// Include libraries
#include <Wire.h>              // Provides functions for I2C communication with the OLED display. (built-in)
#include <Adafruit_GFX.h>      // Basic graphics library used by the OLED library.
#include <Adafruit_SSD1306.h>  // Library for controlling the SSD1306 OLED display.
#include <WiFi.h>              // Library for connecting the ESP32 to a Wi-Fi network.
//#include <time.h>            // Provides functions for retriving time info. (built-in)


// Define OLED parameters
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1          // Pin connected to the OLED reset pin (if not connected, set to -1).
#define SCREEN_ADDRESS 0x3C    // I2C address of the OLED display

// Define WIFI-Time parameters
#define NTP_SERVER "pool.ntp.org"  // Address of the NTP server used for time synchronization ("pool.ntp.org" is a common choice).
#define UTC_OFFSET 3600*5 + 30*60  // Offset from UTC in seconds
#define UTC_OFFSET_DST 0           // Offset during Daylight Saving Time

// variables for time
int days = 0;
int hours = 0;
int minutes = 0;
int seconds = 0;

// An instance (display) of the Adafruit_SSD1306 class to interact with the OLED display.
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);


void setup() {
  Serial.begin(115200);  // Initializes serial communication.

  // Initializes the OLED display using display.begin(). If unsuccessful, an error message is printed.
  if (!display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS)) {
    Serial.println(F("SSD1306 allocation failed"));
    for (;;);
  }

  // Adafruit boot screen
  display.display();
  delay(500);

  // Initiate a connection to a Wi-Fi network.
  WiFi.begin("Wokwi-GUEST", "", 6);   // Arguments = (SSID, password, channel)
  display.clearDisplay();
  print_line("Connecting", 0, 0, 2);
  print_line("to WIFI", 0, 20, 2);

  int counter = 0;
  while (WiFi.status() != WL_CONNECTED) {   // While wifi not connected
    print_line("-", 5 * counter, 40, 4);    // To simulate a loading bar
    counter += 1;
  }

  display.clearDisplay();
  print_line("WIFI", 0, 0, 2);
  print_line("Connected", 0, 20, 2);
  delay(500);

  configTime(UTC_OFFSET, UTC_OFFSET_DST, NTP_SERVER);   // Configure the time with time zone and server.
}


void loop() {
  display.clearDisplay();
  update_time();
  print_time_now();
}


void update_time() {

  // Create a time structure (struct tm) called timeinfo that contains all the details about the time (min, sec, hour, etc…).
  // This line declares a variable named timeinfo of type struct tm.
  struct tm timeinfo;

  // If a function needs to modify the original data,
  // you can pass the address (memory location) of the variable using the & (address-of) operator.
  // This line retrieves the current local time and stores the details in the timeinfo variable.
  getLocalTime(&timeinfo);

  // Declares a character array named time_hour with a size of 3 to store the hour value as a string (including a null terminator).
  char time_hour[3];
  char time_minute[3];
  char time_second[3];
  char time_day[3];

  // This line uses the strftime function to format the hour value from the timeinfo structure
  // according to the format specifier "%H".
  // string from time
  strftime(time_hour, 3, "%H", &timeinfo);
  strftime(time_minute, 3, "%M", &timeinfo);
  strftime(time_second, 3, "%S", &timeinfo);
  strftime(time_day, 3, "%d", &timeinfo);

  // Converts the string in time_hour (which should now represent the hour as a string) to an integer using atoi (ASCII to integer)
  // and stores the converted value in the variable hours.
  // ASCII to integer
  hours = atoi(time_hour);
  minutes = atoi(time_minute);
  seconds = atoi(time_second);
  days = atoi(time_day);
}

void print_time_now(void) {   // update_time() and print_time_now() finctions can be combined.

  struct tm timeinfo;
  getLocalTime(&timeinfo);
  char full_time[9];
  strftime(full_time, 9, "%H:%M:%S", &timeinfo);
  print_line(full_time, 15,0,2);

  /*************
  print_line(String(days), 0, 0, 2);
  print_line(":", 20, 0, 2);
  print_line(String(hours), 30, 0, 2);
  print_line(":", 50, 0, 2);
  print_line(String(minutes), 60, 0, 2);
  print_line(":", 80, 0, 2);
  print_line(String(seconds), 90, 0, 2);
  **************/
}

void print_line(String text, int column, int row, int text_size) {
  display.setTextSize(text_size);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(column, row);
  display.println(text);
  display.display();
}


/************************************************************

// Alternate shorter implementation (Can eliminate update_time() and print_time_now() functions)

void loop() {
  display.clearDisplay();
  print_time();
}

void print_time() {
  struct tm timeinfo;
  getLocalTime(&timeinfo);
  char full_time[9];
  strftime(full_time, 9, "%H:%M:%S", &timeinfo);
  print_line(full_time, 15,0,2);
}
*/