/* syscalls.h
 *
 * A simpler stdio.h to aid in exercises within chapter 8
 */

/* Declarations */
int puts(char *);
long lseek(int fd, long offset, int origin);

/* workarounds for GNU/Linux */
#undef NULL

#define PERMS 0666
#define NULL 0
#define EOF (-1)
#define BUFSIZ 100
#define FOPEN_MAX 20


struct _flags {
	unsigned int _READ : 1;
	unsigned int _WRITE : 1;
	unsigned int _UNBUF : 1;
	unsigned int _EOF : 1;
	unsigned int _ERR : 1;
} flags;

typedef struct _iobuf {
	int cnt;
	char *ptr;
	char *base;
	struct _flags flags;
	int fd;
} FILE;

FILE _iob[FOPEN_MAX] = {
	/* stdin is read-only */
	{ 0, (char *) 0, (char *) 0, {1, 0, 0, 0, 0}, 0 },
	/* stdout is write only */
	{ 0, (char *) 0, (char *) 0, {0, 1, 0, 0, 0}, 1 },
	/* stderr is written AND not buffered */
	{ 0, (char *) 0, (char *) 0, {0, 1, 1, 0, 0}, 2 }
};

#define stdin  (&_iob[0])
#define stdout (&_iob[1])
#define stderr (&_iob[2])

#define feof(p) (((p)->flags._EOF) != 0)
#define ferror(p) (((p)->flags._ERR) != 0)
#define fileno(p) ((p)->fd)

#define getc(p) (--(p)->cnt >= 0 ? (unsigned char) *(p)->ptr++ : _fillbuf(p))
#define putc(x,p) (--(p)->cnt >= 0 ? *(p)->ptr++ = (x) : _flushbuf((x),p))
#define getchar() getc(stdin)
#define putchar(x) putc((x), stdout)

int fempty(struct _flags flags) {
	if (!flags._READ && !flags._WRITE && !flags._UNBUF && !flags._EOF && !flags._ERR) {
		return 1;
	} else {
		return 0;
	}
}

FILE * fopen(char *name, char *mode) {
	int fd;
	FILE *fp;
	if (*mode != 'r' && *mode != 'w' && *mode != 'a' && *mode != '+') {
		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;
	}
	switch (*mode) {
		case '+':
			if ((fd = open(name, O_RDWR, 0)) == -1) {
				fd = creat(name, PERMS);
			}
			break;
		case 'w':
			fd = creat(name, PERMS);
			break;
		case 'a':
			if ((fd = open(name, O_WRONLY, 0)) == -1) {
				fd = creat(name, PERMS);
			}
			lseek(fd, 0L, 2);
			break;
		default:
			fd = open(name, O_RDONLY, 0);
	}
	if (fd == -1) {
		return NULL;
	}
	fp->fd = fd;
	fp->cnt = 0;
	fp->flags._EOF = 0;
	if (*mode == 'r' || *mode == '+') {
		fp->flags._READ = 1;
	}
	if (*mode == 'w' || *mode == '+' || *mode == 'a') {
		fp->flags._WRITE = 1;
	}
	return fp;
}

/* int _fillbuf(FILE *); */

int _fillbuf(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++;
}

int _cleanbuf(FILE *fp) {
	int bufsize = (fp->flags._UNBUF != 0) ? 1 : BUFSIZ;
	if (fp->base != NULL) {
		free(fp->base);
	}
	fp->base = (char *) calloc(bufsize, sizeof (char));
	if (fp->base == NULL) {
		return EOF;
	}
	return 0;
}

/*
 * write the buffer's contents to the file and reset the buffer
 *
 * Returns 0 on success, EOF on errors, with errno set.
 */
int _flushbuf(char c, FILE *fp) {
	int bufsize = (fp->flags._UNBUF != 0) ? 1 : BUFSIZ;
	if (fp->base == NULL) {
		if (_cleanbuf(fp) != 0) {
			errno = ENOMEM;
			return EOF;
		}
	}
	if (fp->flags._WRITE == 0) {
		errno = EBADF;
		return EOF;
	}
	int written = write(fp->fd, fp->base, bufsize);
	if (errno > 0) {
		fp->flags._ERR = 1;
		strerror(errno);
		return EOF;
	}
	if (_cleanbuf(fp) != 0) {
		errno = ENOMEM;
		return EOF;
	}
	fp->ptr = fp->base;
	fp->cnt = bufsize;
	if (c != NULL) {
		putc(c,fp);
	}
	return 0;
}

int fflush(FILE *fp) {
	if (fp == NULL) {
		int i;
		for (i=0; i < FOPEN_MAX; i++) {
			/* maybe check flags and buffers? */
			if (fp->flags._WRITE == 1) {
				if (_flushbuf(NULL, &_iob[i]) == EOF) {
					strerror(errno);
				}
			}
		}
		return 0;
	}
	if (fp->flags._WRITE == 1) {
		if (_flushbuf(NULL, fp) == EOF) {
			strerror(errno);
		}
	}
	return 0;
}

int fclose(FILE *fp) {
	struct _flags f = {0,0,0,0,0};
	if (fp->flags._WRITE == 1) {
		fflush(fp);
	}
	if (fp->base != NULL) {
		free(fp->base);
		fp->base = NULL;
		fp->ptr = NULL;
	}
	fp->cnt = 0;
	fp->flags = f;
	close(fp->fd);
	fp->fd = -1;
	return 0;
}

int puts(char *s) {
	int i;
	for (i=0; s[i] != '\0' && s[i] != EOF; i++) {
		putchar(s[i]);
	}
	putchar('\n');
	return i;
}

/* Set the 'cursor' position within a file for read or write operations
 * Returns 0 on success, EOF on error, with errno set.
 */
int fseek(FILE *fp, long offset, int origin) {
	long pos;
	if ((pos = lseek(fp->fd, offset, origin)) == EOF) {
		return EOF;
	}
	_fillbuf(fp);
	lseek(fp->fd, offset, origin);
	return 0;
}