SQLite

  Fts5Expr *pExpr;                /* Expression for MATCH queries */
  Fts5Sorter *pSorter;            /* Sorter for "ORDER BY rank" queries */
  int csrflags;                   /* Mask of cursor flags (see below) */
  Fts5Cursor *pNext;              /* Next cursor in Fts5Cursor.pCsr list */
  char *zSpecial;                 /* Result of special query */

  /* "rank" function. Populated on demand from vtab.xColumn(). */
  char *zRank;                    /* Custom rank function */
  char *zRankArgs;                /* Custom rank function args */
  Fts5Auxiliary *pRank;           /* Rank callback (or NULL) */
  int nRankArg;                   /* Number of trailing arguments for rank() */
  sqlite3_value **apRankArg;      /* Array of trailing arguments */
  sqlite3_stmt *pRankArgStmt;     /* Origin of objects in apRankArg[] */

  /* Variables used by auxiliary functions */
  i64 iCsrId;                     /* Cursor id */

/*
** Values for Fts5Cursor.csrflags
*/
#define FTS5CSR_REQUIRE_CONTENT   0x01
#define FTS5CSR_REQUIRE_DOCSIZE   0x02
#define FTS5CSR_EOF               0x04
#define FTS5CSR_FREE_ZRANK        0x08

/*
** Macros to Set(), Clear() and Test() cursor flags.
*/
#define CsrFlagSet(pCsr, flag)   ((pCsr)->csrflags |= (flag))
#define CsrFlagClear(pCsr, flag) ((pCsr)->csrflags &= ~(flag))
#define CsrFlagTest(pCsr, flag)  ((pCsr)->csrflags & (flag))

**   3. A full-table scan.
*/
static int fts5BestIndexMethod(sqlite3_vtab *pVTab, sqlite3_index_info *pInfo){
  Fts5Table *pTab = (Fts5Table*)pVTab;
  Fts5Config *pConfig = pTab->pConfig;
  int iCons;
  int ePlan = FTS5_PLAN_SCAN;
  int iRankMatch;

  iCons = fts5FindConstraint(pInfo,SQLITE_INDEX_CONSTRAINT_MATCH,pConfig->nCol);
  if( iCons>=0 ){
    ePlan = FTS5_PLAN_MATCH;
    pInfo->estimatedCost = 1.0;
  }else{
    iCons = fts5FindConstraint(pInfo, SQLITE_INDEX_CONSTRAINT_EQ, -1);

      ePlan = FTS5_PLAN_SORTED_MATCH;
    }

    if( pInfo->orderByConsumed ){
      ePlan |= pInfo->aOrderBy[0].desc ? FTS5_ORDER_DESC : FTS5_ORDER_ASC;
    }
  }

  iRankMatch = fts5FindConstraint(
      pInfo, SQLITE_INDEX_CONSTRAINT_MATCH, pConfig->nCol+1
  );
  if( iRankMatch>=0 ){
    pInfo->aConstraintUsage[iRankMatch].argvIndex = 1 + (iCons>=0);
    pInfo->aConstraintUsage[iRankMatch].omit = 1;
  }
   
  pInfo->idxNum = ePlan;
  return SQLITE_OK;
}

/*
** Implementation of xOpen method.

  for(pp=&pTab->pGlobal->pCsr; (*pp)!=pCsr; pp=&(*pp)->pNext);
  *pp = pCsr->pNext;

  sqlite3_finalize(pCsr->pRankArgStmt);
  sqlite3_free(pCsr->apRankArg);

  sqlite3_free(pCsr->zSpecial);
  if( CsrFlagTest(pCsr, FTS5CSR_FREE_ZRANK) ){
    sqlite3_free(pCsr->zRank);
    sqlite3_free(pCsr->zRankArgs);
  }
  sqlite3_free(pCsr);
  return SQLITE_OK;
}

static int fts5SorterNext(Fts5Cursor *pCsr){
  Fts5Sorter *pSorter = pCsr->pSorter;
  int rc;

