#define INCL_DOS
#include <OS2.H>
#include <stdio.h>
#include <string.h>

#define FALSE 0
#define TRUE !FALSE

static char buf[65536];
static char MatchB[] = {0x1E, 0x06, 0x0E, 0x0E, 0x1F, 0x07, 0xCD, 0x12, 0xA3};
static char MatchE[] = {0x07, 0x1F, 0xC3};
static int Offsets[] = {0x09, 0x18, 0x5A};

extern char PatchCode[];
extern char PatchCode1[];
extern unsigned short PatchSize, Patches[];
extern char PatchCode1[];
extern unsigned short PatchSize1, Patches1[];

static FILESTATUS3 FileStatus;

static void Usage() {
  printf ("Usage:\n");
  printf ("  PatchLDR       (patch using BIOS function Int15/EAX=E820)\n");
  printf ("  PatchLDR E820  (patch using BIOS function Int15/EAX=E820)\n");
  printf ("  PatchLDR DA88  (patch using BIOS function Int15/AX=DA88)\n");
  exit (99);
}

int main (int argc, char *argv[]) {
  APIRET rc;
  FILE *f;
  int i, j;
  unsigned long filelen;
  int MatchBPos, MatchEPos;
  unsigned short VarBase;
  enum {unknown = 0, E820, DA88} Method = 0;
  char doit = FALSE;

  switch (argc) {
    case 0 :
    case 1 : Method = E820; break;
    case 2 : if (!stricmp (argv[1], "E820")) Method = E820;
	     if (!stricmp (argv[1], "DA88")) Method = DA88;
	     break;
  }
  if (Method == unknown) Usage();

  rc = DosQueryPathInfo ("OS2LDR", FIL_STANDARD, &FileStatus, sizeof (FileStatus));
  if (rc == 3) {
    printf ("File OS2LDR not found\n");
    exit (1);
  }

  f = fopen ("OS2LDR", "rb");
  if (f == NULL) {
    printf ("File OS2LDR not found\n");
    exit (1);
  }
  filelen = fread (buf, 1, sizeof (buf), f);
  fclose (f);
  if (filelen == sizeof (buf)) {
    printf ("OS2LDR is too big\n");
    exit (2);
  }

  for (i = 0; i < (filelen - sizeof (MatchB)); i++)
    if (!memcmp (buf + i, MatchB, sizeof (MatchB))) {
      doit = TRUE;
      MatchBPos = i + sizeof (MatchB) + 2;
      break;
    }
  if (!doit) {
    printf ("OS2LDR cannot be patched\n");
    exit (3);
  }
  doit = FALSE;
  for (i = MatchBPos; i < (filelen - sizeof (MatchE)); i++)
    if (!memcmp (buf + i, MatchE, sizeof (MatchE))) {
      doit = TRUE;
      MatchEPos = i - 3;
      break;
    }
  if (!doit) {
    printf ("OS2LDR cannot be patched\n");
    exit (3);
  }
  if ((MatchEPos - MatchBPos) < PatchSize) {
    printf ("OS2LDR cannot be patched\n");
    exit (3);
  }
  VarBase = *(unsigned short *)(buf + MatchBPos + Offsets[0] - (sizeof (MatchB) + 2));
  doit = (*(unsigned short *)(buf + MatchBPos + Offsets[1] - (sizeof (MatchB) + 2)) - VarBase) == 2;
  if (!doit) {
    printf ("OS2LDR cannot be patched\n");
    exit (3);
  }
  doit = (*(unsigned short *)(buf + MatchBPos + Offsets[2] - (sizeof (MatchB) + 2)) - VarBase) == 8;
  if (!doit) {
    printf ("OS2LDR cannot be patched\n");
    exit (3);
  }
  f = fopen ("OS2LDR.bak", "wb");
  if (f == NULL) {
    printf ("New file OS2LDR.bak cannot be created\n");
    exit (4);
  }
  i = fwrite (buf, 1, filelen, f);
  fclose (f);
  if (i != filelen) {
    printf ("New file OS2LDR.bak cannot be created\n");
    exit (4);
  }
  rc = DosSetPathInfo ("OS2LDR.bak", FIL_STANDARD, &FileStatus, sizeof (FileStatus), DSPI_WRTTHRU);

  if (Method == E820) {
    memcpy (buf + MatchBPos, PatchCode, PatchSize);
    memset (buf + MatchBPos + PatchSize, 0x90, MatchEPos - MatchBPos - PatchSize);
    *(unsigned short*)(buf + MatchBPos + Patches[0]) += VarBase;
    *(unsigned short*)(buf + MatchBPos + Patches[1]) += VarBase;
  } else if (Method == DA88) {
    memcpy (buf + MatchBPos, PatchCode1, PatchSize1);
    memset (buf + MatchBPos + PatchSize1, 0x90, MatchEPos - MatchBPos - PatchSize1);
    *(unsigned short*)(buf + MatchBPos + Patches1[0]) += VarBase;
    *(unsigned short*)(buf + MatchBPos + Patches1[1]) += VarBase;
  }

  f = fopen ("OS2LDR", "wb");
  if (f == NULL) {
    printf ("New file OS2LDR cannot be created\n");
    exit (4);
  }
  i = fwrite (buf, 1, filelen, f);
  fclose (f);
  if (i != filelen) {
    printf ("New file OS2LDR cannot be created\n");
    exit (4);
  }
  rc = DosSetPathInfo ("OS2LDR", FIL_STANDARD, &FileStatus, sizeof (FileStatus), DSPI_WRTTHRU);

  return (0);
}