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/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2024 Mike Becker, Olaf Wintermann All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *
 *   2. 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.
 *
 * 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.
 */

#include "cx/tree.h"

#include "cx/array_list.h"

#include <assert.h>

#define CX_TREE_PTR(cur, off) (*(void**)(((char*)(cur))+(off)))
#define CX_TREE_PTR(cur, off) (*(void**)(((char*)(cur))+(off)))
#define tree_parent(node) CX_TREE_PTR(node, loc_parent)
#define tree_children(node) CX_TREE_PTR(node, loc_children)
#define tree_prev(node) CX_TREE_PTR(node, loc_prev)
#define tree_next(node) CX_TREE_PTR(node, loc_next)

void cx_tree_link(
        void *restrict parent,
        void *restrict node,
        ptrdiff_t loc_parent,
        ptrdiff_t loc_children,
        ptrdiff_t loc_prev,
        ptrdiff_t loc_next
) {
    void *current_parent = tree_parent(node);
    if (current_parent == parent) return;
    if (current_parent != NULL) {
        cx_tree_unlink(node, loc_parent, loc_children,
                       loc_prev, loc_next);
    }

    if (tree_children(parent) == NULL) {
        tree_children(parent) = node;
    } else {
        void *children = tree_children(parent);
        tree_prev(children) = node;
        tree_next(node) = children;
        tree_children(parent) = node;
    }
    tree_parent(node) = parent;
}

void cx_tree_unlink(
        void *node,
        ptrdiff_t loc_parent,
        ptrdiff_t loc_children,
        ptrdiff_t loc_prev,
        ptrdiff_t loc_next
) {
    if (tree_parent(node) == NULL) return;

    void *left = tree_prev(node);
    void *right = tree_next(node);
    assert(left == NULL || tree_children(tree_parent(node)) != node);
    if (left == NULL) {
        tree_children(tree_parent(node)) = right;
    } else {
        tree_next(left) = right;
    }
    if (right != NULL) tree_prev(right) = left;
    tree_parent(node) = NULL;
    tree_prev(node) = NULL;
    tree_next(node) = NULL;
}

int cx_tree_search(
        void const *root,
        void const *data,
        cx_tree_search_func sfunc,
        void **result,
        ptrdiff_t loc_children,
        ptrdiff_t loc_next
) {
    int ret;
    *result = NULL;

    // shortcut: compare root before doing anything else
    ret = sfunc(root, data);
    if (ret < 0) {
        return ret;
    } else if (ret == 0 || tree_children(root) == NULL) {
        *result = (void*)root;
        return ret;
    }

    // create a working stack
    size_t work_cap = 32;
    size_t work_size = 0;
    void const **work = malloc(sizeof(void*) * work_cap);
    #define work_add(node) cx_array_add(&work, &work_size, &work_cap, \
        sizeof(void*), &(node), cx_array_default_reallocator)

    // add the children of root to the working stack
    {
        void *c = tree_children(root);
        while (c != NULL) {
            work_add(c);
            c = tree_next(c);
        }
    }

    // remember a candidate for adding the data
    // also remember the exact return code from sfunc
    void *candidate = NULL;
    int ret_candidate = -1;

    // process the working stack
    while (work_size > 0) {
        // pop element
        void const *node = work[--work_size];

        // apply the search function
        ret = sfunc(node, data);

        if (ret == 0) {
            // if found, exit the search
            *result = (void*) node;
            work_size = 0;
            break;
        } else if (ret > 0) {
            // if children might contain the data, add them to the stack
            void *c = tree_children(node);
            while (c != NULL) {
                work_add(c);
                c = tree_next(c);
            }

            // remember this node in case no child is suitable
            if (ret_candidate < 0 || ret < ret_candidate) {
                candidate = (void *) node;
                ret_candidate = ret;
            }
        }
    }

    // not found, but was there a candidate?
    if (ret != 0 && candidate != NULL) {
        ret = ret_candidate;
        *result = candidate;
    }

    // free the working queue and return
    #undef workq_add
    free(work);
    return ret;
}

static bool cx_tree_iter_valid(void const *it) {
    struct cx_tree_iterator_s const *iter = it;
    return iter->node != NULL;
}

static void *cx_tree_iter_current(void const *it) {
    struct cx_tree_iterator_s const *iter = it;
    return iter->node;
}

static void cx_tree_iter_stack_add(
        struct cx_tree_iterator_s *iter,
        void *node
) {
    cx_array_add(&iter->stack, &iter->depth, &iter->stack_capacity,
        sizeof(void*), &node, cx_array_default_reallocator);
}

static void cx_tree_iter_next(void *it) {
    struct cx_tree_iterator_s *iter = it;
    // TODO: support mutating iterator

    // TODO: implement
}


CxTreeIterator cx_tree_iterator(
        void *root,
        int passes,
        ptrdiff_t loc_children,
        ptrdiff_t loc_next
) {
    CxTreeIterator iter;
    iter.loc_children = loc_children;
    iter.loc_next = loc_next;
    iter.requested_passes = passes;

    // invalidate iterator immediately when passes is invalid
    if ((passes & (CX_TREE_ITERATOR_ENTER |
                   CX_TREE_ITERATOR_NEXT_CHILD |
                   CX_TREE_ITERATOR_EXIT)) == 0) {
        iter.stack = NULL;
        iter.node = NULL;
        return iter;
    }

    // allocate stack
    iter.stack_capacity = 16;
    iter.stack = malloc(sizeof(void *) * 16);
    iter.depth = 0;

    // determine start
    if ((passes & CX_TREE_ITERATOR_ENTER) == 0) {
        // we have to skip the first "entering" passes
        void *s = NULL;
        void *n = root;
        iter.counter = 0;
        do {
            iter.counter++;
            iter.source = s;
            iter.node = n;
            cx_tree_iter_stack_add(&iter, n);
            s = n;
            n = tree_children(n);
        } while (n != NULL);
        // found a leaf node s (might be root itself if it has no children)

        // check if there is a sibling
        n = tree_next(s);

        if (n == NULL) {
            // no sibling found, exit back to parent node
            // TODO: implement
        } else {
            // there is a sibling
            if ((passes & CX_TREE_ITERATOR_EXIT) == 0) {
                // no exit requested, conclude that only next_child is requested
                iter.source = s;
                iter.node = n;
                iter.counter++;
                iter.current_pass = CX_TREE_ITERATOR_NEXT_CHILD;
            } else {
                // exit requested, so we have found our first pass
                // iter.node and iter.source are still correct
                iter.current_pass = CX_TREE_ITERATOR_EXIT;
            }
        }
    } else {
        // enter passes are requested, we can start by entering the root node
        iter.source = NULL;
        iter.node = root;
        iter.current_pass = CX_TREE_ITERATOR_ENTER;
        iter.counter = 1;
        iter.depth = 1;
        iter.stack[0] = root;
    }

    // assign base iterator functions
    iter.base.mutating = false;
    iter.base.remove = false;
    iter.base.current_impl = NULL;
    iter.base.valid = cx_tree_iter_valid;
    iter.base.next = cx_tree_iter_next;
    iter.base.current = cx_tree_iter_current;

    return iter;
}