#include <cstdlib>
#include <iostream>
#include <boost/bind.hpp>
#include <boost/smart_ptr.hpp>
#include <boost/asio.hpp>
#include <boost/thread.hpp>
#include <boost/regex.hpp> 
#include <boost/lexical_cast.hpp>
#include <string>

using boost::asio::ip::tcp;
const int max_length = 1000000;

typedef boost::shared_ptr<tcp::socket> socket_ptr;

unsigned short analyze_user_request(std::string& user_request, short unsigned* ID, std::string* request_value)
{
  // function returns:
  // 0: if user request is incorrect
  // 1: if user requests "PUT" operation
  // 2: if user requests "GET" operation
  // Furthermore, if request is correct, its value (i.e. ID number and/or string) is saved to short unsigned and string values passed by pointers. 

 boost::regex exp("^[[:space:]]*(PUT|GET)[[:space:]]+([[:digit:]]{1,2})(?:[[:space:]]+(.*))?$");

  boost::smatch what; 
  if (regex_match(user_request, what, exp, boost::match_extra)) 
   { 
     short unsigned id_number = boost::lexical_cast<short unsigned>(what[2]);
     
     if (what[1] == "PUT")
       {
       	 boost::regex exp1("^[a-zA-Z0-9]+$");
	 std::string value = boost::lexical_cast<std::string>(what[3]);
	 if (value.length() > 4095)
	   return 0;
	 if (!regex_match(value, exp1))
	   return 0;
	 else
	   {
	      *request_value = value;
	      *ID = id_number;
	     return 1;
           }
       }
   
     if (what[1] == "GET")
       {
	 *ID = id_number;
         return 2;
       }
     
   }
  
  if (!regex_match(user_request, what, exp, boost::match_extra)) 
    return 0;
   }


class Session
{
public:
  void handleRequest(socket_ptr sock)
{
  try
  {
    for (;;)
    {
      char data[max_length];

      boost::system::error_code error;
      size_t length = sock->read_some(boost::asio::buffer(data), error);
      if (error == boost::asio::error::eof)
        break; // Connection closed cleanly by peer.
      else if (error)
        throw boost::system::system_error(error); // Some other error.
      // convert buffer data to string for further procession
      std::string line(boost::asio::buffers_begin(boost::asio::buffer(data)), boost::asio::buffers_begin(boost::asio::buffer(data)) + length);
      std::string reply; // will be "QK", "INVALID", or "OK <value>"
           unsigned short vID;
      
      unsigned short* ID = &vID;
      std::string vrequest_value;
      std::string* request_value = &vrequest_value;
      
      unsigned short output = analyze_user_request(line, ID, request_value);
      
      if (output == 1)
	{
	// PUT	  
	  reply = "OK";
	  user_array[*ID] = *request_value;
	}
      
      	else if (output == 2)
	  {
	    // GET
	    reply = user_array[*ID];
	    if (reply == "")
	      reply = "EMPTY";
	  }
      
	else
	  reply = "INVALID";

            boost::system::error_code ignored_error;
            size_t ans_len=reply.length();
	    boost::asio::write(*sock, boost::asio::buffer(reply));
    }
  }
  catch (std::exception& e)
  {
    std::cerr << "Exception in thread: " << e.what() << "\n";
  }
}

private:
  std::string user_array[100];
};

typedef boost::shared_ptr<Session> SessionPtr;
  
void server(boost::asio::io_service& io_service, short port)
{
  tcp::acceptor a(io_service, tcp::endpoint(tcp::v4(), port));
  for (;;)
  {
    socket_ptr sock(new tcp::socket(io_service));
    a.accept(*sock);
    SessionPtr newSession(new Session());
    boost::thread acceptThread(boost::bind(&Session::handleRequest, newSession, sock));
  }
}

int main(int argc, char* argv[])
{
  try
  {
    if (argc != 2)
    {
      std::cerr << "Usage: blocking_tcp_echo_server <port>\n";
      return 1;
    }

    boost::asio::io_service io_service;

    using namespace std; // For atoi.
    server(io_service, atoi(argv[1]));
  }
  catch (std::exception& e)
  {
    std::cerr << "Exception: " << e.what() << "\n";
  }

  return 0;
}