/*

 ** 2001 September 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 C code routines that are called by the parser

 ** in order to generate code for DELETE FROM statements.

 **

 ** $Id$

 */

 #include "sqliteInt.h"

 /*

 ** Look up every table that is named in pSrc.  If any table is not found,

 ** add an error message to pParse->zErrMsg and return NULL.  If all tables

 ** are found, return a pointer to the last table.

 */

 Table *sqlite3SrcListLookup(Parse *pParse, SrcList *pSrc){

   Table *pTab = 0;

   int i;

   struct SrcList_item *pItem;

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

     pTab = sqlite3LocateTable(pParse, pItem->zName, pItem->zDatabase);

     sqlite3DeleteTable(pItem->pTab);

     pItem->pTab = pTab;

     if( pTab ){

       pTab->nRef++;

     }

   }

   return pTab;

 }

 /*

 ** Check to make sure the given table is writable.  If it is not

 ** writable, generate an error message and return 1.  If it is

 ** writable return 0;

 */

 int sqlite3IsReadOnly(Parse *pParse, Table *pTab, int viewOk){

   if( (pTab->readOnly && (pParse->db->flags & SQLITE_WriteSchema)==0

         && pParse->nested==0) 

 #ifndef SQLITE_OMIT_VIRTUALTABLE

       || (pTab->pMod && pTab->pMod->pModule->xUpdate==0)

 #endif

   ){

     sqlite3ErrorMsg(pParse, "table %s may not be modified", pTab->zName);

     return 1;

   }

 #ifndef SQLITE_OMIT_VIEW

   if( !viewOk && pTab->pSelect ){

     sqlite3ErrorMsg(pParse,"cannot modify %s because it is a view",pTab->zName);

     return 1;

   }

 #endif

   return 0;

 }

 /*

 ** Generate code that will open a table for reading.

 */

 void sqlite3OpenTable(

   Parse *p,       /* Generate code into this VDBE */

   int iCur,       /* The cursor number of the table */

   int iDb,        /* The database index in sqlite3.aDb[] */

   Table *pTab,    /* The table to be opened */

   int opcode      /* OP_OpenRead or OP_OpenWrite */

 ){

   Vdbe *v;

   if( IsVirtual(pTab) ) return;

   v = sqlite3GetVdbe(p);

   assert( opcode==OP_OpenWrite || opcode==OP_OpenRead );

   sqlite3TableLock(p, iDb, pTab->tnum, (opcode==OP_OpenWrite), pTab->zName);

   sqlite3VdbeAddOp(v, OP_Integer, iDb, 0);

   VdbeComment((v, "# %s", pTab->zName));

   sqlite3VdbeAddOp(v, opcode, iCur, pTab->tnum);

   sqlite3VdbeAddOp(v, OP_SetNumColumns, iCur, pTab->nCol);

 }

 /*

 ** Generate code for a DELETE FROM statement.

 **

 **     DELETE FROM table_wxyz WHERE a<5 AND b NOT NULL;

 **                 \________/       \________________/

 **                  pTabList              pWhere

 */

 void sqlite3DeleteFrom(

   Parse *pParse,         /* The parser context */

   SrcList *pTabList,     /* The table from which we should delete things */

   Expr *pWhere           /* The WHERE clause.  May be null */

 ){

   Vdbe *v;               /* The virtual database engine */

   Table *pTab;           /* The table from which records will be deleted */

   const char *zDb;       /* Name of database holding pTab */

   int end, addr = 0;     /* A couple addresses of generated code */

   int i;                 /* Loop counter */

   WhereInfo *pWInfo;     /* Information about the WHERE clause */

   Index *pIdx;           /* For looping over indices of the table */

   int iCur;              /* VDBE Cursor number for pTab */

   sqlite3 *db;           /* Main database structure */

   AuthContext sContext;  /* Authorization context */

   int oldIdx = -1;       /* Cursor for the OLD table of AFTER triggers */

   NameContext sNC;       /* Name context to resolve expressions in */

   int iDb;               /* Database number */

   int memCnt = 0;        /* Memory cell used for change counting */

 #ifndef SQLITE_OMIT_TRIGGER

   int isView;                  /* True if attempting to delete from a view */

   int triggers_exist = 0;      /* True if any triggers exist */

 #endif

   sContext.pParse = 0;

   db = pParse->db;

   if( pParse->nErr || db->mallocFailed ){

     goto delete_from_cleanup;

   }

   assert( pTabList->nSrc==1 );

   /* Locate the table which we want to delete.  This table has to be

   ** put in an SrcList structure because some of the subroutines we

   ** will be calling are designed to work with multiple tables and expect

   ** an SrcList* parameter instead of just a Table* parameter.

   */

   pTab = sqlite3SrcListLookup(pParse, pTabList);

   if( pTab==0 )  goto delete_from_cleanup;

