#include <unistd.h>  // close, and in general
#include <sys/types.h>  //read
#include <sys/stat.h>  //read
#include <fcntl.h>  //read
#include <string.h>  // strlen

#include <errno.h>  // errno
#include <error.h>  //strerror

using namespace std;

const char * NL = "\n";
const char * FAIL_TO_OPEN = "Error, failed to open: ";
const char * FAIL_TO_READ = "Error, failed to read from: "; 
const char * FAIL_TO_WRITE = "Error, failed to write data from: "; 

void Header(char * filename) {
    write(STDOUT_FILENO,"Opening: ", 9);
    write(STDOUT_FILENO,filename, strlen(filename));
    write(STDOUT_FILENO,"\n",1);

    return;
}

void Error(char * filename, int errorNumber, const char * msg) {
    char * errorMessage;

    write (STDERR_FILENO, msg, strlen(msg));
    write(STDERR_FILENO,filename, strlen(filename));
    write(STDERR_FILENO, NL, strlen(NL));

    errorMessage = strerror(errorNumber);
    write(STDERR_FILENO, errorMessage, strlen(errorMessage));
    write(STDERR_FILENO, NL, strlen(NL));

    return;
}

const int BUF_SIZE = 256;
void MyCat(char * filename) {
    int fd;
    int error;
    char buffer[BUF_SIZE];
    int inSize, 
        outSize;

    Header(filename);

    fd = open(filename, O_RDONLY);
    if (fd == -1) {
       error = errno;
       Error(filename, error, FAIL_TO_OPEN) ;
    } else {
       
       inSize  =  read(fd,buffer,BUF_SIZE);
       error = errno;
       while (inSize > 0) {
         
           outSize = write(STDOUT_FILENO, buffer, inSize);
	   error = errno;
	   // I'm going to assume only output fail, we really should 
	   // handle incomplete output too.
	   if (outSize < 0) { 
	       Error(filename, error, FAIL_TO_WRITE);
	   }

           inSize  =  read(fd,buffer,BUF_SIZE);
           error = errno;
       }

       if (inSize == -1) {
          Error(filename, error, FAIL_TO_READ);
       }
    }

    write(STDERR_FILENO, NL, strlen(NL));
    return;
}


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

    for(i=1;i<argc;i++) {
        MyCat(argv[i]);
    }

    return 0;
}