#include <sys/types.h>
#include <iostream>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>

#define BUFFER_SIZE 25
#define READ_END 0
#define WRITE_END 1

int main(int argc, char** argv)
{
	//Create the read and write buffers
	char write_msg[BUFFER_SIZE];
	if(argc == 2 && strlen(argv[1]) < BUFFER_SIZE)
	{
		strcpy(write_msg, argv[1]);
	}
	else
	{
		strcpy(write_msg, "Greetings");
	}
	char read_msg[BUFFER_SIZE];
	//set up the file desriptor array and create the pipe
	int fd[2];
	if(pipe(fd) == -1)
	{
		std::cerr<<"Pipe Failed"<<std::endl;
		return 1;
	}

	//Set up and fork the child process
	pid_t pid = fork();
	
	if(pid < 0)
	{
		std::cerr<<"Fork Failed";
		return 1;
	}

	if(pid > 0)
	{
		//This is the parent processes
		//Close the read end of the pipe
		close(fd[READ_END]);

		//Write the message to the pipe
		write(fd[WRITE_END], write_msg, strlen(write_msg)+1);

		//close the write end of the pipe
		close(fd[WRITE_END]);
		wait(NULL);
		std::cout<<"Child finished, parent exiting"<<std::endl;
		return 0;
	}
	else
	{
		//This is the child processes
		//close the write end of the pipe
		close(fd[WRITE_END]);

		//Read the message from the pipe
		read(fd[READ_END], read_msg, BUFFER_SIZE);
		std::cout<<"Child read message: "<<read_msg<<std::endl;

		//close the read end of the pipe
		close(fd[READ_END]);
		//Example of re-writing child processes address space with new program to execute	
		execlp("/bin/ls", "ls", NULL);
		std::cout<<"Child finished, exiting"<<std::endl;
		return 0;
	} 
	
}