/* Searching in a string.  -*- coding: utf-8 -*-

   Copyright (C) 2005-2017 Free Software Foundation, Inc.

   Written by Bruno Haible <bruno@clisp.org>, 2005.

   This program is free software: you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; either version 3 of the License, or

   (at your option) any later version.

   This program is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */

#include <string.h>

#include <stdbool.h>

#include <stddef.h>  /* for NULL, in case a nonstandard string.h lacks it */

#include "malloca.h"

#include "mbuiter.h"

/* Knuth-Morris-Pratt algorithm.  */

#define UNIT unsigned char

#define CANON_ELEMENT(c) c

#include "str-kmp.h"

/* Knuth-Morris-Pratt algorithm.

   See http://en.wikipedia.org/wiki/Knuth-Morris-Pratt_algorithm

   Return a boolean indicating success:

   Return true and set *RESULTP if the search was completed.

   Return false if it was aborted because not enough memory was available.  */

static bool

knuth_morris_pratt_multibyte (const char *haystack, const char *needle,

                              const char **resultp)

{

  size_t m = mbslen (needle);

  mbchar_t *needle_mbchars;

  size_t *table;

  /* Allocate room for needle_mbchars and the table.  */

  void *memory = nmalloca (m, sizeof (mbchar_t) + sizeof (size_t));

  void *table_memory;

  if (memory == NULL)

    return false;

  needle_mbchars = memory;

  table_memory = needle_mbchars + m;

  table = table_memory;

  /* Fill needle_mbchars.  */

  {

    mbui_iterator_t iter;

    size_t j;

    j = 0;

    for (mbui_init (iter, needle); mbui_avail (iter); mbui_advance (iter), j++)

      mb_copy (&needle_mbchars[j], &mbui_cur (iter));

  }

  /* Fill the table.

     For 0 < i < m:

       0 < table[i] <= i is defined such that

       forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x],

       and table[i] is as large as possible with this property.

     This implies:

     1) For 0 < i < m:

          If table[i] < i,

          needle[table[i]..i-1] = needle[0..i-1-table[i]].

     2) For 0 < i < m:

          rhaystack[0..i-1] == needle[0..i-1]

          and exists h, i <= h < m: rhaystack[h] != needle[h]

          implies

          forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1].

     table[0] remains uninitialized.  */

  {

    size_t i, j;

    /* i = 1: Nothing to verify for x = 0.  */

    table[1] = 1;

    j = 0;

    for (i = 2; i < m; i++)

      {

        /* Here: j = i-1 - table[i-1].

           The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold

           for x < table[i-1], by induction.

           Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1].  */

        mbchar_t *b = &needle_mbchars[i - 1];

        for (;;)

          {

            /* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x]

               is known to hold for x < i-1-j.

               Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1].  */

            if (mb_equal (*b, needle_mbchars[j]))

              {

                /* Set table[i] := i-1-j.  */

                table[i] = i - ++j;

                break;

              }

            /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds

               for x = i-1-j, because

                 needle[i-1] != needle[j] = needle[i-1-x].  */

            if (j == 0)

              {

                /* The inequality holds for all possible x.  */

                table[i] = i;

                break;

              }

            /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds

               for i-1-j < x < i-1-j+table[j], because for these x:

                 needle[x..i-2]

                 = needle[x-(i-1-j)..j-1]

                 != needle[0..j-1-(x-(i-1-j))]  (by definition of table[j])

                    = needle[0..i-2-x],

               hence needle[x..i-1] != needle[0..i-1-x].

