/*-------------------------------------------------------------------------
 *
 * paramassign.c
 *		Functions for assigning PARAM_EXEC slots during planning.
 *
 * This module is responsible for managing three planner data structures:
 *
 * root->glob->nParamExec: counts actual assignments of PARAM_EXEC slots.
 * This counter is global to the whole plan since the executor has only one
 * PARAM_EXEC array.  Assignments are permanent for the plan: we never
 * de-assign a slot once added.
 *
 * root->plan_params: a list of PlannerParamItem nodes, recording Vars and
 * PlaceHolderVars that the root's query level needs to supply to lower-level
 * subqueries, along with the PARAM_EXEC number to use for each such value.
 * Elements are added to this list while planning a subquery, and the list
 * is reset to empty after completion of each subquery.
 *
 * root->curOuterParams: a list of NestLoopParam nodes, recording Vars and
 * PlaceHolderVars that some outer level of nestloop needs to pass down to
 * a lower-level plan node in its righthand side.  Elements are added to this
 * list as createplan.c creates lower Plan nodes that need such Params, and
 * are removed when it creates a NestLoop Plan node that will supply those
 * values.
 *
 * The latter two data structures are used to prevent creating multiple
 * PARAM_EXEC slots (each requiring work to fill) when the same upper
 * SubPlan or NestLoop supplies a value that is referenced in more than
 * one place in its child plan nodes.  However, when the same Var has to
 * be supplied to different subplan trees by different SubPlan or NestLoop
 * parent nodes, we don't recognize any commonality; a fresh plan_params or
 * curOuterParams entry will be made (since the old one has been removed
 * when we finished processing the earlier SubPlan or NestLoop) and a fresh
 * PARAM_EXEC number will be assigned.  At one time we tried to avoid
 * allocating duplicate PARAM_EXEC numbers in such cases, but it's harder
 * than it seems to avoid bugs due to overlapping Param lifetimes, so we
 * don't risk that anymore.  Minimizing the number of PARAM_EXEC slots
 * doesn't really save much executor work anyway.
 *
 *
 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  src/backend/optimizer/util/paramassign.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "nodes/nodeFuncs.h"
#include "nodes/plannodes.h"
#include "optimizer/paramassign.h"
#include "optimizer/placeholder.h"
#include "rewrite/rewriteManip.h"


/*
 * Select a PARAM_EXEC number to identify the given Var as a parameter for
 * the current subquery.  (It might already have one.)
 * Record the need for the Var in the proper upper-level root->plan_params.
 */
static int
assign_param_for_var(PlannerInfo *root, Var *var)
{
	ListCell   *ppl;
	PlannerParamItem *pitem;
	Index		levelsup;

	/* Find the query level the Var belongs to */
	for (levelsup = var->varlevelsup; levelsup > 0; levelsup--)
		root = root->parent_root;

	/* If there's already a matching PlannerParamItem there, just use it */
	foreach(ppl, root->plan_params)
	{
		pitem = (PlannerParamItem *) lfirst(ppl);
		if (IsA(pitem->item, Var))
		{
			Var		   *pvar = (Var *) pitem->item;

			/*
			 * This comparison must match _equalVar(), except for ignoring
			 * varlevelsup.  Note that _equalVar() ignores the location.
			 */
			if (pvar->varno == var->varno &&
				pvar->varattno == var->varattno &&
				pvar->vartype == var->vartype &&
				pvar->vartypmod == var->vartypmod &&
				pvar->varcollid == var->varcollid &&
				pvar->varnoold == var->varnoold &&
				pvar->varoattno == var->varoattno)
				return pitem->paramId;
		}
	}

	/* Nope, so make a new one */
	var = copyObject(var);
	var->varlevelsup = 0;

	pitem = makeNode(PlannerParamItem);
	pitem->item = (Node *) var;
	pitem->paramId = root->glob->nParamExec++;

	root->plan_params = lappend(root->plan_params, pitem);

	return pitem->paramId;
}

/*
 * Generate a Param node to replace the given Var,
 * which is expected to have varlevelsup > 0 (ie, it is not local).
 * Record the need for the Var in the proper upper-level root->plan_params.
 */
Param *
replace_outer_var(PlannerInfo *root, Var *var)
{
	Param	   *retval;
	int			i;

