/* The parent will send messages to the child that
 * will be read from the keyboard.
 *
 * MESSAGE FORMAT: First two bytes show the length of the message to read.
 *                 The message will follow the first two bytes
 */


#include <unistd.h>

#include <iostream>
#include <string>

// Headers for wait
#include <sys/types.h>
#include <sys/wait.h>

// Header needed for atoi function
#include <stdlib.h>

using namespace std;


#define READ_PIPE 0
#define WRITE_PIPE 1

int main( int argc, char * argv[] )
{
  cout << "Original Process: PID=" << getpid() << " PPID=" << getppid() << endl;

  // Create a pipe to be used to talk to the child
  int pipeParentFD[2];
  if( pipe(pipeParentFD) == -1 ) {
    cout << "Error, cannot create pipe" << endl;
    return 0;
  }

  int pid = fork();
  if( pid != 0 ) {
    // This is the parent process
    cout << "Parent Process: PID=" << getpid() << " PPID=" << getppid() << endl;

    // We must close the side of the pipes that we do not need
    close( pipeParentFD[READ_PIPE] );

    // Read a line from the keyboard and send it to the child
    string input;
    while( input != "exit" ) {
      getline( cin, input );
      char message[100];
      sprintf( message, "%02d%s", input.length(), input.c_str() );
      cout << "Parent Process: Sending message: " << message << endl;

      // Send the message to the child
      write( pipeParentFD[WRITE_PIPE], message, input.length() + 2 );
    }

    // Wait for the child to finish before exiting
    int status;
    pid = wait( &status );

    // Close the remaining pipe
    close( pipeParentFD[WRITE_PIPE] );
  }
  else {
    // This is the child process
    cout << "Child Process: PID=" << getpid() << " PPID=" << getppid() << endl;

    // We must close the side of the pipe that we do not need
    close( pipeParentFD[WRITE_PIPE] );

    while( true ) {
      // Read the first two bytes. These two bytes tell us how long
      // the message is going to be
      char length[3] = "  ";
      read( pipeParentFD[READ_PIPE], length, 2 );
      int messageLength = atoi(length);

      // Read the rest of the message
      char longMessage[256];
      read( pipeParentFD[READ_PIPE], longMessage, messageLength );
      longMessage[messageLength] = '\0';
      string output = longMessage;

      cout << "Child Process: Read message: " << output << endl;
      if( output == "exit" ) {
	break;
      }
    }

    // Close the remaining pipe
    close( pipeParentFD[READ_PIPE] );
  }

  cout << "Terminating Process PID=" << getpid() << endl;
  return 0;
}