#include <list>
#include <SD.h>
#define CS_PIN 5

File root;
std::list<String> indexList;
std::list<String> outList;

void setup() {
  Serial.begin(115200);

  Serial.print("Initializing SD card... ");

  if (!SD.begin(CS_PIN)) {
    Serial.println("Card initialization failed!");
    while (true);
  }

  Serial.println("initialization done.\n");
  createIndexList("FileB.txt");
  evaluateFile("FileA.txt");
  writeResultToFile("FileC.txt");
}

void loop() {
  delay(100);
  // nothing happens after setup finishes.
}

void createIndexList(String aFile){
  indexList.clear();
  String aLine = "";
  File textFile = SD.open("/"+aFile);
  if (textFile) {
    Serial.println("Creating Index List from "+aFile);
    while (textFile.available()) {
      char c = textFile.read();
      if (c >= ' ') {
        aLine = aLine + c;
      } 
      if (c == 10){
        checkForIndexList(aLine);
        aLine = "";
      }
    }
    textFile.close();
    if (aLine != "") {
      checkForIndexList(aLine);
    }
  } else {
    Serial.println("error opening "+aFile);
  }
  Serial.println();
  showList();
} 

void checkForIndexList(String line){
      String idx = stripIndex(line);
        if (idx > "") { 
          indexList.push_back(idx);
          }
}

String stripIndex(String Line){
  int c1 = Line.indexOf(',');
  int c2 = Line.indexOf(',', c1+1);
  String index = "";
  if (c1 >= 0 && c2 > c1){
    index = Line.substring(c1+1, c2);
  }
  return index;
}

void showList(){
  Serial.println("===== Index List ========");
  for (auto idx : indexList){
    Serial.println(idx);
  }
  Serial.println("=========================\n");
}  

void evaluateFile(String aFile){
  String aLine = "";
  outList.clear();
  File textFile = SD.open("/"+aFile);
  if (textFile) {
    Serial.println("Evaluating "+aFile);
    Serial.println("\n======= New Entries ========");
    while (textFile.available()) {
      char c = textFile.read();
      if (c >= ' ') {
        aLine = aLine + c;
      } 
      if (c == 10){
          checkForOutList(aLine);
          aLine = "";
        }
     }
    textFile.close();
    checkForOutList(aLine);
  } else {
    Serial.println("error opening "+aFile);
  }
  Serial.println("============================\n"); 
} 

void checkForOutList(String line){
        String idx = stripIndex(line);
        if (idx > "") { 
           if (!indexFound(idx)) {
            Serial.println(idx);
            outList.push_back(line);
          }
       }
}      

void checkIndex(String line){
      String idx = stripIndex(line);
        if (idx > "") { 
          indexList.push_back(idx);
          }
}

boolean indexFound(String aIndex){
  boolean found = false;
  for (auto ix : indexList){
    if (aIndex == ix) found = true;
  }
  return found;
} 

void writeResultToFile(String wFile){
  File tFile = SD.open("/"+wFile, FILE_WRITE);
  if (tFile) {
    Serial.println("Writing to "+wFile);
    Serial.println("\n========= Entries ========");
    for (auto txt : outList){
       tFile.println(txt);
       Serial.println(txt);
    }
    tFile.close();
    Serial.println("============================\n"); 
  } else {
    Serial.println("error opening "+wFile);
  }
}