#include "patprep.h"
#include <stdio.h>
#include <string.h>
#include <strings.h>

// This is a copy of the patprep() function from the original 1983 version of
// locate.c. I have annotated it heavily in order to document, in my own mind at
// any rate, exactly what it does, step by step.

// Globfree is limited to 100 characters.
static char globfree[100];

char *patprep(name)
char *name;
{
  register char *endmark, *p, *subp;

  subp = globfree;
  *subp++ = '\0';

  // Go to the very end of the string passed in.
  p = name + strlen(name) - 1;

  /* starting from the END of the string, skip trailing metacharacters (and
     [] ranges) */
  for (; p >= name; p--)
    // Index is mis-named; it returns a pointer to the first
    // instance of the character '*p' in the content of the
    // static string here.  In this case, it's saying that
    // if there is no metacharacter, break out?
    if (index("*?", *p) == 0)
      break;

  if (p < name)
    p = name;

  // Skip past a range operator.
  if (*p == ']')
    for (p--; p >= name; p--)
      if (*p == '[') {
        p--;
        break;
      }

  if (p < name)
    p = name;

  /*
   * if pattern has only metacharacters, check every path (force '/'
   * search)
   */

  // We got to the start of the string. At least give it an anchoring '/',
  // so the matcher has something it can makes sense of.
  if ((p == name) && index("?*[]", *p) != 0)
    *subp++ = '/';
  else {
    // Okay, from where we were, scan backwards until we find another
    // metacharacter or the root of the search string, in which case we have
    // a literal substring.
    for (endmark = p; p >= name; p--)
      if (index("]*?", *p) != 0)
        break;

    // From the first non-metacharacter found to the first metacharacter (or
    // EOL), copy that substring into the 100-byte reserve.
    for (++p; (p <= endmark) && subp < (globfree + sizeof(globfree));)
      *subp++ = *p++;
  }
  // Give a null ending.
  *subp = '\0';
  // Return a pointer to the last byte of the pattern reserve.
  return (--subp);
}