/*
** 2017 July 15
**
** 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.
**
*************************************************************************
**
** This file contains the implementation of the "unionvtab" and "swarmvtab"
** virtual tables. These modules provide read-only access to multiple tables,
** possibly in multiple database files, via a single database object.
** The source tables must have the following characteristics:
**
**   * They must all be rowid tables (not VIRTUAL or WITHOUT ROWID
**     tables or views).
**
**   * Each table must have the same set of columns, declared in
**     the same order and with the same declared types.
**
**   * The tables must not feature a user-defined column named "_rowid_".
**
**   * Each table must contain a distinct range of rowid values.
**
** The difference between the two virtual table modules is that for 
** "unionvtab", all source tables must be located in the main database or
** in databases ATTACHed to the main database by the user. For "swarmvtab",
** the tables may be located in any database file on disk. The "swarmvtab"
** implementation takes care of opening and closing database files
** automatically.
**
** UNIONVTAB
**
**   A "unionvtab" virtual table is created as follows:
**
**     CREATE VIRTUAL TABLE <name> USING unionvtab(<sql-statement>);
**
**   The implementation evalutes <sql statement> whenever a unionvtab virtual
**   table is created or opened. It should return one row for each source
**   database table. The four columns required of each row are:
**
**     1. The name of the database containing the table ("main" or "temp" or
**        the name of an attached database). Or NULL to indicate that all
**        databases should be searched for the table in the usual fashion.
**
**     2. The name of the database table.
**
**     3. The smallest rowid in the range of rowids that may be stored in the
**        database table (an integer).
**
**     4. The largest rowid in the range of rowids that may be stored in the
**        database table (an integer).
**
** SWARMVTAB
**
**   A "swarmvtab" virtual table is created similarly to a unionvtab table:
**
**     CREATE VIRTUAL TABLE <name>
**      USING swarmvtab(<sql-statement>, <callback>);
**
**   The difference is that for a swarmvtab table, the first column returned
**   by the <sql statement> must return a path or URI that can be used to open
**   the database file containing the source table.  The <callback> option
**   is optional.  If included, it is the name of an application-defined
**   SQL function that is invoked with the URI of the file, if the file
**   does not already exist on disk.
*/

#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT1
#include <assert.h>
#include <string.h>

#ifndef SQLITE_OMIT_VIRTUALTABLE

/*
** Largest and smallest possible 64-bit signed integers. These macros
** copied from sqliteInt.h.
*/
#ifndef LARGEST_INT64
# define LARGEST_INT64  (0xffffffff|(((sqlite3_int64)0x7fffffff)<<32))
#endif
#ifndef SMALLEST_INT64
# define SMALLEST_INT64 (((sqlite3_int64)-1) - LARGEST_INT64)
#endif

/*
** The following is also copied from sqliteInt.h. To facilitate coverage
** testing.
*/
#ifndef ALWAYS
# if defined(SQLITE_COVERAGE_TEST) || defined(SQLITE_MUTATION_TEST)
#  define ALWAYS(X)      (1)
#  define NEVER(X)       (0)
# elif !defined(NDEBUG)
#  define ALWAYS(X)      ((X)?1:(assert(0),0))
#  define NEVER(X)       ((X)?(assert(0),1):0)
# else
#  define ALWAYS(X)      (X)
#  define NEVER(X)       (X)
# endif
#endif

/*
** The swarmvtab module attempts to keep the number of open database files
** at or below this limit. This may not be possible if there are too many
** simultaneous queries.
*/
#define SWARMVTAB_MAX_OPEN 9

typedef struct UnionCsr UnionCsr;
typedef struct UnionTab UnionTab;
typedef struct UnionSrc UnionSrc;

/*
** Each source table (row returned by the initialization query) is 
** represented by an instance of the following structure stored in the
** UnionTab.aSrc[] array.
*/
struct UnionSrc {
  char *zDb;                      /* Database containing source table */
  char *zTab;                     /* Source table name */
  sqlite3_int64 iMin;             /* Minimum rowid */
  sqlite3_int64 iMax;             /* Maximum rowid */

  /* Fields used by swarmvtab only */
  char *zFile;                    /* Database file containing table zTab */
  int nUser;                      /* Current number of users */
  sqlite3 *db;                    /* Database handle */
  UnionSrc *pNextClosable;        /* Next in list of closable sources */
};

/*
** Virtual table  type for union vtab.
*/
struct UnionTab {
  sqlite3_vtab base;              /* Base class - must be first */
  sqlite3 *db;                    /* Database handle */
  int bSwarm;                     /* 1 for "swarmvtab", 0 for "unionvtab" */
  int iPK;                        /* INTEGER PRIMARY KEY column, or -1 */
  int nSrc;                       /* Number of elements in the aSrc[] array */
  UnionSrc *aSrc;                 /* Array of source tables, sorted by rowid */

