#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>

#define NEWFILE (O_WRONLY|O_CREAT|O_TRUNC)
#define BUFSIZE 1024
#define size 1

int my_read(int fd, char *buf, size_t count);
int my_write(int fd, char *bur, size_t count);

static char read_buf[BUFSIZE];
static int read_offset=BUFSIZE;
static int read_max=BUFSIZE;
static char write_buf[BUFSIZE];
static int write_offset=0;

int main(void)
{
    	char infile[ ]={"test.dat"};
    	char outfile[ ]={"backup.dat"};
    	char buf[size];
	int infd, outfd, count;

	if(infd=open(infile, O_RDONLY)==-1)
	{
    		printf("ERROR, OPEN READ FILE FAILED: \n", sys_errlist[errno]);
    		exit(255);
	}
	if(outfd=open(outfile, NEWFILE, 0600)==-1)
	{
    		printf("ERROR, OPEN WRITE FILE FAILED: \n", sys_errlist[errno]);
    		exit(255);
	}
	while(count=read(infd,buf,sizeof(buf))>0)
	{
    		if(write(outfd, buf, count)!=count)
    		{
        		printf("ERROR, WRITE FILE FAILED: \n", sys_errlist[errno]);
        		exit(255);
		}
    	}
	if(count==-1)
	{
        	printf("ERROR, READ FILE FAILED: \n", sys_errlist[errno]);
        	exit(255);
	}
	close(infd);
	if(write_offset>0)
	{
    		write(outfd, write_buf, write_offset);
   		write_offset=0;
	}
	close(outfd);
}


int my_read(int fd, char *buf, size_t count)
{
    	int i;

    	for(i=0; i<count; ++i)
    	{
        	if(read_offset==read_max)
        	{
            		read_offset=0;
            		read_max=read(fd, read_buf, sizeof(read_buf));

            		if(!read_max)
                	return i;
        	}
        	*buf++=read_buf[read_offset++];
	}
	return i;
}


int my_write(int fd, char *buf, size_t count)
{
    	int i,n;
    	for(i=0; i<count; ++i)
    	{
        	write_buf[write_offset++]=*buf++;
        	if(write_offset==BUFSIZE)
        	{
            		write_offset=0;
           	 	n=write(fd, write_buf, sizeof(write_buf));

            		if(n!=BUFSIZE)
                		return -1;
         	}
    	}
	return -1;
}