static int fts5CursorFirstSorted(Fts5Table *pTab, Fts5Cursor *pCsr, int bAsc){
  Fts5Config *pConfig = pTab->pConfig;
  Fts5Sorter *pSorter;
  int nPhrase;
  int nByte;
  int rc = SQLITE_OK;
  char *zSql;
  const char *zRank = pCsr->zRank;
  const char *zRankArgs = pCsr->zRankArgs;
  
  nPhrase = sqlite3Fts5ExprPhraseCount(pCsr->pExpr);
  nByte = sizeof(Fts5Sorter) + sizeof(int) * nPhrase;
  pSorter = (Fts5Sorter*)sqlite3_malloc(nByte);
  if( pSorter==0 ) return SQLITE_NOMEM;
  memset(pSorter, 0, nByte);
  pSorter->nIdx = nPhrase;

  /* TODO: It would be better to have some system for reusing statement
  ** handles here, rather than preparing a new one for each query. But that
  ** is not possible as SQLite reference counts the virtual table objects.
  ** And since the statement required here reads from this very virtual 
  ** table, saving it creates a circular reference.
  **
  ** If SQLite a built-in statement cache, this wouldn't be a problem. */
  zSql = sqlite3_mprintf("SELECT rowid, rank FROM %Q.%Q ORDER BY %s(%s%s%s) %s",
      pConfig->zDb, pConfig->zName, zRank, pConfig->zName,
      (zRankArgs ? ", " : ""),
      (zRankArgs ? zRankArgs : ""),
      bAsc ? "ASC" : "DESC"
  );
  if( zSql==0 ){
    rc = SQLITE_NOMEM;
  }else{
    rc = sqlite3_prepare_v2(pConfig->db, zSql, -1, &pSorter->pStmt, 0);
    sqlite3_free(zSql);

  return 0;
}


static int fts5FindRankFunction(Fts5Cursor *pCsr){
  Fts5Table *pTab = (Fts5Table*)(pCsr->base.pVtab);
  Fts5Config *pConfig = pTab->pConfig;

  int rc = SQLITE_OK;
  Fts5Auxiliary *pAux;
  const char *zRank = pCsr->zRank;
  const char *zRankArgs = pCsr->zRankArgs;

  if( zRankArgs ){
    char *zSql = sqlite3_mprintf("SELECT %s", zRankArgs);
    if( zSql==0 ){
      rc = SQLITE_NOMEM;
    }else{
      sqlite3_stmt *pStmt = 0;
      rc = sqlite3_prepare_v2(pConfig->db, zSql, -1, &pStmt, 0);
      sqlite3_free(zSql);
      assert( rc==SQLITE_OK || pCsr->pRankArgStmt==0 );

    }
  }

  pCsr->pRank = pAux;
  return rc;
}


static int fts5CursorParseRank(
  Fts5Config *pConfig,
  Fts5Cursor *pCsr, 
  sqlite3_value *pRank
){
  int rc = SQLITE_OK;
  if( pRank ){
    const char *z = (const char*)sqlite3_value_text(pRank);
    char *zRank = 0;
    char *zRankArgs = 0;

    rc = sqlite3Fts5ConfigParseRank(z, &zRank, &zRankArgs);
    if( rc==SQLITE_OK ){
      pCsr->zRank = zRank;
      pCsr->zRankArgs = zRankArgs;
      CsrFlagSet(pCsr, FTS5CSR_FREE_ZRANK);
    }else if( rc==SQLITE_ERROR ){
      pCsr->base.pVtab->zErrMsg = sqlite3_mprintf(
          "parse error in rank function: %s", z
      );
    }
  }else{
    if( pConfig->zRank ){
      pCsr->zRank = (char*)pConfig->zRank;
      pCsr->zRankArgs = (char*)pConfig->zRankArgs;
    }else{
      pCsr->zRank = (char*)FTS5_DEFAULT_RANK;
      pCsr->zRankArgs = 0;
    }
  }
  return rc;
}