  /* Used by swarmvtab only */
  char *zSourceStr;               /* Expected unionSourceToStr() value */
  char *zNotFoundCallback;        /* UDF to invoke if file not found on open */
  UnionSrc *pClosable;            /* First in list of closable sources */
  int nOpen;                      /* Current number of open sources */
  int nMaxOpen;                   /* Maximum number of open sources */
};

/*
** Virtual table cursor type for union vtab.
*/
struct UnionCsr {
  sqlite3_vtab_cursor base;       /* Base class - must be first */
  sqlite3_stmt *pStmt;            /* SQL statement to run */

  /* Used by swarmvtab only */
  sqlite3_int64 iMaxRowid;        /* Last rowid to visit */
  int iTab;                       /* Index of table read by pStmt */
};

/*
** Given UnionTab table pTab and UnionSrc object pSrc, return the database
** handle that should be used to access the table identified by pSrc. This
** is the main db handle for "unionvtab" tables, or the source-specific 
** handle for "swarmvtab".
*/
#define unionGetDb(pTab, pSrc) ((pTab)->bSwarm ? (pSrc)->db : (pTab)->db)

/*
** If *pRc is other than SQLITE_OK when this function is called, it
** always returns NULL. Otherwise, it attempts to allocate and return
** a pointer to nByte bytes of zeroed memory. If the memory allocation
** is attempted but fails, NULL is returned and *pRc is set to 
** SQLITE_NOMEM.
*/

    char q = z[0];

    /* Set stack variable q to the close-quote character */
    if( q=='[' || q=='\'' || q=='"' || q=='`' ){
      int iIn = 1;
      int iOut = 0;
      if( q=='[' ) q = ']';  
      while( ALWAYS(z[iIn]) ){
        if( z[iIn]==q ){
          if( z[iIn+1]!=q ){
            /* Character iIn was the close quote. */
            iIn++;
            break;
          }else{
            /* Character iIn and iIn+1 form an escaped quote character. Skip

static sqlite3_stmt *unionPrepare(
  int *pRc,                       /* IN/OUT: Error code */
  sqlite3 *db,                    /* Database handle */
  const char *zSql,               /* SQL statement to prepare */
  char **pzErr                    /* OUT: Error message */
){
  sqlite3_stmt *pRet = 0;
  assert( pzErr );
  if( *pRc==SQLITE_OK ){
    int rc = sqlite3_prepare_v2(db, zSql, -1, &pRet, 0);
    if( rc!=SQLITE_OK ){
      *pzErr = sqlite3_mprintf("sql error: %s", sqlite3_errmsg(db));
      *pRc = rc;
    }
  }

/*
** Call sqlite3_reset() on SQL statement pStmt. If *pRc is set to 
** SQLITE_OK when this function is called, then it is set to the
** value returned by sqlite3_reset() before this function exits.
** In this case, *pzErr may be set to point to an error message
** buffer allocated by sqlite3_malloc().
*/
#if 0
static void unionReset(int *pRc, sqlite3_stmt *pStmt, char **pzErr){
  int rc = sqlite3_reset(pStmt);
  if( *pRc==SQLITE_OK ){
    *pRc = rc;
    if( rc ){
      *pzErr = sqlite3_mprintf("%s", sqlite3_errmsg(sqlite3_db_handle(pStmt)));
    }
  }
}
#endif

/*
** Call sqlite3_finalize() on SQL statement pStmt. If *pRc is set to 
** SQLITE_OK when this function is called, then it is set to the
** value returned by sqlite3_finalize() before this function exits.
*/
static void unionFinalize(int *pRc, sqlite3_stmt *pStmt, char **pzErr){
  sqlite3 *db = sqlite3_db_handle(pStmt);
  int rc = sqlite3_finalize(pStmt);
  if( *pRc==SQLITE_OK ){
    *pRc = rc;
    if( rc ){
      *pzErr = sqlite3_mprintf("%s", sqlite3_errmsg(db));
    }
  }
}

/*
** This function is a no-op for unionvtab. For swarmvtab, it attempts to
** close open database files until at most nMax are open. An SQLite error
** code is returned if an error occurs, or SQLITE_OK otherwise.
*/
static void unionCloseSources(UnionTab *pTab, int nMax){
  while( pTab->pClosable && pTab->nOpen>nMax ){
    UnionSrc **pp;
    for(pp=&pTab->pClosable; (*pp)->pNextClosable; pp=&(*pp)->pNextClosable);
    assert( (*pp)->db );
    sqlite3_close((*pp)->db);
    (*pp)->db = 0;
    *pp = 0;
    pTab->nOpen--;
  }
}