   /* Figure out if we have any triggers and if the table being

   ** deleted from is a view

   */

 #ifndef SQLITE_OMIT_TRIGGER

   triggers_exist = sqlite3TriggersExist(pParse, pTab, TK_DELETE, 0);

   isView = pTab->pSelect!=0;

 #else

 # define triggers_exist 0

 # define isView 0

 #endif

 #ifdef SQLITE_OMIT_VIEW

 # undef isView

 # define isView 0

 #endif

   if( sqlite3IsReadOnly(pParse, pTab, triggers_exist) ){

     goto delete_from_cleanup;

   }

   iDb = sqlite3SchemaToIndex(db, pTab->pSchema);

   assert( iDb<db->nDb );

   zDb = db->aDb[iDb].zName;

   if( sqlite3AuthCheck(pParse, SQLITE_DELETE, pTab->zName, 0, zDb) ){

     goto delete_from_cleanup;

   }

   /* If pTab is really a view, make sure it has been initialized.

   */

   if( sqlite3ViewGetColumnNames(pParse, pTab) ){

     goto delete_from_cleanup;

   }

   /* Allocate a cursor used to store the old.* data for a trigger.

   */

   if( triggers_exist ){ 

     oldIdx = pParse->nTab++;

   }

   /* Resolve the column names in the WHERE clause.

   */

   assert( pTabList->nSrc==1 );

   iCur = pTabList->a[0].iCursor = pParse->nTab++;

   memset(&sNC, 0, sizeof(sNC));

   sNC.pParse = pParse;

   sNC.pSrcList = pTabList;

   if( sqlite3ExprResolveNames(&sNC, pWhere) ){

     goto delete_from_cleanup;

   }

   /* Start the view context

   */

   if( isView ){

     sqlite3AuthContextPush(pParse, &sContext, pTab->zName);

   }

   /* Begin generating code.

   */

   v = sqlite3GetVdbe(pParse);

   if( v==0 ){

     goto delete_from_cleanup;

   }

   if( pParse->nested==0 ) sqlite3VdbeCountChanges(v);

   sqlite3BeginWriteOperation(pParse, triggers_exist, iDb);

   /* If we are trying to delete from a view, realize that view into

   ** a ephemeral table.

   */

   if( isView ){

     Select *pView = sqlite3SelectDup(db, pTab->pSelect);

     sqlite3Select(pParse, pView, SRT_EphemTab, iCur, 0, 0, 0, 0);

     sqlite3SelectDelete(pView);

   }

   /* Initialize the counter of the number of rows deleted, if

   ** we are counting rows.

   */

   if( db->flags & SQLITE_CountRows ){

     memCnt = pParse->nMem++;

     sqlite3VdbeAddOp(v, OP_MemInt, 0, memCnt);

   }

   /* Special case: A DELETE without a WHERE clause deletes everything.

   ** It is easier just to erase the whole table.  Note, however, that

   ** this means that the row change count will be incorrect.

   */

   if( pWhere==0 && !triggers_exist && !IsVirtual(pTab) ){

     if( db->flags & SQLITE_CountRows ){

       /* If counting rows deleted, just count the total number of

       ** entries in the table. */

       int endOfLoop = sqlite3VdbeMakeLabel(v);

       int addr2;

       if( !isView ){

         sqlite3OpenTable(pParse, iCur, iDb, pTab, OP_OpenRead);

       }

       sqlite3VdbeAddOp(v, OP_Rewind, iCur, sqlite3VdbeCurrentAddr(v)+2);

       addr2 = sqlite3VdbeAddOp(v, OP_MemIncr, 1, memCnt);

       sqlite3VdbeAddOp(v, OP_Next, iCur, addr2);

       sqlite3VdbeResolveLabel(v, endOfLoop);

       sqlite3VdbeAddOp(v, OP_Close, iCur, 0);

     }

     if( !isView ){

       sqlite3VdbeAddOp(v, OP_Clear, pTab->tnum, iDb);

       if( !pParse->nested ){

         sqlite3VdbeChangeP3(v, -1, pTab->zName, P3_STATIC);

       }

       for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){

         assert( pIdx->pSchema==pTab->pSchema );

         sqlite3VdbeAddOp(v, OP_Clear, pIdx->tnum, iDb);

       }

     }

   } 

   /* The usual case: There is a WHERE clause so we have to scan through

   ** the table and pick which records to delete.

   */

   else{

     /* Begin the database scan

     */

     pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, 0);

     if( pWInfo==0 ) goto delete_from_cleanup;

     /* Remember the rowid of every item to be deleted.

