/*
 * rbtree.c -- generic red black tree
 *
 * Copyright (c) 2001-2007, NLnet Labs. All rights reserved.
 * 
 * This software is open source.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer.
 * 
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 * 
 * Neither the name of the NLNET LABS nor the names of its contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

/**
 * \file
 * Implementation of a redblack tree.
 */

#include "config.h"
#include "log.h"
#include "fptr_wlist.h"
#include "util/rbtree.h"

/** Node colour black */
#define BLACK   0
/** Node colour red */
#define RED     1

/** the NULL node, global alloc */
rbnode_type     rbtree_null_node = {
        RBTREE_NULL,            /* Parent.  */
        RBTREE_NULL,            /* Left.  */
        RBTREE_NULL,            /* Right.  */
        NULL,                   /* Key.  */
        BLACK                   /* Color.  */
};

/** rotate subtree left (to preserve redblack property) */
static void rbtree_rotate_left(rbtree_type *rbtree, rbnode_type *node);
/** rotate subtree right (to preserve redblack property) */
static void rbtree_rotate_right(rbtree_type *rbtree, rbnode_type *node);
/** Fixup node colours when insert happened */
static void rbtree_insert_fixup(rbtree_type *rbtree, rbnode_type *node);
/** Fixup node colours when delete happened */
static void rbtree_delete_fixup(rbtree_type* rbtree, rbnode_type* child,
        rbnode_type* child_parent);

/*
 * Creates a new red black tree, initializes and returns a pointer to it.
 *
 * Return NULL on failure.
 *
 */
rbtree_type *
rbtree_create (int (*cmpf)(const void *, const void *))
{
        rbtree_type *rbtree;

        /* Allocate memory for it */
        rbtree = (rbtree_type *) malloc(sizeof(rbtree_type));
        if (!rbtree) {
                return NULL;
        }

        /* Initialize it */
        rbtree_init(rbtree, cmpf);

        return rbtree;
}

void 
rbtree_init(rbtree_type *rbtree, int (*cmpf)(const void *, const void *))
{
        /* Initialize it */
        rbtree->root = RBTREE_NULL;
        rbtree->count = 0;
        rbtree->cmp = cmpf;
}

/*
 * Rotates the node to the left.
 *
 */
static void
rbtree_rotate_left(rbtree_type *rbtree, rbnode_type *node)
{
        rbnode_type *right = node->right;
        node->right = right->left;
        if (right->left != RBTREE_NULL)
                right->left->parent = node;

        right->parent = node->parent;

        if (node->parent != RBTREE_NULL) {
                if (node == node->parent->left) {
                        node->parent->left = right;
                } else  {
                        node->parent->right = right;
                }
        } else {
                rbtree->root = right;
        }
        right->left = node;
        node->parent = right;
}

/*
 * Rotates the node to the right.
 *
 */
static void
rbtree_rotate_right(rbtree_type *rbtree, rbnode_type *node)
{
        rbnode_type *left = node->left;
        node->left = left->right;
        if (left->right != RBTREE_NULL)
                left->right->parent = node;

        left->parent = node->parent;

        if (node->parent != RBTREE_NULL) {
                if (node == node->parent->right) {
                        node->parent->right = left;
                } else  {
                        node->parent->left = left;
                }
        } else {
                rbtree->root = left;
        }
        left->right = node;
        node->parent = left;
}

static void
rbtree_insert_fixup(rbtree_type *rbtree, rbnode_type *node)
{
        rbnode_type     *uncle;

        /* While not at the root and need fixing... */
        while (node != rbtree->root && node->parent->color == RED) {
                /* If our parent is left child of our grandparent... */
                if (node->parent == node->parent->parent->left) {
                        uncle = node->parent->parent->right;

                        /* If our uncle is red... */
                        if (uncle->color == RED) {
                                /* Paint the parent and the uncle black... */
                                node->parent->color = BLACK;
                                uncle->color = BLACK;

                                /* And the grandparent red... */
                                node->parent->parent->color = RED;

                                /* And continue fixing the grandparent */
                                node = node->parent->parent;
                        } else {                                /* Our uncle is black... */
                                /* Are we the right child? */
                                if (node == node->parent->right) {
                                        node = node->parent;
                                        rbtree_rotate_left(rbtree, node);
                                }
                                /* Now we're the left child, repaint and rotate... */
                                node->parent->color = BLACK;
                                node->parent->parent->color = RED;
                                rbtree_rotate_right(rbtree, node->parent->parent);
                        }
                } else {
                        uncle = node->parent->parent->left;

