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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
    CX_ARRAY_DECLARE(void const*, work);
    cx_array_initialize(work, 32);

    // add the children of root to the working stack
    {
        void *c = tree_children(root);
        while (c != NULL) {
            cx_array_simple_add(work, 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) {
                cx_array_simple_add(work, 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
    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_next(void *it) {
    struct cx_tree_iterator_s *iter = it;
    ptrdiff_t const loc_next = iter->loc_next;
    ptrdiff_t const loc_children = iter->loc_children;

    void *children;

    // check if we are currently exiting or entering nodes
    if (iter->exiting) {
        children = NULL;
        // skipping on exit is pointless, just clear the flag
        iter->skip = false;
    } else {
        if (iter->skip) {
            // skip flag is set, pretend that there are no children
            iter->skip = false;
            children = NULL;
        } else {
            // try to enter the children (if any)
            children = tree_children(iter->node);
        }
    }

    if (children == NULL) {
        // search for the next node
        void *next;
        cx_tree_iter_search_next:
        // check if there is a sibling
        if (iter->exiting) {
            next = iter->next;
        } else {
            next = tree_next(iter->node);
            iter->next = next;
        }
        if (next == NULL) {
            // no sibling, we are done with this node and exit
            if (iter->visit_on_exit && !iter->exiting) {
                // iter is supposed to visit the node again
                iter->exiting = true;
            } else {
                iter->exiting = false;
                if (iter->depth == 1) {
                    // there is no parent - we have iterated the entire tree
                    // invalidate the iterator and free the node stack
                    iter->node = iter->next = NULL;
                    iter->stack_capacity = iter->depth = 0;
                    free(iter->stack);
                    iter->stack = NULL;
                } else {
                    // the parent node can be obtained from the top of stack
                    // this way we can avoid the loc_parent in the iterator
                    iter->depth--;
                    iter->node = iter->stack[iter->depth - 1];
                    // retry with the parent node to find a sibling
                    goto cx_tree_iter_search_next;
                }
            }
        } else {
            if (iter->visit_on_exit && !iter->exiting) {
                // iter is supposed to visit the node again
                iter->exiting = true;
            } else {
                iter->exiting = false;
                // move to the sibling
                iter->counter++;
                iter->node = next;
                // new top of stack is the sibling
                iter->stack[iter->depth - 1] = next;
            }
        }
    } else {
        // node has children, push the first child onto the stack and enter it
        cx_array_simple_add(iter->stack, children);
        iter->node = children;
        iter->counter++;
    }
}

CxTreeIterator cx_tree_iterator(
        void *root,
        bool visit_on_exit,
        ptrdiff_t loc_children,
        ptrdiff_t loc_next
) {
    CxTreeIterator iter;
    iter.loc_children = loc_children;
    iter.loc_next = loc_next;
    iter.visit_on_exit = visit_on_exit;

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

    // visit the root node
    iter.node = root;
    iter.next = NULL;
    iter.counter = 1;
    iter.depth = 1;
    iter.stack[0] = root;
    iter.exiting = false;
    iter.skip = false;

    // 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;
}

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

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

__attribute__((__nonnull__))
static void cx_tree_visitor_enqueue_siblings(
        struct cx_tree_visitor_s *iter, void *node, ptrdiff_t loc_next) {
    node = tree_next(node);
    while (node != NULL) {
        struct cx_tree_visitor_queue_s *q;
        q = malloc(sizeof(struct cx_tree_visitor_queue_s));
        q->depth = iter->queue_last->depth;
        q->node = node;
        iter->queue_last->next = q;
        iter->queue_last = q;
        node = tree_next(node);
    }
    iter->queue_last->next = NULL;
}

static void cx_tree_visitor_next(void *it) {
    struct cx_tree_visitor_s *iter = it;
    ptrdiff_t const loc_next = iter->loc_next;
    ptrdiff_t const loc_children = iter->loc_children;

    // add the children of the current node to the queue
    // unless the skip flag is set
    void *children;
    if (iter->skip) {
        iter->skip = false;
        children = NULL;
    } else {
        children = tree_children(iter->node);
    }
    if (children != NULL) {
        struct cx_tree_visitor_queue_s *q;
        q = malloc(sizeof(struct cx_tree_visitor_queue_s));
        q->depth = iter->depth + 1;
        q->node = children;
        if (iter->queue_last == NULL) {
            assert(iter->queue_next == NULL);
            iter->queue_next = q;
        } else {
            iter->queue_last->next = q;
        }
        iter->queue_last = q;
        cx_tree_visitor_enqueue_siblings(iter, children, loc_next);
    }

    // check if there is a next node
    if (iter->queue_next == NULL) {
        iter->node = NULL;
        return;
    }

    // dequeue the next node
    iter->node = iter->queue_next->node;
    iter->depth = iter->queue_next->depth;
    {
        struct cx_tree_visitor_queue_s *q = iter->queue_next;
        iter->queue_next = q->next;
        if (iter->queue_next == NULL) {
            assert(iter->queue_last == q);
            iter->queue_last = NULL;
        }
        free(q);
    }

    // increment the node counter
    iter->counter++;
}

CxTreeVisitor cx_tree_visitor(
        void *root,
        ptrdiff_t loc_children,
        ptrdiff_t loc_next
) {
    CxTreeVisitor iter;
    iter.loc_children = loc_children;
    iter.loc_next = loc_next;

    // allocate stack
    iter.depth = 0;

    // visit the root node
    iter.node = root;
    iter.counter = 1;
    iter.depth = 1;
    iter.skip = false;
    iter.queue_next = NULL;
    iter.queue_last = NULL;

    // assign base iterator functions
    iter.base.mutating = false;
    iter.base.remove = false;
    iter.base.current_impl = NULL;
    iter.base.valid = cx_tree_visitor_valid;
    iter.base.next = cx_tree_visitor_next;
    iter.base.current = cx_tree_visitor_current;

    return iter;
}