     */

     sqlite3VdbeAddOp(v, IsVirtual(pTab) ? OP_VRowid : OP_Rowid, iCur, 0);

     sqlite3VdbeAddOp(v, OP_FifoWrite, 0, 0);

     if( db->flags & SQLITE_CountRows ){

       sqlite3VdbeAddOp(v, OP_MemIncr, 1, memCnt);

     }

     /* End the database scan loop.

     */

     sqlite3WhereEnd(pWInfo);

     /* Open the pseudo-table used to store OLD if there are triggers.

     */

     if( triggers_exist ){

       sqlite3VdbeAddOp(v, OP_OpenPseudo, oldIdx, 0);

       sqlite3VdbeAddOp(v, OP_SetNumColumns, oldIdx, pTab->nCol);

     }

     /* Delete every item whose key was written to the list during the

     ** database scan.  We have to delete items after the scan is complete

     ** because deleting an item can change the scan order.

     */

     end = sqlite3VdbeMakeLabel(v);

     /* This is the beginning of the delete loop when there are

     ** row triggers.

     */

     if( triggers_exist ){

       addr = sqlite3VdbeAddOp(v, OP_FifoRead, 0, end);

       if( !isView ){

         sqlite3VdbeAddOp(v, OP_Dup, 0, 0);

         sqlite3OpenTable(pParse, iCur, iDb, pTab, OP_OpenRead);

       }

       sqlite3VdbeAddOp(v, OP_MoveGe, iCur, 0);

       sqlite3VdbeAddOp(v, OP_Rowid, iCur, 0);

       sqlite3VdbeAddOp(v, OP_RowData, iCur, 0);

       sqlite3VdbeAddOp(v, OP_Insert, oldIdx, 0);

       if( !isView ){

         sqlite3VdbeAddOp(v, OP_Close, iCur, 0);

       }

       (void)sqlite3CodeRowTrigger(pParse, TK_DELETE, 0, TRIGGER_BEFORE, pTab,

           -1, oldIdx, (pParse->trigStack)?pParse->trigStack->orconf:OE_Default,

           addr);

     }

     if( !isView ){

       /* Open cursors for the table we are deleting from and all its

       ** indices.  If there are row triggers, this happens inside the

       ** OP_FifoRead loop because the cursor have to all be closed

       ** before the trigger fires.  If there are no row triggers, the

       ** cursors are opened only once on the outside the loop.

       */

       sqlite3OpenTableAndIndices(pParse, pTab, iCur, OP_OpenWrite);

       /* This is the beginning of the delete loop when there are no

       ** row triggers */

       if( !triggers_exist ){ 

         addr = sqlite3VdbeAddOp(v, OP_FifoRead, 0, end);

       }

       /* Delete the row */

 #ifndef SQLITE_OMIT_VIRTUALTABLE

       if( IsVirtual(pTab) ){

         pParse->pVirtualLock = pTab;

         sqlite3VdbeOp3(v, OP_VUpdate, 0, 1, (const char*)pTab->pVtab, P3_VTAB);

       }else

 #endif

       {

         sqlite3GenerateRowDelete(db, v, pTab, iCur, pParse->nested==0);

       }

     }

     /* If there are row triggers, close all cursors then invoke

     ** the AFTER triggers

     */

     if( triggers_exist ){

       if( !isView ){

         for(i=1, pIdx=pTab->pIndex; pIdx; i++, pIdx=pIdx->pNext){

           sqlite3VdbeAddOp(v, OP_Close, iCur + i, pIdx->tnum);

         }

         sqlite3VdbeAddOp(v, OP_Close, iCur, 0);

       }

       (void)sqlite3CodeRowTrigger(pParse, TK_DELETE, 0, TRIGGER_AFTER, pTab, -1,

           oldIdx, (pParse->trigStack)?pParse->trigStack->orconf:OE_Default,

           addr);

     }

     /* End of the delete loop */

     sqlite3VdbeAddOp(v, OP_Goto, 0, addr);

     sqlite3VdbeResolveLabel(v, end);

     /* Close the cursors after the loop if there are no row triggers */

     if( !triggers_exist && !IsVirtual(pTab) ){

       for(i=1, pIdx=pTab->pIndex; pIdx; i++, pIdx=pIdx->pNext){

         sqlite3VdbeAddOp(v, OP_Close, iCur + i, pIdx->tnum);

       }

       sqlite3VdbeAddOp(v, OP_Close, iCur, 0);