                        /* If our uncle is red... */
                        if (uncle->color == RED) {
                                /* Paint the parent and the uncle black... */
                                node->parent->color = BLACK;
                                uncle->color = BLACK;

                                /* And the grandparent red... */
                                node->parent->parent->color = RED;

                                /* And continue fixing the grandparent */
                                node = node->parent->parent;
                        } else {                                /* Our uncle is black... */
                                /* Are we the right child? */
                                if (node == node->parent->left) {
                                        node = node->parent;
                                        rbtree_rotate_right(rbtree, node);
                                }
                                /* Now we're the right child, repaint and rotate... */
                                node->parent->color = BLACK;
                                node->parent->parent->color = RED;
                                rbtree_rotate_left(rbtree, node->parent->parent);
                        }
                }
        }
        rbtree->root->color = BLACK;
}


/*
 * Inserts a node into a red black tree.
 *
 * Returns NULL on failure or the pointer to the newly added node
 * otherwise.
 */
rbnode_type *
rbtree_insert (rbtree_type *rbtree, rbnode_type *data)
{
        /* XXX Not necessary, but keeps compiler quiet... */
        int r = 0;

        /* We start at the root of the tree */
        rbnode_type     *node = rbtree->root;
        rbnode_type     *parent = RBTREE_NULL;

        fptr_ok(fptr_whitelist_rbtree_cmp(rbtree->cmp));
        /* Lets find the new parent... */
        while (node != RBTREE_NULL) {
                /* Compare two keys, do we have a duplicate? */
                if ((r = rbtree->cmp(data->key, node->key)) == 0) {
                        return NULL;
                }
                parent = node;

                if (r < 0) {
                        node = node->left;
                } else {
                        node = node->right;
                }
        }

        /* Initialize the new node */
        data->parent = parent;
        data->left = data->right = RBTREE_NULL;
        data->color = RED;
        rbtree->count++;

        /* Insert it into the tree... */
        if (parent != RBTREE_NULL) {
                if (r < 0) {
                        parent->left = data;
                } else {
                        parent->right = data;
                }
        } else {
                rbtree->root = data;
        }

        /* Fix up the red-black properties... */
        rbtree_insert_fixup(rbtree, data);

        return data;
}

/*
 * Searches the red black tree, returns the data if key is found or NULL otherwise.
 *
 */
rbnode_type *
rbtree_search (rbtree_type *rbtree, const void *key)
{
        rbnode_type *node;

        if (rbtree_find_less_equal(rbtree, key, &node)) {
                return node;
        } else {
                return NULL;
        }
}

/** helpers for delete: swap node colours */
static void swap_int8(uint8_t* x, uint8_t* y) 
{ 
        uint8_t t = *x; *x = *y; *y = t; 
}

/** helpers for delete: swap node pointers */
static void swap_np(rbnode_type** x, rbnode_type** y) 
{
        rbnode_type* t = *x; *x = *y; *y = t; 
}

/** Update parent pointers of child trees of 'parent' */
static void change_parent_ptr(rbtree_type* rbtree, rbnode_type* parent,
        rbnode_type* old, rbnode_type* new)
{
        if(parent == RBTREE_NULL)
        {
                log_assert(rbtree->root == old);
                if(rbtree->root == old) rbtree->root = new;
                return;
        }
        log_assert(parent->left == old || parent->right == old
                || parent->left == new || parent->right == new);
        if(parent->left == old) parent->left = new;
        if(parent->right == old) parent->right = new;
}
/** Update parent pointer of a node 'child' */
static void change_child_ptr(rbnode_type* child, rbnode_type* old,
        rbnode_type* new)
{
        if(child == RBTREE_NULL) return;
        log_assert(child->parent == old || child->parent == new);
        if(child->parent == old) child->parent = new;
}

rbnode_type* 
rbtree_delete(rbtree_type *rbtree, const void *key)
{
        rbnode_type *to_delete;
        rbnode_type *child;
        if((to_delete = rbtree_search(rbtree, key)) == 0) return 0;
        rbtree->count--;