	Assert(var->varlevelsup > 0 && var->varlevelsup < root->query_level);

	/* Find the Var in the appropriate plan_params, or add it if not present */
	i = assign_param_for_var(root, var);

	retval = makeNode(Param);
	retval->paramkind = PARAM_EXEC;
	retval->paramid = i;
	retval->paramtype = var->vartype;
	retval->paramtypmod = var->vartypmod;
	retval->paramcollid = var->varcollid;
	retval->location = var->location;

	return retval;
}

/*
 * Select a PARAM_EXEC number to identify the given PlaceHolderVar as a
 * parameter for the current subquery.  (It might already have one.)
 * Record the need for the PHV in the proper upper-level root->plan_params.
 *
 * This is just like assign_param_for_var, except for PlaceHolderVars.
 */
static int
assign_param_for_placeholdervar(PlannerInfo *root, PlaceHolderVar *phv)
{
	ListCell   *ppl;
	PlannerParamItem *pitem;
	Index		levelsup;

	/* Find the query level the PHV belongs to */
	for (levelsup = phv->phlevelsup; levelsup > 0; levelsup--)
		root = root->parent_root;

	/* If there's already a matching PlannerParamItem there, just use it */
	foreach(ppl, root->plan_params)
	{
		pitem = (PlannerParamItem *) lfirst(ppl);
		if (IsA(pitem->item, PlaceHolderVar))
		{
			PlaceHolderVar *pphv = (PlaceHolderVar *) pitem->item;

			/* We assume comparing the PHIDs is sufficient */
			if (pphv->phid == phv->phid)
				return pitem->paramId;
		}
	}

	/* Nope, so make a new one */
	phv = copyObject(phv);
	IncrementVarSublevelsUp((Node *) phv, -((int) phv->phlevelsup), 0);
	Assert(phv->phlevelsup == 0);

	pitem = makeNode(PlannerParamItem);
	pitem->item = (Node *) phv;
	pitem->paramId = root->glob->nParamExec++;

	root->plan_params = lappend(root->plan_params, pitem);

	return pitem->paramId;
}

/*
 * Generate a Param node to replace the given PlaceHolderVar,
 * which is expected to have phlevelsup > 0 (ie, it is not local).
 * Record the need for the PHV in the proper upper-level root->plan_params.
 *
 * This is just like replace_outer_var, except for PlaceHolderVars.
 */
Param *
replace_outer_placeholdervar(PlannerInfo *root, PlaceHolderVar *phv)
{
	Param	   *retval;
	int			i;

	Assert(phv->phlevelsup > 0 && phv->phlevelsup < root->query_level);

	/* Find the PHV in the appropriate plan_params, or add it if not present */
	i = assign_param_for_placeholdervar(root, phv);

	retval = makeNode(Param);
	retval->paramkind = PARAM_EXEC;
	retval->paramid = i;
	retval->paramtype = exprType((Node *) phv->phexpr);
	retval->paramtypmod = exprTypmod((Node *) phv->phexpr);
	retval->paramcollid = exprCollation((Node *) phv->phexpr);
	retval->location = -1;

	return retval;
}

/*
 * Generate a Param node to replace the given Aggref
 * which is expected to have agglevelsup > 0 (ie, it is not local).
 * Record the need for the Aggref in the proper upper-level root->plan_params.
 */
Param *
replace_outer_agg(PlannerInfo *root, Aggref *agg)
{
	Param	   *retval;
	PlannerParamItem *pitem;
	Index		levelsup;

	Assert(agg->agglevelsup > 0 && agg->agglevelsup < root->query_level);

	/* Find the query level the Aggref belongs to */
	for (levelsup = agg->agglevelsup; levelsup > 0; levelsup--)
		root = root->parent_root;

