status() != WL_CONNECTED && millis() - startTime < WIFI_TIMEOUT)
    {
        delay(500);
        Serial.print(".");
    }
    
    if(WiFi.status() == WL_CONNECTED)
    {
        wifiConnected = true;
        Serial.println("\nWiFi connected!");
        Serial.print("IP address: ");
        Serial.println(WiFi.localIP());
        
        // Configure time for NTP
        configTime(0, 0, "pool.ntp.org", "time.nist.gov");
        Serial.println("NTP time configured");
    }
    else
    {
        wifiConnected = false;
        Serial.println("\nWiFi connection failed!");
    }
}

// =====================================================================
// FUNCTION: Generate JWT Token
// =====================================================================
String generateJWT(const String& username)
{
    String payload = username + String(millis());
    
    // Simple hash for signature
    uint32_t hash = 5381;
    for(unsigned int i = 0; i < payload.length(); i++)
    {
        hash = ((hash << 5) + hash) + payload.charAt(i);
    }
    
    String token = "ESP32." + payload + "." + String(hash);
    return token;
}

// =====================================================================
// FUNCTION: Verify Session Token
// =====================================================================
bool verifySession()
{
    // Check if session is expired
    if(millis() > sessionExpire && sessionExpire > 0)
    {
        currentSessionToken = "";
        return false;
    }
    
    return currentSessionToken.length() > 0;
}

// =====================================================================
// WEB API HANDLERS
// =====================================================================

// =====================================================================
// HANDLER: Login Endpoint
// =====================================================================
void handleLogin()
{
    if(webServer.method() != HTTP_POST)
    {
        webServer.send(405, "application/json", "{\"error\":\"Method not allowed\"}");
        return;
    }
    
    String body = webServer.arg("plain");
    DynamicJsonDocument doc(256);
    
    if(deserializeJson(doc, body) != DeserializationError::Ok)
    {
        webServer.send(400, "application/json", "{\"error\":\"Invalid JSON\"}");
        return;
    }
    
    String username = doc["username"] | "";
    String password = doc["password"] | "";
    
    // Verify credentials
    if(username == DEFAULT_USERNAME && password == DEFAULT_PASSWORD)
    {
        // Generate session token
        currentSessionToken = generateJWT(username);
        sessionExpire = millis() + SESSION_TIMEOUT;
        
        DynamicJsonDocument response(256);
        response["success"] = true;
        response["token"] = currentSessionToken;
        response["expires_in"] = SESSION_TIMEOUT / 1000;
        
        String jsonResponse;
        serializeJson(response, jsonResponse);
        webServer.send(200, "application/json", jsonResponse);
        
        addLogEntry(3, 0, true, true, "Login successful");
    }
    else
    {
        webServer.send(401, "application/json", "{\"error\":\"Invalid credentials\"}");
        addLogEntry(3, 0, false, false, "Login failed");
    }
}

// =====================================================================
// HANDLER: Get Relay Status
// =====================================================================
void handleGetRelayStatus()
{
    if(!verifySession())
    {
        webServer.send(401, "application/json", "{\"error\":\"Unauthorized\"}");
        return;
    }
    
    DynamicJsonDocument response(512);
    response["timestamp"] = millis() / 1000;
    response["modbus_connected"] = modbusConnected;
    response["wifi_connected"] = wifiConnected;
    
    JsonArray relays = response.createNestedArray("relays");
    for(uint8_t i = 0; i < NUM_RELAYS; i++)
    {
        JsonObject relay = relays.createNestedObject();
        relay["index"] = i;
        relay["state"] = relayStates[i] ? "ON" : "OFF";
    }
    
    String jsonResponse;
    serializeJson(response, jsonResponse);
    webServer.send(200, "application/json", jsonResponse);
}

// =====================================================================
// HANDLER: Control Relay
// =====================================================================
void handleControlRelay()
{
    if(!verifySession())
    {
        webServer.send(401, "application/json", "{\"error\":\"Unauthorized\"}");
        return;
    }
    
    if(webServer.method() != HTTP_POST)
    {
        webServer.send(405, "application/json", "{\"error\":\"Method not allowed\"}");
        return;
    }
    
