/*-------------------------------------------------------------------------
 *
 * bufpage.c--
 *    POSTGRES standard buffer page code.
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    $Header: /cvsroot/pgsql/src/backend/storage/page/bufpage.c,v 1.3 1996/11/08 05:59:03 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include <string.h>
#include <sys/types.h>
#include <sys/file.h>

#include "postgres.h"

#include "storage/item.h"
#include "storage/buf.h"
#include "storage/bufmgr.h"
#include "utils/palloc.h"
#include "utils/memutils.h"
#include "storage/bufpage.h"

#include "lib/qsort.h"

static bool PageManagerShuffle = true;	/* default is shuffle mode */

/* ----------------------------------------------------------------
 *			Buffer support functions
 * ----------------------------------------------------------------
 */
/*
 * BufferGetPageSize --
 *	Returns the page size within a buffer.
 *
 * Notes:
 *	Assumes buffer is valid.
 *
 *	The buffer can be a raw disk block and need not contain a valid
 *	(formatted) disk page.
 */
Size
BufferGetPageSize(Buffer buffer)
{
    Size	pageSize;
    
    Assert(BufferIsValid(buffer));
    pageSize = BLCKSZ;	/* XXX dig out of buffer descriptor */
    
    Assert(PageSizeIsValid(pageSize));
    return (pageSize);
}

/*
 * BufferGetPage --
 *	Returns the page associated with a buffer.
 */
Page
BufferGetPage(Buffer buffer)
{
    return (Page) BufferGetBlock(buffer);
}


/* ----------------------------------------------------------------
 *			Page support functions
 * ----------------------------------------------------------------
 */

/*
 * PageInit --
 *	Initializes the contents of a page.
 */
void
PageInit(Page page, Size pageSize, Size specialSize)
{
    PageHeader p = (PageHeader) page;

    Assert(pageSize == BLCKSZ);
    Assert(pageSize >
	   specialSize + sizeof(PageHeaderData) - sizeof(ItemIdData));
    
    specialSize = DOUBLEALIGN(specialSize);

    p->pd_lower = sizeof(PageHeaderData) - sizeof(ItemIdData);
    p->pd_upper = pageSize - specialSize;
    p->pd_special = pageSize - specialSize;
    PageSetPageSize(page, pageSize);
}

/*
 * PageGetItem --
 *	Retrieves an item on the given page.
 *
 * Note:
 *	This does change the status of any of the resources passed.
 *	The semantics may change in the future.
 */
Item
PageGetItem(Page page, ItemId itemId)
{
    Item	item;
    
    Assert(PageIsValid(page));
    Assert((*itemId).lp_flags & LP_USED);
    
    item = (Item)(((char *)page) + (*itemId).lp_off);
    
    return (item);
}

/*
 * PageAddItem --
 *	Adds item to the given page.
 *
 * Note:
 *	This does not assume that the item resides on a single page.
 *	It is the responsiblity of the caller to act appropriately
 *	depending on this fact.  The "pskip" routines provide a
 *	friendlier interface, in this case.
 *	
 *	This does change the status of any of the resources passed.
 *	The semantics may change in the future.
 *
 *	This routine should probably be combined with others?
 */
/* ----------------
 *	PageAddItem
 *
 *	add an item to a page.
 *
 *   Notes on interface:
 *  	If offsetNumber is valid, shuffle ItemId's down to make room
 * 	to use it, if PageManagerShuffle is true.  If PageManagerShuffle is
 *  	false, then overwrite the specified ItemId.  (PageManagerShuffle is
 *  	true by default, and is modified by calling PageManagerModeSet.)
 *  	If offsetNumber is not valid, then assign one by finding the first 
 *  	one that is both unused and deallocated.
 *
 *   NOTE: If offsetNumber is valid, and PageManagerShuffle is true, it
 *  	is assumed that there is room on the page to shuffle the ItemId's
 *  	down by one.
 * ----------------
 */
OffsetNumber
PageAddItem(Page page,
	    Item item,
	    Size size,
	    OffsetNumber offsetNumber,
	    ItemIdFlags flags)
{
    register 		i;
    Size		alignedSize;
    Offset		lower;
    Offset		upper;
    ItemId		itemId;
    ItemId		fromitemId, toitemId;
    OffsetNumber 	limit;
    
    bool shuffled = false;
    
