#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include "8-02_syscalls.h"

/* The C Programming Language: 2nd Edition
 *
 * Exercise 8-2: Rewrite `fopen` and `_fillbuf` with fields instead of explicit
 * bit operations. Compare code size and execution speed.
 *
 * Notes: Fields, in this case, are struct fields. I implemented them as 1-bit
 * integers to simulate bit fields via struct.
 *
 * The resulting binary of this file (plus the custom header) runs through this
 * source file in about 0.001s. However, the binary is 1KB larger.
 */

#define PERMS 0666

int getc(FILE *);

int my__fillbuf(my_FILE *fp) {
	int bufsize;
	if (fp->flags._READ == 0) {
		return EOF;
	}
	bufsize = (fp->flags._UNBUF != 0) ? 1 : BUFSIZ;
	if (fp->base == NULL) {
		if ((fp->base = (char *) calloc(bufsize, sizeof (char))) == NULL) {
			return EOF;
		}
	}
	fp->ptr = fp->base;
	fp->cnt = read(fp->fd, fp->ptr, bufsize);
	if (--fp->cnt < 0) {
		if (fp->cnt == -1) {
			fp->flags._EOF = 1;
		} else {
			fp->flags._ERR = 1;
		}
		fp->cnt = 0;
		return EOF;
	}
	return (unsigned char) *fp->ptr++;
}

my_FILE * my_fopen(char *name, char *mode) {
	int fd;
	my_FILE *fp;
	if (*mode != 'r' && *mode != 'w' && *mode != 'a') {
		return NULL;
	}
	for (fp = _iob; fp < _iob + FOPEN_MAX; fp++) {
		if (fp->flags._READ == 0 && fp->flags._WRITE == 0) {
			break;
		}
	}
	if (fp >= _iob + FOPEN_MAX) {
		return NULL;
	}
	if (*mode == 'w') {
		fd = creat(name, PERMS);
	} else if (*mode == 'a') {
		if ((fd = open(name, O_WRONLY, 0)) == -1) {
			fd = creat(name, PERMS);
		}
		lseek(fd, 0L, 2);
	} else {
		fd = open(name, O_RDONLY, 0);
	}
	if (fd == -1) {
		return NULL;
	}
	fp->fd = fd;
	fp->cnt = 0;
	if (*mode == 'r') {
		fp->flags._READ = 1;
	} else {
		fp->flags._WRITE = 1;
	}
	return fp;
}

int main() {
	my_FILE *fp = my_fopen("8-02_fopen-and-fillbuf.c", "r");
	if (fp != NULL) {
		puts("We could read the file.\n");
		/* pro tip: don't declare this as 'unsigned' or you'll create an
		 * endless loop thanks to EOF typically being negative. Don't waste
		 * half an hour on a newbie mistake like I did. :)
		 */
		char c;
		while ((c = my_getc(fp)) != EOF) {
			putchar(c);
		}
	} else {
		puts("Could not open file for reading.");
	}
	return 0;
}