               Furthermore

                 needle[i-1-j+table[j]..i-2]

                 = needle[table[j]..j-1]

                 = needle[0..j-1-table[j]]  (by definition of table[j]).  */

            j = j - table[j];

          }

        /* Here: j = i - table[i].  */

      }

  }

  /* Search, using the table to accelerate the processing.  */

  {

    size_t j;

    mbui_iterator_t rhaystack;

    mbui_iterator_t phaystack;

    *resultp = NULL;

    j = 0;

    mbui_init (rhaystack, haystack);

    mbui_init (phaystack, haystack);

    /* Invariant: phaystack = rhaystack + j.  */

    while (mbui_avail (phaystack))

      if (mb_equal (needle_mbchars[j], mbui_cur (phaystack)))

        {

          j++;

          mbui_advance (phaystack);

          if (j == m)

            {

              /* The entire needle has been found.  */

              *resultp = mbui_cur_ptr (rhaystack);

              break;

            }

        }

      else if (j > 0)

        {

          /* Found a match of needle[0..j-1], mismatch at needle[j].  */

          size_t count = table[j];

          j -= count;

          for (; count > 0; count--)

            {

              if (!mbui_avail (rhaystack))

                abort ();

              mbui_advance (rhaystack);

            }

        }

      else

        {

          /* Found a mismatch at needle[0] already.  */

          if (!mbui_avail (rhaystack))

            abort ();

          mbui_advance (rhaystack);

          mbui_advance (phaystack);

        }

  }

  freea (memory);

  return true;

}

/* Find the first occurrence of the character string NEEDLE in the character

   string HAYSTACK.  Return NULL if NEEDLE is not found in HAYSTACK.  */

char *

mbsstr (const char *haystack, const char *needle)

{

  /* Be careful not to look at the entire extent of haystack or needle

     until needed.  This is useful because of these two cases:

       - haystack may be very long, and a match of needle found early,

       - needle may be very long, and not even a short initial segment of

         needle may be found in haystack.  */

  if (MB_CUR_MAX > 1)

    {

      mbui_iterator_t iter_needle;

      mbui_init (iter_needle, needle);

      if (mbui_avail (iter_needle))

        {

          /* Minimizing the worst-case complexity:

             Let n = mbslen(haystack), m = mbslen(needle).

             The na誰ve algorithm is O(n*m) worst-case.

             The Knuth-Morris-Pratt algorithm is O(n) worst-case but it needs a

             memory allocation.

             To achieve linear complexity and yet amortize the cost of the

             memory allocation, we activate the Knuth-Morris-Pratt algorithm

             only once the na誰ve algorithm has already run for some time; more

             precisely, when

               - the outer loop count is >= 10,

               - the average number of comparisons per outer loop is >= 5,

               - the total number of comparisons is >= m.

             But we try it only once.  If the memory allocation attempt failed,

             we don't retry it.  */

          bool try_kmp = true;

          size_t outer_loop_count = 0;

          size_t comparison_count = 0;

          size_t last_ccount = 0;                  /* last comparison count */

          mbui_iterator_t iter_needle_last_ccount; /* = needle + last_ccount */

          mbui_iterator_t iter_haystack;

          mbui_init (iter_needle_last_ccount, needle);

          mbui_init (iter_haystack, haystack);

          for (;; mbui_advance (iter_haystack))

            {

              if (!mbui_avail (iter_haystack))

                /* No match.  */

                return NULL;

              /* See whether it's advisable to use an asymptotically faster

                 algorithm.  */

              if (try_kmp

                  && outer_loop_count >= 10

                  && comparison_count >= 5 * outer_loop_count)

                {

                  /* See if needle + comparison_count now reaches the end of

                     needle.  */

                  size_t count = comparison_count - last_ccount;

                  for (;

                       count > 0 && mbui_avail (iter_needle_last_ccount);

                       count--)

                    mbui_advance (iter_needle_last_ccount);

                  last_ccount = comparison_count;

                  if (!mbui_avail (iter_needle_last_ccount))

                    {

                      /* Try the Knuth-Morris-Pratt algorithm.  */

                      const char *result;

                      bool success =

                        knuth_morris_pratt_multibyte (haystack, needle,

                                                      &result);

                      if (success)

                        return (char *) result;

                      try_kmp = false;

