/**
 * @brief This C++ program is designed to compute the SHA-256 hash of a user-provided string.
 * Here's a breakdown of how it works:
 * Prompts the user to enter a string.
 * Reads the input string from the standard input (using getline).
 * Calls the SHA256 function with the user-provided string and prints the resulting SHA-256 hash.
 *
 * @author Yavuz Sava (woose)
 * @date 13/12/2024
 */

#include <iostream>
#include <openssl/sha.h>
#include <openssl/crypto.h>
#include <openssl/evp.h>
#include <sstream>
#include <iomanip>
using namespace std;
string SHA256(const string str)
{
    unsigned char hash[SHA256_DIGEST_LENGTH]; // Initialize a new context for digest operations using the EVP API
    EVP_MD_CTX *ctx = EVP_MD_CTX_new();
    EVP_DigestInit_ex(ctx, EVP_sha256(), NULL); // Set up the context to use the SHA-256 algorithm
    EVP_DigestUpdate(ctx, str.c_str(), str.size()); // Update the digest with the input string's bytes
    EVP_DigestFinal_ex(ctx, hash, NULL); // Finish computing the hash and store it in the 'hash' buffer
    EVP_MD_CTX_free(ctx); // Free up the context used for digest operations
    stringstream ss;
    for (int i = 0; i < SHA256_DIGEST_LENGTH; ++i) // Convert each byte of the hash into a two-digit hexadecimal number
    ss << hex << setw(2) << setfill('0') << (int)hash[i];
    return ss.str();
}
int main()
{
    string str;
    cout << "Enter a string to encrypt: ";
    getline(cin, str);
    // Compute the SHA-256 hash of the input string
    cout << "Encrypted string using SHA-256 algorithm: " << SHA256(str) << endl;
    return 0;
}