/*-------------------------------------------------------------------------
 *
 * spgscan.c
 *	  routines for scanning SP-GiST indexes
 *
 *
 * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *			src/backend/access/spgist/spgscan.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/relscan.h"
#include "access/spgist_private.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "storage/bufmgr.h"
#include "utils/datum.h"
#include "utils/memutils.h"
#include "utils/rel.h"


typedef void (*storeRes_func) (SpGistScanOpaque so, ItemPointer heapPtr,
							   Datum leafValue, bool isnull, bool recheck);

typedef struct ScanStackEntry
{
	Datum		reconstructedValue; /* value reconstructed from parent */
	void	   *traversalValue; /* opclass-specific traverse value */
	int			level;			/* level of items on this page */
	ItemPointerData ptr;		/* block and offset to scan from */
} ScanStackEntry;


/* Free a ScanStackEntry */
static void
freeScanStackEntry(SpGistScanOpaque so, ScanStackEntry *stackEntry)
{
	if (!so->state.attLeafType.attbyval &&
		DatumGetPointer(stackEntry->reconstructedValue) != NULL)
		pfree(DatumGetPointer(stackEntry->reconstructedValue));
	if (stackEntry->traversalValue)
		pfree(stackEntry->traversalValue);

	pfree(stackEntry);
}

/* Free the entire stack */
static void
freeScanStack(SpGistScanOpaque so)
{
	ListCell   *lc;

	foreach(lc, so->scanStack)
	{
		freeScanStackEntry(so, (ScanStackEntry *) lfirst(lc));
	}
	list_free(so->scanStack);
	so->scanStack = NIL;
}

/*
 * Initialize scanStack to search the root page, resetting
 * any previously active scan
 */
static void
resetSpGistScanOpaque(SpGistScanOpaque so)
{
	ScanStackEntry *startEntry;

	freeScanStack(so);

	/*
	 * clear traversal context before proceeding to the next scan; this must
	 * not happen before the freeScanStack above, else we get double-free
	 * crashes.
	 */
	MemoryContextReset(so->traversalCxt);

	if (so->searchNulls)
	{
		/* Stack a work item to scan the null index entries */
		startEntry = (ScanStackEntry *) palloc0(sizeof(ScanStackEntry));
		ItemPointerSet(&startEntry->ptr, SPGIST_NULL_BLKNO, FirstOffsetNumber);
		so->scanStack = lappend(so->scanStack, startEntry);
	}

	if (so->searchNonNulls)
	{
		/* Stack a work item to scan the non-null index entries */
		startEntry = (ScanStackEntry *) palloc0(sizeof(ScanStackEntry));
		ItemPointerSet(&startEntry->ptr, SPGIST_ROOT_BLKNO, FirstOffsetNumber);
		so->scanStack = lappend(so->scanStack, startEntry);
	}

	if (so->want_itup)
	{
		/* Must pfree reconstructed tuples to avoid memory leak */
		int			i;

		for (i = 0; i < so->nPtrs; i++)
			pfree(so->reconTups[i]);
	}
	so->iPtr = so->nPtrs = 0;
}

/*
 * Prepare scan keys in SpGistScanOpaque from caller-given scan keys
 *
 * Sets searchNulls, searchNonNulls, numberOfKeys, keyData fields of *so.
 *
 * The point here is to eliminate null-related considerations from what the
 * opclass consistent functions need to deal with.  We assume all SPGiST-
 * indexable operators are strict, so any null RHS value makes the scan
 * condition unsatisfiable.  We also pull out any IS NULL/IS NOT NULL
 * conditions; their effect is reflected into searchNulls/searchNonNulls.
 */
static void
spgPrepareScanKeys(IndexScanDesc scan)
{
	SpGistScanOpaque so = (SpGistScanOpaque) scan->opaque;
	bool		qual_ok;
	bool		haveIsNull;
	bool		haveNotNull;
	int			nkeys;
	int			i;

	if (scan->numberOfKeys <= 0)
	{
		/* If no quals, whole-index scan is required */
		so->searchNulls = true;
		so->searchNonNulls = true;
		so->numberOfKeys = 0;
		return;
	}

