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

File file;
String buffer;

int32_t session_val = 1;
uint32_t fileCounter = 1;

unsigned long lastMicros = 0;
char fileName[13];

/* Constants for Timing */
// unsigned long startAnalogTimer = 0;               // Micros and Milis requires unsigned long
unsigned long endAnalogTimer = 0;
// unsigned long startFileTimer = 0; 
unsigned long endFileTimer = 0; 

bool fileWrite = true; 

void setup() {

  SPI_initialization(9600);
  // reserve 1kB for String used as a buffer
  buffer.reserve(1024);

  if (!SD.begin()) {
    Serial.println("Card failed, or not present");
    while (1);
  }
  
}

void loop() {

  file = open_SD_tmp_File_sessionFile(fileCounter,session_val);

  unsigned long startFileTimer = millis();
  while ( (millis() - startFileTimer) < 50)
  {
    // Serial.println(millis()-startFileTimer);
    unsigned long startAnalogTimer = micros();
    while ( (micros() - startAnalogTimer) < 1000)
    {
      // Serial.println(micros() - startAnalogTimer);
      // add a new line to the buffer
      buffer += micros() - startAnalogTimer;
      buffer += ",";
      buffer += analogRead(A0);
      buffer += "\r\n";
      
      // Serial.println(buffer);
    }

    unsigned int chunkSize = file.availableForWrite();
    if (chunkSize && buffer.length() >= chunkSize) {
      // write to file 
      file.write(buffer.c_str(), chunkSize);
      // remove written data from buffer
      buffer.remove(0, chunkSize);
    }
  }
  Serial.println("closing file");
  file.close();

  if (fileWrite) {
    file = SD.open("00010001.txt");
    // if the file is available, write to it:
    if (file) {
      Serial.print("opening... ");
      Serial.println(file.name());
      while (file.available()) {
        Serial.write(file.read());
      }
      file.close();
    }
    // if the file isn't open, pop up an error:
    else {
      Serial.println("error opening datalog.txt");
    }
    delay(3000);
    }
}

/*open_SD_tmp_File_sessionFile:
  **Opens/Creates a file in the SD card
  **Required: The file must be closed manually 
  **File name format: SSSSXXXX.txt S:session,X:file count
*/
File open_SD_tmp_File_sessionFile(int fileIndex, int session)
{
  
  Serial.println("\nInitilizing write to file... "); 

  //.tmp

  fourDigits(session, fileName);
  fourDigits(fileIndex, fileName + 4);
  snprintf(fileName + 8, 5, ".txt");

  file = SD.open(fileName, FILE_WRITE);

  if (file) {
    Serial.println("File created successfully!");
  } else {
    Serial.println("Error opening file");
  }
  Serial.println(file.name());

  return file;
}




void SPI_initialization(const uint32_t baudRate) {
  Serial.begin(baudRate);

  while (!Serial && millis() < 15000) {
    ;
  }
  Serial.println("\n\n-----New Serial Communication Secured-----");
}

char* fourDigits(int32_t digits, char* result) {
  if (digits < 10) {
    sprintf(result, "000%d", digits);
  } else if (digits < 100) {
    sprintf(result, "00%d", digits);
  } else if (digits < 1000) {
    sprintf(result, "0%d", digits);
  } else {
    sprintf(result, "%d", digits);
  }

  return result;
}