    /*
     *  Find first unallocated offsetNumber
     */
    limit = OffsetNumberNext(PageGetMaxOffsetNumber(page));
    
    /* was offsetNumber passed in? */
    if (OffsetNumberIsValid(offsetNumber)) {
	if (PageManagerShuffle == true) {
	    /* shuffle ItemId's (Do the PageManager Shuffle...) */
	    for (i = (limit - 1); i >= offsetNumber; i--) {
		fromitemId = &((PageHeader)page)->pd_linp[i - 1];
		toitemId = &((PageHeader)page)->pd_linp[i];
		*toitemId = *fromitemId;
	    }
	    shuffled = true;	/* need to increase "lower" */
	} else { /* overwrite mode */
	    itemId = &((PageHeader)page)->pd_linp[offsetNumber - 1];
	    if (((*itemId).lp_flags & LP_USED)  || 
		((*itemId).lp_len != 0)) {
		elog(WARN, "PageAddItem: tried overwrite of used ItemId");
		return (InvalidOffsetNumber);
	    }
	}
    } else {	/* offsetNumber was not passed in, so find one */
	/* look for "recyclable" (unused & deallocated) ItemId */
	for (offsetNumber = 1; offsetNumber < limit; offsetNumber++) {
	    itemId = &((PageHeader)page)->pd_linp[offsetNumber - 1];
	    if ((((*itemId).lp_flags & LP_USED) == 0) && 
		((*itemId).lp_len == 0)) 
		break;
	}
    }
    if (offsetNumber > limit)
	lower = (Offset) (((char *) (&((PageHeader)page)->pd_linp[offsetNumber])) - ((char *) page));
    else if (offsetNumber == limit || shuffled == true)
	lower = ((PageHeader)page)->pd_lower + sizeof (ItemIdData);
    else
	lower = ((PageHeader)page)->pd_lower;
    
    alignedSize = DOUBLEALIGN(size);
    
    upper = ((PageHeader)page)->pd_upper - alignedSize;
    
    if (lower > upper) {
	return (InvalidOffsetNumber);
    }
    
    itemId = &((PageHeader)page)->pd_linp[offsetNumber - 1];
    (*itemId).lp_off = upper;
    (*itemId).lp_len = size;
    (*itemId).lp_flags = flags;
    memmove((char *)page + upper, item, size);
    ((PageHeader)page)->pd_lower = lower;
    ((PageHeader)page)->pd_upper = upper;
    
    return (offsetNumber);
}

/*
 * PageGetTempPage --
 *	Get a temporary page in local memory for special processing
 */
Page
PageGetTempPage(Page page, Size specialSize)
{
    Size	pageSize;
    Size	size;
    Page	temp;
    PageHeader	thdr;
    
    pageSize = PageGetPageSize(page);
    
    if ((temp = (Page) palloc(pageSize)) == (Page) NULL)
	elog(FATAL, "Cannot allocate %d bytes for temp page.", pageSize);
    thdr = (PageHeader) temp;
    
    /* copy old page in */
    memmove(temp, page, pageSize);
    
    /* clear out the middle */
    size = (pageSize - sizeof(PageHeaderData)) + sizeof(ItemIdData);
    size -= DOUBLEALIGN(specialSize);
    memset((char *) &(thdr->pd_linp[0]), 0, size);
    