        /* make sure we have at most one non-leaf child */
        if(to_delete->left != RBTREE_NULL && to_delete->right != RBTREE_NULL)
        {
                /* swap with smallest from right subtree (or largest from left) */
                rbnode_type *smright = to_delete->right;
                while(smright->left != RBTREE_NULL)
                        smright = smright->left;
                /* swap the smright and to_delete elements in the tree,
                 * but the rbnode_type is first part of user data struct
                 * so cannot just swap the keys and data pointers. Instead
                 * readjust the pointers left,right,parent */

                /* swap colors - colors are tied to the position in the tree */
                swap_int8(&to_delete->color, &smright->color);

                /* swap child pointers in parents of smright/to_delete */
                change_parent_ptr(rbtree, to_delete->parent, to_delete, smright);
                if(to_delete->right != smright)
                        change_parent_ptr(rbtree, smright->parent, smright, to_delete);

                /* swap parent pointers in children of smright/to_delete */
                change_child_ptr(smright->left, smright, to_delete);
                change_child_ptr(smright->left, smright, to_delete);
                change_child_ptr(smright->right, smright, to_delete);
                change_child_ptr(smright->right, smright, to_delete);
                change_child_ptr(to_delete->left, to_delete, smright);
                if(to_delete->right != smright)
                        change_child_ptr(to_delete->right, to_delete, smright);
                if(to_delete->right == smright)
                {
                        /* set up so after swap they work */
                        to_delete->right = to_delete;
                        smright->parent = smright;
                }

                /* swap pointers in to_delete/smright nodes */
                swap_np(&to_delete->parent, &smright->parent);
                swap_np(&to_delete->left, &smright->left);
                swap_np(&to_delete->right, &smright->right);

                /* now delete to_delete (which is at the location where the smright previously was) */
        }
        log_assert(to_delete->left == RBTREE_NULL || to_delete->right == RBTREE_NULL);

        if(to_delete->left != RBTREE_NULL) child = to_delete->left;
        else child = to_delete->right;

        /* unlink to_delete from the tree, replace to_delete with child */
        change_parent_ptr(rbtree, to_delete->parent, to_delete, child);
        change_child_ptr(child, to_delete, to_delete->parent);

        if(to_delete->color == RED)
        {
                /* if node is red then the child (black) can be swapped in */
        }
        else if(child->color == RED)
        {
                /* change child to BLACK, removing a RED node is no problem */
                if(child!=RBTREE_NULL) child->color = BLACK;
        }
        else rbtree_delete_fixup(rbtree, child, to_delete->parent);

        /* unlink completely */
        to_delete->parent = RBTREE_NULL;
        to_delete->left = RBTREE_NULL;
        to_delete->right = RBTREE_NULL;
        to_delete->color = BLACK;
        return to_delete;
}

static void rbtree_delete_fixup(rbtree_type* rbtree, rbnode_type* child,
        rbnode_type* child_parent)
{
        rbnode_type* sibling;
        int go_up = 1;

        /* determine sibling to the node that is one-black short */
        if(child_parent->right == child) sibling = child_parent->left;
        else sibling = child_parent->right;

        while(go_up)
        {
                if(child_parent == RBTREE_NULL)
                {
                        /* removed parent==black from root, every path, so ok */
                        return;
                }

                if(sibling->color == RED)
                {       /* rotate to get a black sibling */
                        child_parent->color = RED;
                        sibling->color = BLACK;
                        if(child_parent->right == child)
                                rbtree_rotate_right(rbtree, child_parent);
                        else    rbtree_rotate_left(rbtree, child_parent);
                        /* new sibling after rotation */
                        if(child_parent->right == child) sibling = child_parent->left;
                        else sibling = child_parent->right;
                }

                if(child_parent->color == BLACK 
                        && sibling->color == BLACK
                        && sibling->left->color == BLACK
                        && sibling->right->color == BLACK)
                {       /* fixup local with recolor of sibling */
                        if(sibling != RBTREE_NULL)
                                sibling->color = RED;

                        child = child_parent;
                        child_parent = child_parent->parent;
                        /* prepare to go up, new sibling */
                        if(child_parent->right == child) sibling = child_parent->left;
                        else sibling = child_parent->right;
                }
                else go_up = 0;
        }

        if(child_parent->color == RED
                && sibling->color == BLACK
                && sibling->left->color == BLACK
                && sibling->right->color == BLACK) 
        {
                /* move red to sibling to rebalance */
                if(sibling != RBTREE_NULL)
                        sibling->color = RED;
                child_parent->color = BLACK;
                return;
        }
        log_assert(sibling != RBTREE_NULL);

