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

/* 
Arduino Mega SDI pins:
https://forum.arduino.cc/t/sd-card-shield-configuration-on-arduino-mega-2560-rev3/161376/6$0

SPI	// Mega
SS	// 53
MOSI	// 51
MISO	// 50
SCK	// 52
*/
const int chipSelect = 53;

File root;
String buffer;
String searchVal = "#I78X8OV5";
unsigned long CurrentTime;
unsigned long StartTime;
float ElapsedTime;
unsigned long LineCount = 0;

void setup() {
  // init Serial comm
  Serial.begin(9600);

  // for raspi-logging protokoll, check if UART/Serial is there
  while (!Serial);

  // Check if SD-Card is there
  Serial.print("Initializing SD card...");
  if (!SD.begin(chipSelect)) {
    // ERROR-HANDLING!
    Serial.println("Error on SD-Card.");
    while (true);
  }
  Serial.println("initialization done.");

  root = SD.open("/");

  printDirectory(root, 1);

  Serial.println("done!");
}

void loop() {}

void printDirectory(File dir, int numTabs) {

  while (true) {

    File entry =  dir.openNextFile();

    if (! entry) {
      // no more files
      break;
    }

    for (uint8_t i = 0; i < numTabs; i++) {
      Serial.print('\t');
    }

    Serial.println(entry.name());
    
    StartTime = millis();
    while (entry.available()) {
      buffer = entry.readStringUntil('\n');
      LineCount += 1;
      StartTime = millis();
      //Serial.println(buffer); //Printing for debugging purpose         
      if (buffer == searchVal){ // checking integer
        Serial.println("found");
        CurrentTime = millis();
        ElapsedTime = CurrentTime - StartTime;
        Serial.print("duration [s]:\t");   // prints a tab)
        Serial.print(ElapsedTime);
        Serial.print("\t on line:\t");
        Serial.println(LineCount);
        break;
      } 
    }
  
    entry.close();
  }

}