    /* set high, low water marks */
    thdr->pd_lower = sizeof (PageHeaderData) - sizeof (ItemIdData);
    thdr->pd_upper = pageSize - DOUBLEALIGN(specialSize);
    
    return (temp);
}

/*
 * PageRestoreTempPage --
 *	Copy temporary page back to permanent page after special processing
 *	and release the temporary page.
 */
void
PageRestoreTempPage(Page tempPage, Page oldPage)
{
    Size	pageSize;
    
    pageSize = PageGetPageSize(tempPage);
    memmove((char *) oldPage, (char *) tempPage, pageSize);
    
    pfree(tempPage);
}

/*
 * PageGetMaxOffsetNumber --
 *	Returns the maximum offset number used by the given page.
 *
 *	NOTE: The offset is invalid if the page is non-empty.
 *	Test whether PageIsEmpty before calling this routine
 *	and/or using its return value.
 */
OffsetNumber
PageGetMaxOffsetNumber(Page page)
{
    LocationIndex	low;
    OffsetNumber	i;
    
    low = ((PageHeader) page)->pd_lower;
    i = (low - (sizeof(PageHeaderData) - sizeof(ItemIdData)))
	/ sizeof(ItemIdData);
    
    return(i);
}	

/* ----------------
 *	itemid stuff for PageRepairFragmentation
 * ----------------
 */
struct itemIdSortData {
    int		offsetindex;	/* linp array index */
    ItemIdData  itemiddata;
};

static int
itemidcompare(struct itemIdSortData *itemidp1, struct itemIdSortData *itemidp2)
{
    if (itemidp1->itemiddata.lp_off == itemidp2->itemiddata.lp_off)
	return(0);
    else if (itemidp1->itemiddata.lp_off < itemidp2->itemiddata.lp_off)
	return(1);
    else
	return(-1);
}

/*
 * PageRepairFragmentation --
 *	Frees fragmented space on a page.
 */
void
PageRepairFragmentation(Page page)
{
    int 		i;
    struct itemIdSortData 	*itemidbase, *itemidptr;
    ItemId 		lp;
    int 		nline, nused;
    int 		itemidcompare();
    Offset 		upper;
    Size 		alignedSize;
    
    nline = (int16) PageGetMaxOffsetNumber(page);
    nused = 0;
    for (i=0; i<nline; i++) {
	lp = ((PageHeader)page)->pd_linp + i;
	if ((*lp).lp_flags & LP_USED)
	    nused++;
    }
    
    if (nused == 0) {
	for (i=0; i<nline; i++) {
	    lp = ((PageHeader)page)->pd_linp + i;
	    if ((*lp).lp_len > 0) 	/* unused, but allocated */
		(*lp).lp_len = 0;	/* indicate unused & deallocated */
	}
	
	((PageHeader)page)->pd_upper = ((PageHeader)page)->pd_special;
    } else {	/* nused != 0 */
	itemidbase = (struct itemIdSortData *) 
	    palloc(sizeof(struct itemIdSortData) * nused);
	memset((char *) itemidbase, 0, sizeof(struct itemIdSortData) * nused);
	itemidptr = itemidbase;
	for (i=0; i<nline; i++) {
	    lp = ((PageHeader)page)->pd_linp + i;
	    if ((*lp).lp_flags & LP_USED) {
		itemidptr->offsetindex = i;
		itemidptr->itemiddata = *lp;
		itemidptr++;
	    } else {
		if ((*lp).lp_len > 0) 	/* unused, but allocated */
		    (*lp).lp_len = 0;	/* indicate unused & deallocated */
	    }
	}
	
	/* sort itemIdSortData array...*/
	pg_qsort((char *) itemidbase, nused, sizeof(struct itemIdSortData),
		 (void*) itemidcompare);
	
	/* compactify page */
	((PageHeader)page)->pd_upper = ((PageHeader)page)->pd_special;
	
	for (i=0, itemidptr = itemidbase; i<nused; i++, itemidptr++) {
	    lp = ((PageHeader)page)->pd_linp + itemidptr->offsetindex;
	    alignedSize = DOUBLEALIGN((*lp).lp_len);
	    upper = ((PageHeader)page)->pd_upper - alignedSize;
	    memmove((char *) page + upper,
		    (char *)page + (*lp).lp_off, 
		    (*lp).lp_len);
	    (*lp).lp_off = upper;
	    ((PageHeader)page)->pd_upper = upper;
	}
	
	pfree(itemidbase);
    }
}

/*
 * PageGetFreeSpace --
 *	Returns the size of the free (allocatable) space on a page.
 */
Size
PageGetFreeSpace(Page page)
{
    Size	space;
    