     }

   }

   /*

   ** Return the number of rows that were deleted. If this routine is 

   ** generating code because of a call to sqlite3NestedParse(), do not

   ** invoke the callback function.

   */

   if( db->flags & SQLITE_CountRows && pParse->nested==0 && !pParse->trigStack ){

     sqlite3VdbeAddOp(v, OP_MemLoad, memCnt, 0);

     sqlite3VdbeAddOp(v, OP_Callback, 1, 0);

     sqlite3VdbeSetNumCols(v, 1);

     sqlite3VdbeSetColName(v, 0, COLNAME_NAME, "rows deleted", P3_STATIC);

   }

 delete_from_cleanup:

   sqlite3AuthContextPop(&sContext);

   sqlite3SrcListDelete(pTabList);

   sqlite3ExprDelete(pWhere);

   return;

 }

 /*

 ** This routine generates VDBE code that causes a single row of a

 ** single table to be deleted.

 **

 ** The VDBE must be in a particular state when this routine is called.

 ** These are the requirements:

 **

 **   1.  A read/write cursor pointing to pTab, the table containing the row

 **       to be deleted, must be opened as cursor number "base".

 **

 **   2.  Read/write cursors for all indices of pTab must be open as

 **       cursor number base+i for the i-th index.

 **

 **   3.  The record number of the row to be deleted must be on the top

 **       of the stack.

 **

 ** This routine pops the top of the stack to remove the record number

 ** and then generates code to remove both the table record and all index

 ** entries that point to that record.

 */

 void sqlite3GenerateRowDelete(

   sqlite3 *db,       /* The database containing the index */

   Vdbe *v,           /* Generate code into this VDBE */

   Table *pTab,       /* Table containing the row to be deleted */

   int iCur,          /* Cursor number for the table */

   int count          /* Increment the row change counter */

 ){

   int addr;

   addr = sqlite3VdbeAddOp(v, OP_NotExists, iCur, 0);

   sqlite3GenerateRowIndexDelete(v, pTab, iCur, 0);

   sqlite3VdbeAddOp(v, OP_Delete, iCur, (count?OPFLAG_NCHANGE:0));

   if( count ){

     sqlite3VdbeChangeP3(v, -1, pTab->zName, P3_STATIC);

   }

   sqlite3VdbeJumpHere(v, addr);

 }

 /*

 ** This routine generates VDBE code that causes the deletion of all

 ** index entries associated with a single row of a single table.

 **

 ** The VDBE must be in a particular state when this routine is called.

 ** These are the requirements:

 **

 **   1.  A read/write cursor pointing to pTab, the table containing the row

 **       to be deleted, must be opened as cursor number "iCur".

 **

 **   2.  Read/write cursors for all indices of pTab must be open as

 **       cursor number iCur+i for the i-th index.

 **

 **   3.  The "iCur" cursor must be pointing to the row that is to be

 **       deleted.

 */

 void sqlite3GenerateRowIndexDelete(

   Vdbe *v,           /* Generate code into this VDBE */

   Table *pTab,       /* Table containing the row to be deleted */

   int iCur,          /* Cursor number for the table */

   char *aIdxUsed     /* Only delete if aIdxUsed!=0 && aIdxUsed[i]!=0 */

 ){

   int i;

   Index *pIdx;

   for(i=1, pIdx=pTab->pIndex; pIdx; i++, pIdx=pIdx->pNext){

     if( aIdxUsed!=0 && aIdxUsed[i-1]==0 ) continue;

     sqlite3GenerateIndexKey(v, pIdx, iCur);

     sqlite3VdbeAddOp(v, OP_IdxDelete, iCur+i, 0);

   }

 }

 /*

 ** Generate code that will assemble an index key and put it on the top

 ** of the tack.  The key with be for index pIdx which is an index on pTab.

 ** iCur is the index of a cursor open on the pTab table and pointing to

 ** the entry that needs indexing.

 */

 void sqlite3GenerateIndexKey(

   Vdbe *v,           /* Generate code into this VDBE */

   Index *pIdx,       /* The index for which to generate a key */

   int iCur           /* Cursor number for the pIdx->pTable table */

 ){

   int j;

   Table *pTab = pIdx->pTable;

   sqlite3VdbeAddOp(v, OP_Rowid, iCur, 0);

   for(j=0; j<pIdx->nColumn; j++){

     int idx = pIdx->aiColumn[j];

     if( idx==pTab->iPKey ){

       sqlite3VdbeAddOp(v, OP_Dup, j, 0);

     }else{

       sqlite3VdbeAddOp(v, OP_Column, iCur, idx);

       sqlite3ColumnDefault(v, pTab, idx);

     }

   }

   sqlite3VdbeAddOp(v, OP_MakeIdxRec, pIdx->nColumn, 0);

   sqlite3IndexAffinityStr(v, pIdx);

 }