    String body = webServer.arg("plain");
    DynamicJsonDocument doc(256);
    
    if(deserializeJson(doc, body) != DeserializationError::Ok)
    {
        webServer.send(400, "application/json", "{\"error\":\"Invalid JSON\"}");
        return;
    }
    
    uint8_t relayIndex = doc["relay"] | 255;
    String action = doc["action"] | "";
    
    if(relayIndex >= NUM_RELAYS)
    {
        webServer.send(400, "application/json", "{\"error\":\"Invalid relay index\"}");
        return;
    }
    
    bool turnOn = (action == "ON");
    bool success = modbusWriteCoil(relayIndex, turnOn);
    
    DynamicJsonDocument response(256);
    response["success"] = success;
    response["relay"] = relayIndex;
    response["state"] = turnOn ? "ON" : "OFF";
    
    String jsonResponse;
    serializeJson(response, jsonResponse);
    
    webServer.send(success ? 200 : 500, "application/json", jsonResponse);
}

// =====================================================================
// HANDLER: Get Modbus Logs
// =====================================================================
void handleGetLogs()
{
    if(!verifySession())
    {
        webServer.send(401, "application/json", "{\"error\":\"Unauthorized\"}");
        return;
    }
    
    // Parse query parameters for filtering
    String typeFilter = webServer.arg("type");
    String limit = webServer.arg("limit");
    int maxEntries = limit.length() > 0 ? limit.toInt() : 100;
    
    if(maxEntries > 1000) maxEntries = 1000;
    if(maxEntries < 1) maxEntries = 10;
    
    DynamicJsonDocument response(8192);
    response["total_entries"] = modbusLog.size();
    response["returned"] = 0;
    
    JsonArray logs = response.createNestedArray("logs");
    
    int count = 0;
    int startIdx = modbusLog.size() > maxEntries ? modbusLog.size() - maxEntries : 0;
    
    for(int i = startIdx; i < (int)modbusLog.size() && count < maxEntries; i++)
    {
        LogEntry& entry = modbusLog[i];
        
        // Apply type filter if specified
        if(typeFilter.length() > 0)
        {
            uint8_t filterType = typeFilter.toInt();
            if(entry.type != filterType) continue;
        }
        
        JsonObject logEntry = logs.createNestedObject();
        logEntry["timestamp"] = entry.timestamp;
        logEntry["type"] = entry.type;
        logEntry["relay"] = entry.relayIndex;
        logEntry["value"] = entry.value ? "ON" : "OFF";
        logEntry["success"] = entry.success;
        logEntry["details"] = entry.details;
        
        count++;
    }
    
    response["returned"] = count;
    
    String jsonResponse;
    serializeJson(response, jsonResponse);
    webServer.send(200, "application/json", jsonResponse);
}

// =====================================================================
// HANDLER: Export Logs as CSV
// =====================================================================
void handleExportLogs()
{
    if(!verifySession())
    {
        webServer.send(401, "application/json", "{\"error\":\"Unauthorized\"}");
        return;
    }
    
    String csv = "Timestamp,Type,Relay,Value,Success,Details\n";
    
    for(const auto& entry : modbusLog)
    {
        csv += String(entry.timestamp) + ",";
        csv += String(entry.type) + ",";
        csv += String(entry.relayIndex) + ",";
        csv += (entry.value ? "ON" : "OFF") + String(",");
        csv += (entry.success ? "true" : "false") + String(",");
        csv += String(entry.details) + "\n";
    }
    
    webServer.send(200, "text/csv", csv);
}

// =====================================================================
// HANDLER: OTA Firmware Update
// =====================================================================
void handleOTAUpdate()
{
    if(!verifySession())
    {
        webServer.send(401, "application/json", "{\"error\":\"Unauthorized\"}");
        return;
    }
    
    if(webServer.method() != HTTP_POST)
    {
        webServer.send(405, "application/json", "{\"error\":\"Method not allowed\"}");
        return;
    }
    
    if(!Update.hasError())
    {
        DynamicJsonDocument response(256);
        response["success"] = true;
        response["message"] = "Firmware update completed. Device rebooting...";
        
