/*
 * linux/fs/hfs/bdelete.c
 *
 * Copyright (C) 1995-1997  Paul H. Hargrove
 * This file may be distributed under the terms of the GNU General Public License.
 *
 * This file contains the code to delete records in a B-tree.
 *
 * "XXX" in a comment is a note to myself to consider changing something.
 *
 * In function preconditions the term "valid" applied to a pointer to
 * a structure means that the pointer is non-NULL and the structure it
 * points to has all fields initialized to consistent values.
 */

#include "hfs_btree.h"

/*================ Variable-like macros ================*/

#define FULL (HFS_SECTOR_SIZE - sizeof(struct NodeDescriptor))
#define NO_SPACE (HFS_SECTOR_SIZE+1)

/*================ File-local functions ================*/

/*
 * bdelete_nonempty()
 *
 * Description:
 *   Deletes a record from a given bnode without regard to it becoming empty.
 * Input Variable(s):
 *   struct hfs_brec* brec: pointer to the brec for the deletion
 *   struct hfs_belem* belem: which node in 'brec' to delete from
 * Output Variable(s):
 *   NONE
 * Returns:
 *   void
 * Preconditions:
 *   'brec' points to a valid (struct hfs_brec).
 *   'belem' points to a valid (struct hfs_belem) in 'brec'.
 * Postconditions:
 *   The record has been inserted in the position indicated by 'brec'.
 */
static void bdelete_nonempty(struct hfs_brec *brec, struct hfs_belem *belem)
{
        int i, rec, nrecs, tomove;
        hfs_u16 size;
        hfs_u8 *start;
        struct hfs_bnode *bnode = belem->bnr.bn;

        rec = belem->record;
        nrecs = bnode->ndNRecs;
        size = bnode_rsize(bnode, rec);
        tomove = bnode_offset(bnode, nrecs+1) - bnode_offset(bnode, rec+1);
        
        /* adjust the record table */
        for (i = rec+1; i <= nrecs; ++i) {
                hfs_put_hs(bnode_offset(bnode,i+1) - size, RECTBL(bnode,i));
        }

        /* move it down */
        start = bnode_key(bnode, rec);
        memmove(start, start + size, tomove);

        /* update record count */
        --bnode->ndNRecs;
}

/*
 * del_root()
 *
 * Description:
 *   Delete the current root bnode.
 * Input Variable(s):
 *   struct hfs_bnode_ref *root: reference to the root bnode
 * Output Variable(s):
 *   NONE
 * Returns:
 *   int: 0 on success, error code on failure
 * Preconditions:
 *   'root' refers to the root bnode with HFS_LOCK_WRITE access.
 *   None of 'root's children are held with HFS_LOCK_WRITE access.
 * Postconditions:
 *   The current 'root' node is removed from the tree and the depth
 *    of the tree is reduced by one.
 *   If 'root' is an index node with exactly one child, then that
 *    child becomes the new root of the tree.
 *   If 'root' is an empty leaf node the tree becomes empty.
 *   Upon return access to 'root' is relinquished.
 */
static int del_root(struct hfs_bnode_ref *root)
{
        struct hfs_btree *tree = root->bn->tree;
        struct hfs_bnode_ref child;
        hfs_u32 node;

        if (root->bn->ndNRecs > 1) {
                return 0;
        } else if (root->bn->ndNRecs == 0) {
                /* tree is empty */
                tree->bthRoot = 0;
                tree->root = NULL;
                tree->bthRoot = 0;
                tree->bthFNode = 0;
                tree->bthLNode = 0;
                --tree->bthDepth;
                tree->dirt = 1;
                if (tree->bthDepth) {
                        hfs_warn("hfs_bdelete: empty tree with bthDepth=%d\n",
                                 tree->bthDepth);
                        goto bail;
                }
                return hfs_bnode_free(root);
        } else if (root->bn->ndType == ndIndxNode) {
                /* tree is non-empty */
                node = hfs_get_hl(bkey_record(bnode_datastart(root->bn)));

                child = hfs_bnode_find(tree, node, HFS_LOCK_READ);
                if (!child.bn) {
                        hfs_warn("hfs_bdelete: can't read child node.\n");
                        goto bail;
                }
                        
                child.bn->sticky = HFS_STICKY;
                if (child.bn->next) {
                        child.bn->next->prev = child.bn->prev;
                }
                if (child.bn->prev) {
                        child.bn->prev->next = child.bn->next;
                }
                if (bhash(tree, child.bn->node) == child.bn) {
                        bhash(tree, child.bn->node) = child.bn->next;
                }
                child.bn->next = NULL;
                child.bn->prev = NULL;

                tree->bthRoot = child.bn->node;
                tree->root = child.bn;