	/*
	 * It does not seem worthwhile to try to de-duplicate references to outer
	 * aggs.  Just make a new slot every time.
	 */
	agg = copyObject(agg);
	IncrementVarSublevelsUp((Node *) agg, -((int) agg->agglevelsup), 0);
	Assert(agg->agglevelsup == 0);

	pitem = makeNode(PlannerParamItem);
	pitem->item = (Node *) agg;
	pitem->paramId = root->glob->nParamExec++;

	root->plan_params = lappend(root->plan_params, pitem);

	retval = makeNode(Param);
	retval->paramkind = PARAM_EXEC;
	retval->paramid = pitem->paramId;
	retval->paramtype = agg->aggtype;
	retval->paramtypmod = -1;
	retval->paramcollid = agg->aggcollid;
	retval->location = agg->location;

	return retval;
}

/*
 * Generate a Param node to replace the given GroupingFunc expression which is
 * expected to have agglevelsup > 0 (ie, it is not local).
 * Record the need for the GroupingFunc in the proper upper-level
 * root->plan_params.
 */
Param *
replace_outer_grouping(PlannerInfo *root, GroupingFunc *grp)
{
	Param	   *retval;
	PlannerParamItem *pitem;
	Index		levelsup;
	Oid			ptype = exprType((Node *) grp);

	Assert(grp->agglevelsup > 0 && grp->agglevelsup < root->query_level);

	/* Find the query level the GroupingFunc belongs to */
	for (levelsup = grp->agglevelsup; levelsup > 0; levelsup--)
		root = root->parent_root;

	/*
	 * It does not seem worthwhile to try to de-duplicate references to outer
	 * aggs.  Just make a new slot every time.
	 */
	grp = copyObject(grp);
	IncrementVarSublevelsUp((Node *) grp, -((int) grp->agglevelsup), 0);
	Assert(grp->agglevelsup == 0);

	pitem = makeNode(PlannerParamItem);
	pitem->item = (Node *) grp;
	pitem->paramId = root->glob->nParamExec++;

	root->plan_params = lappend(root->plan_params, pitem);

	retval = makeNode(Param);
	retval->paramkind = PARAM_EXEC;
	retval->paramid = pitem->paramId;
	retval->paramtype = ptype;
	retval->paramtypmod = -1;
	retval->paramcollid = InvalidOid;
	retval->location = grp->location;

	return retval;
}

/*
 * Generate a Param node to replace the given Var,
 * which is expected to come from some upper NestLoop plan node.
 * Record the need for the Var in root->curOuterParams.
 */
Param *
replace_nestloop_param_var(PlannerInfo *root, Var *var)
{
	Param	   *param;
	NestLoopParam *nlp;
	ListCell   *lc;

	/* Is this Var already listed in root->curOuterParams? */
	foreach(lc, root->curOuterParams)
	{
		nlp = (NestLoopParam *) lfirst(lc);
		if (equal(var, nlp->paramval))
		{
			/* Yes, so just make a Param referencing this NLP's slot */
			param = makeNode(Param);
			param->paramkind = PARAM_EXEC;
			param->paramid = nlp->paramno;
			param->paramtype = var->vartype;
			param->paramtypmod = var->vartypmod;
			param->paramcollid = var->varcollid;
			param->location = var->location;
			return param;
		}
	}

	/* No, so assign a PARAM_EXEC slot for a new NLP */
	param = generate_new_exec_param(root,
									var->vartype,
									var->vartypmod,
									var->varcollid);
	param->location = var->location;

	/* Add it to the list of required NLPs */
	nlp = makeNode(NestLoopParam);
	nlp->paramno = param->paramid;
	nlp->paramval = copyObject(var);
	root->curOuterParams = lappend(root->curOuterParams, nlp);