        String jsonResponse;
        serializeJson(response, jsonResponse);
        webServer.send(200, "application/json", jsonResponse);
        
        delay(1000);
        ESP.restart();
    }
    else
    {
        DynamicJsonDocument response(256);
        response["success"] = false;
        response["error"] = Update.errorString();
        
        String jsonResponse;
        serializeJson(response, jsonResponse);
        webServer.send(500, "application/json", jsonResponse);
    }
}

// =====================================================================
// HANDLER: Web Dashboard HTML
// =====================================================================
void handleDashboard()
{
    String html = R"rawliteral(
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>ESP32-S3 Modbus Master Dashboard</title>
    <style>
        * { margin: 0; padding: 0; box-sizing: border-box; }
        body { font-family: 'Segoe UI', sans-serif; background: linear-gradient(135deg, #667eea 0%, #764ba2 100%); min-height: 100vh; padding: 20px; }
        .container { max-width: 1200px; margin: 0 auto; }
        .header { background: white; padding: 30px; border-radius: 10px; box-shadow: 0 4px 6px rgba(0,0,0,0.1); margin-bottom: 30px; display: flex; justify-content: space-between; align-items: center; }
        .header h1 { color: #333; font-size: 28px; }
        .header .status { display: flex; gap: 20px; align-items: center; }
        .status-item { display: flex; align-items: center; gap: 10px; padding: 10px 15px; background: #f0f0f0; border-radius: 5px; }
        .status-indicator { width: 12px; height: 12px; border-radius: 50%; display: inline-block; }
        .status-indicator.online { background: #4CAF50; }
        .status-indicator.offline { background: #f44336; }
        .main-grid { display: grid; grid-template-columns: 2fr 1fr; gap: 30px; margin-bottom: 30px; }
        .relay-panel { background: white; padding: 30px; border-radius: 10px; box-shadow: 0 4px 6px rgba(0,0,0,0.1); }
        .relay-panel h2 { color: #333; margin-bottom: 20px; font-size: 20px; }
        .relay-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 15px; }
        .relay-button { aspect-ratio: 1; border: none; border-radius: 10px; font-size: 16px; font-weight: bold; cursor: pointer; transition: all 0.3s ease; background: #e0e0e0; color: #333; display: flex; flex-direction: column; align-items: center; justify-content: center; gap: 5px; }
        .relay-button.on { background: #4CAF50; color: white; box-shadow: 0 4px 12px rgba(76, 175, 80, 0.4); }
        .relay-button.off { background: #f44336; color: white; box-shadow: 0 4px 12px rgba(244, 67, 54, 0.4); }
        .relay-button:hover { transform: translateY(-2px); box-shadow: 0 6px 12px rgba(0,0,0,0.2); }
        .relay-label { font-size: 12px; opacity: 0.8; }
        .sidebar { background: white; padding: 30px; border-radius: 10px; box-shadow: 0 4px 6px rgba(0,0,0,0.1); height: fit-content; }
        .sidebar h3 { color: #333; margin-bottom: 15px; }
        .sidebar-item { padding: 10px; margin-bottom: 10px; background: #f0f0f0; border-radius: 5px; font-size: 14px; }
        .sidebar-item label { display: block; color: #666; font-size: 12px; margin-bottom: 5px; }
        .sidebar-item span { display: block; color: #333; font-weight: bold; }
        .logs-panel { background: white; padding: 30px; border-radius: 10px; box-shadow: 0 4px 6px rgba(0,0,0,0.1); margin-bottom: 30px; }
        .logs-panel h2 { color: #333; margin-bottom: 20px; }
        .logs-table { width: 100%; border-collapse: collapse; font-size: 13px; }
        .logs-table th { background: #667eea; color: white; padding: 12px; text-align: left; font-weight: 600; }
        .logs-table td { padding: 12px; border-bottom: 1px solid #e0e0e0; }
        .logs-table tr:hover { background: #f5f5f5; }
        .log-success { color: #4CAF50; font-weight: bold; }
        .log-error { color: #f44336; font-weight: bold; }
        .button-group { display: flex; gap: 10px; margin-bottom: 20px; }
        .btn { padding: 12px 24px; border: none; border-radius: 5px; cursor: pointer; font-size: 14px; font-weight: 600; transition: all 0.3s ease; }
        .btn-primary { background: #667eea; color: white; }
        .btn-primary:hover { background: #5568d3; transform: translateY(-2px); }
        .btn-secondary { background: #e0e0e0; color: #333; }
        .btn-secondary:hover { background: #d0d0d0; }
        .login-page { display: flex; justify-content: center; align-items: center; min-height: 100vh; }
        .login-box { background: white; padding: 40px; border-radius: 10px; box-shadow: 0 4px 6px rgba(0,0,0,0.1); width: 100%; max-width: 400px; }
        .login-box h1 { color: #333; margin-bottom: 30px; text-align: center; }
        .form-group { margin-bottom: 20px; }
        .form-group label { display: block; color: #333; font-weight: 600; margin-bottom: 8px; }
        .form-group input { width: 100%; padding: 12px; border: 1px solid #ddd; border-radius: 5px; font-size: 14px; transition: border-color 0.3s ease; }
        .form-group input:focus { outline: none; border-color: #667eea; box-shadow: 0 0 0 3px rgba(102, 126, 234, 0.1); }
        .alert { padding: 12px; border-radius: 5px; margin-bottom: 20px; display: none; }
        .alert.error { background: #ffebee; color: #c62828; display: block; }
        .hidden { display: none !important; }
    </style>
</head>
<body>
    <div class="login-page" id="loginPage">
        <div class="login-box">
            <h1>ESP32-S3 Modbus Master</h1>
            <div class="alert error" id="loginError"></div>
            <form id="loginForm">
                <div class="form-group">
                    <label for="username">Username</label>
                    <input type="text" id="username" name="username" placeholder="admin" required>
                </div>
                <div class="form-group">
                    <label for="password">Password</label>
                    <input type="password" id="password" name="password" placeholder="••••••" required>
                </div>
                <button type="submit" class="btn btn-primary" style="width: 100%;">Login</button>
            </form>
        </div>
    </div>
    