                    }

                }

              outer_loop_count++;

              comparison_count++;

              if (mb_equal (mbui_cur (iter_haystack), mbui_cur (iter_needle)))

                /* The first character matches.  */

                {

                  mbui_iterator_t rhaystack;

                  mbui_iterator_t rneedle;

                  memcpy (&rhaystack, &iter_haystack, sizeof (mbui_iterator_t));

                  mbui_advance (rhaystack);

                  mbui_init (rneedle, needle);

                  if (!mbui_avail (rneedle))

                    abort ();

                  mbui_advance (rneedle);

                  for (;; mbui_advance (rhaystack), mbui_advance (rneedle))

                    {

                      if (!mbui_avail (rneedle))

                        /* Found a match.  */

                        return (char *) mbui_cur_ptr (iter_haystack);

                      if (!mbui_avail (rhaystack))

                        /* No match.  */

                        return NULL;

                      comparison_count++;

                      if (!mb_equal (mbui_cur (rhaystack), mbui_cur (rneedle)))

                        /* Nothing in this round.  */

                        break;

                    }

                }

            }

        }

      else

        return (char *) haystack;

    }

  else

    {

      if (*needle != '\0')

        {

          /* Minimizing the worst-case complexity:

             Let n = strlen(haystack), m = strlen(needle).

             The na誰ve algorithm is O(n*m) worst-case.

             The Knuth-Morris-Pratt algorithm is O(n) worst-case but it needs a

             memory allocation.

             To achieve linear complexity and yet amortize the cost of the

             memory allocation, we activate the Knuth-Morris-Pratt algorithm

             only once the na誰ve algorithm has already run for some time; more

             precisely, when

               - the outer loop count is >= 10,

               - the average number of comparisons per outer loop is >= 5,

               - the total number of comparisons is >= m.

             But we try it only once.  If the memory allocation attempt failed,

             we don't retry it.  */

          bool try_kmp = true;

          size_t outer_loop_count = 0;

          size_t comparison_count = 0;

          size_t last_ccount = 0;                  /* last comparison count */

          const char *needle_last_ccount = needle; /* = needle + last_ccount */

          /* Speed up the following searches of needle by caching its first

             character.  */

          char b = *needle++;

          for (;; haystack++)

            {

              if (*haystack == '\0')

                /* No match.  */

                return NULL;

              /* See whether it's advisable to use an asymptotically faster

                 algorithm.  */

              if (try_kmp

                  && outer_loop_count >= 10

                  && comparison_count >= 5 * outer_loop_count)

                {

                  /* See if needle + comparison_count now reaches the end of

                     needle.  */

                  if (needle_last_ccount != NULL)

                    {

                      needle_last_ccount +=

                        strnlen (needle_last_ccount,

                                 comparison_count - last_ccount);

                      if (*needle_last_ccount == '\0')

                        needle_last_ccount = NULL;

                      last_ccount = comparison_count;

                    }

                  if (needle_last_ccount == NULL)

                    {

                      /* Try the Knuth-Morris-Pratt algorithm.  */

                      const unsigned char *result;

                      bool success =

                        knuth_morris_pratt ((const unsigned char *) haystack,

                                            (const unsigned char *) (needle - 1),

                                            strlen (needle - 1),

                                            &result);

                      if (success)

                        return (char *) result;

                      try_kmp = false;

                    }

                }

              outer_loop_count++;

              comparison_count++;

              if (*haystack == b)

                /* The first character matches.  */

                {

                  const char *rhaystack = haystack + 1;

                  const char *rneedle = needle;

                  for (;; rhaystack++, rneedle++)

                    {

                      if (*rneedle == '\0')

                        /* Found a match.  */

                        return (char *) haystack;

                      if (*rhaystack == '\0')

                        /* No match.  */

                        return NULL;

                      comparison_count++;

                      if (*rhaystack != *rneedle)

                        /* Nothing in this round.  */

                        break;

                    }

                }

            }

        }

      else

        return (char *) haystack;

    }

}