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

#define MAX_BUF 500

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

	// Open a file
	int fd = open("asst2test.txt", O_RDWR | O_CREAT);
	if (fd < 0) {
		printf("Error opening asst2test.txt\n");
	}

	// Write to file
	int r = write(fd, "test\n", strlen("test\n"));
	if (r != strlen("test\n")) {
		printf("Error writing, only wrote %d when expected %d\n", r, strlen("test\n"));
	}

	// Dup file
	int dup_fd = dup2(fd, 5);
	if (dup_fd < 0) {
		printf("Error dup2\n");
	}

	// Write from dup - should continue off where it last left off
	r = write(dup_fd, "test2\n", strlen("test2\n"));
	if (r != strlen("test2\n")) {
		printf("Error writing, only wrote %d when expected %d\n", r, strlen("test2\n"));
	}

	// Set shared fp back to 0
	r = lseek(dup_fd, 0, SEEK_SET);
	if (r < 0) {
		printf("lseek failed\n");
	}

	// Attempt to read from first fd
	char buf[MAX_BUF];
	int i = 0;
	do  {
		printf("* attemping read of %d bytes\n", MAX_BUF -i);
		r = read(fd, &buf[i], MAX_BUF - i);
		printf("* read %d bytes\n", r);
		i += r;
	} while (i < MAX_BUF && r > 0);
	printf("We read:\n%s", buf);

	// Close dup'd fd and reset fp to 0
	close(dup_fd);
	lseek(fd, 0, SEEK_SET);

	// Reading from original fd should still work
	i = 0;
	do  {
		printf("* attemping read of %d bytes\n", MAX_BUF -i);
		r = read(fd, &buf[i], MAX_BUF - i);
		printf("* read %d bytes\n", r);
		i += r;
	} while (i < MAX_BUF && r > 0);
	printf("We read:\n%s", buf);

	// Dup the fd again, onto the same value as before
	dup_fd = dup2(fd, 5);
	if (dup_fd < 0) {
		printf("Error dup2 2\n");
	}

	// Reset fp to 0 using original fd, then close original fd
	lseek(fd, 0, SEEK_SET);
	close(fd);

	// Attempt to read from the dup'd fd - should work
	i = 0;
	do  {
		printf("* attemping read of %d bytes\n", MAX_BUF -i);
		r = read(dup_fd, &buf[i], MAX_BUF - i);
		printf("* read %d bytes\n", r);
		i += r;
	} while (i < MAX_BUF && r > 0);
	printf("We read:\n%s", buf);

	return 0;
}