Init 1

#ifndef TRIE_H
#define TRIE_H

#include <stdio.h>
#include <stdbool.h>
#include "list.h"

typedef struct trie Trie;

/*
 * Trie node, it contains a fixed size array (every node can have at max the
 * alphabet length size of children), a flag defining if the node represent
 * the end of a word and then if it contains a value defined by data.
 */
struct trie_node {
    char chr;
    List *children;
    void *data;
};

/*
 * Trie ADT, it is formed by a root struct trie_node, and the total size of the
 * Trie
 */
struct trie {
    struct trie_node *root;
    size_t size;
};

// Returns new trie node (initialized to NULLs)
struct trie_node *trie_create_node(char);

// Returns a new Trie, which is formed by a root node and a size
struct trie *trie_create(void);

void trie_init(Trie *);

// Return the size of the trie
size_t trie_size(const Trie *);

/*
 * The leaf represents the node with the associated data
 *           .
 *          / \
 *         h   s: s -> value
 *        / \
 *       e   k: hk -> value
 *      /
 *     l: hel -> value
 *
 * Here we got 3 <key:value> pairs:
 * - s   -> value
 * - hk  -> value
 * - hel -> value
 */
void *trie_insert(Trie *, const char *, const void *);

bool trie_delete(Trie *, const char *);

/* Returns true if key presents in trie, else false, the last pointer to
   pointer is used to store the value associated with the searched key, if
   present */
bool trie_find(const Trie *, const char *, void **);

void trie_node_free(struct trie_node *, size_t *);

void trie_release(Trie *);

/* Remove all keys matching a given prefix in a linear time complexity (O(n))*/
void trie_prefix_delete(Trie *, const char *);

/*
 * Apply a given function to all nodes which keys match a given prefix. The
 * function accepts two arguments, a struct trie_node pointer which correspond
 * to each node on the trie after the prefix node and a void pointer, used for
 * additional data which can be useful to the execution of `mapfunc`.
 */
void trie_prefix_map_tuple(Trie *, const char *,
                           void (*mapfunc)(struct trie_node *, void *), void *);

#endif

#define ALPHABET_SIZE 94

/* Trie node, it contains a fixed size array (every node can have at max the
   alphabet length size of children), a flag defining if the node represent
   the end of a word and then if it contains a value defined by data. */

struct trie_node {
    struct trie_node *children[ALPHABET_SIZE];
    void *data;
};

#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include "list.h"
#include "trie.h"

static struct list_node *merge_tnode_list(struct list_node *list1,
                                          struct list_node *list2) {
    struct list_node dummy_head = { NULL, NULL }, *tail = &dummy_head;
    while (list1 && list2) {

        /* cast to cluster_node */
        char chr1 = ((struct trie_node *) list1->data)->chr;
        char chr2 = ((struct trie_node *) list2->data)->chr;

        struct list_node **min = chr1 <= chr2 ? &list1 : &list2;
        struct list_node *next = (*min)->next;
        tail = tail->next = *min;
        *min = next;
    }
    tail->next = list1 ? list1 : list2;
    return dummy_head.next;
}

struct list_node *merge_sort_tnode(struct list_node *head) {
    struct list_node *list1 = head;
    if (!list1 || !list1->next)
        return list1;
    /* find the middle */
    struct list_node *list2 = bisect_list(list1);
    return merge_tnode_list(merge_sort_tnode(list1), merge_sort_tnode(list2));
}

/* Search for a given node based on a comparison of char stored in structure
 * and a value, O(n) at worst
 */
static struct list_node *linear_search(const List *list, int value) {
    if (!list || list->len == 0)
        return NULL;
    for (struct list_node *cur = list->head; cur != NULL; cur = cur->next) {
        if (((struct trie_node *) cur->data)->chr == value)
            return cur;
        else if (((struct trie_node *) cur->data)->chr > value)
            break;
    }
    return NULL;
}

/* Auxiliary comparison function, uses on list searches, this one compare the
 * char field stored in each struct trie_node structure contained in each node of the
 * list.
 */
static int with_char(void *arg1, void *arg2) {
    struct trie_node *tn1 = ((struct list_node *) arg1)->data;
    struct trie_node *tn2 = ((struct list_node *) arg2)->data;
    if (tn1->chr == tn2->chr)
        return 0;
    return -1;
}