/*
** xDisconnect method.
*/
static int unionDisconnect(sqlite3_vtab *pVtab){
  if( pVtab ){
    UnionTab *pTab = (UnionTab*)pVtab;
    int i;
    for(i=0; i<pTab->nSrc; i++){
      UnionSrc *pSrc = &pTab->aSrc[i];
      sqlite3_free(pSrc->zDb);
      sqlite3_free(pSrc->zTab);
      sqlite3_free(pSrc->zFile);
      sqlite3_close(pSrc->db);
    }
    sqlite3_free(pTab->zSourceStr);
    sqlite3_free(pTab->zNotFoundCallback);
    sqlite3_free(pTab->aSrc);
    sqlite3_free(pTab);
  }
  return SQLITE_OK;
}

/*
** Check that the table identified by pSrc is a rowid table. If not,
** return SQLITE_ERROR and set (*pzErr) to point to an English language
** error message. If the table is a rowid table and no error occurs,
** return SQLITE_OK and leave (*pzErr) unmodified.
*/
static int unionIsIntkeyTable(
  sqlite3 *db,                    /* Database handle */
  UnionSrc *pSrc,                 /* Source table to test */
  char **pzErr                    /* OUT: Error message */
){
  int bPk = 0;
  const char *zType = 0;
  int rc;

  sqlite3_table_column_metadata(
      db, pSrc->zDb, pSrc->zTab, "_rowid_", &zType, 0, 0, &bPk, 0
  );
  rc = sqlite3_errcode(db);
  if( rc==SQLITE_ERROR 
   || (rc==SQLITE_OK && (!bPk || sqlite3_stricmp("integer", zType)))
  ){
    rc = SQLITE_ERROR;
    *pzErr = sqlite3_mprintf("no such rowid table: %s%s%s",
        (pSrc->zDb ? pSrc->zDb : ""),
        (pSrc->zDb ? "." : ""),
        pSrc->zTab
    );
  }
  return rc;
}

/*
** This function is a no-op if *pRc is other than SQLITE_OK when it is
** called. In this case it returns NULL.
**
** Otherwise, this function checks that the source table passed as the
** second argument (a) exists, (b) is not a view and (c) has a column 
** named "_rowid_" of type "integer" that is the primary key.
** If this is not the case, *pRc is set to SQLITE_ERROR and NULL is
** returned.
**
** Finally, if the source table passes the checks above, a nul-terminated
** string describing the column names and types belonging to the source
** table is returned. Tables with the same set of column names and types 
** cause this function to return identical strings. Is is the responsibility
** of the caller to free the returned string using sqlite3_free() when
** it is no longer required.
*/
static char *unionSourceToStr(
  int *pRc,                       /* IN/OUT: Error code */
  UnionTab *pTab,                 /* Virtual table object */
  UnionSrc *pSrc,                 /* Source table to test */

  char **pzErr                    /* OUT: Error message */
){
  char *zRet = 0;
  if( *pRc==SQLITE_OK ){
    sqlite3 *db = unionGetDb(pTab, pSrc);

    int rc = unionIsIntkeyTable(db, pSrc, pzErr);
    sqlite3_stmt *pStmt = unionPrepare(&rc, db, 
        "SELECT group_concat(quote(name) || '.' || quote(type)) "
        "FROM pragma_table_info(?, ?)", pzErr

    );












    if( rc==SQLITE_OK ){
      sqlite3_bind_text(pStmt, 1, pSrc->zTab, -1, SQLITE_STATIC);
      sqlite3_bind_text(pStmt, 2, pSrc->zDb, -1, SQLITE_STATIC);
      if( SQLITE_ROW==sqlite3_step(pStmt) ){
        const char *z = (const char*)sqlite3_column_text(pStmt, 0);
        zRet = unionStrdup(&rc, z);
      }
      unionFinalize(&rc, pStmt, pzErr);
    }

    *pRc = rc;
  }

  return zRet;
}

/*
** Check that all configured source tables exist and have the same column
** names and datatypes. If this is not the case, or if some other error
** occurs, return an SQLite error code. In this case *pzErr may be set
** to point to an error message buffer allocated by sqlite3_mprintf().
** Or, if no problems regarding the source tables are detected and no
** other error occurs, SQLITE_OK is returned.
*/
static int unionSourceCheck(UnionTab *pTab, char **pzErr){
  int rc = SQLITE_OK;
  char *z0 = 0;
  int i;

  assert( *pzErr==0 );
  z0 = unionSourceToStr(&rc, pTab, &pTab->aSrc[0], pzErr);
  for(i=1; i<pTab->nSrc; i++){
    char *z = unionSourceToStr(&rc, pTab, &pTab->aSrc[i], pzErr);
    if( rc==SQLITE_OK && sqlite3_stricmp(z, z0) ){
      *pzErr = sqlite3_mprintf("source table schema mismatch");
      rc = SQLITE_ERROR;
    }
    sqlite3_free(z);
  }
  sqlite3_free(z0);

