/*

 ** 2008 August 16

 **

 ** 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 routines used for walking the parser tree for

 ** an SQL statement.

 **

 ** $Id: walker.c,v 1.1 2008/08/20 16:35:10 drh Exp $

 */

 #include "sqliteInt.h"

 #include <stdlib.h>

 #include <string.h>

 /*

 ** Walk an expression tree.  Invoke the callback once for each node

 ** of the expression, while decending.  (In other words, the callback

 ** is invoked before visiting children.)

 **

 ** The return value from the callback should be one of the WRC_*

 ** constants to specify how to proceed with the walk.

 **

 **    WRC_Continue      Continue descending down the tree.

 **

 **    WRC_Prune         Do not descend into child nodes.  But allow

 **                      the walk to continue with sibling nodes.

 **

 **    WRC_Abort         Do no more callbacks.  Unwind the stack and

 **                      return the top-level walk call.

 **

 ** The return value from this routine is WRC_Abort to abandon the tree walk

 ** and WRC_Continue to continue.

 */

 int sqlite3WalkExpr(Walker *pWalker, Expr *pExpr){

   int rc;

   if( pExpr==0 ) return WRC_Continue;

   rc = pWalker->xExprCallback(pWalker, pExpr);

   if( rc==WRC_Continue ){

     if( sqlite3WalkExpr(pWalker, pExpr->pLeft) ) return WRC_Abort;

     if( sqlite3WalkExpr(pWalker, pExpr->pRight) ) return WRC_Abort;

     if( sqlite3WalkExprList(pWalker, pExpr->pList) ) return WRC_Abort;

     if( sqlite3WalkSelect(pWalker, pExpr->pSelect) ){

       return WRC_Abort;

     }

   }

   return rc & WRC_Abort;

 }

 /*

 ** Call sqlite3WalkExpr() for every expression in list p or until

 ** an abort request is seen.

 */

 int sqlite3WalkExprList(Walker *pWalker, ExprList *p){

   int i, rc = WRC_Continue;

   struct ExprList_item *pItem;

   if( p ){

     for(i=p->nExpr, pItem=p->a; i>0; i--, pItem++){

       if( sqlite3WalkExpr(pWalker, pItem->pExpr) ) return WRC_Abort;

     }

   }

   return rc & WRC_Continue;

 }

 /*

 ** Walk all expressions associated with SELECT statement p.  Do

 ** not invoke the SELECT callback on p, but do (of course) invoke

 ** any expr callbacks and SELECT callbacks that come from subqueries.

 ** Return WRC_Abort or WRC_Continue.

 */

 int sqlite3WalkSelectExpr(Walker *pWalker, Select *p){

   if( sqlite3WalkExprList(pWalker, p->pEList) ) return WRC_Abort;

   if( sqlite3WalkExpr(pWalker, p->pWhere) ) return WRC_Abort;

   if( sqlite3WalkExprList(pWalker, p->pGroupBy) ) return WRC_Abort;

   if( sqlite3WalkExpr(pWalker, p->pHaving) ) return WRC_Abort;

   if( sqlite3WalkExprList(pWalker, p->pOrderBy) ) return WRC_Abort;

   if( sqlite3WalkExpr(pWalker, p->pLimit) ) return WRC_Abort;

   if( sqlite3WalkExpr(pWalker, p->pOffset) ) return WRC_Abort;

   return WRC_Continue;

 }

 /*

 ** Walk the parse trees associated with all subqueries in the

 ** FROM clause of SELECT statement p.  Do not invoke the select

 ** callback on p, but do invoke it on each FROM clause subquery

 ** and on any subqueries further down in the tree.  Return 

 ** WRC_Abort or WRC_Continue;

 */

 int sqlite3WalkSelectFrom(Walker *pWalker, Select *p){

   SrcList *pSrc;

   int i;

   struct SrcList_item *pItem;

   pSrc = p->pSrc;

   if( pSrc ){

     for(i=pSrc->nSrc, pItem=pSrc->a; i>0; i--, pItem++){

       if( sqlite3WalkSelect(pWalker, pItem->pSelect) ){

         return WRC_Abort;

       }

     }

   }

   return WRC_Continue;

 } 

 /*

 ** Call sqlite3WalkExpr() for every expression in Select statement p.

 ** Invoke sqlite3WalkSelect() for subqueries in the FROM clause and

 ** on the compound select chain, p->pPrior.

 **

 ** Return WRC_Continue under normal conditions.  Return WRC_Abort if

 ** there is an abort request.

 **

 ** If the Walker does not have an xSelectCallback() then this routine

 ** is a no-op returning WRC_Continue.

 */

 int sqlite3WalkSelect(Walker *pWalker, Select *p){

   int rc;

   if( p==0 || pWalker->xSelectCallback==0 ) return WRC_Continue;

   rc = WRC_Continue;

   while( p  ){

     rc = pWalker->xSelectCallback(pWalker, p);

     if( rc ) break;

     if( sqlite3WalkSelectExpr(pWalker, p) ) return WRC_Abort;

     if( sqlite3WalkSelectFrom(pWalker, p) ) return WRC_Abort;

     p = p->pPrior;

   }

   return rc & WRC_Abort;

 }