	/* And return the replacement Param */
	return param;
}

/*
 * Generate a Param node to replace the given PlaceHolderVar,
 * which is expected to come from some upper NestLoop plan node.
 * Record the need for the PHV in root->curOuterParams.
 *
 * This is just like replace_nestloop_param_var, except for PlaceHolderVars.
 */
Param *
replace_nestloop_param_placeholdervar(PlannerInfo *root, PlaceHolderVar *phv)
{
	Param	   *param;
	NestLoopParam *nlp;
	ListCell   *lc;

	/* Is this PHV already listed in root->curOuterParams? */
	foreach(lc, root->curOuterParams)
	{
		nlp = (NestLoopParam *) lfirst(lc);
		if (equal(phv, nlp->paramval))
		{
			/* Yes, so just make a Param referencing this NLP's slot */
			param = makeNode(Param);
			param->paramkind = PARAM_EXEC;
			param->paramid = nlp->paramno;
			param->paramtype = exprType((Node *) phv->phexpr);
			param->paramtypmod = exprTypmod((Node *) phv->phexpr);
			param->paramcollid = exprCollation((Node *) phv->phexpr);
			param->location = -1;
			return param;
		}
	}

	/* No, so assign a PARAM_EXEC slot for a new NLP */
	param = generate_new_exec_param(root,
									exprType((Node *) phv->phexpr),
									exprTypmod((Node *) phv->phexpr),
									exprCollation((Node *) phv->phexpr));

	/* Add it to the list of required NLPs */
	nlp = makeNode(NestLoopParam);
	nlp->paramno = param->paramid;
	nlp->paramval = (Var *) copyObject(phv);
	root->curOuterParams = lappend(root->curOuterParams, nlp);

	/* And return the replacement Param */
	return param;
}

/*
 * process_subquery_nestloop_params
 *	  Handle params of a parameterized subquery that need to be fed
 *	  from an outer nestloop.
 *
 * Currently, that would be *all* params that a subquery in FROM has demanded
 * from the current query level, since they must be LATERAL references.
 *
 * subplan_params is a list of PlannerParamItems that we intend to pass to
 * a subquery-in-FROM.  (This was constructed in root->plan_params while
 * planning the subquery, but isn't there anymore when this is called.)
 *
 * The subplan's references to the outer variables are already represented
 * as PARAM_EXEC Params, since that conversion was done by the routines above
 * while planning the subquery.  So we need not modify the subplan or the
 * PlannerParamItems here.  What we do need to do is add entries to
 * root->curOuterParams to signal the parent nestloop plan node that it must
 * provide these values.  This differs from replace_nestloop_param_var in
 * that the PARAM_EXEC slots to use have already been determined.
 *
 * Note that we also use root->curOuterRels as an implicit parameter for
 * sanity checks.
 */
void
process_subquery_nestloop_params(PlannerInfo *root, List *subplan_params)
{
	ListCell   *lc;

	foreach(lc, subplan_params)
	{
		PlannerParamItem *pitem = castNode(PlannerParamItem, lfirst(lc));

		if (IsA(pitem->item, Var))
		{
			Var		   *var = (Var *) pitem->item;
			NestLoopParam *nlp;
			ListCell   *lc;

			/* If not from a nestloop outer rel, complain */
			if (!bms_is_member(var->varno, root->curOuterRels))
				elog(ERROR, "non-LATERAL parameter required by subquery");

			/* Is this param already listed in root->curOuterParams? */
			foreach(lc, root->curOuterParams)
			{
				nlp = (NestLoopParam *) lfirst(lc);
				if (nlp->paramno == pitem->paramId)
				{
					Assert(equal(var, nlp->paramval));
					/* Present, so nothing to do */
					break;
				}
			}
			if (lc == NULL)
			{
				/* No, so add it */
				nlp = makeNode(NestLoopParam);
				nlp->paramno = pitem->paramId;
				nlp->paramval = copyObject(var);
				root->curOuterParams = lappend(root->curOuterParams, nlp);
			}
		}
		else if (IsA(pitem->item, PlaceHolderVar))
		{
			PlaceHolderVar *phv = (PlaceHolderVar *) pitem->item;
			NestLoopParam *nlp;
			ListCell   *lc;

