#include <Wire.h>
#include <Adafruit_SSD1306.h>
#include <SPI.h>
#include <SD.h>

#define OLED_RESET    -1  //-1 indicate NO_Reset_Pin for O_LED
#define SD_CS_PIN     53  // Chip_select_pin for SD_card

// Initialize O_LED_display
Adafruit_SSD1306 display(128, 64, &Wire, OLED_RESET);

File myFile;

void setup() {
  Serial.begin(9600);

  // Initialize O_LED with 0x3C address(I2C)
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("SSD1306 allocation failed"));
    while (true); 
  }
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);

  // Initialize SD_card
  if (!SD.begin(SD_CS_PIN)) {   // SD_CS_PIN = 53
    Serial.println(F("SD card initialization failed!"));
    display.println(F("SD init failed"));
    display.display();
    while (true);
  }
  Serial.println(F("SD card initialized"));

  // Write to a file on SD_card for storing
  myFile = SD.open("Sample_1.txt", FILE_WRITE);
  if (myFile) {   
    Serial.println(F("Writing to Sample_1.txt..."));
    
    myFile.println(F("Hello, Guys!\n"));
    myFile.println(F("This the Interaction\n"));
    myFile.println(F("of SPI with SD-Card\n"));
    myFile.println(F("and ATmega2560.\n"));

    myFile.close();
    Serial.println(F("Data written to SD card"));
  } else {
    Serial.println(F("Error opening Sample_1.txt"));
  }
  //F() macro stores text in flash_memory, 
  //not in RAM, to save_memory.
  
  // Display message on O_LED that 
  // both initailize_and_write is Done
  display.clearDisplay();
  display.setCursor(0, 0);
  display.print("SD Card initialized");
  display.setCursor(0, 10);
  display.print("Writing to file...");
  display.display();
  delay(2000);
}

void loop() {
  // Check if the file_exists and read its contents
  if (SD.exists("Sample_1.txt")) {
    myFile = SD.open("Sample_1.txt");
    if (myFile) {
      display.clearDisplay();
      display.setCursor(0, 0);
      display.print("Reading from file:");
      display.display();
      delay(1000);
      display.clearDisplay();
      display.setCursor(0, 0);
      while (myFile.available()) {
        display.print((char)myFile.read());
      }
      myFile.close();
      display.display();
    } else {
      Serial.println(F("Error opening Sample_1.txt for reading"));
    }
  } else {
    Serial.println(F("File does not exist"));
  }

  delay(5000);  // Wait for 5 seconds before reading again
                // and after print what the content in the SD-Card
}