/*
** This is the xFilter interface for the virtual table.  See
** the virtual table xFilter method documentation for additional
** information.
** 
** There are three possible query strategies:
**
**   1. Full-text search using a MATCH operator.
**   2. A by-rowid lookup.
**   3. A full-table scan.
*/
static int fts5FilterMethod(
  sqlite3_vtab_cursor *pCursor,   /* The cursor used for this query */
  int idxNum,                     /* Strategy index */
  const char *idxStr,             /* Unused */
  int nVal,                       /* Number of elements in apVal */
  sqlite3_value **apVal           /* Arguments for the indexing scheme */
){
  Fts5Table *pTab = (Fts5Table*)(pCursor->pVtab);
  Fts5Cursor *pCsr = (Fts5Cursor*)pCursor;
  int bAsc = ((idxNum & FTS5_ORDER_ASC) ? 1 : 0);
  int rc = SQLITE_OK;

  assert( nVal<=2 );
  assert( pCsr->pStmt==0 );
  assert( pCsr->pExpr==0 );
  assert( pCsr->csrflags==0 );
  assert( pCsr->pRank==0 );
  assert( pCsr->zRank==0 );
  assert( pCsr->zRankArgs==0 );

  if( pTab->pSortCsr ){
    /* If pSortCsr is non-NULL, then this call is being made as part of 
    ** processing for a "... MATCH <expr> ORDER BY rank" query (ePlan is
    ** set to FTS5_PLAN_SORTED_MATCH). pSortCsr is the cursor that will
    ** return results to the user for this query. The current cursor 
    ** (pCursor) is used to execute the query issued by function 
    ** fts5CursorFirstSorted() above.  */
    assert( FTS5_PLAN(idxNum)==FTS5_PLAN_SCAN );
    pCsr->idxNum = FTS5_PLAN_SOURCE;
    pCsr->pExpr = pTab->pSortCsr->pExpr;
    rc = fts5CursorFirst(pTab, pCsr, bAsc);
  }else{
    int ePlan = FTS5_PLAN(idxNum);
    pCsr->idxNum = idxNum;
    if( ePlan==FTS5_PLAN_MATCH || ePlan==FTS5_PLAN_SORTED_MATCH ){
      const char *zExpr = (const char*)sqlite3_value_text(apVal[0]);

      rc = fts5CursorParseRank(pTab->pConfig, pCsr, (nVal==2 ? apVal[1] : 0));
      if( rc==SQLITE_OK ){
        if( zExpr[0]=='*' ){
          /* The user has issued a query of the form "MATCH '*...'". This
          ** indicates that the MATCH expression is not a full text query,
          ** but a request for an internal parameter.  */
          rc = fts5SpecialMatch(pTab, pCsr, &zExpr[1]);
        }else{
          char **pzErr = &pTab->base.zErrMsg;
          rc = sqlite3Fts5ExprNew(pTab->pConfig, zExpr, &pCsr->pExpr, pzErr);
          if( rc==SQLITE_OK ){
            if( ePlan==FTS5_PLAN_MATCH ){
              rc = fts5CursorFirst(pTab, pCsr, bAsc);
            }else{
              rc = fts5CursorFirstSorted(pTab, pCsr, bAsc);
            }
          }
        }
      }
    }else{
      /* This is either a full-table scan (ePlan==FTS5_PLAN_SCAN) or a lookup
      ** by rowid (ePlan==FTS5_PLAN_ROWID).  */
      int eStmt = fts5StmtType(idxNum);

void sqlite3Fts5Dequote(char *z);

/* Load the contents of the %_config table */
int sqlite3Fts5ConfigLoad(Fts5Config*, int);

/* Set the value of a single config attribute */
int sqlite3Fts5ConfigSetValue(Fts5Config*, const char*, sqlite3_value*, int*);

int sqlite3Fts5ConfigParseRank(const char*, char**, char**);

/*
** End of interface to code in fts5_config.c.
**************************************************************************/

/**************************************************************************
** Interface to code in fts5_buffer.c.