    <div id="dashboard" class="hidden">
        <div class="container">
            <div class="header">
                <h1>ESP32-S3 Modbus Master Dashboard</h1>
                <div class="status">
                    <div class="status-item">
                        <span class="status-indicator online" id="wifiStatus"></span>
                        <span>WiFi: <span id="wifiStatusText">Connecting...</span></span>
                    </div>
                    <div class="status-item">
                        <span class="status-indicator online" id="modbusStatus"></span>
                        <span>Modbus: <span id="modbusStatusText">Ready</span></span>
                    </div>
                    <button class="btn btn-secondary" onclick="logout()">Logout</button>
                </div>
            </div>
            
            <div class="main-grid">
                <div class="relay-panel">
                    <h2>Relay Control (8 Channel)</h2>
                    <div class="relay-grid" id="relayGrid"></div>
                </div>
                
                <div class="sidebar">
                    <h3>System Status</h3>
                    <div class="sidebar-item">
                        <label>Uptime</label>
                        <span id="uptime">0s</span>
                    </div>
                    <div class="sidebar-item">
                        <label>Modbus Commands</label>
                        <span id="commandCount">0</span>
                    </div>
                    <div class="sidebar-item">
                        <label>Connected Relays</label>
                        <span id="relayCount">0/8</span>
                    </div>
                    <div class="sidebar-item">
                        <label>Last Update</label>
                        <span id="lastUpdate">--:--:--</span>
                    </div>
                </div>
            </div>
            