        /* get a new sibling, by rotating at sibling. See which child
           of sibling is red */
        if(child_parent->right == child
                && sibling->color == BLACK
                && sibling->right->color == RED
                && sibling->left->color == BLACK)
        {
                sibling->color = RED;
                sibling->right->color = BLACK;
                rbtree_rotate_left(rbtree, sibling);
                /* new sibling after rotation */
                if(child_parent->right == child) sibling = child_parent->left;
                else sibling = child_parent->right;
        }
        else if(child_parent->left == child
                && sibling->color == BLACK
                && sibling->left->color == RED
                && sibling->right->color == BLACK)
        {
                sibling->color = RED;
                sibling->left->color = BLACK;
                rbtree_rotate_right(rbtree, sibling);
                /* new sibling after rotation */
                if(child_parent->right == child) sibling = child_parent->left;
                else sibling = child_parent->right;
        }

        /* now we have a black sibling with a red child. rotate and exchange colors. */
        sibling->color = child_parent->color;
        child_parent->color = BLACK;
        if(child_parent->right == child)
        {
                log_assert(sibling->left->color == RED);
                sibling->left->color = BLACK;
                rbtree_rotate_right(rbtree, child_parent);
        }
        else
        {
                log_assert(sibling->right->color == RED);
                sibling->right->color = BLACK;
                rbtree_rotate_left(rbtree, child_parent);
        }
}

int
rbtree_find_less_equal(rbtree_type *rbtree, const void *key,
        rbnode_type **result)
{
        int r;
        rbnode_type *node;

        log_assert(result);
        
        /* We start at root... */
        node = rbtree->root;

        *result = NULL;
        fptr_ok(fptr_whitelist_rbtree_cmp(rbtree->cmp));

        /* While there are children... */
        while (node != RBTREE_NULL) {
                r = rbtree->cmp(key, node->key);
                if (r == 0) {
                        /* Exact match */
                        *result = node;
                        return 1;
                } 
                if (r < 0) {
                        node = node->left;
                } else {
                        /* Temporary match */
                        *result = node;
                        node = node->right;
                }
        }
        return 0;
}

/*
 * Finds the first element in the red black tree
 *
 */
rbnode_type *
rbtree_first (rbtree_type *rbtree)
{
        rbnode_type *node;

        for (node = rbtree->root; node->left != RBTREE_NULL; node = node->left);
        return node;
}

rbnode_type *
rbtree_last (rbtree_type *rbtree)
{
        rbnode_type *node;

        for (node = rbtree->root; node->right != RBTREE_NULL; node = node->right);
        return node;
}

/*
 * Returns the next node...
 *
 */
rbnode_type *
rbtree_next (rbnode_type *node)
{
        rbnode_type *parent;

        if (node->right != RBTREE_NULL) {
                /* One right, then keep on going left... */
                for (node = node->right; node->left != RBTREE_NULL; node = node->left);
        } else {
                parent = node->parent;
                while (parent != RBTREE_NULL && node == parent->right) {
                        node = parent;
                        parent = parent->parent;
                }
                node = parent;
        }
        return node;
}

rbnode_type *
rbtree_previous(rbnode_type *node)
{
        rbnode_type *parent;

        if (node->left != RBTREE_NULL) {
                /* One left, then keep on going right... */
                for (node = node->left; node->right != RBTREE_NULL; node = node->right);
        } else {
                parent = node->parent;
                while (parent != RBTREE_NULL && node == parent->left) {
                        node = parent;
                        parent = parent->parent;
                }
                node = parent;
        }
        return node;
}

/** recursive descent traverse */
static void 
traverse_post(void (*func)(rbnode_type*, void*), void* arg, rbnode_type* node)
{
        if(!node || node == RBTREE_NULL)
                return;
        /* recurse */
        traverse_post(func, arg, node->left);
        traverse_post(func, arg, node->right);
        /* call user func */
        (*func)(node, arg);
}

void 
traverse_postorder(rbtree_type* tree, void (*func)(rbnode_type*, void*),
        void* arg)
{
        traverse_post(func, arg, tree->root);
}