  return rc;
}


/*
** Try to open the swarmvtab database.  If initially unable, invoke the
** not-found callback UDF and then try again.
*/
static int unionOpenDatabaseInner(UnionTab *pTab, UnionSrc *pSrc, char **pzErr){
  int rc = SQLITE_OK;
  static const int openFlags = 
       SQLITE_OPEN_READONLY | SQLITE_OPEN_URI;
  rc = sqlite3_open_v2(pSrc->zFile, &pSrc->db, openFlags, 0);
  if( rc==SQLITE_OK ) return rc;
  if( pTab->zNotFoundCallback ){
    char *zSql = sqlite3_mprintf("SELECT \"%w\"(%Q);",
                    pTab->zNotFoundCallback, pSrc->zFile);
    if( zSql==0 ){
      *pzErr = sqlite3_mprintf("out of memory");
      return SQLITE_NOMEM;
    }
    rc = sqlite3_exec(pTab->db, zSql, 0, 0, pzErr);
    sqlite3_free(zSql);
    if( rc ) return rc;
    rc = sqlite3_open_v2(pSrc->zFile, &pSrc->db, openFlags, 0);
  }
  if( rc!=SQLITE_OK ){
    *pzErr = sqlite3_mprintf("%s", sqlite3_errmsg(pSrc->db));
  }
  return rc;
}

/*
** This function may only be called for swarmvtab tables. The results of
** calling it on a unionvtab table are undefined.
**
** For a swarmvtab table, this function ensures that source database iSrc
** is open. If the database is opened successfully and the schema is as
** expected, or if it is already open when this function is called, SQLITE_OK
** is returned.
**
** Alternatively If an error occurs while opening the databases, or if the
** database schema is unsuitable, an SQLite error code is returned and (*pzErr)
** may be set to point to an English language error message. In this case it is
** the responsibility of the caller to eventually free the error message buffer
** using sqlite3_free(). 
*/
static int unionOpenDatabase(UnionTab *pTab, int iSrc, char **pzErr){
  int rc = SQLITE_OK;
  UnionSrc *pSrc = &pTab->aSrc[iSrc];

  assert( pTab->bSwarm && iSrc<pTab->nSrc );
  if( pSrc->db==0 ){
    unionCloseSources(pTab, pTab->nMaxOpen-1);
    rc = unionOpenDatabaseInner(pTab, pSrc, pzErr);
    if( rc==SQLITE_OK ){
      char *z = unionSourceToStr(&rc, pTab, pSrc, pzErr);
      if( rc==SQLITE_OK ){
        if( pTab->zSourceStr==0 ){
          pTab->zSourceStr = z;
        }else{
          if( sqlite3_stricmp(z, pTab->zSourceStr) ){
            *pzErr = sqlite3_mprintf("source table schema mismatch");
            rc = SQLITE_ERROR;

          }
          sqlite3_free(z);
        }
      }
    }

    if( rc==SQLITE_OK ){
      pSrc->pNextClosable = pTab->pClosable;
      pTab->pClosable = pSrc;
      pTab->nOpen++;
    }else{
      sqlite3_close(pSrc->db);
      pSrc->db = 0;
    }
  }

  return rc;
}


/*
** This function is a no-op for unionvtab tables. For swarmvtab, increment 
** the reference count for source table iTab. If the reference count was
** zero before it was incremented, also remove the source from the closable
** list.
*/
static void unionIncrRefcount(UnionTab *pTab, int iTab){
  if( pTab->bSwarm ){
    UnionSrc *pSrc = &pTab->aSrc[iTab];
    assert( pSrc->nUser>=0 && pSrc->db );
    if( pSrc->nUser==0 ){
      UnionSrc **pp;
      for(pp=&pTab->pClosable; *pp!=pSrc; pp=&(*pp)->pNextClosable);
      *pp = pSrc->pNextClosable;
      pSrc->pNextClosable = 0;
    }

    pSrc->nUser++;
  }
}

/*
** Finalize the SQL statement pCsr->pStmt and return the result.
**
** If this is a swarmvtab table (not unionvtab) and pCsr->pStmt was not
** NULL when this function was called, also decrement the reference
** count on the associated source table. If this means the source tables
** refcount is now zero, add it to the closable list.
*/
static int unionFinalizeCsrStmt(UnionCsr *pCsr){
  int rc = SQLITE_OK;
  if( pCsr->pStmt ){
    UnionTab *pTab = (UnionTab*)pCsr->base.pVtab;
    UnionSrc *pSrc = &pTab->aSrc[pCsr->iTab];
    rc = sqlite3_finalize(pCsr->pStmt);
    pCsr->pStmt = 0;
    if( pTab->bSwarm ){
      pSrc->nUser--;
      assert( pSrc->nUser>=0 );
      if( pSrc->nUser==0 ){
        pSrc->pNextClosable = pTab->pClosable;
        pTab->pClosable = pSrc;
      }
      unionCloseSources(pTab, pTab->nMaxOpen);
    }
  }
  return rc;
}

