#include <stdio.h>
#include <string>
#include <string.h>
#include <memory>
using std::unique_ptr;
#include <openssl/err.h>
#include <openssl/bn.h>
#include <openssl/rsa.h>
#include <openssl/evp.h>
#include <openssl/pem.h>

EVP_CIPHER_CTX *ctx;
RSA* rsa;
BIGNUM* bn;
// assumes that the digest is at least of length 256/8 bytes.
uint32_t generate_sha256_hash(const unsigned char *message, size_t message_len, unsigned char *digest)
{
	EVP_MD_CTX *mdctx; unsigned int digest_len;

	if((mdctx = EVP_MD_CTX_create()) == NULL)
	{
		printf("EVP_MD_CTX_create returned NULL - could not create context\n"); fflush(stdout); return 0x1;
	}

	if(EVP_DigestInit_ex(mdctx, EVP_sha256(), NULL) != 1)
	{
                printf("EVP_DigestInit_ex returned 0 - could not initialize hash with SHA256\n"); fflush(stdout); return 0x2;
	}

        if(EVP_DigestUpdate(mdctx, message, message_len) != 1)
        {
                printf("EVP_DigestUpdate returned 0 - could not compute SHA256 hash\n"); fflush(stdout); return 0x3;
        }

	if(1 != EVP_DigestFinal_ex(mdctx, digest, &digest_len))
        {
                printf("EVP_DigestFinal_ex returned 0 - could not finalize SHA256 hash\n"); fflush(stdout); return 0x4;
        }

	if(digest_len != 32)
	{
		printf("EVP_DigestFinal_ex returned a digest length of 0x%x instead of 0x20\n", digest_len); fflush(stdout); return 0x5;
	}
	EVP_MD_CTX_destroy(mdctx);
	return 0;
}
//////////////////////////////////////////////////////////////////////////
//////////////////////////////////////
void crypto_cleanup()
{
	RSA_free(rsa);
	BN_free(bn);
	EVP_CIPHER_CTX_free(ctx);
}

// Code adapted from here: https://wiki.openssl.org/index.php/EVP_Authenticated_Encryption_and_Decryption
int aes_gcm_128(int enc, unsigned char *key, unsigned char *iv, unsigned char* plaintext, uint32_t plaintext_len, unsigned char *ciphertext,  uint32_t* op_ciphertext_len, unsigned char* tag)
{
	int len;
	int ciphertext_len;
	if(ctx == NULL)
	{
		/* Create and initialise the context */
		if(!(ctx = EVP_CIPHER_CTX_new())) { ERR_print_errors_fp(stderr); fflush(stderr);return 0x1; }
	}

	/* Initialise the encryption operation. */
	if(1 != EVP_CipherInit_ex(ctx, EVP_aes_128_gcm(), NULL, key, iv, enc))
	{
		EVP_CIPHER_CTX_init(ctx);
		ERR_print_errors_fp(stderr);
		return 0x2;
	}
	/* Provide the message to be encrypted, and obtain the encrypted output.
	 * EVP_EncryptUpdate can be called multiple times if necessary
	 */
	if(1 != EVP_CipherUpdate(ctx, ciphertext, &len, plaintext, plaintext_len))
	{
                EVP_CIPHER_CTX_init(ctx);
                ERR_print_errors_fp(stderr);
		return 0x3;
	}
	ciphertext_len = len;

	if(enc == 0)
        {
                if(1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, 16, tag))
                {
                       EVP_CIPHER_CTX_init(ctx);
                       ERR_print_errors_fp(stderr); fflush(stderr);
                        return 0x5;
                }
        }


	/* Finalise the encryption. Normally ciphertext bytes may be written at
	 * this stage, but this does not occur in GCM mode
	 */
	// TODO: ^^^ Why the heck does it not occur in GCM mode ?
	if(1 != EVP_CipherFinal_ex(ctx, ciphertext + len, &len))
	{
		EVP_CIPHER_CTX_init(ctx);
		ERR_print_errors_fp(stderr); fflush(stderr);
                return 0x4;
	}
	ciphertext_len += len;

	/* Get the tag */
	if(enc == 1)
	{
		if(1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, 16, tag))
		{
                	EVP_CIPHER_CTX_init(ctx);
                	ERR_print_errors_fp(stderr); fflush(stderr);
	                return 0x5;
		}
	}

	/* Clean up */
	EVP_CIPHER_CTX_init(ctx);

	*op_ciphertext_len=ciphertext_len;
	return 0;
}

uint32_t base64_encoding_wrapper(unsigned char* src, uint32_t length, unsigned char* dest)
{
	return EVP_EncodeBlock(dest, src, length);

}

uint32_t base64_decoding_wrapper(const char* src, uint32_t length, unsigned char* dest)
{
        int length_with_padding = EVP_DecodeBlock(dest, (const unsigned char*) src, length);
        if(length_with_padding == -1)
                return length_with_padding;
        char* first_equals_character = strstr((char*)src, "=");
        if(first_equals_character != NULL)
        {
                if(first_equals_character == (char*)src + length - 1) // the first equals character is also the last character in the string ==> Only one equals
                        length_with_padding -= 1;
                else // assuming that the base64 string is valid (EVP_DecodeBlock would have thrown an error in that case).
                        length_with_padding -= 2;
        }

        return length_with_padding;
}