/*

** 2006 September 30

**

** The author disclaims copyright to this source code.  In place of

** a legal notice, here is a blessing:

**

**    May you do good and not evil.

**    May you find forgiveness for yourself and forgive others.

**    May you share freely, never taking more than you give.

**

*************************************************************************

** Implementation of the full-text-search tokenizer that implements

** a Porter stemmer.

*/

/*

** The code in this file is only compiled if:

**

**     * The FTS3 module is being built as an extension

**       (in which case SQLITE_CORE is not defined), or

**

**     * The FTS3 module is being built into the core of

**       SQLite (in which case SQLITE_ENABLE_FTS3 is defined).

*/

#if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS3)

#include <assert.h>

#include <stdlib.h>

#include <stdio.h>

#include <string.h>

#include <ctype.h>

#include "fts3_tokenizer.h"

/*

** Class derived from sqlite3_tokenizer

*/

typedef struct porter_tokenizer {

  sqlite3_tokenizer base;      /* Base class */

} porter_tokenizer;

/*

** Class derived from sqlit3_tokenizer_cursor

*/

typedef struct porter_tokenizer_cursor {

  sqlite3_tokenizer_cursor base;

  const char *zInput;          /* input we are tokenizing */

  int nInput;                  /* size of the input */

  int iOffset;                 /* current position in zInput */

  int iToken;                  /* index of next token to be returned */

  char *zToken;                /* storage for current token */

  int nAllocated;              /* space allocated to zToken buffer */

} porter_tokenizer_cursor;

/* Forward declaration */

static const sqlite3_tokenizer_module porterTokenizerModule;

/*

** Create a new tokenizer instance.

*/

static int porterCreate(

  int argc, const char * const *argv,

  sqlite3_tokenizer **ppTokenizer

){

  porter_tokenizer *t;

  t = (porter_tokenizer *) sqlite3_malloc(sizeof(*t));

  if( t==NULL ) return SQLITE_NOMEM;

  memset(t, 0, sizeof(*t));

  *ppTokenizer = &t->base;

  return SQLITE_OK;

}

/*

** Destroy a tokenizer

*/

static int porterDestroy(sqlite3_tokenizer *pTokenizer){

  sqlite3_free(pTokenizer);

  return SQLITE_OK;

}

/*

** Prepare to begin tokenizing a particular string.  The input

** string to be tokenized is zInput[0..nInput-1].  A cursor

** used to incrementally tokenize this string is returned in 

** *ppCursor.

*/

static int porterOpen(

  sqlite3_tokenizer *pTokenizer,         /* The tokenizer */

  const char *zInput, int nInput,        /* String to be tokenized */

  sqlite3_tokenizer_cursor **ppCursor    /* OUT: Tokenization cursor */

){

  porter_tokenizer_cursor *c;

  c = (porter_tokenizer_cursor *) sqlite3_malloc(sizeof(*c));

  if( c==NULL ) return SQLITE_NOMEM;

  c->zInput = zInput;

  if( zInput==0 ){

    c->nInput = 0;

  }else if( nInput<0 ){

    c->nInput = (int)strlen(zInput);

  }else{

    c->nInput = nInput;

  }

  c->iOffset = 0;                 /* start tokenizing at the beginning */

  c->iToken = 0;

  c->zToken = NULL;               /* no space allocated, yet. */

  c->nAllocated = 0;

  *ppCursor = &c->base;

  return SQLITE_OK;

}

/*

** Close a tokenization cursor previously opened by a call to

** porterOpen() above.

*/

static int porterClose(sqlite3_tokenizer_cursor *pCursor){

  porter_tokenizer_cursor *c = (porter_tokenizer_cursor *) pCursor;

  sqlite3_free(c->zToken);

  sqlite3_free(c);

  return SQLITE_OK;

}

/*

** Vowel or consonant

*/

static const char cType[] = {

   0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0,

   1, 1, 1, 2, 1

};