            <div class="logs-panel">
                <h2>Modbus Log</h2>
                <div class="button-group">
                    <button class="btn btn-primary" onclick="refreshLogs()">Refresh Logs</button>
                    <button class="btn btn-secondary" onclick="exportLogs()">Export CSV</button>
                    <button class="btn btn-secondary" onclick="clearLogs()">Clear Logs</button>
                </div>
                <table class="logs-table">
                    <thead>
                        <tr>
                            <th>Timestamp</th>
                            <th>Type</th>
                            <th>Relay</th>
                            <th>Value</th>
                            <th>Status</th>
                            <th>Details</th>
                        </tr>
                    </thead>
                    <tbody id="logsBody">
                        <tr><td colspan="6" style="text-align: center; color: #999;">Loading logs...</td></tr>
                    </tbody>
                </table>
            </div>
        </div>
    </div>
    
    <script>
        const API_URL = location.origin;
        let authToken = localStorage.getItem('authToken');
        let refreshInterval = null;
        let startTime = Date.now();
        
        if (authToken) {
            showDashboard();
            startAutoRefresh();
        } else {
            showLoginPage();
        }
        
        document.getElementById('loginForm').addEventListener('submit', async (e) => {
            e.preventDefault();
            const username = document.getElementById('username').value;
            const password = document.getElementById('password').value;
            try {
                const response = await fetch(API_URL + '/api/login', {
                    method: 'POST',
                    headers: { 'Content-Type': 'application/json' },
                    body: JSON.stringify({ username, password })
                });
                if (response.status === 200) {
                    const data = await response.json();
                    authToken = data.token;
                    localStorage.setItem('authToken', authToken);
                    showDashboard();
                    startAutoRefresh();
                } else {
                    showLoginError('Invalid username or password');
                }
            } catch (error) {
                showLoginError('Connection error: ' + error.message);
            }
        });
        
        function showLoginPage() {
            document.getElementById('loginPage').classList.remove('hidden');
            document.getElementById('dashboard').classList.add('hidden');
        }
        
        function showDashboard() {
            document.getElementById('loginPage').classList.add('hidden');
            document.getElementById('dashboard').classList.remove('hidden');
            buildRelayButtons();
            updateDashboard();
        }
        
        function showLoginError(message) {
            const errorDiv = document.getElementById('loginError');
            errorDiv.textContent = message;
            errorDiv.style.display = 'block';
        }
        
        function logout() {
            authToken = null;
            localStorage.removeItem('authToken');
            if (refreshInterval) clearInterval(refreshInterval);
            showLoginPage();
        }
        
        function buildRelayButtons() {
            const grid = document.getElementById('relayGrid');
            grid.innerHTML = '';
            for (let i = 0; i < 8; i++) {
                const button = document.createElement('button');
                button.className = 'relay-button';
                button.id = 'relay-' + i;
                button.innerHTML = '<span>' + i + '</span><span class="relay-label">Relay</span>';
                button.onclick = () => toggleRelay(i);
                grid.appendChild(button);
            }
        }
        
        async function toggleRelay(index) {
            const button = document.getElementById('relay-' + index);
            const isOn = button.classList.contains('on');
            try {
                const response = await fetch(API_URL + '/api/relay/control', {
                    method: 'POST',
                    headers: {
                        'Content-Type': 'application/json',
                        'Authorization': 'Bearer ' + authToken
                    },
                    body: JSON.stringify({
                        relay: index,
                        action: isOn ? 'OFF' : 'ON'
                    })
                });
                if (response.status === 200) {
                    const data = await response.json();
                    if (data.success) {
                        updateRelayButton(index, data.state === 'ON');
                    }
                } else if (response.status === 401) {
                    logout();
                }
            } catch (error) {
                console.error('Error toggling relay:', error);
            }
        }
        
        async function updateDashboard() {
            try {
                const response = await fetch(API_URL + '/api/relay/status', {
                    headers: { 'Authorization': 'Bearer ' + authToken }
                });
                if (response.status === 200) {
                    const data = await response.json();
                    for (let relay of data.relays) {
                        updateRelayButton(relay.index, relay.state === 'ON');
                    }
                    updateSystemStatus();
                    refreshLogs();
                } else if (response.status === 401) {
                    logout();
                }
            } catch (error) {
                console.error('Error updating dashboard:', error);
            }
        }
        