/* 
** xConnect/xCreate method.
**
** The argv[] array contains the following:
**
**   argv[0]   -> module name  ("unionvtab" or "swarmvtab")
**   argv[1]   -> database name
**   argv[2]   -> table name
**   argv[3]   -> SQL statement
**   argv[4]   -> not-found callback UDF name
*/
static int unionConnect(
  sqlite3 *db,
  void *pAux,
  int argc, const char *const*argv,
  sqlite3_vtab **ppVtab,
  char **pzErr
){
  UnionTab *pTab = 0;
  int rc = SQLITE_OK;
  int bSwarm = (pAux==0 ? 0 : 1);
  const char *zVtab = (bSwarm ? "swarmvtab" : "unionvtab");


  if( sqlite3_stricmp("temp", argv[1]) ){
    /* unionvtab tables may only be created in the temp schema */
    *pzErr = sqlite3_mprintf("%s tables must be created in TEMP schema", zVtab);
    rc = SQLITE_ERROR;
  }else if( argc!=4 && argc!=5 ){
    *pzErr = sqlite3_mprintf("wrong number of arguments for %s", zVtab);
    rc = SQLITE_ERROR;
  }else{
    int nAlloc = 0;               /* Allocated size of pTab->aSrc[] */
    sqlite3_stmt *pStmt = 0;      /* Argument statement */
    char *zArg = unionStrdup(&rc, argv[3]);      /* Copy of argument to CVT */

    /* Prepare the SQL statement. Instead of executing it directly, sort

      /* Check for problems with the specified range of rowids */
      if( iMax<iMin || (pTab->nSrc>0 && iMin<=pTab->aSrc[pTab->nSrc-1].iMax) ){
        *pzErr = sqlite3_mprintf("rowid range mismatch error");
        rc = SQLITE_ERROR;
      }

      if( rc==SQLITE_OK ){
        pSrc = &pTab->aSrc[pTab->nSrc++];

        pSrc->zTab = unionStrdup(&rc, zTab);
        pSrc->iMin = iMin;
        pSrc->iMax = iMax;
        if( bSwarm ){
          pSrc->zFile = unionStrdup(&rc, zDb);
        }else{
          pSrc->zDb = unionStrdup(&rc, zDb);
        }
      }
    }
    unionFinalize(&rc, pStmt, pzErr);
    pStmt = 0;

    /* Capture the not-found callback UDF name */
    if( argc>=5 ){
      pTab->zNotFoundCallback = unionStrdup(&rc, argv[4]);
      unionDequote(pTab->zNotFoundCallback);
    }

    /* It is an error if the SELECT statement returned zero rows. If only
    ** because there is no way to determine the schema of the virtual 
    ** table in this case.  */
    if( rc==SQLITE_OK && pTab->nSrc==0 ){
      *pzErr = sqlite3_mprintf("no source tables configured");
      rc = SQLITE_ERROR;
    }

    /* For unionvtab, verify that all source tables exist and have 
    ** compatible schemas. For swarmvtab, attach the first database and
    ** check that the first table is a rowid table only.  */
    if( rc==SQLITE_OK ){
      pTab->db = db;
      pTab->bSwarm = bSwarm;
      pTab->nMaxOpen = SWARMVTAB_MAX_OPEN;
      if( bSwarm ){
        rc = unionOpenDatabase(pTab, 0, pzErr);
      }else{
        rc = unionSourceCheck(pTab, pzErr);
      }
    }

    /* Compose a CREATE TABLE statement and pass it to declare_vtab() */
    if( rc==SQLITE_OK ){
      UnionSrc *pSrc = &pTab->aSrc[0];
      sqlite3 *tdb = unionGetDb(pTab, pSrc);
      pStmt = unionPreparePrintf(&rc, pzErr, tdb, "SELECT "
          "'CREATE TABLE xyz('"
          "    || group_concat(quote(name) || ' ' || type, ', ')"
          "    || ')',"
          "max((cid+1) * (type='INTEGER' COLLATE nocase AND pk=1))-1 "
          "FROM pragma_table_info(%Q, ?)", 
          pSrc->zTab, pSrc->zDb
      );
    }
    if( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
      const char *zDecl = (const char*)sqlite3_column_text(pStmt, 0);
      rc = sqlite3_declare_vtab(db, zDecl);
      pTab->iPK = sqlite3_column_int(pStmt, 1);
    }

