#include <fcntl.h>
#include "files.h"
#define PERMS 0666

FILE _iob[OPEN_MAX] = {     /*r,w,u,f,e*/
     { 0, (char *) 0, (char *) 0, {1,0,0,0,0}, 0},
     { 0, (char *) 0, (char *) 0, {0,1,0,0,0}, 1},
     { 0, (char *) 0, (char *) 0, {0,1,1,0,0}, 2},
};

/* seek to a specific location in fp */
int fseek(FILE *fp, long offset, int origin) {
     int rc = 0;
     int nc;
     
     if (fp->flags.is_read) {
	  if (origin == 1)
	       offset -= fp->cnt;
	  rc = lseek(fp, offset, origin);
	  fp->cnt = 0;
     } else if (fp->flags.is_write) {
	  if ((nc = fp->ptr - fp->base) > 0)
	       if (write(fp->fd, fp->base, nc) != nc)
		    rc = -1;
	  if (rc != -1)
	       rc = lseek(fp, offset, origin);
	  fp->cnt = 0;
     }

     return (rc == -1) ? -1 : 0;
}
     
/* write buffered data in fp to disk (dirty work) */
int _flush(FILE *fp) {
     int nc;

     /* make sure stream is valid */
     if (fp < _iob || fp >= _iob + OPEN_MAX)
	  return EOF;

     /* make sure stream is writable */
     if (!fp->flags.is_write)
	  return EOF;

     /* write any buffered data to disk */
     nc = fp->ptr - fp->base;
     if (write(fp->fd, fp->base, nc) != nc) {
	  fp->flags.is_err = 1;
	  return EOF;
     }

     /* reset cnt and ptr */
     fp->cnt = (fp->flags.is_unbuf) ? 1 : BUFSIZ;
     fp->ptr = fp->base;

     return 0;
}

/* write any buffered output in fp to disk */
int fflush(FILE *fp) {
     FILE *afp = _iob;

     if (fp != NULL) {
	  return _flush(fp);
     } else
	  while (afp++ < _iob + OPEN_MAX)
	       _flush(afp);

     return 0;
}

/* close down and free up fp */
int fclose(FILE *fp) {
     int rc;

     /* make sure stream is valid */
     if (fp < _iob || fp >= _iob + OPEN_MAX)
	  return EOF;

     /* flush it */
     rc = _flush(fp);

     /* free the buffer */
     if (fp->base != NULL)
	  free((void *) fp);

     /* reset ptr, cnt, and base */
     fp->base = fp->ptr = NULL;
     fp->cnt = 0;

     /* turn off any flags */
     fp->flags.is_write = fp->flags.is_read = fp->flags.is_unbuf = 
	  fp->flags.is_err = fp->flags.is_eof = 0;

     /* close stream */
     close(fp->fd);

     return 0;
}

     
/* read in a block of fp and return first byte */
int _fillbuf(FILE *fp) {
     int bufsize;

     if (fp->flags.is_eof || fp->flags.is_err ||
	  !(fp->flags.is_read))
	 return EOF;
     bufsize = (fp->flags.is_unbuf) ? 1 : BUFSIZ;
     if (fp->base == NULL)
	  if ((fp->base = (char *) malloc(bufsize)) == 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.is_eof = 1;
	  else
	       fp->flags.is_err = 1;
	  fp->cnt = 0;
	  return EOF;
     }
     return (unsigned char) *fp->ptr++;
}

/* allocate buffer space for fp and write x */
int _flushbuf(int x, FILE *fp) {
     int bufsize;
     int n;

     /* make sure fp is valid */
     if (fp < &_iob[0] || fp >= &_iob[OPEN_MAX])
	  return EOF;
     /* make sure we are able to write */
     if (fp->flags.is_err || fp->flags.is_eof ||
	 !(fp->flags.is_write))
	 return EOF;
     
     /* buffered or unbuffered? */
     if (fp->flags.is_unbuf)
	  bufsize = 1;
     else
	  bufsize = BUFSIZ;

     /* allocate buffer if not done already */
     if (fp->base == NULL) {
	  if ((fp->base = (char *) malloc(bufsize)) == NULL) {
	       fp->flags.is_err = 1;
	       return EOF;
	  }
     } else { /* write any existing data to disk */
	  n = fp->ptr - fp->base;
	  if (write(fp->fd, fp->base, n) != n) {
	       fp->flags.is_err = 1;
	       return EOF;
	  }
     }

     /* reset ptr and cnt */
     fp->ptr = fp->base;
     fp->cnt = bufsize;
 
      if (--fp->cnt < 0) {
	  if (fp->cnt == -1)
	       fp->flags.is_eof = 1;
	  else
	       fp->flags.is_err = 1;
	  return EOF;
     }
     *fp->ptr++ = x;

     return x;
}

FILE *fopen(char *name, char *mode) {
     int fd;
     FILE *fp;

     if (*mode != 'r' && *mode != 'w' && *mode != 'a')
	  return NULL;
     for (fp = _iob; fp < _iob + OPEN_MAX; fp++)
	  if ((fp->flags.is_read + fp->flags.is_write) == 0)
	       break;
     if (fp >= _iob + OPEN_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;
     fp->base = NULL;
     if (*mode == 'r')
	  fp->flags.is_read = 1;
     else
	  fp->flags.is_write = 1;
     return fp;
}