	/* Examine the given quals */
	qual_ok = true;
	haveIsNull = haveNotNull = false;
	nkeys = 0;
	for (i = 0; i < scan->numberOfKeys; i++)
	{
		ScanKey		skey = &scan->keyData[i];

		if (skey->sk_flags & SK_SEARCHNULL)
			haveIsNull = true;
		else if (skey->sk_flags & SK_SEARCHNOTNULL)
			haveNotNull = true;
		else if (skey->sk_flags & SK_ISNULL)
		{
			/* ordinary qual with null argument - unsatisfiable */
			qual_ok = false;
			break;
		}
		else
		{
			/* ordinary qual, propagate into so->keyData */
			so->keyData[nkeys++] = *skey;
			/* this effectively creates a not-null requirement */
			haveNotNull = true;
		}
	}

	/* IS NULL in combination with something else is unsatisfiable */
	if (haveIsNull && haveNotNull)
		qual_ok = false;

	/* Emit results */
	if (qual_ok)
	{
		so->searchNulls = haveIsNull;
		so->searchNonNulls = haveNotNull;
		so->numberOfKeys = nkeys;
	}
	else
	{
		so->searchNulls = false;
		so->searchNonNulls = false;
		so->numberOfKeys = 0;
	}
}

IndexScanDesc
spgbeginscan(Relation rel, int keysz, int orderbysz)
{
	IndexScanDesc scan;
	SpGistScanOpaque so;

	scan = RelationGetIndexScan(rel, keysz, 0);

	so = (SpGistScanOpaque) palloc0(sizeof(SpGistScanOpaqueData));
	if (keysz > 0)
		so->keyData = (ScanKey) palloc(sizeof(ScanKeyData) * keysz);
	else
		so->keyData = NULL;
	initSpGistState(&so->state, scan->indexRelation);
	so->tempCxt = AllocSetContextCreate(CurrentMemoryContext,
										"SP-GiST search temporary context",
										ALLOCSET_DEFAULT_SIZES);
	so->traversalCxt = AllocSetContextCreate(CurrentMemoryContext,
											 "SP-GiST traversal-value context",
											 ALLOCSET_DEFAULT_SIZES);

	/* Set up indexTupDesc and xs_hitupdesc in case it's an index-only scan */
	so->indexTupDesc = scan->xs_hitupdesc = RelationGetDescr(rel);

	scan->opaque = so;

	return scan;
}

void
spgrescan(IndexScanDesc scan, ScanKey scankey, int nscankeys,
		  ScanKey orderbys, int norderbys)
{
	SpGistScanOpaque so = (SpGistScanOpaque) scan->opaque;

	/* copy scankeys into local storage */
	if (scankey && scan->numberOfKeys > 0)
	{
		memmove(scan->keyData, scankey,
				scan->numberOfKeys * sizeof(ScanKeyData));
	}

	/* preprocess scankeys, set up the representation in *so */
	spgPrepareScanKeys(scan);

	/* set up starting stack entries */
	resetSpGistScanOpaque(so);

	/* count an indexscan for stats */
	pgstat_count_index_scan(scan->indexRelation);
}

void
spgendscan(IndexScanDesc scan)
{
	SpGistScanOpaque so = (SpGistScanOpaque) scan->opaque;

	MemoryContextDelete(so->tempCxt);
	MemoryContextDelete(so->traversalCxt);

	if (so->keyData)
		pfree(so->keyData);

	if (so->state.deadTupleStorage)
		pfree(so->state.deadTupleStorage);

	pfree(so);
}

/*
 * Test whether a leaf tuple satisfies all the scan keys
 *
 * *leafValue is set to the reconstructed datum, if provided
 * *recheck is set true if any of the operators are lossy
 */
static bool
spgLeafTest(Relation index, SpGistScanOpaque so,
			SpGistLeafTuple leafTuple, bool isnull,
			int level, Datum reconstructedValue,
			void *traversalValue,
			Datum *leafValue, bool *recheck)
{
	bool		result;
	Datum		leafDatum;
	spgLeafConsistentIn in;
	spgLeafConsistentOut out;
	FmgrInfo   *procinfo;
	MemoryContext oldCtx;

	if (isnull)
	{
		/* Should not have arrived on a nulls page unless nulls are wanted */
		Assert(so->searchNulls);
		*leafValue = (Datum) 0;
		*recheck = false;
		return true;
	}

	leafDatum = SGLTDATUM(leafTuple, &so->state);