/*

** isConsonant() and isVowel() determine if their first character in

** the string they point to is a consonant or a vowel, according

** to Porter ruls.  

**

** A consonate is any letter other than 'a', 'e', 'i', 'o', or 'u'.

** 'Y' is a consonant unless it follows another consonant,

** in which case it is a vowel.

**

** In these routine, the letters are in reverse order.  So the 'y' rule

** is that 'y' is a consonant unless it is followed by another

** consonent.

*/

static int isVowel(const char*);

static int isConsonant(const char *z){

  int j;

  char x = *z;

  if( x==0 ) return 0;

  assert( x>='a' && x<='z' );

  j = cType[x-'a'];

  if( j<2 ) return j;

  return z[1]==0 || isVowel(z + 1);

}

static int isVowel(const char *z){

  int j;

  char x = *z;

  if( x==0 ) return 0;

  assert( x>='a' && x<='z' );

  j = cType[x-'a'];

  if( j<2 ) return 1-j;

  return isConsonant(z + 1);

}

/*

** Let any sequence of one or more vowels be represented by V and let

** C be sequence of one or more consonants.  Then every word can be

** represented as:

**

**           [C] (VC){m} [V]

**

** In prose:  A word is an optional consonant followed by zero or

** vowel-consonant pairs followed by an optional vowel.  "m" is the

** number of vowel consonant pairs.  This routine computes the value

** of m for the first i bytes of a word.

**

** Return true if the m-value for z is 1 or more.  In other words,

** return true if z contains at least one vowel that is followed

** by a consonant.

**

** In this routine z[] is in reverse order.  So we are really looking

** for an instance of of a consonant followed by a vowel.

*/

static int m_gt_0(const char *z){

  while( isVowel(z) ){ z++; }

  if( *z==0 ) return 0;

  while( isConsonant(z) ){ z++; }

  return *z!=0;

}

/* Like mgt0 above except we are looking for a value of m which is

** exactly 1

*/

static int m_eq_1(const char *z){

  while( isVowel(z) ){ z++; }

  if( *z==0 ) return 0;

  while( isConsonant(z) ){ z++; }

  if( *z==0 ) return 0;

  while( isVowel(z) ){ z++; }

  if( *z==0 ) return 1;

  while( isConsonant(z) ){ z++; }

  return *z==0;

}

/* Like mgt0 above except we are looking for a value of m>1 instead

** or m>0

*/

static int m_gt_1(const char *z){

  while( isVowel(z) ){ z++; }

  if( *z==0 ) return 0;

  while( isConsonant(z) ){ z++; }

  if( *z==0 ) return 0;

  while( isVowel(z) ){ z++; }

  if( *z==0 ) return 0;

  while( isConsonant(z) ){ z++; }

  return *z!=0;

}

/*

** Return TRUE if there is a vowel anywhere within z[0..n-1]

*/

static int hasVowel(const char *z){

  while( isConsonant(z) ){ z++; }

  return *z!=0;

}

/*

** Return TRUE if the word ends in a double consonant.

**

** The text is reversed here. So we are really looking at

** the first two characters of z[].

*/

static int doubleConsonant(const char *z){

  return isConsonant(z) && z[0]==z[1] && isConsonant(z+1);

}

/*

** Return TRUE if the word ends with three letters which

** are consonant-vowel-consonent and where the final consonant

** is not 'w', 'x', or 'y'.

**

** The word is reversed here.  So we are really checking the

** first three letters and the first one cannot be in [wxy].

*/

static int star_oh(const char *z){

  return

    z[0]!=0 && isConsonant(z) &&

    z[0]!='w' && z[0]!='x' && z[0]!='y' &&

    z[1]!=0 && isVowel(z+1) &&

    z[2]!=0 && isConsonant(z+2);

}

/*

** If the word ends with zFrom and xCond() is true for the stem

** of the word that preceeds the zFrom ending, then change the 

** ending to zTo.

**

** The input word *pz and zFrom are both in reverse order.  zTo

** is in normal order. 

**

** Return TRUE if zFrom matches.  Return FALSE if zFrom does not

** match.  Not that TRUE is returned even if xCond() fails and

** no substitution occurs.

*/

static int stem(

  char **pz,             /* The word being stemmed (Reversed) */

  const char *zFrom,     /* If the ending matches this... (Reversed) */

  const char *zTo,       /* ... change the ending to this (not reversed) */

  int (*xCond)(const char*)   /* Condition that must be true */

){

  char *z = *pz;

  while( *zFrom && *zFrom==*z ){ z++; zFrom++; }

  if( *zFrom!=0 ) return 0;

  if( xCond && !xCond(z) ) return 1;

  while( *zTo ){

    *(--z) = *(zTo++);

