#include <Keypad.h>
#include <SPI.h>//include the SPI bus library
#include <MFRC522.h>//include the RFID reader library

#define SS_PIN 10  //slave select pin
#define RST_PIN A0  //reset pin
MFRC522 mfrc522(SS_PIN, RST_PIN);        // instatiate a MFRC522 reader object.
MFRC522::MIFARE_Key key;//create a MIFARE_Key struct named 'key', which will hold the card information
const byte numRows= 4; //number of rows on the keypad
const byte numCols= 4; //number of columns on the keypad
char keymap[numRows][numCols]=
{
{'1', '2', '3', 'A'},
{'4', '5', '6', 'B'},
{'7', '8', '9', 'C'},
{'*', '0', '#', 'D'}
};
byte rowPins[numRows] = {9,8,7,6}; //Rows 0 to 3
byte colPins[numCols]= {5,4,3,2}; //Columns 0 to 3
Keypad myKeypad= Keypad(makeKeymap(keymap), rowPins, colPins, numRows, numCols);
void setup()
{
  Serial.begin(9600);        // Initialize serial communications with the PC
  SPI.begin();               // Init SPI bus
  mfrc522.PCD_Init();        // Init MFRC522 card (in case you wonder what PCD means: proximity coupling device)
  Serial.println("Scan a MIFARE Classic card");
  for (byte i = 0; i < 6; i++) {
    key.keyByte[i] = 0xFF;//keyByte is defined in the "MIFARE_Key" 'struct' definition in the .h file of the library
  }
}
int block=1;//this is the block number we will write into and then read. Do not write into 'sector trailer' block, since this can make the block unusable.
byte blockcontent[16] = {"The_Pink_Banker_"};//an array with 16 bytes to be written into one of the 64 card blocks is defined
//byte blockcontent[16] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};//all zeros. This can be used to delete a block.
byte readbackblock[18]; //This array is used for reading out a block. The MIFARE_Read method requires a buffer that is at least 18 bytes to hold the 16 bytes of a block.
void loop()
{
  char keypressed = myKeypad.getKey();
  if (keypressed != NO_KEY)
  {
    Serial.println(keypressed);
   }
    if ( ! mfrc522.PICC_IsNewCardPresent()) {//if PICC_IsNewCardPresent returns 1, a new card has been found and we continue
    return;//if it did not find a new card is returns a '0' and we return to the start of the loop
  }

  // Select one of the cards
  if ( ! mfrc522.PICC_ReadCardSerial()) {//if PICC_ReadCardSerial returns 1, the "uid" struct (see MFRC522.h lines 238-45)) contains the ID of the read card.
    return;//if it returns a '0' something went wrong and we return to the start of the loop
  }
         Serial.println("card selected");
         writeBlock(block, blockcontent);//the blockcontent array is written into the card block
         readBlock(1, readbackblock);//read the block back
         Serial.print("read block: ");
         for (int j=0 ; j<16 ; j++)//print the block contents
         {
           Serial.write (readbackblock[j]);//Serial.write() transmits the ASCII numbers as human readable characters to serial monitor
         }
         mfrc522.PICC_DumpToSerial(&(mfrc522.uid));
         Serial.println("");
}