			/* If not from a nestloop outer rel, complain */
			if (!bms_is_subset(find_placeholder_info(root, phv, false)->ph_eval_at,
							   root->curOuterRels))
				elog(ERROR, "non-LATERAL parameter required by subquery");

			/* Is this param already listed in root->curOuterParams? */
			foreach(lc, root->curOuterParams)
			{
				nlp = (NestLoopParam *) lfirst(lc);
				if (nlp->paramno == pitem->paramId)
				{
					Assert(equal(phv, nlp->paramval));
					/* Present, so nothing to do */
					break;
				}
			}
			if (lc == NULL)
			{
				/* No, so add it */
				nlp = makeNode(NestLoopParam);
				nlp->paramno = pitem->paramId;
				nlp->paramval = (Var *) copyObject(phv);
				root->curOuterParams = lappend(root->curOuterParams, nlp);
			}
		}
		else
			elog(ERROR, "unexpected type of subquery parameter");
	}
}

/*
 * Identify any NestLoopParams that should be supplied by a NestLoop plan
 * node with the specified lefthand rels.  Remove them from the active
 * root->curOuterParams list and return them as the result list.
 */
List *
identify_current_nestloop_params(PlannerInfo *root, Relids leftrelids)
{
	List	   *result;
	ListCell   *cell;
	ListCell   *prev;
	ListCell   *next;

	result = NIL;
	prev = NULL;
	for (cell = list_head(root->curOuterParams); cell; cell = next)
	{
		NestLoopParam *nlp = (NestLoopParam *) lfirst(cell);

		next = lnext(cell);

		/*
		 * We are looking for Vars and PHVs that can be supplied by the
		 * lefthand rels.  The "bms_overlap" test is just an optimization to
		 * allow skipping find_placeholder_info() if the PHV couldn't match.
		 */
		if (IsA(nlp->paramval, Var) &&
			bms_is_member(nlp->paramval->varno, leftrelids))
		{
			root->curOuterParams = list_delete_cell(root->curOuterParams,
													cell, prev);
			result = lappend(result, nlp);
		}
		else if (IsA(nlp->paramval, PlaceHolderVar) &&
				 bms_overlap(((PlaceHolderVar *) nlp->paramval)->phrels,
							 leftrelids) &&
				 bms_is_subset(find_placeholder_info(root,
													 (PlaceHolderVar *) nlp->paramval,
													 false)->ph_eval_at,
							   leftrelids))
		{
			root->curOuterParams = list_delete_cell(root->curOuterParams,
													cell, prev);
			result = lappend(result, nlp);
		}
		else
			prev = cell;
	}
	return result;
}

/*
 * Generate a new Param node that will not conflict with any other.
 *
 * This is used to create Params representing subplan outputs or
 * NestLoop parameters.
 *
 * We don't need to build a PlannerParamItem for such a Param, but we do
 * need to record the PARAM_EXEC slot number as being allocated.
 */
Param *
generate_new_exec_param(PlannerInfo *root, Oid paramtype, int32 paramtypmod,
						Oid paramcollation)
{
	Param	   *retval;

	retval = makeNode(Param);
	retval->paramkind = PARAM_EXEC;
	retval->paramid = root->glob->nParamExec++;
	retval->paramtype = paramtype;
	retval->paramtypmod = paramtypmod;
	retval->paramcollid = paramcollation;
	retval->location = -1;

	return retval;
}

/*
 * Assign a (nonnegative) PARAM_EXEC ID for a special parameter (one that
 * is not actually used to carry a value at runtime).  Such parameters are
 * used for special runtime signaling purposes, such as connecting a
 * recursive union node to its worktable scan node or forcing plan
 * re-evaluation within the EvalPlanQual mechanism.  No actual Param node
 * exists with this ID, however.
 */
int
assign_special_exec_param(PlannerInfo *root)
{
	return root->glob->nParamExec++;
}