	/* use temp context for calling leaf_consistent */
	oldCtx = MemoryContextSwitchTo(so->tempCxt);

	in.scankeys = so->keyData;
	in.nkeys = so->numberOfKeys;
	in.reconstructedValue = reconstructedValue;
	in.traversalValue = traversalValue;
	in.level = level;
	in.returnData = so->want_itup;
	in.leafDatum = leafDatum;

	out.leafValue = (Datum) 0;
	out.recheck = false;

	procinfo = index_getprocinfo(index, 1, SPGIST_LEAF_CONSISTENT_PROC);
	result = DatumGetBool(FunctionCall2Coll(procinfo,
											index->rd_indcollation[0],
											PointerGetDatum(&in),
											PointerGetDatum(&out)));

	*leafValue = out.leafValue;
	*recheck = out.recheck;

	MemoryContextSwitchTo(oldCtx);

	return result;
}

/*
 * Walk the tree and report all tuples passing the scan quals to the storeRes
 * subroutine.
 *
 * If scanWholeIndex is true, we'll do just that.  If not, we'll stop at the
 * next page boundary once we have reported at least one tuple.
 */
static void
spgWalk(Relation index, SpGistScanOpaque so, bool scanWholeIndex,
		storeRes_func storeRes, Snapshot snapshot)
{
	Buffer		buffer = InvalidBuffer;
	bool		reportedSome = false;

	while (scanWholeIndex || !reportedSome)
	{
		ScanStackEntry *stackEntry;
		BlockNumber blkno;
		OffsetNumber offset;
		Page		page;
		bool		isnull;

		/* Pull next to-do item from the list */
		if (so->scanStack == NIL)
			break;				/* there are no more pages to scan */

		stackEntry = (ScanStackEntry *) linitial(so->scanStack);
		so->scanStack = list_delete_first(so->scanStack);

redirect:
		/* Check for interrupts, just in case of infinite loop */
		CHECK_FOR_INTERRUPTS();

		blkno = ItemPointerGetBlockNumber(&stackEntry->ptr);
		offset = ItemPointerGetOffsetNumber(&stackEntry->ptr);

		if (buffer == InvalidBuffer)
		{
			buffer = ReadBuffer(index, blkno);
			LockBuffer(buffer, BUFFER_LOCK_SHARE);
		}
		else if (blkno != BufferGetBlockNumber(buffer))
		{
			UnlockReleaseBuffer(buffer);
			buffer = ReadBuffer(index, blkno);
			LockBuffer(buffer, BUFFER_LOCK_SHARE);
		}
		/* else new pointer points to the same page, no work needed */

		page = BufferGetPage(buffer);
		TestForOldSnapshot(snapshot, index, page);

		isnull = SpGistPageStoresNulls(page) ? true : false;

		if (SpGistPageIsLeaf(page))
		{
			SpGistLeafTuple leafTuple;
			OffsetNumber max = PageGetMaxOffsetNumber(page);
			Datum		leafValue = (Datum) 0;
			bool		recheck = false;

			if (SpGistBlockIsRoot(blkno))
			{
				/* When root is a leaf, examine all its tuples */
				for (offset = FirstOffsetNumber; offset <= max; offset++)
				{
					leafTuple = (SpGistLeafTuple)
						PageGetItem(page, PageGetItemId(page, offset));
					if (leafTuple->tupstate != SPGIST_LIVE)
					{
						/* all tuples on root should be live */
						elog(ERROR, "unexpected SPGiST tuple state: %d",
							 leafTuple->tupstate);
					}

					Assert(ItemPointerIsValid(&leafTuple->heapPtr));
					if (spgLeafTest(index, so,
									leafTuple, isnull,
									stackEntry->level,
									stackEntry->reconstructedValue,
									stackEntry->traversalValue,
									&leafValue,
									&recheck))
					{
						storeRes(so, &leafTuple->heapPtr,
								 leafValue, isnull, recheck);
						reportedSome = true;
					}
				}
			}
			else
			{
				/* Normal case: just examine the chain we arrived at */
				while (offset != InvalidOffsetNumber)
				{
					Assert(offset >= FirstOffsetNumber && offset <= max);
					leafTuple = (SpGistLeafTuple)
						PageGetItem(page, PageGetItemId(page, offset));
					if (leafTuple->tupstate != SPGIST_LIVE)
					{
						if (leafTuple->tupstate == SPGIST_REDIRECT)
						{
							/* redirection tuple should be first in chain */
							Assert(offset == ItemPointerGetOffsetNumber(&stackEntry->ptr));
							/* transfer attention to redirect point */
							stackEntry->ptr = ((SpGistDeadTuple) leafTuple)->pointer;
							Assert(ItemPointerGetBlockNumber(&stackEntry->ptr) != SPGIST_METAPAGE_BLKNO);
							goto redirect;
						}
						if (leafTuple->tupstate == SPGIST_DEAD)
						{
							/* dead tuple should be first in chain */
							Assert(offset == ItemPointerGetOffsetNumber(&stackEntry->ptr));
							/* No live entries on this page */
							Assert(leafTuple->nextOffset == InvalidOffsetNumber);
							break;
						}
						/* We should not arrive at a placeholder */
						elog(ERROR, "unexpected SPGiST tuple state: %d",
							 leafTuple->tupstate);
					}

