SQLite

  if( rc!=SQLITE_OK ){
    sqlite3_result_error_code(pCtx, rc);
  }
}
/*
** End of highlight() implementation.
**************************************************************************/

/*
** Context object passed to the fts5SentenceFinderCb() function.
*/
typedef struct Fts5SFinder Fts5SFinder;
struct Fts5SFinder {
  int iPos;                       /* Current token position */
  int nFirstAlloc;                /* Allocated size of aFirst[] */
  int nFirst;                     /* Number of entries in aFirst[] */
  int *aFirst;                    /* Array of first token in each sentence */
  const char *zDoc;               /* Document being tokenized */
};

/*
** Add an entry to the Fts5SFinder.aFirst[] array. Grow the array if
** necessary. Return SQLITE_OK if successful, or SQLITE_NOMEM if an
** error occurs.
*/
static int fts5SentenceFinderAdd(Fts5SFinder *p, int iAdd){
  if( p->nFirstAlloc==p->nFirst ){
    int nNew = p->nFirstAlloc ? p->nFirstAlloc*2 : 64;
    int *aNew;

    aNew = (int*)sqlite3_realloc(p->aFirst, nNew*sizeof(int));
    if( aNew==0 ) return SQLITE_NOMEM;
    p->aFirst = aNew;
    p->nFirstAlloc = nNew;
  }
  p->aFirst[p->nFirst++] = iAdd;
  return SQLITE_OK;
}

/*
** This function is an xTokenize() callback used by the auxiliary snippet()
** function. Its job is to identify tokens that are the first in a sentence.
** For each such token, an entry is added to the SFinder.aFirst[] array.
*/
static int fts5SentenceFinderCb(
  void *pContext,                 /* Pointer to HighlightContext object */
  int tflags,                     /* Mask of FTS5_TOKEN_* flags */
  const char *pToken,             /* Buffer containing token */
  int nToken,                     /* Size of token in bytes */
  int iStartOff,                  /* Start offset of token */
  int iEndOff                     /* End offset of token */
){
  int rc = SQLITE_OK;

  if( (tflags & FTS5_TOKEN_COLOCATED)==0 ){
    Fts5SFinder *p = (Fts5SFinder*)pContext;
    if( p->iPos>0 ){
      int i;
      char c = 0;
      for(i=iStartOff-1; i>=0; i--){
        c = p->zDoc[i];
        if( c!=' ' && c!='\t' && c!='\n' && c!='\r' ) break;
      }
      if( i!=iStartOff-1 && (c=='.' || c==':') ){
        rc = fts5SentenceFinderAdd(p, p->iPos);
      }
    }else{
      rc = fts5SentenceFinderAdd(p, 0);
    }
    p->iPos++;
  }
  return rc;
}

static int fts5SnippetScore(
  const Fts5ExtensionApi *pApi,   /* API offered by current FTS version */
  Fts5Context *pFts,              /* First arg to pass to pApi functions */
  int nDocsize,                   /* Size of column in tokens */
  unsigned char *aSeen,           /* Array with one element per query phrase */
  int iCol,                       /* Column to score */
  int iPos,                       /* Starting offset to score */
  int nToken,                     /* Max tokens per snippet */
  int *pnScore,                   /* OUT: Score */
  int *piPos                      /* OUT: Adjusted offset */
){
  int rc;
  int i;
  int ip = 0;
  int ic = 0;
  int iOff = 0;
  int iFirst = -1;
  int nInst;
  int nScore = 0;

  rc = pApi->xInstCount(pFts, &nInst);
  for(i=0; i<nInst && rc==SQLITE_OK; i++){
    rc = pApi->xInst(pFts, i, &ip, &ic, &iOff);
    if( rc==SQLITE_OK && ic==iCol && iOff>=iPos && iOff<(iPos+nToken) ){
      nScore += (aSeen[ip] ? 1 : 1000);
      aSeen[ip] = 1;
      if( iFirst<0 ) iFirst = iOff;
    }
  }