// Check for children in a struct trie_node, if a node has no children is considered
// free
static bool trie_is_free_node(const struct trie_node *node) {
    return node->children->len == 0 ? true : false;
}

static struct trie_node *trie_node_find(const struct trie_node *node,
                                        const char *prefix) {
    struct trie_node *retnode = (struct trie_node *) node;

    // Move to the end of the prefix first
    for (; *prefix; prefix++) {

        // O(n), the best we can have
        struct list_node *child = linear_search(retnode->children, *prefix);

        // No key with the full prefix in the trie
        if (!child)
            return NULL;
        retnode = child->data;
    }
    return retnode;
}

// Returns new trie node (initialized to NULL)
struct trie_node *trie_create_node(char c) {
    struct trie_node *new_node = malloc(sizeof(*new_node));
    if (new_node) {
        new_node->chr = c;
        new_node->data = NULL;
        new_node->children = list_create(NULL);
    }
    return new_node;
}

// Returns new Trie, with a NULL root and 0 size
Trie *trie_create(void) {
    Trie *trie = malloc(sizeof(*trie));
    trie_init(trie);
    return trie;
}

void trie_init(Trie *trie) {
    trie->root = trie_create_node(' ');
    trie->size = 0;
}

size_t trie_size(const Trie *trie) {
    return trie->size;
}

/*
 * If not present, inserts key into trie, if the key is prefix of trie node,
 * just marks leaf node by assigning the new data pointer. Returns a pointer
 * to the new inserted data.
 *
 * Being a Trie, it should guarantees O(m) performance for insertion on the
 * worst case, where `m` is the length of the key.
 */
static void *trie_node_insert(struct trie_node *root, const char *key,
                              const void *data, size_t *size) {
    struct trie_node *cursor = root;
    struct trie_node *cur_node = NULL;
    struct list_node *tmp = NULL;

    // Iterate through the key char by char
    for (; *key; key++) {

        /*
         * We can use a linear search as on a linked list O(n) is the best find
         * algorithm we can use, as binary search would have the same if not
         * worse performance by not having direct access to node like in an
         * array.
         *
         * Anyway we expect to have an average O(n/2) -> O(n) cause at every
         * insertion the list is sorted so we expect to find our char in the
         * middle on average.
         *
         * As a future improvement it's advisable to substitute list with a
         * B-tree or RBTree to improve searching complexity to O(logn) at best,
         * avg and worst while maintaining O(n) space complexity, but it really
         * depends also on the size of the alphabet.
         */
        tmp = linear_search(cursor->children, *key);

        // No match, we add a new node and sort the list with the new added link
        if (!tmp) {
            cur_node = trie_create_node(*key);
            cursor->children = list_push(cursor->children, cur_node);
            cursor->children->head = merge_sort_tnode(cursor->children->head);
        } else {
            // Match found, no need to sort the list, the child already exists
            cur_node = tmp->data;
        }
        cursor = cur_node;
    }

    /*
     * Clear out if already taken (e.g. we are in a leaf node), rc = 0 to not
     * change the trie size, otherwise 1 means that we added a new node,
     * effectively changing the size
     */
    if (!cursor->data)
        (*size)++;
    cursor->data = (void *) data;
    return cursor->data;
}

/*
 * Private function, iterate recursively through the trie structure starting
 * from a given node, deleting the target value
 */
static bool trie_node_recursive_delete(struct trie_node *node, const char *key,
                                       size_t *size, bool *found) {
    if (!node)
        return false;

    // Base case
    if (*key == '\0') {
        if (node->data) {

            // Update found flag
            *found = true;

            // Free resources, covering the case of a sub-prefix
            if (node->data) {
                free(node->data);
                node->data = NULL;
            }
            free(node->data);
            node->data = NULL;
            if (*size > 0)
                (*size)--;

            // If empty, node to be deleted
            return trie_is_free_node(node);
        }
    } else {

        // O(n), the best we can have
        struct list_node *cur = linear_search(node->children, *key);
        if (!cur)
            return false;
        struct trie_node *child = cur->data;
        if (trie_node_recursive_delete(child, key + 1, size, found)) {

            // Messy solution, requiring probably avoidable allocations
            struct trie_node t = {*key, NULL, NULL};
            struct list_node tmp = {&t, NULL};
            list_remove(node->children, &tmp, with_char);

            // last node marked, delete it
            trie_node_free(child, size);

            // recursively climb up, and delete eligible nodes
            return (!node->data && trie_is_free_node(node));
        }
    }
    return false;
}

