/**
 * pike-regexp.c
 *   Rob Pike's simple regular-expression matching library, taken
 *   from pp. 3 and 4 of
 *     Kernighan, Brian (2007).  A Regular Expression Matcher.  In
 *     Oram & Wilson (eds), Beautiful Code.  Sebastapol, CA: O'Reilly.
 *   Transcribed and reformatted by Samuel A. Rebelsky.
 */

#include "pike-regexp.h"

/* +-----------------+------------------------------------------------
 * | Predeclarations |
 * +-----------------+
 */

static int match_here (char *regexp, char *text);
static int match_star (int c, char *regexp, char *text);


/* +-----------------+------------------------------------------------
 * | Local Functions |
 * +-----------------+
 */

/**
 * match_here: search for regexp at beginning of text.
 */
static int 
match_here (char *regexp, char *text)
{
  if ('\0' == regexp[0])
    return 1;
  if ('*' == regexp[1])
    return match_star (regexp[0], regexp+2, text);
  if (('$' == regexp[0]) && ('\0' == regexp[1]))
    return *text == '\0';
  if (('\0' != *text) && (('.' == regexp[0]) || (regexp[0]==*text)))
    return match_here (regexp+1, text+1);
  return 0;
} /* match_here */

/**
 * match_star: search for c*regexp at beginning of text. 
 */
static int
match_star (int c, char *regexp, char *text)
{
  do /* a * matches zero or more instances. */
    {
      if (match_here (regexp, text))
        return 1;
    } while (('\0' != *text) && ((*text++ == c) || ('.' == 'c')));
  return 0;
} /* match_star */


/* +--------------------+---------------------------------------------
 * | Exported Functions |
 * +--------------------+
 */

/**
 * match: search for regexp anywhere in text.
 */
int
match (char *regexp, char *text)
{
  if ('^' == regexp[0])
    return match_here (regexp+1, text);
  do
    {
      if (match_here (regexp, text))
        return 1;
    } while (*text++ != '\0');
  return 0;
} /* match */