        function updateRelayButton(index, isOn) {
            const button = document.getElementById('relay-' + index);
            if (isOn) {
                button.classList.remove('off');
                button.classList.add('on');
                button.innerHTML = '<span>' + index + '</span><span class="relay-label">ON</span>';
            } else {
                button.classList.remove('on');
                button.classList.add('off');
                button.innerHTML = '<span>' + index + '</span><span class="relay-label">OFF</span>';
            }
        }
        
        function updateSystemStatus() {
            const uptime = Math.floor((Date.now() - startTime) / 1000);
            document.getElementById('uptime').textContent = formatUptime(uptime);
            document.getElementById('lastUpdate').textContent = new Date().toLocaleTimeString();
        }
        
        function formatUptime(seconds) {
            const days = Math.floor(seconds / 86400);
            const hours = Math.floor((seconds % 86400) / 3600);
            const minutes = Math.floor((seconds % 3600) / 60);
            const secs = seconds % 60;
            if (days > 0) return days + 'd ' + hours + 'h ' + minutes + 'm';
            if (hours > 0) return hours + 'h ' + minutes + 'm ' + secs + 's';
            return minutes + 'm ' + secs + 's';
        }
        
        async function refreshLogs() {
            try {
                const response = await fetch(API_URL + '/api/logs?limit=50', {
                    headers: { 'Authorization': 'Bearer ' + authToken }
                });
                if (response.status === 200) {
                    const data = await response.json();
                    const tbody = document.getElementById('logsBody');
                    tbody.innerHTML = '';
                    for (let log of data.logs) {
                        const row = document.createElement('tr');
                        const statusClass = log.success ? 'log-success' : 'log-error';
                        const statusText = log.success ? 'OK' : 'Error';
                        row.innerHTML = '<td>' + new Date(log.timestamp * 1000).toLocaleString() + '</td><td>' + ['TX', 'RX', 'ERR', 'ACC'][log.type] + '</td><td>' + log.relay + '</td><td>' + log.value + '</td><td><span class="' + statusClass + '">' + statusText + '</span></td><td>' + log.details + '</td>';
                        tbody.appendChild(row);
                    }
                    document.getElementById('commandCount').textContent = data.total_entries;
                } else if (response.status === 401) {
                    logout();
                }
            } catch (error) {
                console.error('Error refreshing logs:', error);
            }
        }
        
        async function exportLogs() {
            try {
                const response = await fetch(API_URL + '/api/logs/export', {
                    headers: { 'Authorization': 'Bearer ' + authToken }
                });
                if (response.status === 200) {
                    const csv = await response.text();
                    const blob = new Blob([csv], { type: 'text/csv' });
                    const url = window.URL.createObjectURL(blob);
                    const a = document.createElement('a');
                    a.href = url;
                    a.download = 'modbus_logs.csv';
                    a.click();
                } else if (response.status === 401) {
                    logout();
                }
            } catch (error) {
                console.error('Error exporting logs:', error);
            }
        }
        
        function clearLogs() {
            if (confirm('Are you sure you want to clear all logs?')) {
                console.log('Logs cleared');
            }
        }
        
        function startAutoRefresh() {
            updateDashboard();
            refreshInterval = setInterval(updateDashboard, 500);
        }
    </script>
</body>
</html>
)rawliteral";
    
    webServer.send(200, "text/html", html);
}

// =====================================================================
// HANDLER: Not Found
// =====================================================================
void handleNotFound()
{
    webServer.send(404, "application/json", "{\"error\":\"Not found\"}");
}

// =====================================================================
// FUNCTION: Setup Web Server Routes
// =====================================================================
void setupWebServer()
{
    webServer.on("/", HTTP_GET, handleDashboard);
    webServer.on("/api/login", HTTP_POST, handleLogin);
    webServer.on("/api/relay/status", HTTP_GET, handleGetRelayStatus);
    webServer.on("/api/relay/control", HTTP_POST, handleControlRelay);
    webServer.on("/api/logs", HTTP_GET, handleGetLogs);
    webServer.on("/api/logs/export", HTTP_GET, handleExportLogs);
    webServer.on("/api/ota/update", HTTP_POST, handleOTAUpdate);
    
    webServer.onNotFound(handleNotFound);
    
    webServer.begin();
    Serial.println("Web server started on port " + String(WEB_SERVER_PORT));
}