** this is:
**
**   + Bareword (function name)
**   + Open parenthesis - "("
**   + Zero or more SQL literals in a comma separated list
**   + Close parenthesis - ")"
*/
int sqlite3Fts5ConfigParseRank(
  const char *zIn,                /* Input string */
  char **pzRank,                  /* OUT: Rank function name */
  char **pzRankArgs               /* OUT: Rank function arguments */
){
  const char *p = zIn;
  const char *pRank;
  char *zRank = 0;

    }
  }

  else if( 0==sqlite3_stricmp(zKey, "rank") ){
    const char *zIn = (const char*)sqlite3_value_text(pVal);
    char *zRank;
    char *zRankArgs;
    rc = sqlite3Fts5ConfigParseRank(zIn, &zRank, &zRankArgs);
    if( rc==SQLITE_OK ){
      sqlite3_free(pConfig->zRank);
      sqlite3_free(pConfig->zRankArgs);
      pConfig->zRank = zRank;
      pConfig->zRankArgs = zRankArgs;
    }else if( rc==SQLITE_ERROR ){
      rc = SQLITE_OK;

  SELECT rowid, firstinst(t2) FROM t2 WHERE t2 MATCH 'a' ORDER BY rowid ASC
} {
  1 0 2 4 3 6   5  103
  6 9 7 0 9 102 10 8
}

do_execsql_test 4.1.2 {
  SELECT rowid, rank FROM t2 
  WHERE t2 MATCH 'a' AND rank MATCH 'firstinst()' 
  ORDER BY rowid ASC
} {
  1 0 2 4 3 6   5  103
  6 9 7 0 9 102 10 8
}

do_execsql_test 4.1.3 {
  SELECT rowid, rank FROM t2 
  WHERE t2 MATCH 'a' AND rank MATCH 'firstinst()'
  ORDER BY rank DESC
} {
  5 103  9 102  6 9  10 8  3 6  2 4  7 0  1 0 
}

do_execsql_test 4.1.4 {
  INSERT INTO t2(t2, rank) VALUES('rank', 'firstinst()');
  SELECT rowid, rank FROM t2 WHERE t2 MATCH 'a' ORDER BY rowid ASC
} {
  1 0 2 4 3 6   5  103
  6 9 7 0 9 102 10 8
}

do_execsql_test 4.1.5 {
  SELECT rowid, rank FROM t2 WHERE t2 MATCH 'a' ORDER BY rank DESC
} {
  5 103  9 102  6 9  10 8  3 6  2 4  7 0  1 0 
}

do_execsql_test 4.1.6 {
  INSERT INTO t2(t2, rank) VALUES('rank', 'firstinst (    ) ');
  SELECT rowid, rank FROM t2 WHERE t2 MATCH 'a' ORDER BY rank DESC
} {
  5 103  9 102  6 9  10 8  3 6  2 4  7 0  1 0 
}

proc rowidplus {cmd ival} { 

do_execsql_test 4.2.2 {
  INSERT INTO t2(t2, rank) VALUES('rank', 'rowidplus(111) ');
  SELECT rowid, rank FROM t2 WHERE t2 MATCH 'o + q + g'
} {
  10 121
}

do_execsql_test 4.2.3 {
  SELECT rowid, rank FROM t2 
  WHERE t2 MATCH 'o + q + g' AND rank MATCH 'rowidplus(112)'
} {
  10 122
}

proc rowidmod {cmd imod} { 
  expr [$cmd xRowid] % $imod
}
sqlite3_fts5_create_function db rowidmod rowidmod
do_execsql_test 4.3.1 {
  CREATE VIRTUAL TABLE t3 USING fts5(x);
  INSERT INTO t3 VALUES('a one');
  INSERT INTO t3 VALUES('a two');
  INSERT INTO t3 VALUES('a three');
  INSERT INTO t3 VALUES('a four');
  INSERT INTO t3 VALUES('a five');
  INSERT INTO t3(t3, rank) VALUES('rank', 'bm25()');
}
breakpoint

do_execsql_test 4.3.2 {
  SELECT * FROM t3
  WHERE t3 MATCH 'a' AND rank MATCH 'rowidmod(4)' 
  ORDER BY rank ASC
} {
  {a four} {a five} {a one} {a two} {a three}
}
do_execsql_test 4.3.3 {
  SELECT *, rank FROM t3
  WHERE t3 MATCH 'a' AND rank MATCH 'rowidmod(3)' 
  ORDER BY rank ASC
} {
  {a three} 0 {a four} 1 {a one} 1 {a five} 2 {a two} 2
}


finish_test