  }

  *pz = z;

  return 1;

}

/*

** This is the fallback stemmer used when the porter stemmer is

** inappropriate.  The input word is copied into the output with

** US-ASCII case folding.  If the input word is too long (more

** than 20 bytes if it contains no digits or more than 6 bytes if

** it contains digits) then word is truncated to 20 or 6 bytes

** by taking 10 or 3 bytes from the beginning and end.

*/

static void copy_stemmer(const char *zIn, int nIn, char *zOut, int *pnOut){

  int i, mx, j;

  int hasDigit = 0;

  for(i=0; i<nIn; i++){

    int c = zIn[i];

    if( c>='A' && c<='Z' ){

      zOut[i] = c - 'A' + 'a';

    }else{

      if( c>='0' && c<='9' ) hasDigit = 1;

      zOut[i] = c;

    }

  }

  mx = hasDigit ? 3 : 10;

  if( nIn>mx*2 ){

    for(j=mx, i=nIn-mx; i<nIn; i++, j++){

      zOut[j] = zOut[i];

    }

    i = j;

  }

  zOut[i] = 0;

  *pnOut = i;

}

/*

** Stem the input word zIn[0..nIn-1].  Store the output in zOut.

** zOut is at least big enough to hold nIn bytes.  Write the actual

** size of the output word (exclusive of the '\0' terminator) into *pnOut.

**

** Any upper-case characters in the US-ASCII character set ([A-Z])

** are converted to lower case.  Upper-case UTF characters are

** unchanged.

**

** Words that are longer than about 20 bytes are stemmed by retaining

** a few bytes from the beginning and the end of the word.  If the

** word contains digits, 3 bytes are taken from the beginning and

** 3 bytes from the end.  For long words without digits, 10 bytes

** are taken from each end.  US-ASCII case folding still applies.

** 

** If the input word contains not digits but does characters not 

** in [a-zA-Z] then no stemming is attempted and this routine just 

** copies the input into the input into the output with US-ASCII

** case folding.

**

** Stemming never increases the length of the word.  So there is

** no chance of overflowing the zOut buffer.

*/

static void porter_stemmer(const char *zIn, int nIn, char *zOut, int *pnOut){

  int i, j, c;

  char zReverse[28];

  char *z, *z2;

  if( nIn<3 || nIn>=sizeof(zReverse)-7 ){

    /* The word is too big or too small for the porter stemmer.

    ** Fallback to the copy stemmer */

    copy_stemmer(zIn, nIn, zOut, pnOut);

    return;

  }

  for(i=0, j=sizeof(zReverse)-6; i<nIn; i++, j--){

    c = zIn[i];

    if( c>='A' && c<='Z' ){

      zReverse[j] = c + 'a' - 'A';

    }else if( c>='a' && c<='z' ){

      zReverse[j] = c;

    }else{

      /* The use of a character not in [a-zA-Z] means that we fallback

      ** to the copy stemmer */

      copy_stemmer(zIn, nIn, zOut, pnOut);

      return;

    }

  }

  memset(&zReverse[sizeof(zReverse)-5], 0, 5);

  z = &zReverse[j+1];

  /* Step 1a */

  if( z[0]=='s' ){

    if(

     !stem(&z, "sess", "ss", 0) &&

     !stem(&z, "sei", "i", 0)  &&

     !stem(&z, "ss", "ss", 0)

    ){

      z++;

    }

  }

  /* Step 1b */  

  z2 = z;

  if( stem(&z, "dee", "ee", m_gt_0) ){

    /* Do nothing.  The work was all in the test */

  }else if( 

     (stem(&z, "gni", "", hasVowel) || stem(&z, "de", "", hasVowel))

      && z!=z2

  ){

     if( stem(&z, "ta", "ate", 0) ||

         stem(&z, "lb", "ble", 0) ||

         stem(&z, "zi", "ize", 0) ){

       /* Do nothing.  The work was all in the test */

     }else if( doubleConsonant(z) && (*z!='l' && *z!='s' && *z!='z') ){

       z++;

     }else if( m_eq_1(z) && star_oh(z) ){

       *(--z) = 'e';

