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#include "mbedtls/rsa.h"
#include "mbedtls/pk.h"
#include "mbedtls/sha1.h"
#include "mbedtls/platform.h"
#include "mbedtls/config.h"
#include "mbedtls/oid.h"
#include "mbedtls/ctr_drbg.h"
#include "mbedtls/x509.h"
#include "mbedtls/x509_csr.h"
#include "mbedtls/error.h"
#include<string.h>
#include "mbedtls/md.h"
#include "mbedtls/entropy.h"
#include "mbedtls/bignum.h"
#include "SPIFFS.h"
#include "FS.h"
#include <SD.h>
#include <SPI.h>

#define DFL_FILENAME            "/spiffs/client.key"
#define DFL_DEBUG_LEVEL         0
#define DFL_OUTPUT_FILENAME     "/spiffs/client.csr"
#define DFL_SUBJECT_NAME        "CN=Cert,O=mbed TLS,C=UK"
#define DFL_KEY_USAGE           0
#define DFL_NS_CERT_TYPE        0

#define mbedtls_printf printf

struct options
{
    const char *filename;       /* filename of the key file             */
    int debug_level;            /* level of debugging                   */
    const char *output_file;    /* where to store the constructed key file  */
    const char *subject_name;   /* subject name for certificate request */
    unsigned char key_usage;    /* key usage flags                      */
    unsigned char ns_cert_type; /* NS cert type                         */
} opt;
void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  Serial.println();
  int ret = 1;
  mbedtls_entropy_context entropy;
  mbedtls_ctr_drbg_context ctr_drbg;
  
  char buf[1024];
  
  mbedtls_ctr_drbg_init( &ctr_drbg );
  mbedtls_entropy_init( &entropy );
  if( ( ret = mbedtls_ctr_drbg_seed( &ctr_drbg, mbedtls_entropy_func, &entropy,
                             (const unsigned char *) pers,
                             strlen( pers ) ) ) != 0 )
  {
      mbedtls_printf( " failed\n  !  mbedtls_ctr_drbg_seed returned %d", ret );
      return;
  }
  
  mbedtls_pk_context key;
  mbedtls_x509write_csr req;

  mbedtls_x509write_csr_init( &req );
  mbedtls_x509write_csr_set_md_alg( &req, MBEDTLS_MD_SHA256 );
  mbedtls_pk_init( &key );
  memset( buf, 0, sizeof( buf ) );
  
  opt.filename            = DFL_FILENAME;
  opt.debug_level         = DFL_DEBUG_LEVEL;
  opt.output_file         = DFL_OUTPUT_FILENAME;
  opt.subject_name        = DFL_SUBJECT_NAME;
  opt.key_usage           = DFL_KEY_USAGE;
  opt.ns_cert_type        = DFL_NS_CERT_TYPE;

  if( opt.key_usage )
      mbedtls_x509write_csr_set_key_usage( &req, opt.key_usage );

  if( opt.ns_cert_type )
      mbedtls_x509write_csr_set_ns_cert_type( &req, opt.ns_cert_type );

  mbedtls_printf( "  . Seeding the random number generator..." );
  
  mbedtls_entropy_init( &entropy );
  if( ( ret = mbedtls_ctr_drbg_seed( &ctr_drbg, mbedtls_entropy_func, &entropy,
                             (const unsigned char *) pers,
                             strlen( pers ) ) ) != 0 )
  {
      mbedtls_printf( " failed\n  !  mbedtls_ctr_drbg_seed returned %d", ret );
      return;
  }

  mbedtls_printf( " ok\n" );

  /*
   * 1.0. Check the subject name for validity
   */
  mbedtls_printf( "  . Checking subject name..." );

  if( ( ret = mbedtls_x509write_csr_set_subject_name( &req, opt.subject_name ) ) != 0 )
  {
      mbedtls_printf( " failed\n  !  mbedtls_x509write_csr_set_subject_name returned %d", ret );
      return;
  }

  mbedtls_printf( " ok\n" );

  /*
   * 1.1. Load the key
   */
  mbedtls_printf( "  . Loading the private key ..." );
  SPIFFS.begin();

  ret = mbedtls_pk_parse_keyfile( &key, opt.filename, NULL );
  Serial.println(ret);

  if( ret != 0 )
  {
      mbedtls_printf( " failed\n  !  mbedtls_pk_parse_keyfile returned %d", ret );
      return;
  }

  mbedtls_x509write_csr_set_key( &req, &key );

  mbedtls_printf( " ok\n" );

  /*
   * 1.2. Writing the request
   */
  mbedtls_printf( "  . Writing the certificate request ..." );

  if( ( ret = write_certificate_request( &req, opt.output_file,
                                         mbedtls_ctr_drbg_random, &ctr_drbg ) ) != 0 )
  {
      mbedtls_printf( " failed\n  !  write_certifcate_request %d", ret );
      return;
  }

  mbedtls_printf( " ok\n" );

  mbedtls_mpi_free( &N ); mbedtls_mpi_free( &P ); mbedtls_mpi_free( &Q );
  mbedtls_mpi_free( &D ); mbedtls_mpi_free( &E ); mbedtls_mpi_free( &DP );
  mbedtls_mpi_free( &DQ ); mbedtls_mpi_free( &QP );
  mbedtls_rsa_free( &rsa );
  mbedtls_ctr_drbg_free( &ctr_drbg );
  mbedtls_entropy_free( &entropy );
  
  }

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#define MBEDTLS_ERR_PK_KEY_INVALID_FORMAT  -0x3D00  /**< Invalid key tag or value. */

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mbedtls_rsa_gen_key( mbedtls_pk_rsa( key ), mbedtls_ctr_drbg_random, &ctr_drbg, 1024, 65537 );

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mbedtls_x509write_csr_set_md_alg( &req, MBEDTLS_MD_SHA256 );
if( opt.key_usage )
      mbedtls_x509write_csr_set_key_usage( &req, opt.key_usage );

   if( opt.ns_cert_type )
      mbedtls_x509write_csr_set_ns_cert_type( &req, opt.ns_cert_type );
   /*
   * 0. Seed the PRNG
   */
  mbedtls_printf( "  . Seeding the random number generator..." );

  mbedtls_entropy_init( &entropy );
  if( ( ret = mbedtls_ctr_drbg_seed( &ctr_drbg, mbedtls_entropy_func, &entropy,
                             (const unsigned char *) pers,
                             strlen( pers ) ) ) != 0 )
  {
      mbedtls_printf( " failed\n  !  mbedtls_ctr_drbg_seed returned %d", ret );
      return;
  }

  mbedtls_printf( " ok\n" );
  

  /*
   * 1.0. Check the subject name for validity
   */
  mbedtls_printf( "  . Checking subject name..." );

  if( ( ret = mbedtls_x509write_csr_set_subject_name( &req, opt1.subject_name ) ) != 0 )
  {
      mbedtls_printf( " failed\n  !  mbedtls_x509write_csr_set_subject_name returned %d", ret );
      return;
  }
  
  mbedtls_x509write_csr_set_key( &req, &key );
  
  /*
   * 1.2. Writing the request
   */

  mbedtls_printf( "  . Writing the certificate request ..." );
  unsigned char output_buf[4096];
  
  memset(output_buf,0,sizeof(output_buf));
  
  if((ret = mbedtls_x509write_csr_pem(&req, output_buf, 4096, NULL, &ctr_drbg))<0){
    Serial.println("Writing csr in PEM format failed with exit code "+ ret);
    return;
  }