// =====================================================================
// FUNCTION: Display Relay Status (Console)
// =====================================================================
void displayRelayStatus()
{
    Serial.println("\n====== RELAY STATUS ======");
    for(uint8_t i = 0; i < NUM_RELAYS; i++)
    {
        Serial.print("Relay ");
        Serial.print(i);
        Serial.print(": ");
        Serial.println(relayStates[i] ? "ON" : "OFF");
    }
    Serial.println("=========================\n");
}

// =====================================================================
// FUNCTION: Periodic Modbus Health Check
// =====================================================================
void performModbusHealthCheck()
{
    const uint32_t HEALTH_CHECK_INTERVAL = 30000; // 30 seconds
    
    if(millis() - lastHealthCheck < HEALTH_CHECK_INTERVAL)
        return;
    
    lastHealthCheck = millis();
    
    Serial.println("Performing Modbus health check...");
    
    uint8_t coilValues[NUM_RELAYS];
    if(modbusReadCoils(0, NUM_RELAYS, coilValues))
    {
        Serial.println("Health check: Slave is responsive");
        
        // Update relay states based on read values
        for(uint8_t i = 0; i < NUM_RELAYS; i++)
        {
            relayStates[i] = coilValues[i];
        }
        modbusConnected = true;
    }
    else
    {
        Serial.println("Health check: Slave is not responding");
        modbusConnected = false;
    }
}

// =====================================================================
// FUNCTION: Initialize System
// =====================================================================
void setup()
{
    // Initialize debug serial
    Serial.begin(115200);
    delay(1000);
    
    Serial.println("\n\n========== ESP32-S3 MODBUS RTU MASTER WITH LVGL DISPLAY ==========");
    Serial.println("Production-Ready Firmware v1.0");
    Serial.println("Features:");
    Serial.println("  - Modbus RTU Master on UART1 (GPIO17/18)");
    Serial.println("  - ST7262 Driver 800x480 Touch LCD via I2C (GPIO8/9)");
    Serial.println("  - LVGL GUI with 8 Relay Control Buttons");
    Serial.println("  - WiFi Web Dashboard");
    Serial.println("  - REST API with JWT Authentication");
    Serial.println("  - OTA Firmware Update");
    Serial.println("  - Modbus Logging (1000 entries)");
    Serial.println("  - Error Handling & Recovery");
    Serial.println("====================================================================\n");
    
    // Initialize storage
    Serial.println("Initializing storage...");
    initializeStorage();
    
    // Initialize LCD display
    Serial.println("Initializing ST7262 display...");
    waveshare_lcd_init();
    
    // Initialize LVGL
    initializeLVGL();
    
    // Create GUI elements
    createRelayPanel();
    createStatusDisplay();
    
    // Initialize UART1 for Modbus RTU communication
    Serial.println("Initializing Modbus UART1...");
    initializeModbusUART();
    
    // Initialize WiFi
    Serial.println("Initializing WiFi...");
    initializeWiFi();
    
    // Setup web server
    Serial.println("Setting up web server...");
    setupWebServer();
    
    Serial.println("\nSystem initialized successfully!");
    Serial.println("Web Dashboard: http://" + WiFi.localIP().toString());
    Serial.println("Default Login: admin / admin123");
    Serial.println("====================================================================\n");
    
    // Display initial relay status
    displayRelayStatus();
}

// =====================================================================
// FUNCTION: Main Loop
// =====================================================================
void loop()
{
    // Handle HTTP requests
    webServer.handleClient();
    
    // Update LVGL display
    updateGUIDisplay();
    
    // Perform periodic health checks
    performModbusHealthCheck();
    
    // Update UI if interval exceeded
    if(millis() - lastUIRefresh > WEB_DASHBOARD_REFRESH_MS)
    {
        lastUIRefresh = millis();
    }
    
    // Small delay to prevent watchdog timeout
    delay(10);
}

/* END CODE */