    unionFinalize(&rc, pStmt, pzErr);
  }

  if( rc!=SQLITE_OK ){
    unionDisconnect((sqlite3_vtab*)pTab);
    pTab = 0;
  }

  *ppVtab = (sqlite3_vtab*)pTab;
  return rc;
}


/*
** xOpen
*/
static int unionOpen(sqlite3_vtab *p, sqlite3_vtab_cursor **ppCursor){
  UnionCsr *pCsr;
  int rc = SQLITE_OK;
  (void)p;  /* Suppress harmless warning */
  pCsr = (UnionCsr*)unionMalloc(&rc, sizeof(UnionCsr));
  *ppCursor = &pCsr->base;
  return rc;
}

/*
** xClose
*/
static int unionClose(sqlite3_vtab_cursor *cur){
  UnionCsr *pCsr = (UnionCsr*)cur;
  unionFinalizeCsrStmt(pCsr);
  sqlite3_free(pCsr);
  return SQLITE_OK;
}

/*
** This function does the work of the xNext() method. Except that, if it
** returns SQLITE_ROW, it should be called again within the same xNext()
** method call. See unionNext() for details.
*/
static int doUnionNext(UnionCsr *pCsr){
  int rc = SQLITE_OK;
  assert( pCsr->pStmt );
  if( sqlite3_step(pCsr->pStmt)!=SQLITE_ROW ){
    UnionTab *pTab = (UnionTab*)pCsr->base.pVtab;
    rc = unionFinalizeCsrStmt(pCsr);
    if( rc==SQLITE_OK && pTab->bSwarm ){
      pCsr->iTab++;
      if( pCsr->iTab<pTab->nSrc ){
        UnionSrc *pSrc = &pTab->aSrc[pCsr->iTab];
        if( pCsr->iMaxRowid>=pSrc->iMin ){
          /* It is necessary to scan the next table. */
          rc = unionOpenDatabase(pTab, pCsr->iTab, &pTab->base.zErrMsg);
          pCsr->pStmt = unionPreparePrintf(&rc, &pTab->base.zErrMsg, pSrc->db,
              "SELECT rowid, * FROM %Q %s %lld",
              pSrc->zTab,
              (pSrc->iMax>pCsr->iMaxRowid ? "WHERE _rowid_ <=" : "-- "),
              pCsr->iMaxRowid
          );
          if( rc==SQLITE_OK ){
            assert( pCsr->pStmt );
            unionIncrRefcount(pTab, pCsr->iTab);
            rc = SQLITE_ROW;
          }
        }
      }
    }
  }

  return rc;
}

/*
** xNext
*/
static int unionNext(sqlite3_vtab_cursor *cur){

  int rc;


  do {
    rc = doUnionNext((UnionCsr*)cur);


  }while( rc==SQLITE_ROW );

  return rc;
}

/*
** xColumn
*/
static int unionColumn(

        }else{
          iMin++;
        }
      }
    }
  }


  unionFinalizeCsrStmt(pCsr);
  if( bZero ){
    return SQLITE_OK;
  }

  for(i=0; i<pTab->nSrc; i++){
    UnionSrc *pSrc = &pTab->aSrc[i];
    if( iMin>pSrc->iMax || iMax<pSrc->iMin ){

        zSql = sqlite3_mprintf("%z WHERE rowid>=%lld", zSql, iMin);
        zWhere = "AND";
      }
      if( iMax!=LARGEST_INT64 && iMax<pSrc->iMax ){
        zSql = sqlite3_mprintf("%z %s rowid<=%lld", zSql, zWhere, iMax);
      }
    }

    if( pTab->bSwarm ){
      pCsr->iTab = i;
      pCsr->iMaxRowid = iMax;
      rc = unionOpenDatabase(pTab, i, &pTab->base.zErrMsg);
      break;
    }
  }

  if( zSql==0 ){
    return rc;
  }else{
    sqlite3 *db = unionGetDb(pTab, &pTab->aSrc[pCsr->iTab]);
    pCsr->pStmt = unionPrepare(&rc, db, zSql, &pTab->base.zErrMsg);
    if( pCsr->pStmt ){
      unionIncrRefcount(pTab, pCsr->iTab);
    }
    sqlite3_free(zSql);
  }
  if( rc!=SQLITE_OK ) return rc;
  return unionNext(pVtabCursor);
}

/*
** xBestIndex.
**

    0,                            /* xRollback */
    0,                            /* xFindMethod */
    0,                            /* xRename */
    0,                            /* xSavepoint */
    0,                            /* xRelease */
    0                             /* xRollbackTo */
  };
  int rc;

  rc = sqlite3_create_module(db, "unionvtab", &unionModule, 0);
  if( rc==SQLITE_OK ){
    rc = sqlite3_create_module(db, "swarmvtab", &unionModule, (void*)db);
  }
  return rc;
}