                /* re-assign bthFNode and bthLNode if the new root is
                   a leaf node. */
                if (child.bn->ndType == ndLeafNode) {
                        tree->bthFNode = node;
                        tree->bthLNode = node;
                }
                hfs_bnode_relse(&child);

                tree->bthRoot = node;
                --tree->bthDepth;
                tree->dirt = 1;
                if (!tree->bthDepth) {
                        hfs_warn("hfs_bdelete: non-empty tree with "
                                 "bthDepth == 0\n");
                        goto bail;
                }
                return hfs_bnode_free(root);    /* marks tree dirty */
        }
        hfs_bnode_relse(root);
        return 0;

bail:
        hfs_bnode_relse(root);
        return -EIO;
}


/*
 * delete_empty_bnode()
 *
 * Description:
 *   Removes an empty non-root bnode from between 'left' and 'right'
 * Input Variable(s):
 *   hfs_u32 left_node: node number of 'left' or zero if 'left' is invalid
 *   struct hfs_bnode_ref *left: reference to the left neighbor of the
 *    bnode to remove, or invalid if no such neighbor exists.
 *   struct hfs_bnode_ref *center: reference to the bnode to remove
 *   hfs_u32 right_node: node number of 'right' or zero if 'right' is invalid
 *   struct hfs_bnode_ref *right: reference to the right neighbor of the
 *    bnode to remove, or invalid if no such neighbor exists.
 * Output Variable(s):
 *   NONE
 * Returns:
 *   void
 * Preconditions:
 *   'left_node' is as described above.
 *   'left' points to a valid (struct hfs_bnode_ref) having HFS_LOCK_WRITE
 *    access and referring to the left neighbor of 'center' if such a
 *    neighbor exists, or invalid if no such neighbor exists.
 *   'center' points to a valid (struct hfs_bnode_ref) having HFS_LOCK_WRITE
 *    access and referring to the bnode to delete.
 *   'right_node' is as described above.
 *   'right' points to a valid (struct hfs_bnode_ref) having HFS_LOCK_WRITE
 *    access and referring to the right neighbor of 'center' if such a
 *    neighbor exists, or invalid if no such neighbor exists.
 * Postconditions:
 *   If 'left' is valid its 'ndFLink' field becomes 'right_node'.
 *   If 'right' is valid its 'ndBLink' field becomes 'left_node'.
 *   If 'center' was the first leaf node then the tree's 'bthFNode'
 *    field becomes 'right_node' 
 *   If 'center' was the last leaf node then the tree's 'bthLNode'
 *    field becomes 'left_node' 
 *   'center' is NOT freed and access to the nodes is NOT relinquished.
 */
static void delete_empty_bnode(hfs_u32 left_node, struct hfs_bnode_ref *left,
                               struct hfs_bnode_ref *center,
                               hfs_u32 right_node, struct hfs_bnode_ref *right)
{
        struct hfs_bnode *bnode = center->bn;

        if (left_node) {
                left->bn->ndFLink = right_node;
        } else if (bnode->ndType == ndLeafNode) {
                bnode->tree->bthFNode = right_node;
                bnode->tree->dirt = 1;
        }

        if (right_node) {
                right->bn->ndBLink = left_node;
        } else if (bnode->ndType == ndLeafNode) {
                bnode->tree->bthLNode = left_node;
                bnode->tree->dirt = 1;
        }
}

