#define TINY_GSM_MODEM_SIM800  
#include <WiFi.h>
#include "ThingSpeak.h"
#include <TinyGPS++.h>
#include <TinyGSM.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <WebServer.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET    -1
#define SDA_PIN 21
#define SCL_PIN 22

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);
TinyGPSPlus gps;  

const char* ssid = "Wokwi-GUEST";
const char* password = "";

// Optional: Use Static IP (Uncomment if needed)
/*
IPAddress local_IP(192, 168, 1, 100);
IPAddress gateway(192, 168, 1, 1);
IPAddress subnet(255, 255, 255, 0);
IPAddress primaryDNS(8, 8, 8, 8);
IPAddress secondaryDNS(8, 8, 4, 4);
*/

WiFiClient client;
WebServer server(80);  
unsigned long channelNumber = 2842883;
const char* writeAPIKey = "L1C5GZXEZHOL8IDX";

#define GPS_RX_PIN 16
#define GPS_TX_PIN 17
HardwareSerial gpsSerial(2); 

#define GSM_RX_PIN 26
#define GSM_TX_PIN 27
HardwareSerial gsmSerial(1);
TinyGsm modem(gsmSerial);

unsigned long previousMillis = 0;
const long interval = 15000;  // 15 seconds for ThingSpeak free account

void connectWiFi() {
  Serial.println("Connecting to WiFi...");
  WiFi.disconnect(true);  // Reset WiFi to clear previous failures
  delay(1000);
  
  // Uncomment if using Static IP
  // WiFi.config(local_IP, gateway, subnet, primaryDNS, secondaryDNS);

  WiFi.begin(ssid, password);
  unsigned long startAttemptTime = millis();
  const unsigned long timeout = 10000;  // 10-second timeout

  while (WiFi.status() != WL_CONNECTED && millis() - startAttemptTime < timeout) {
    delay(500);
    Serial.print(".");
  }

  if (WiFi.status() == WL_CONNECTED) {
    Serial.println("\nConnected to WiFi");
  } else {
    Serial.println("\nFailed to connect to WiFi. Restarting...");
    ESP.restart();  // Restart ESP if WiFi fails
  }
}

void setup() {
  Serial.begin(115200);
  gpsSerial.begin(9600, SERIAL_8N1, GPS_RX_PIN, GPS_TX_PIN);
  gsmSerial.begin(9600, SERIAL_8N1, GSM_RX_PIN, GSM_TX_PIN);

  connectWiFi();

  ThingSpeak.begin(client);

  Serial.println("Initializing GSM module...");
  modem.init();
  delay(3000);
  if (!modem.restart()) {
    Serial.println("Failed to initialize GSM modem");
  } else {
    Serial.println("GSM modem ready");
  }

  Wire.begin(SDA_PIN, SCL_PIN);
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {  
    Serial.println("SSD1306 allocation failed");
    for (;;);
  }
  
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(10, 10);
  display.println("GPS Tracker Ready");
  display.display();

  server.on("/", handleRoot);
  server.on("/location", sendLocation);
  server.begin();
  Serial.println("Web server started.");
}

void loop() {
  server.handleClient();  

  while (gpsSerial.available() > 0) {
    gps.encode(gpsSerial.read());
  }

  unsigned long currentMillis = millis();
  if (currentMillis - previousMillis >= interval) {
    previousMillis = currentMillis;

    if (gps.location.isValid()) {
      float latitude = gps.location.lat();
      float longitude = gps.location.lng();

      Serial.print("Latitude: ");
      Serial.println(latitude);
      Serial.print("Longitude: ");
      Serial.println(longitude);

      display.clearDisplay();
      display.setCursor(10, 10);
      display.println("GPS Location:");
      display.setCursor(10, 30);
      display.print("Lat: ");
      display.println(latitude, 6);
      display.setCursor(10, 45);
      display.print("Lon: ");
      display.println(longitude, 6);
      display.display();

      if (WiFi.status() == WL_CONNECTED) {
        ThingSpeak.setField(1, latitude);
        ThingSpeak.setField(2, longitude);
        int result = ThingSpeak.writeFields(channelNumber, writeAPIKey);
        if (result == 200) {
          Serial.println("Data sent to ThingSpeak successfully");
        } else {
          Serial.print("Error sending data to ThingSpeak: ");
          Serial.println(result);
        }
      } else {
        Serial.println("WiFi disconnected! Reconnecting...");
        connectWiFi();  // Reconnect WiFi if lost
      }
    } else {
      Serial.println("Waiting for valid GPS signal...");
    }
  }
}

void handleRoot() {
  server.send(200, "text/html", "<html><body><h1>ESP32 GPS Tracker</h1><p>View real-time location <a href='/location'>here</a>.</p></body></html>");
}

void sendLocation() {
  if (gps.location.isValid()) {
    String json = "{";
    json += "\"latitude\": " + String(gps.location.lat(), 6) + ",";
    json += "\"longitude\": " + String(gps.location.lng(), 6);
    json += "}";
    server.send(200, "application/json", json);
  } else {
    server.send(200, "application/json", "{\"error\": \"No valid GPS signal\"}");
  }
}