    
    space = ((PageHeader)page)->pd_upper - ((PageHeader)page)->pd_lower;
    
    if (space < sizeof (ItemIdData)) {
	return (0);
    }
    space -= sizeof (ItemIdData);		/* XXX not always true */
    
    return (space);
}

/*
 * PageManagerModeSet --
 *
 *   Sets mode to either: ShufflePageManagerMode (the default) or
 *   OverwritePageManagerMode.  For use by access methods code
 *   for determining semantics of PageAddItem when the offsetNumber
 *   argument is passed in.
 */
void
PageManagerModeSet(PageManagerMode mode)
{
    if (mode == ShufflePageManagerMode)
	PageManagerShuffle = true;
    else if (mode == OverwritePageManagerMode)
	PageManagerShuffle = false;
}

/*
 *----------------------------------------------------------------
 * PageIndexTupleDelete
 *----------------------------------------------------------------
 *
 *	This routine does the work of removing a tuple from an index page.
 */
void
PageIndexTupleDelete(Page page, OffsetNumber offnum)
{
    PageHeader 	phdr;
    char 	*addr;
    ItemId 	tup;
    Size 	size;
    char 	*locn;
    int 	nbytes;
    int		offidx;
    
    phdr = (PageHeader) page;
    
    /* change offset number to offset index */
    offidx = offnum - 1;
    
    tup = PageGetItemId(page, offnum);
    size = ItemIdGetLength(tup);
    size = DOUBLEALIGN(size);
    
    /* location of deleted tuple data */
    locn = (char *) (page + ItemIdGetOffset(tup));
    
    /*
     * First, we want to get rid of the pd_linp entry for the index
     * tuple.  We copy all subsequent linp's back one slot in the
     * array.
     */
    
    nbytes = phdr->pd_lower -
	((char *)&phdr->pd_linp[offidx + 1] - (char *) phdr);
    memmove((char *) &(phdr->pd_linp[offidx]),
	    (char *) &(phdr->pd_linp[offidx + 1]),
	    nbytes);
    
    /*
     * Now move everything between the old upper bound (beginning of tuple
     * space) and the beginning of the deleted tuple forward, so that
     * space in the middle of the page is left free.  If we've just deleted
     * the tuple at the beginning of tuple space, then there's no need
     * to do the copy (and bcopy on some architectures SEGV's if asked
     * to move zero bytes).
     */
    
    /* beginning of tuple space */
    addr = (char *) (page + phdr->pd_upper);
    
    if (locn != addr)
	memmove(addr + size, addr, (int) (locn - addr));
    
    /* adjust free space boundary pointers */
    phdr->pd_upper += size;
    phdr->pd_lower -= sizeof (ItemIdData);
    
    /* finally, we need to adjust the linp entries that remain */
    if (!PageIsEmpty(page))
	PageIndexTupleDeleteAdjustLinePointers(phdr, locn, size);
}

/*
 *----------------------------------------------------------------
 * PageIndexTupleDeleteAdjustLinePointers
 *----------------------------------------------------------------
 *
 *	Once the line pointers and tuple data have been shifted around
 *	on the page, we need to go down the line pointer vector and
 *	adjust pointers to reflect new locations.  Anything that used
 *	to be before the deleted tuple's data was moved forward by the
 *	size of the deleted tuple.
 *
 *	This routine does the work of adjusting the line pointers.
 *	Location is where the tuple data used to lie; size is how
 *	much space it occupied.  We assume that size has been aligned
 *	as required by the time we get here.
 *
 *	This routine should never be called on an empty page.
 */
void
PageIndexTupleDeleteAdjustLinePointers(PageHeader phdr,
				       char *location,
				       Size size)
{
    int i;
    
    /* location is an index into the page... */
    location -= (int) phdr;
    
    for (i = PageGetMaxOffsetNumber((Page) phdr) - 1; i >= 0; i--) {
	if (phdr->pd_linp[i].lp_off <= (unsigned) location) {
	    phdr->pd_linp[i].lp_off += size;
	}
    }
}