/*
 * balance()
 *
 * Description:
 *   Attempt to equalize space usage in neighboring bnodes.
 * Input Variable(s):
 *   struct hfs_bnode *left: the left bnode.
 *   struct hfs_bnode *right: the right bnode.
 * Output Variable(s):
 *   NONE
 * Returns:
 *   void
 * Preconditions:
 *   'left' and 'right' point to valid (struct hfs_bnode)s obtained
 *    with HFS_LOCK_WRITE access, and are neighbors.
 * Postconditions:
 *   Records are shifted either left or right to make the space usage
 *   nearly equal.  When exact equality is not possible the break
 *   point is chosen to reduce data movement.
 *   The key corresponding to 'right' in its parent is NOT updated.
 */
static void balance(struct hfs_bnode *left, struct hfs_bnode *right)
{
        int index, left_free, right_free, half;

        left_free = bnode_freespace(left);
        right_free = bnode_freespace(right);
        half = (left_free + right_free)/2;

        if (left_free < right_free) {
                /* shift right to balance */
                index = left->ndNRecs + 1;
                while (right_free >= half) {
                        --index;
                        right_free -= bnode_rsize(left,index)+sizeof(hfs_u16);
                }
                if (index < left->ndNRecs) {
#if defined(DEBUG_ALL) || defined(DEBUG_BALANCE)
                        hfs_warn("shifting %d of %d recs right to balance: ",
                               left->ndNRecs - index, left->ndNRecs);
#endif
                        hfs_bnode_shift_right(left, right, index+1);
#if defined(DEBUG_ALL) || defined(DEBUG_BALANCE)
                        hfs_warn("%d,%d\n", left->ndNRecs, right->ndNRecs);
#endif
                }
        } else {
                /* shift left to balance */
                index = 0;
                while (left_free >= half) {
                        ++index;
                        left_free -= bnode_rsize(right,index)+sizeof(hfs_u16);
                }
                if (index > 1) {
#if defined(DEBUG_ALL) || defined(DEBUG_BALANCE)
                        hfs_warn("shifting %d of %d recs left to balance: ",
                               index-1, right->ndNRecs);
#endif
                        hfs_bnode_shift_left(left, right, index-1);
#if defined(DEBUG_ALL) || defined(DEBUG_BALANCE)
                        hfs_warn("%d,%d\n", left->ndNRecs, right->ndNRecs);
#endif
                }
        }
}

/*
 * bdelete()
 *
 * Delete the given record from a B-tree.
 */
static int bdelete(struct hfs_brec *brec)
{
        struct hfs_btree *tree = brec->tree;
        struct hfs_belem *belem = brec->bottom;
        struct hfs_belem *parent = (belem-1);
        struct hfs_bnode *bnode;
        hfs_u32 left_node, right_node;
        struct hfs_bnode_ref left, right;
        int left_space, right_space, min_space;
        int fix_right_key;
        int fix_key;
        
        while ((belem > brec->top) &&
               (belem->flags & (HFS_BPATH_UNDERFLOW | HFS_BPATH_FIRST))) {
                bnode = belem->bnr.bn;
                fix_key = belem->flags & HFS_BPATH_FIRST;
                fix_right_key = 0;

                bdelete_nonempty(brec, belem);

                if (bnode->node == tree->root->node) {
                        del_root(&belem->bnr);
                        --brec->bottom;
                        goto done;
                }

                /* check for btree corruption which could lead to deadlock */
                left_node = bnode->ndBLink;
                right_node = bnode->ndFLink;
                if ((left_node && hfs_bnode_in_brec(left_node, brec)) ||
                    (right_node && hfs_bnode_in_brec(right_node, brec)) ||
                    (left_node == right_node)) {
                        hfs_warn("hfs_bdelete: corrupt btree\n");
                        hfs_brec_relse(brec, NULL);
                        return -EIO;
                }

                /* grab the left neighbor if it exists */
                if (left_node) {
                        hfs_bnode_lock(&belem->bnr, HFS_LOCK_RESRV);
                        left = hfs_bnode_find(tree,left_node,HFS_LOCK_WRITE);
                        if (!left.bn) {
                                hfs_warn("hfs_bdelete: unable to read left "
                                         "neighbor.\n");
                                hfs_brec_relse(brec, NULL);
                                return -EIO;
                        }
                        hfs_bnode_lock(&belem->bnr, HFS_LOCK_WRITE);
                        if (parent->record != 1) {
                                left_space = bnode_freespace(left.bn);
                        } else {
                                left_space = NO_SPACE;
                        }
                } else {
                        left.bn = NULL;
                        left_space = NO_SPACE;
                }