     }

  }

  /* Step 1c */

  if( z[0]=='y' && hasVowel(z+1) ){

    z[0] = 'i';

  }

  /* Step 2 */

  switch( z[1] ){

   case 'a':

     stem(&z, "lanoita", "ate", m_gt_0) ||

     stem(&z, "lanoit", "tion", m_gt_0);

     break;

   case 'c':

     stem(&z, "icne", "ence", m_gt_0) ||

     stem(&z, "icna", "ance", m_gt_0);

     break;

   case 'e':

     stem(&z, "rezi", "ize", m_gt_0);

     break;

   case 'g':

     stem(&z, "igol", "log", m_gt_0);

     break;

   case 'l':

     stem(&z, "ilb", "ble", m_gt_0) ||

     stem(&z, "illa", "al", m_gt_0) ||

     stem(&z, "iltne", "ent", m_gt_0) ||

     stem(&z, "ile", "e", m_gt_0) ||

     stem(&z, "ilsuo", "ous", m_gt_0);

     break;

   case 'o':

     stem(&z, "noitazi", "ize", m_gt_0) ||

     stem(&z, "noita", "ate", m_gt_0) ||

     stem(&z, "rota", "ate", m_gt_0);

     break;

   case 's':

     stem(&z, "msila", "al", m_gt_0) ||

     stem(&z, "ssenevi", "ive", m_gt_0) ||

     stem(&z, "ssenluf", "ful", m_gt_0) ||

     stem(&z, "ssensuo", "ous", m_gt_0);

     break;

   case 't':

     stem(&z, "itila", "al", m_gt_0) ||

     stem(&z, "itivi", "ive", m_gt_0) ||

     stem(&z, "itilib", "ble", m_gt_0);

     break;

  }

  /* Step 3 */

  switch( z[0] ){

   case 'e':

     stem(&z, "etaci", "ic", m_gt_0) ||

     stem(&z, "evita", "", m_gt_0)   ||

     stem(&z, "ezila", "al", m_gt_0);

     break;

   case 'i':

     stem(&z, "itici", "ic", m_gt_0);

     break;

   case 'l':

     stem(&z, "laci", "ic", m_gt_0) ||

     stem(&z, "luf", "", m_gt_0);

     break;

   case 's':

     stem(&z, "ssen", "", m_gt_0);

     break;

  }

  /* Step 4 */

  switch( z[1] ){

   case 'a':

     if( z[0]=='l' && m_gt_1(z+2) ){

       z += 2;

     }

     break;

   case 'c':

     if( z[0]=='e' && z[2]=='n' && (z[3]=='a' || z[3]=='e')  && m_gt_1(z+4)  ){

       z += 4;

     }

     break;

   case 'e':

     if( z[0]=='r' && m_gt_1(z+2) ){

       z += 2;

     }

     break;

   case 'i':

     if( z[0]=='c' && m_gt_1(z+2) ){

       z += 2;

     }

     break;

   case 'l':

     if( z[0]=='e' && z[2]=='b' && (z[3]=='a' || z[3]=='i') && m_gt_1(z+4) ){

       z += 4;

     }

     break;

   case 'n':

     if( z[0]=='t' ){

       if( z[2]=='a' ){

         if( m_gt_1(z+3) ){

           z += 3;

         }

       }else if( z[2]=='e' ){

         stem(&z, "tneme", "", m_gt_1) ||

         stem(&z, "tnem", "", m_gt_1) ||

         stem(&z, "tne", "", m_gt_1);

       }

     }

     break;

   case 'o':

     if( z[0]=='u' ){

       if( m_gt_1(z+2) ){

         z += 2;

       }

     }else if( z[3]=='s' || z[3]=='t' ){

       stem(&z, "noi", "", m_gt_1);

     }

     break;

   case 's':

     if( z[0]=='m' && z[2]=='i' && m_gt_1(z+3) ){

       z += 3;

     }

     break;

   case 't':

     stem(&z, "eta", "", m_gt_1) ||

     stem(&z, "iti", "", m_gt_1);

     break;

   case 'u':

     if( z[0]=='s' && z[2]=='o' && m_gt_1(z+3) ){

       z += 3;

     }

     break;

   case 'v':

   case 'z':

     if( z[0]=='e' && z[2]=='i' && m_gt_1(z+3) ){

       z += 3;

     }