					Assert(ItemPointerIsValid(&leafTuple->heapPtr));
					if (spgLeafTest(index, so,
									leafTuple, isnull,
									stackEntry->level,
									stackEntry->reconstructedValue,
									stackEntry->traversalValue,
									&leafValue,
									&recheck))
					{
						storeRes(so, &leafTuple->heapPtr,
								 leafValue, isnull, recheck);
						reportedSome = true;
					}

					offset = leafTuple->nextOffset;
				}
			}
		}
		else					/* page is inner */
		{
			SpGistInnerTuple innerTuple;
			spgInnerConsistentIn in;
			spgInnerConsistentOut out;
			FmgrInfo   *procinfo;
			SpGistNodeTuple *nodes;
			SpGistNodeTuple node;
			int			i;
			MemoryContext oldCtx;

			innerTuple = (SpGistInnerTuple) PageGetItem(page,
														PageGetItemId(page, offset));

			if (innerTuple->tupstate != SPGIST_LIVE)
			{
				if (innerTuple->tupstate == SPGIST_REDIRECT)
				{
					/* transfer attention to redirect point */
					stackEntry->ptr = ((SpGistDeadTuple) innerTuple)->pointer;
					Assert(ItemPointerGetBlockNumber(&stackEntry->ptr) != SPGIST_METAPAGE_BLKNO);
					goto redirect;
				}
				elog(ERROR, "unexpected SPGiST tuple state: %d",
					 innerTuple->tupstate);
			}

			/* use temp context for calling inner_consistent */
			oldCtx = MemoryContextSwitchTo(so->tempCxt);

			in.scankeys = so->keyData;
			in.nkeys = so->numberOfKeys;
			in.reconstructedValue = stackEntry->reconstructedValue;
			in.traversalMemoryContext = so->traversalCxt;
			in.traversalValue = stackEntry->traversalValue;
			in.level = stackEntry->level;
			in.returnData = so->want_itup;
			in.allTheSame = innerTuple->allTheSame;
			in.hasPrefix = (innerTuple->prefixSize > 0);
			in.prefixDatum = SGITDATUM(innerTuple, &so->state);
			in.nNodes = innerTuple->nNodes;
			in.nodeLabels = spgExtractNodeLabels(&so->state, innerTuple);

			/* collect node pointers */
			nodes = (SpGistNodeTuple *) palloc(sizeof(SpGistNodeTuple) * in.nNodes);
			SGITITERATE(innerTuple, i, node)
			{
				nodes[i] = node;
			}

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

			if (!isnull)
			{
				/* use user-defined inner consistent method */
				procinfo = index_getprocinfo(index, 1, SPGIST_INNER_CONSISTENT_PROC);
				FunctionCall2Coll(procinfo,
								  index->rd_indcollation[0],
								  PointerGetDatum(&in),
								  PointerGetDatum(&out));
			}
			else
			{
				/* force all children to be visited */
				out.nNodes = in.nNodes;
				out.nodeNumbers = (int *) palloc(sizeof(int) * in.nNodes);
				for (i = 0; i < in.nNodes; i++)
					out.nodeNumbers[i] = i;
			}

			MemoryContextSwitchTo(oldCtx);

			/* If allTheSame, they should all or none of 'em match */
			if (innerTuple->allTheSame)
				if (out.nNodes != 0 && out.nNodes != in.nNodes)
					elog(ERROR, "inconsistent inner_consistent results for allTheSame inner tuple");

			for (i = 0; i < out.nNodes; i++)
			{
				int			nodeN = out.nodeNumbers[i];