  *pnScore = nScore;
  if( piPos ){
    int iLast = iOff + pApi->xPhraseSize(pFts, ip);
    int iAdj = iFirst - (nToken - (iLast-iFirst)) / 2;

    if( (iAdj+nToken)>nDocsize ) iAdj = nDocsize - nToken;
    if( iAdj<0 ) iAdj = 0;
    *piPos = iAdj;
  }

  return rc;
}

/*
** Implementation of snippet() function.
*/
static void fts5SnippetFunction(
  const Fts5ExtensionApi *pApi,   /* API offered by current FTS version */
  Fts5Context *pFts,              /* First arg to pass to pApi functions */

  int nToken;                     /* 5th argument to snippet() */
  int nInst = 0;                  /* Number of instance matches this row */
  int i;                          /* Used to iterate through instances */
  int nPhrase;                    /* Number of phrases in query */
  unsigned char *aSeen;           /* Array of "seen instance" flags */
  int iBestCol;                   /* Column containing best snippet */
  int iBestStart = 0;             /* First token of best snippet */

  int nBestScore = 0;             /* Score of best snippet */
  int nColSize = 0;               /* Total size of iBestCol in tokens */
  Fts5SFinder sFinder;            /* Used to find the beginnings of sentences */
  int nCol;

  if( nVal!=5 ){
    const char *zErr = "wrong number of arguments to function snippet()";
    sqlite3_result_error(pCtx, zErr, -1);
    return;
  }

  nCol = pApi->xColumnCount(pFts);
  memset(&ctx, 0, sizeof(HighlightContext));
  iCol = sqlite3_value_int(apVal[0]);
  ctx.zOpen = (const char*)sqlite3_value_text(apVal[1]);
  ctx.zClose = (const char*)sqlite3_value_text(apVal[2]);
  zEllips = (const char*)sqlite3_value_text(apVal[3]);
  nToken = sqlite3_value_int(apVal[4]);


  iBestCol = (iCol>=0 ? iCol : 0);
  nPhrase = pApi->xPhraseCount(pFts);
  aSeen = sqlite3_malloc(nPhrase);
  if( aSeen==0 ){
    rc = SQLITE_NOMEM;
  }

  if( rc==SQLITE_OK ){
    rc = pApi->xInstCount(pFts, &nInst);
  }


  memset(&sFinder, 0, sizeof(Fts5SFinder));

  for(i=0; i<nCol; i++){
    if( iCol<0 || iCol==i ){
      int nDoc;
      int nDocsize;
      int ii;
      sFinder.iPos = 0;
      sFinder.nFirst = 0;
      rc = pApi->xColumnText(pFts, i, &sFinder.zDoc, &nDoc);
      if( rc!=SQLITE_OK ) break;
      rc = pApi->xTokenize(pFts, 
          sFinder.zDoc, nDoc, (void*)&sFinder,fts5SentenceFinderCb
      );
      if( rc!=SQLITE_OK ) break;
      rc = pApi->xColumnSize(pFts, i, &nDocsize);
      if( rc!=SQLITE_OK ) break;

      for(ii=0; rc==SQLITE_OK && ii<sFinder.nFirst; ii++){
        int nScore;

        memset(aSeen, 0, nPhrase);
        rc = fts5SnippetScore(pApi, pFts, nDocsize, aSeen, i, 
            sFinder.aFirst[ii], nToken, &nScore, 0
        );

