/* Copyright (C) 2018 DJ Delorie, see COPYING.DJ for details */
/* Copyright (C) 2014 DJ Delorie, see COPYING.DJ for details */
/* Copyright (C) 2011 DJ Delorie, see COPYING.DJ for details */
/* Copyright (C) 2002 DJ Delorie, see COPYING.DJ for details */
/* Copyright (C) 2001 DJ Delorie, see COPYING.DJ for details */
/* Copyright (C) 1996 DJ Delorie, see COPYING.DJ for details */
/* Copyright (C) 1995 DJ Delorie, see COPYING.DJ for details */
#include <libc/stubs.h>
#include <stdarg.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <go32.h>
#include <dpmi.h>
#include <io.h>
#include <dos.h>
#include <libc/dosio.h>
#include <sys/fsext.h>
#include <libc/fsexthlp.h>
#include <stdbool.h>

int
_open(const char* filename, int oflag)
{
  __dpmi_regs r = {0};
  int rv;
  int use_lfn = _USE_LFN;
  bool retry_with_lfn = false;

  if (filename == 0)
  {
    errno = EINVAL;
    return -1;
  }

  if (__FSEXT_call_open_handlers_wrapper(__FSEXT_open, &rv, filename, oflag))
    return rv;

  if (use_lfn && _os_trueversion == 0x532)
  {
    /* Windows 2000 or XP; or NT with LFN TSR.  Windows 2000 behaves
       badly when using IOCTL and write-truncate calls on LFN handles.
       We convert the long name to a short name and open existing files
       via short name.  New files use LFN, but we know they aren't
       character devices. */
    r.x.flags = 1;			/* Always set CF before calling a 0x71NN function. */
    r.x.ax = 0x7160;
    r.x.cx = 1;				/* Get short name equivalent */
    r.x.ds = __tb_segment;
    r.x.si = __tb_offset;		/* Long name to convert - putpath */
    r.x.es = __tb_segment;
    r.x.di = __tb_offset + _put_path(filename);	/* Short name destination */
    __dpmi_int(0x21, &r);
    if (!(r.x.flags & 1))		/* Get short name success */
    {
      retry_with_lfn = true;
      r.x.ax = 0x6c00;
      r.x.bx = (oflag & 0xff);
      r.x.dx = 1;			/* Open existing file */
      r.x.si = r.x.di;
      goto do_open;
    }
    else
    {
      /* Short name get failed, file doesn't exist or is device (same error) */
      r.x.flags = 1;			/* Always set CF before calling a 0x71NN function. */
      r.x.ax = 0x7143;			/* Get attributes */
      r.h.bl = 0;
      r.x.dx = __tb_offset;		/* Original long name */
      __dpmi_int(0x21, &r);		/* This is same as lfn _chmod */
      if (!(r.x.flags & 1))		/* Name exists, probably device */
      {
        r.x.ax = 0x6c00;
        r.x.bx = (oflag & 0xff);
        r.x.dx = 1;                     /* Open existing file */
        r.x.si = __tb_offset;		/* Treat original name as short */
        r.x.cx = 0;
        __dpmi_int(0x21, &r);
        if (!(r.x.flags & 1))		/* Success! */
        {
          goto do_hset;
        }
	/* Fail on short name open after _chmod said OK.
	   Device with directory?  We should re-try with LFN.
	   Permission?  Readonly file?  We should quit.
	   Let it fall through to the LFN open which should succeed.  */
      }
    }
  }
fallback:
  if (use_lfn)
  {
    r.x.flags = 1;		/* Always set CF before calling a 0x71NN function. */
    r.x.ax = 0x716c;
    r.x.bx = (oflag & 0xff);
    /* The FAT32 bit should _not_ be set on Windows 2000, because
       that bit fails function 716Ch on W2K.  The test below is
       based on the assumption that W2K returns DOS version 5.  */
    if (7 <= _osmajor && _osmajor < 10)
    {
      r.x.bx |= 0x1000; /* 0x1000 is FAT32 extended size. */
    }
    r.x.dx = 1;			/* Open existing file */
    r.x.si = __tb_offset;
  }
  else
  {
    if (7 <= _osmajor && _osmajor < 10)
    {
      r.x.ax = 0x6c00;
      r.x.bx = (oflag & 0xff) | 0x1000; /* 0x1000 is FAT32 extended size. */
      /* FAT32 extended size flag doesn't help on WINDOZE 4.1 (98). It
	 seems it has a bug which only lets you create these big files
	 if LFN is enabled. */
      r.x.dx = 1;                        /* Open existing file */
      r.x.si = __tb_offset;
    }
    else
    {
      r.h.ah = 0x3d;
      r.h.al = oflag;
      r.x.dx = __tb_offset;
    }
  }
  r.x.ds = __tb_segment;
  _put_path(filename);
do_open:
  r.x.cx = 0;
  __dpmi_int(0x21, &r);

  if (r.x.ax == 0x7100)
  {
    /*  Never assume that the complete LFN API is implemented,
        so check that AX != 0x7100.  E.G.: MSDOS 6.22 and DOSLFN 0.40.
        If not supported fall back on SFN API 0x3D.  */
    use_lfn = 0;
    r.h.ah = 0x3d;
    r.h.al = oflag;
    r.x.dx = __tb_offset;
    goto do_open;
  }
  else if (r.x.flags & 1)
  {
    if ((r.x.ax == 2 || r.x.ax == 3) && retry_with_lfn)
    {
      /* On partitions like NTFS and exFAT, files and paths with long names
         do not have 8.3 aliases.  If an attempt to open the file with short
         name failed with "file not found" or "path not found", retry with
         the LFN API. */
      retry_with_lfn = false;
      goto fallback;
    }
    errno = __doserr_to_errno(r.x.ax);
    return -1;
  }
do_hset:
  __file_handle_set(r.x.ax, O_BINARY);
  return r.x.ax;
}