#endif /* SQLITE_OMIT_VIRTUALTABLE */

#ifdef _WIN32
__declspec(dllexport)
#endif

# 2017-07-15
#
# 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.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this file is the "swarmvtab" extension
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix swarmvtab

ifcapable !vtab {
  finish_test
  return
}

load_static_extension db unionvtab

set nFile $sqlite_open_file_count

do_execsql_test 1.0 {
  CREATE TABLE t0(a INTEGER PRIMARY KEY, b TEXT);
  WITH s(i) AS ( SELECT 1 UNION ALL SELECT i+1 FROM s WHERE i<400) 
  INSERT INTO t0 SELECT i, hex(randomblob(50)) FROM s;

  CREATE TABLE dir(f, t, imin, imax);
}

do_test 1.1 {
  for {set i 0} {$i < 40} {incr i} {
    set iMin [expr $i*10 + 1]
    set iMax [expr $iMin+9]

    forcedelete "test.db$i"
    execsql [subst {
      ATTACH 'test.db$i' AS aux;
      CREATE TABLE aux.t$i (a INTEGER PRIMARY KEY, b TEXT);
      INSERT INTO aux.t$i SELECT * FROM t0 WHERE a BETWEEN $iMin AND $iMax;
      DETACH aux;
      INSERT INTO dir VALUES('test.db$i', 't$i', $iMin, $iMax);
    }]
  }

  execsql {
    CREATE VIRTUAL TABLE temp.s1 USING swarmvtab('SELECT * FROM dir');
  }
} {}

do_execsql_test 1.2 { 
  DROP TABLE s1; 
} {}

do_execsql_test 1.3 {
  CREATE VIRTUAL TABLE temp.s1 USING swarmvtab('SELECT * FROM dir');
  SELECT count(*) FROM s1 WHERE rowid<50;
} {49}

proc do_compare_test {tn where} {
  set sql [subst {
    SELECT (SELECT group_concat(a || ',' || b, ',') FROM t0 WHERE $where) 
           IS 
           (SELECT group_concat(a || ',' || b, ',') FROM s1 WHERE $where)
  }]

  uplevel [list do_execsql_test $tn $sql 1]
}

do_compare_test 1.4.1 "rowid = 700"
do_compare_test 1.4.2 "rowid = -1"
do_compare_test 1.4.3 "rowid = 0"
do_compare_test 1.4.4 "rowid = 55"
do_compare_test 1.4.5 "rowid BETWEEN 20 AND 100"
do_compare_test 1.4.6 "rowid > 350"
do_compare_test 1.4.7 "rowid >= 350"
do_compare_test 1.4.8 "rowid >= 200"
do_compare_test 1.4.9 "1"

# Multiple simultaneous cursors.
#
do_execsql_test 1.5.1.(5-seconds-or-so) {
  SELECT count(*) FROM s1 a, s1 b WHERE b.rowid<=200;
} {80000}
do_execsql_test 1.5.2 {
  SELECT count(*) FROM s1 a, s1 b, s1 c 
  WHERE a.rowid=b.rowid AND b.rowid=c.rowid;
} {400}

# Empty source tables.
#
do_test 1.6.0 {
  for {set i 0} {$i < 20} {incr i} {
    sqlite3 db2 test.db$i
    db2 eval " DELETE FROM t$i "
    db2 close
  }
  db eval { DELETE FROM t0 WHERE rowid<=200 }
} {}

do_compare_test 1.6.1 "rowid = 700"
do_compare_test 1.6.2 "rowid = -1"
do_compare_test 1.6.3 "rowid = 0"
do_compare_test 1.6.4 "rowid = 55"
do_compare_test 1.6.5 "rowid BETWEEN 20 AND 100"
do_compare_test 1.6.6 "rowid > 350"
do_compare_test 1.6.7 "rowid >= 350"
do_compare_test 1.6.8 "rowid >= 200"
do_compare_test 1.6.9 "1"
do_compare_test 1.6.10 "rowid >= 5"

do_test 1.x {
  set sqlite_open_file_count
} [expr $nFile+9]

do_test 1.y { db close } {}

# Delete all the database files created above.
#
for {set i 0} {$i < 40} {incr i} { forcedelete "test.db$i" }

#-------------------------------------------------------------------------
# Test some error conditions:
#
#   2.1: Database file does not exist.
#   2.2: Table does not exist.
#   2.3: Table schema does not match.
#
reset_db
load_static_extension db unionvtab
do_test 2.0.1 {
  db eval {
    CREATE TABLE t0(a INTEGER PRIMARY KEY, b TEXT);
    WITH s(i) AS ( SELECT 1 UNION ALL SELECT i+1 FROM s WHERE i<400) 
      INSERT INTO t0 SELECT i, hex(randomblob(50)) FROM s;
    CREATE TABLE dir(f, t, imin, imax);
  }