                /* grab the right neighbor if it exists */
                if (right_node) {
                        right = hfs_bnode_find(tree,right_node,HFS_LOCK_WRITE);
                        if (!right.bn) {
                                hfs_warn("hfs_bdelete: unable to read right "
                                         "neighbor.\n");
                                hfs_bnode_relse(&left);
                                hfs_brec_relse(brec, NULL);
                                return -EIO;
                        }
                        if (parent->record < parent->bnr.bn->ndNRecs) {
                                right_space = bnode_freespace(right.bn);
                        } else {
                                right_space = NO_SPACE;
                        }
                } else {
                        right.bn = NULL;
                        right_space = NO_SPACE;
                }

                if (left_space < right_space) {
                        min_space = left_space;
                } else {
                        min_space = right_space;
                }

                if (min_space == NO_SPACE) {
                        hfs_warn("hfs_bdelete: no siblings?\n");
                        hfs_brec_relse(brec, NULL);
                        return -EIO;
                }

                if (bnode->ndNRecs == 0) {
                        delete_empty_bnode(left_node, &left, &belem->bnr,
                                           right_node, &right);
                } else if (min_space + bnode_freespace(bnode) >= FULL) {
                        if ((right_space == NO_SPACE) ||
                            ((right_space == min_space) &&
                             (left_space != NO_SPACE))) {
                                hfs_bnode_shift_left(left.bn, bnode,
                                                     bnode->ndNRecs);
                        } else {
                                hfs_bnode_shift_right(bnode, right.bn, 1);
                                fix_right_key = 1;
                        }
                        delete_empty_bnode(left_node, &left, &belem->bnr,
                                           right_node, &right);
                } else if (min_space == right_space) {
                        balance(bnode, right.bn);
                        fix_right_key = 1;
                } else {
                        balance(left.bn, bnode);
                        fix_key = 1;
                }

                if (fix_right_key) {
                        hfs_bnode_update_key(brec, belem, right.bn, 1);
                }

                hfs_bnode_relse(&left);
                hfs_bnode_relse(&right);

                if (bnode->ndNRecs) {
                        if (fix_key) {
                                hfs_bnode_update_key(brec, belem, bnode, 0);
                        }
                        goto done;
                }

                hfs_bnode_free(&belem->bnr);
                --brec->bottom;
                belem = parent;
                --parent;
        }

        if (belem < brec->top) {
                hfs_warn("hfs_bdelete: Missing parent.\n");
                hfs_brec_relse(brec, NULL);
                return -EIO;
        }

        bdelete_nonempty(brec, belem);

done:
        hfs_brec_relse(brec, NULL);
        return 0;
}

/*================ Global functions ================*/

/*
 * hfs_bdelete()
 *
 * Delete the requested record from a B-tree.
 */
int hfs_bdelete(struct hfs_btree *tree, const struct hfs_bkey *key)
{ 
        struct hfs_belem *belem;
        struct hfs_bnode *bnode;
        struct hfs_brec brec;
        int retval;

        if (!tree || (tree->magic != HFS_BTREE_MAGIC) || !key) {
                hfs_warn("hfs_bdelete: invalid arguments.\n");
                return -EINVAL;
        }

        retval = hfs_bfind(&brec, tree, key, HFS_BFIND_DELETE);
        if (!retval) {
                belem = brec.bottom;
                bnode = belem->bnr.bn;

                belem->flags = 0;
                if ((bnode->ndNRecs * sizeof(hfs_u16) + bnode_end(bnode) -
                     bnode_rsize(bnode, belem->record)) < FULL/2) {
                        belem->flags |= HFS_BPATH_UNDERFLOW;
                }
                if (belem->record == 1) {
                        belem->flags |= HFS_BPATH_FIRST;
                }

                if (!belem->flags) {
                        hfs_brec_lock(&brec, brec.bottom);
                } else {
                        hfs_brec_lock(&brec, NULL);
                }

                retval = bdelete(&brec);
                if (!retval) {
                        --brec.tree->bthNRecs;
                        brec.tree->dirt = 1;
                }
                hfs_brec_relse(&brec, NULL);
        }
        return retval;
}