Blockchain example

blockchain.cpp

#include <chrono>
#include <sstream>
#include <string>
#include <memory>
#include <iostream>
#include <cstdlib>

#include "picosha2.h"

class block {
public:
  block(const long int ts, const std::string &data, const std::string &prev_hash)
    : _ts(ts), _data(data), _prev_hash(prev_hash) { }

  std::string hash(void) const {
    std::stringstream ss;

    ss << _ts 
       << _data 
       << _prev_hash; 

    std::string src = ss.str();
    std::vector<unsigned char> hash(32);
    picosha2::hash256(src.begin(), src.end(), hash.begin(), hash.end());

    return picosha2::bytes_to_hex_string(hash.begin(), hash.end());
  }

  static block create_seed(void) {
    auto temp_ts = std::chrono::system_clock::now().time_since_epoch();

    return block(
      temp_ts.count(),
      "Seed block",
      ""
    );
  }

  static block create_next(const block &b, const std::string &data) {
    auto temp_ts = std::chrono::system_clock::now().time_since_epoch();

    return block(
      temp_ts.count(),
      data, 
      b.hash()
    );    
  }

public:
  const long ts() const   { return _ts; }
  const std::string& data() const { return _data; }
  const std::string& prev_hash() const { return _prev_hash; }

private:
  long _ts;
  std::string _data;
  std::string _prev_hash;
};

void print_chain(std::vector<block> chain) {

  int i = 0;

  for (block& b : chain) {

    std::cout <<
      "index: " << i << std::endl <<
      "ts: " << b.ts() << std::endl <<
      "data: " << b.data() << std::endl << 
      "this: " << b.hash() << std::endl <<
      "prev: " << b.prev_hash() << std::endl <<
      "-------------------------------------" << std::endl;

    i ++;
    
  }

}

std::string make_data() {

  std::stringstream ss;

  int a = std::rand();
  int b = std::rand();
  int c = std::rand();

  ss << 
    "{ \"a\": " << a << "," <<
      "\"b\": " << b << "," <<
      "\"c\": " << c << " }";

  return ss.str();

}

int main(int argc, char *argv[]) {

  std::vector<block> chain = { 
    block::create_seed()
  };

  for (int i = 0; i < 5; i ++) {
    // get the last block in the chain
    auto last = chain[chain.size() - 1];

    // create the next block
    chain.push_back(block::create_next(last, make_data()));
  }

  print_chain(chain);

  return 0;
}