  for {set i 0} {$i < 40} {incr i} {
    set iMin [expr $i*10 + 1]
    set iMax [expr $iMin+9]

    forcedelete "test.db$i"
    db eval [subst {
      ATTACH 'test.db$i' AS aux;
      CREATE TABLE aux.t$i (a INTEGER PRIMARY KEY, b TEXT);
      INSERT INTO aux.t$i SELECT * FROM t0 WHERE a BETWEEN $iMin AND $iMax;
      DETACH aux;
      INSERT INTO dir VALUES('test.db$i', 't$i', $iMin, $iMax);
    }]
  }
  execsql {
    CREATE VIRTUAL TABLE temp.s1 USING swarmvtab('SELECT * FROM dir');
  }
} {}

do_test 2.0.2 {
  forcedelete test.db5

  sqlite3 db2 test.db15
  db2 eval { DROP TABLE t15 }
  db2 close

  sqlite3 db2 test.db25
  db2 eval { 
    DROP TABLE t25;
    CREATE TABLE t25(x, y, z PRIMARY KEY);
  }
  db2 close
} {}

do_catchsql_test 2.1 {
  SELECT * FROM s1 WHERE rowid BETWEEN 1 AND 100;
} {1 {unable to open database file}}
do_catchsql_test 2.2 {
  SELECT * FROM s1 WHERE rowid BETWEEN 101 AND 200;
} {1 {no such rowid table: t15}}
do_catchsql_test 2.3 {
  SELECT * FROM s1 WHERE rowid BETWEEN 201 AND 300;
} {1 {source table schema mismatch}}

finish_test

# 2017-07-15
#
# 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.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this file is the "swarmvtab" extension
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix swarmvtab

ifcapable !vtab {
  finish_test
  return
}


db close
foreach name [glob -nocomplain test*.db] {
  forcedelete $name
}
sqlite3 db test.db
load_static_extension db unionvtab
proc create_database {filename} {
  sqlite3 dbx $filename
  set num [regsub -all {[^0-9]+} $filename {}]
  set num [string trimleft $num 0]
  set start [expr {$num*1000}]
  set end [expr {$start+999}]
  dbx eval {
    CREATE TABLE t2(a INTEGER PRIMARY KEY,b);
    WITH RECURSIVE c(x) AS (
      VALUES($start) UNION ALL SELECT x+1 FROM c WHERE x<$end
    )
    INSERT INTO t2(a,b) SELECT x, printf('**%05d**',x) FROM c;
  }
  dbx close
}
db func create_database create_database
do_execsql_test 100 {
  CREATE TABLE t1(filename, tablename, istart, iend);
  WITH RECURSIVE c(x) AS (VALUES(1) UNION ALL SELECT x+1 FROM c WHERE x<99)
  INSERT INTO t1 SELECT printf('test%03d.db',x),'t2',x*1000,x*1000+999 FROM c;
  CREATE VIRTUAL TABLE temp.v1 USING swarmvtab(
    'SELECT * FROM t1', 'create_database'
  );
} {}
do_execsql_test 110 {
  SELECT b FROM v1 WHERE a=3875;
} {**03875**}
do_test 120 {
  lsort [glob -nocomplain test?*.db]
} {test001.db test003.db}
do_execsql_test 130 {
  SELECT b FROM v1 WHERE a BETWEEN 3999 AND 4000 ORDER BY a;
} {**03999** **04000**}
do_test 140 {
  lsort [glob -nocomplain test?*.db]
} {test001.db test003.db test004.db}
do_execsql_test 150 {
  SELECT b FROM v1 WHERE a>=99998;
} {**99998** **99999**}
do_test 160 {
  lsort -dictionary [glob -nocomplain test?*.db]
} {test001.db test003.db test004.db test099.db}

finish_test

}
do_faultsim_test 1.2 -faults oom* -prep {
} -body {
  execsql { SELECT * FROM uuu }
} -test {
  faultsim_test_result {0 {1 one 2 two 3 three 10 ten 11 eleven 12 twelve 20 twenty 21 twenty-one 22 twenty-two}} 
}

#-------------------------------------------------------------------------
# Error while registering the two vtab modules.
do_faultsim_test 2.0 -faults * -prep {
  catch { db close }
  sqlite3 db :memory:
} -body {
  load_static_extension db unionvtab
} -test {
  faultsim_test_result {0 {}} {1 {initialization of unionvtab failed: }}
}



finish_test