/*-------------------------------------------------------------------------
 *
 * nodeFunctionscan.c
 *	  Support routines for scanning RangeFunctions (functions in rangetable).
 *
 * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/executor/nodeFunctionscan.c,v 1.56 2010/07/12 17:01:05 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
/*
 * INTERFACE ROUTINES
 *		ExecFunctionScan		scans a function.
 *		ExecFunctionNext		retrieve next tuple in sequential order.
 *		ExecInitFunctionScan	creates and initializes a functionscan node.
 *		ExecEndFunctionScan		releases any storage allocated.
 *		ExecReScanFunctionScan	rescans the function
 */
#include "postgres.h"

#include "executor/nodeFunctionscan.h"
#include "funcapi.h"
#include "utils/builtins.h"


static TupleTableSlot *FunctionNext(FunctionScanState *node);

/* ----------------------------------------------------------------
 *						Scan Support
 * ----------------------------------------------------------------
 */
/* ----------------------------------------------------------------
 *		FunctionNext
 *
 *		This is a workhorse for ExecFunctionScan
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
FunctionNext(FunctionScanState *node)
{
	TupleTableSlot *slot;
	EState	   *estate;
	ScanDirection direction;
	Tuplestorestate *tuplestorestate;

	/*
	 * get information from the estate and scan state
	 */
	estate = node->ss.ps.state;
	direction = estate->es_direction;

	tuplestorestate = node->tuplestorestate;

	/*
	 * If first time through, read all tuples from function and put them in a
	 * tuplestore. Subsequent calls just fetch tuples from tuplestore.
	 */
	if (tuplestorestate == NULL)
	{
		node->tuplestorestate = tuplestorestate =
			ExecMakeTableFunctionResult(node->funcexpr,
										node->ss.ps.ps_ExprContext,
										node->tupdesc,
										node->eflags & EXEC_FLAG_BACKWARD);
	}

	/*
	 * Get the next tuple from tuplestore. Return NULL if no more tuples.
	 */
	slot = node->ss.ss_ScanTupleSlot;
	(void) tuplestore_gettupleslot(tuplestorestate,
								   ScanDirectionIsForward(direction),
								   false,
								   slot);
	return slot;
}

/*
 * FunctionRecheck -- access method routine to recheck a tuple in EvalPlanQual
 */
static bool
FunctionRecheck(FunctionScanState *node, TupleTableSlot *slot)
{
	/* nothing to check */
	return true;
}

/* ----------------------------------------------------------------
 *		ExecFunctionScan(node)
 *
 *		Scans the function sequentially and returns the next qualifying
 *		tuple.
 *		We call the ExecScan() routine and pass it the appropriate
 *		access method functions.
 * ----------------------------------------------------------------
 */
TupleTableSlot *
ExecFunctionScan(FunctionScanState *node)
{
	return ExecScan(&node->ss,
					(ExecScanAccessMtd) FunctionNext,
					(ExecScanRecheckMtd) FunctionRecheck);
}

/* ----------------------------------------------------------------
 *		ExecInitFunctionScan
 * ----------------------------------------------------------------
 */
FunctionScanState *
ExecInitFunctionScan(FunctionScan *node, EState *estate, int eflags)
{
	FunctionScanState *scanstate;
	Oid			funcrettype;
	TypeFuncClass functypclass;
	TupleDesc	tupdesc = NULL;

	/* check for unsupported flags */
	Assert(!(eflags & EXEC_FLAG_MARK));

	/*
	 * FunctionScan should not have any children.
	 */
	Assert(outerPlan(node) == NULL);
	Assert(innerPlan(node) == NULL);

	/*
	 * create new ScanState for node
	 */
	scanstate = makeNode(FunctionScanState);
	scanstate->ss.ps.plan = (Plan *) node;
	scanstate->ss.ps.state = estate;
	scanstate->eflags = eflags;

	/*
	 * Miscellaneous initialization
	 *
	 * create expression context for node
	 */
	ExecAssignExprContext(estate, &scanstate->ss.ps);