				Assert(nodeN >= 0 && nodeN < in.nNodes);
				if (ItemPointerIsValid(&nodes[nodeN]->t_tid))
				{
					ScanStackEntry *newEntry;

					/* Create new work item for this node */
					newEntry = palloc(sizeof(ScanStackEntry));
					newEntry->ptr = nodes[nodeN]->t_tid;
					if (out.levelAdds)
						newEntry->level = stackEntry->level + out.levelAdds[i];
					else
						newEntry->level = stackEntry->level;
					/* Must copy value out of temp context */
					if (out.reconstructedValues)
						newEntry->reconstructedValue =
							datumCopy(out.reconstructedValues[i],
									  so->state.attLeafType.attbyval,
									  so->state.attLeafType.attlen);
					else
						newEntry->reconstructedValue = (Datum) 0;

					/*
					 * Elements of out.traversalValues should be allocated in
					 * in.traversalMemoryContext, which is actually a long
					 * lived context of index scan.
					 */
					newEntry->traversalValue = (out.traversalValues) ?
						out.traversalValues[i] : NULL;

					so->scanStack = lcons(newEntry, so->scanStack);
				}
			}
		}

		/* done with this scan stack entry */
		freeScanStackEntry(so, stackEntry);
		/* clear temp context before proceeding to the next one */
		MemoryContextReset(so->tempCxt);
	}

	if (buffer != InvalidBuffer)
		UnlockReleaseBuffer(buffer);
}

/* storeRes subroutine for getbitmap case */
static void
storeBitmap(SpGistScanOpaque so, ItemPointer heapPtr,
			Datum leafValue, bool isnull, bool recheck)
{
	tbm_add_tuples(so->tbm, heapPtr, 1, recheck);
	so->ntids++;
}

int64
spggetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
{
	SpGistScanOpaque so = (SpGistScanOpaque) scan->opaque;

	/* Copy want_itup to *so so we don't need to pass it around separately */
	so->want_itup = false;

	so->tbm = tbm;
	so->ntids = 0;

	spgWalk(scan->indexRelation, so, true, storeBitmap, scan->xs_snapshot);

	return so->ntids;
}

/* storeRes subroutine for gettuple case */
static void
storeGettuple(SpGistScanOpaque so, ItemPointer heapPtr,
			  Datum leafValue, bool isnull, bool recheck)
{
	Assert(so->nPtrs < MaxIndexTuplesPerPage);
	so->heapPtrs[so->nPtrs] = *heapPtr;
	so->recheck[so->nPtrs] = recheck;
	if (so->want_itup)
	{
		/*
		 * Reconstruct index data.  We have to copy the datum out of the temp
		 * context anyway, so we may as well create the tuple here.
		 */
		so->reconTups[so->nPtrs] = heap_form_tuple(so->indexTupDesc,
												   &leafValue,
												   &isnull);
	}
	so->nPtrs++;
}

bool
spggettuple(IndexScanDesc scan, ScanDirection dir)
{
	SpGistScanOpaque so = (SpGistScanOpaque) scan->opaque;

	if (dir != ForwardScanDirection)
		elog(ERROR, "SP-GiST only supports forward scan direction");

	/* Copy want_itup to *so so we don't need to pass it around separately */
	so->want_itup = scan->xs_want_itup;

	for (;;)
	{
		if (so->iPtr < so->nPtrs)
		{
			/* continuing to return tuples from a leaf page */
			scan->xs_ctup.t_self = so->heapPtrs[so->iPtr];
			scan->xs_recheck = so->recheck[so->iPtr];
			scan->xs_hitup = so->reconTups[so->iPtr];
			so->iPtr++;
			return true;
		}

		if (so->want_itup)
		{
			/* Must pfree reconstructed tuples to avoid memory leak */
			int			i;

			for (i = 0; i < so->nPtrs; i++)
				pfree(so->reconTups[i]);
		}
		so->iPtr = so->nPtrs = 0;

		spgWalk(scan->indexRelation, so, false, storeGettuple,
				scan->xs_snapshot);

		if (so->nPtrs == 0)
			break;				/* must have completed scan */
	}

	return false;
}

bool
spgcanreturn(Relation index, int attno)
{
	SpGistCache *cache;

	/* We can do it if the opclass config function says so */
	cache = spgGetCache(index);

	return cache->config.canReturnData;
}
