#include <stdio.h>
#include <string.h>
#include <ctype.h>

#define LINE_SZ  200
#define A_MEG   (4 * 1024 * 1024)

char  buff1[A_MEG], buff2[A_MEG];

void update_file(char *fname);

int
main(int ac, char *av[])
{
  int i;

  if (ac < 2){
    printf("Usage:\n   %s file [file ...]\n", av[0]);
  }
  
  for (i = 1; i < ac; i++){
    update_file(av[i]);
  }
}


void
update_file(char *fname)
{
	FILE  *fp;
	char   h[500][LINE_SZ];
	int    count = 0;
	int    header_done;
	int    table_line = -1;
	int    fit_in, i;
	long   update_pos, resume_pos, next_read_pos;
	char  *p;
	char   old_sz[20], new_sz[20];
	size_t bytes_read;
	int    record_bytes = 0;
    int    c, n;
    int    hbytes, old_sz_num;

    printf("Processing %s ...\n", fname);
	fp = fopen(fname, "r+");
	if (fp == NULL) {
		printf("Could not open %s.\n", fname);
		return;
	}
    
	count = 0;
	header_done = 0;
	while (!header_done && fgets(h[count], LINE_SZ, fp)) {
      if (!strncasecmp(h[count], "END", strlen("END")) &&
          isspace(h[count][strlen("END")])) {

        header_done = 1;
        
        next_read_pos = ftell(fp);
        while(isspace(c = fgetc(fp)));
        ungetc(c, fp);
        hbytes = ftell(fp);
        
        fseek(fp, next_read_pos, SEEK_SET);
        
      }
      else if (!strncasecmp(h[count], "^TABLE", strlen("^TABLE"))) {
        table_line = count;
      }
      else if (!strncasecmp(h[count], "RECORD_BYTES",
                            strlen("RECORD_BYTES"))) {
        record_bytes = atoi(strchr(h[count], '=') + 1);
      }
      count++;
	}

	if (!count || (table_line < 0)) {
      printf("Could not find enough information in file %s.\n", fname);
      fclose(fp);
      return;
	}
    
    
	/* Check for cramped fit-in */
	fit_in = 0;
	p = strchr(h[table_line], '=');
	if (!p) {
      printf("Fatal! File %s. ^TABLE does not contain \"=\"\n", fname);
      fclose(fp);
      return;
	}
	while (*++p == ' ');

    old_sz_num = atoi(p);
	sprintf(old_sz, "%d", old_sz_num);
    sprintf(new_sz, "%d", (hbytes / record_bytes) + 1);

    if (strcmp(old_sz, new_sz) != 0){
      printf("Updating %s [RECORD_BYTES=%d, HEADER=%d, ^TABLE=%s -> %s] ...\n",
             fname, record_bytes, hbytes, old_sz, new_sz);
    }
    else {
      printf("Skipping %s [RECORD_BYTES=%d, HEADER=%d, ^TABLE=%s] ...\n",
             fname, record_bytes, hbytes, old_sz);
      fclose(fp);
      return;
    }
    

	if (strlen(old_sz) >= strlen(new_sz)) {
		fit_in = 1;	/* No additional space needed */
	} else if (h[table_line][strlen(h[table_line]) - 2] == ' ') {
		fit_in = 2;	/* Space avaliable in the same line */
	} else if (h[count - 1][strlen(h[count - 1]) - 2] == ' ') {
		fit_in = 3;	/* Space available in END line */
	} else {
		fit_in = 0;	/* Cannot fit in, shuffle things down */
		sprintf(new_sz, "%d", atoi(new_sz) + 1);
	}

	/* Position the file for overwrite */
	update_pos = 0;
	for (i = 0; i < table_line; i++) {
		update_pos += strlen(h[i]);
	}

	switch (fit_in) {
	    case 1:
	    case 2:
          /* Blank out region */
          for (i = 0; (p[i] != '\0') && (p[i] != '\n'); i++){
            p[i] = ' ';
          }
          
          memcpy(p, new_sz, strlen(new_sz));
          /* sprintf(p, "%s", new_sz); */

          /* Position to the first line that needs updating */
          fseek(fp, update_pos, SEEK_SET);
          fputs(h[table_line], fp);
          break;

	    case 3:
          sprintf(p, "%s\n", new_sz);
          p = &h[count - 1][strlen(h[count - 1]) - 2];
          strcpy(p, p + 1);
          
          /* Position to the first line that needs updating */
          fseek(fp, update_pos, SEEK_SET);
          for (i = table_line; i < count; i++) {
            fputs(h[i], fp);
          }
          break;

	    default:
		    sprintf(p, "%s\n", new_sz);

		    bytes_read = fread(buff1, 1, A_MEG, fp);
		    next_read_pos = ftell(fp);

		    /* Position to the first line that needs updating */
		    fseek(fp, update_pos, SEEK_SET);

		    for (i = table_line; i < count; i++) {
			    fputs(h[i], fp);
		    }
		    fprintf(fp, "%*s", record_bytes - 1, "");
		    resume_pos = ftell(fp);

		    while (bytes_read == A_MEG) {
			    fseek(fp, next_read_pos, SEEK_SET);
			    bytes_read = fread(buff2, 1, A_MEG, fp);
			    next_read_pos = ftell(fp);

			    fseek(fp, resume_pos, SEEK_SET);
			    fwrite(buff1, 1, A_MEG, fp);

			    memmove(buff1, buff2, A_MEG); /* Setup for next time around */
		    }
		    fseek(fp, resume_pos, SEEK_SET);
		    fwrite(buff1, 1, bytes_read, fp);

		    break;
	}
	fclose(fp);
}