	/*
	 * tuple table initialization
	 */
	ExecInitResultTupleSlot(estate, &scanstate->ss.ps);
	ExecInitScanTupleSlot(estate, &scanstate->ss);

	/*
	 * initialize child expressions
	 */
	scanstate->ss.ps.targetlist = (List *)
		ExecInitExpr((Expr *) node->scan.plan.targetlist,
					 (PlanState *) scanstate);
	scanstate->ss.ps.qual = (List *)
		ExecInitExpr((Expr *) node->scan.plan.qual,
					 (PlanState *) scanstate);

	/*
	 * Now determine if the function returns a simple or composite type, and
	 * build an appropriate tupdesc.
	 */
	functypclass = get_expr_result_type(node->funcexpr,
										&funcrettype,
										&tupdesc);

	if (functypclass == TYPEFUNC_COMPOSITE)
	{
		/* Composite data type, e.g. a table's row type */
		Assert(tupdesc);
		/* Must copy it out of typcache for safety */
		tupdesc = CreateTupleDescCopy(tupdesc);
	}
	else if (functypclass == TYPEFUNC_SCALAR)
	{
		/* Base data type, i.e. scalar */
		char	   *attname = strVal(linitial(node->funccolnames));

		tupdesc = CreateTemplateTupleDesc(1, false);
		TupleDescInitEntry(tupdesc,
						   (AttrNumber) 1,
						   attname,
						   funcrettype,
						   -1,
						   0);
	}
	else if (functypclass == TYPEFUNC_RECORD)
	{
		tupdesc = BuildDescFromLists(node->funccolnames,
									 node->funccoltypes,
									 node->funccoltypmods);
	}
	else
	{
		/* crummy error message, but parser should have caught this */
		elog(ERROR, "function in FROM has unsupported return type");
	}

	/*
	 * For RECORD results, make sure a typmod has been assigned.  (The
	 * function should do this for itself, but let's cover things in case it
	 * doesn't.)
	 */
	BlessTupleDesc(tupdesc);

	scanstate->tupdesc = tupdesc;
	ExecAssignScanType(&scanstate->ss, tupdesc);

	/*
	 * Other node-specific setup
	 */
	scanstate->tuplestorestate = NULL;
	scanstate->funcexpr = ExecInitExpr((Expr *) node->funcexpr,
									   (PlanState *) scanstate);

	scanstate->ss.ps.ps_TupFromTlist = false;

	/*
	 * Initialize result tuple type and projection info.
	 */
	ExecAssignResultTypeFromTL(&scanstate->ss.ps);
	ExecAssignScanProjectionInfo(&scanstate->ss);

	return scanstate;
}

/* ----------------------------------------------------------------
 *		ExecEndFunctionScan
 *
 *		frees any storage allocated through C routines.
 * ----------------------------------------------------------------
 */
void
ExecEndFunctionScan(FunctionScanState *node)
{
	/*
	 * Free the exprcontext
	 */
	ExecFreeExprContext(&node->ss.ps);

	/*
	 * clean out the tuple table
	 */
	ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);
	ExecClearTuple(node->ss.ss_ScanTupleSlot);

	/*
	 * Release tuplestore resources
	 */
	if (node->tuplestorestate != NULL)
		tuplestore_end(node->tuplestorestate);
	node->tuplestorestate = NULL;
}

/* ----------------------------------------------------------------
 *		ExecReScanFunctionScan
 *
 *		Rescans the relation.
 * ----------------------------------------------------------------
 */
void
ExecReScanFunctionScan(FunctionScanState *node)
{
	ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);

	ExecScanReScan(&node->ss);

	/*
	 * If we haven't materialized yet, just return.
	 */
	if (!node->tuplestorestate)
		return;

	/*
	 * Here we have a choice whether to drop the tuplestore (and recompute the
	 * function outputs) or just rescan it.  We must recompute if the
	 * expression contains parameters, else we rescan.	XXX maybe we should
	 * recompute if the function is volatile?
	 */
	if (node->ss.ps.chgParam != NULL)
	{
		tuplestore_end(node->tuplestorestate);
		node->tuplestorestate = NULL;
	}
	else
		tuplestore_rescan(node->tuplestorestate);
}