        /* Bonus of 100 points for starting at the start of a sentence */
        nScore += 100;            

        if( rc==SQLITE_OK && nScore>nBestScore ){
          nBestScore = nScore;
          iBestCol = i;
          iBestStart = sFinder.aFirst[ii];
          nColSize = nDocsize;
        }
      }

      for(ii=0; rc==SQLITE_OK && ii<nInst; ii++){
        int ip, ic, io;
        int nScore;
        rc = pApi->xInst(pFts, ii, &ip, &ic, &io);
        if( ic!=i || rc!=SQLITE_OK ) continue;
        memset(aSeen, 0, nPhrase);
        rc = fts5SnippetScore(pApi, pFts, nDocsize, aSeen, i,
            io, nToken, &nScore, &io
        );
        if( rc==SQLITE_OK && nScore>nBestScore ){
          nBestScore = nScore;
          iBestCol = i;
          iBestStart = io;

          nColSize = nDocsize;
        }
      }
    }
  }



  if( rc==SQLITE_OK ){
    rc = pApi->xColumnText(pFts, iBestCol, &ctx.zIn, &ctx.nIn);
  }
  if( ctx.zIn ){
    if( rc==SQLITE_OK ){
      rc = fts5CInstIterInit(pApi, pFts, iBestCol, &ctx.iter);
    }









    ctx.iRangeStart = iBestStart;
    ctx.iRangeEnd = iBestStart + nToken - 1;

    if( iBestStart>0 ){
      fts5HighlightAppend(&rc, &ctx, zEllips, -1);
    }

      rc = pApi->xTokenize(pFts, ctx.zIn, ctx.nIn, (void*)&ctx,fts5HighlightCb);
    }
    if( ctx.iRangeEnd>=(nColSize-1) ){
      fts5HighlightAppend(&rc, &ctx, &ctx.zIn[ctx.iOff], ctx.nIn - ctx.iOff);
    }else{
      fts5HighlightAppend(&rc, &ctx, zEllips, -1);
    }
  }
  if( rc==SQLITE_OK ){
    sqlite3_result_text(pCtx, (const char*)ctx.zOut, -1, SQLITE_TRANSIENT);
  }else{
    sqlite3_result_error_code(pCtx, rc);
  }
  sqlite3_free(ctx.zOut);

  sqlite3_free(aSeen);
  sqlite3_free(sFinder.aFirst);
}

/************************************************************************/

/*
** The first time the bm25() function is called for a query, an instance
** of the following structure is allocated and populated.

  } [list $res]


}


foreach {tn doc res} {

  1.1 {X o o o o o o} {[X] o o o o o o}
  1.2 {o X o o o o o} {o [X] o o o o o}
  1.3 {o o X o o o o} {o o [X] o o o o}
  1.4 {o o o X o o o} {o o o [X] o o o}
  1.5 {o o o o X o o} {o o o o [X] o o}
  1.6 {o o o o o X o} {o o o o o [X] o}
  1.7 {o o o o o o X} {o o o o o o [X]}

  7.3 {o o X o o X o o o} {...o [X] o o [X] o o...}
  7.4 {o o o X o o X o o} {...o [X] o o [X] o o}
  7.5 {o o o o X o o X o} {...o o [X] o o [X] o}
  7.6 {o o o o o X o o X} {...o o o [X] o o [X]}

  8.1 {o o o o X o o o o o o o o o o o o o o o o o o o o o X X X o o o}
      {...o o [X] [X] [X] o o...}
  8.2 {o o o o. X o o o o o o o o o o o o o o o o o o o o o X X X o o o} 
      {...[X] o o o o o o...}


} {
  do_snippet_test 1.$tn $doc X $res
}

if {[detail_is_full]} {
  foreach {tn doc res} {
    1.1 {X Y o o o o o} {[X Y] o o o o o}

     the maximum x value.
  }
  3 "ROW" {
     ...returns the value of y on the same [row] that contains 
     the maximum x value.
  }
  4 "rollback" {
     ...Instead, the pending statement
     will return SQLITE_ABORT upon next access after the [ROLLBACK].
  }
  5 "rOllback" {
     ...Instead, the pending statement
     will return SQLITE_ABORT upon next access after the [ROLLBACK].
  }
  6 "lang*" {
     Added support for the FTS4 [languageid] option.
  }
} {
  do_test 2.$tn {