/*
 * Returns true if key is present in trie, else false. Also for lookup the
 * big-O runtime is guaranteed O(m) with `m` as length of the key.
 */
static bool trie_node_search(const struct trie_node *root,
                             const char *key, void **ret) {

    // Walk the trie till the end of the key
    struct trie_node *cursor = trie_node_find(root, key);
    *ret = (cursor && cursor->data) ? cursor->data : NULL;

    // Return false if no complete key found, true otherwise
    return !*ret ? false : true;
}

/*
 * Insert a new key-value pair in the Trie structure, returning a pointer to
 * the new inserted data in order to simplify some operations as the addition
 * of expiring keys with a set TTL.
 */
void *trie_insert(Trie *trie, const char *key, const void *data) {
    assert(trie && key);
    return trie_node_insert(trie->root, key, data, &trie->size);
}

bool trie_delete(Trie *trie, const char *key) {
    assert(trie && key);
    bool found = false;
    if (strlen(key) > 0)
        trie_node_recursive_delete(trie->root, key, &(trie->size), &found);
    return found;
}

bool trie_find(const Trie *trie, const char *key, void **ret) {
    assert(trie && key);
    return trie_node_search(trie->root, key, ret);
}

/*
 * Remove and delete all keys matching a given prefix in the trie
 * e.g. hello*
 * - hello
 * hellot
 * helloworld
 * hello
 */
void trie_prefix_delete(Trie *trie, const char *prefix) {
    assert(trie && prefix);

    // Walk the trie till the end of the key
    struct trie_node *cursor = trie_node_find(trie->root, prefix);

    // No complete key found
    if (!cursor)
        return;

    // Simply remove the key if it has no children, no need to clear the list
    if (cursor->children->len == 0) {
        trie_delete(trie, prefix);
        return;
    }
    struct list_node *cur = cursor->children->head;
    // Clear out all possible sub-paths
    for (; cur; cur = cur->next) {
        trie_node_free(cur->data, &(trie->size));
        cur->data = NULL;
    }

    // Set the current node (the one storing the last character of the prefix)
    // as a leaf and delete the prefix key as well
    trie_delete(trie, prefix);
    list_clear(cursor->children, 1);
}

/* Iterate through children of each node starting from a given node, applying
   a defined function which take a struct trie_node as argument */
static void trie_prefix_map_func2(struct trie_node *node,
                                  void (*mapfunc)(struct trie_node *, void *), void *arg) {
    if (trie_is_free_node(node)) {
        mapfunc(node, arg);
        return;
    }
    struct list_node *child = node->children->head;
    for (; child; child = child->next)
        trie_prefix_map_func2(child->data, mapfunc, arg);
    mapfunc(node, arg);
}

/*
 * Apply a function to every key below a given prefix, if prefix is null the
 * function will be applied to all the trie. The function applied accepts an
 * additional arguments for optional extra data.
 */
void trie_prefix_map_tuple(Trie *trie, const char *prefix,
                           void (*mapfunc)(struct trie_node *, void *), void *arg) {
    assert(trie);
    if (!prefix) {
        trie_prefix_map_func2(trie->root, mapfunc, arg);
    } else {

        // Walk the trie till the end of the key
        struct trie_node *node = trie_node_find(trie->root, prefix);

        // No complete key found
        if (!node)
            return;

        // Check all possible sub-paths and add to count where there is a leaf
        trie_prefix_map_func2(node, mapfunc, arg);
    }
}

/* Release memory of a node while updating size of the trie */
void trie_node_free(struct trie_node *node, size_t *size) {

    // Base case
    if (!node)
        return;

    // Recursive call to all children of the node
    if (node->children) {
        struct list_node *cur = node->children->head;
        for (; cur; cur = cur->next)
            trie_node_free(cur->data, size);
        list_release(node->children, 0);
        node->children = NULL;
    }

    // Release memory on data stored on the node
    if (node->data) {
        free(node->data);
        if (*size > 0)
            (*size)--;
    } else if (node->data) {
        free(node->data);
        if (*size > 0)
            (*size)--;
    }

    // Release the node itself
    free(node);
}

void trie_release(Trie *trie) {
    if (!trie)
        return;
    trie_node_free(trie->root, &(trie->size));
    free(trie);
}

sol/
 ├── src/
 │    ├── mqtt.h
 |    ├── mqtt.c
 │    ├── network.h
 │    ├── network.c
 │    ├── list.h
 │    ├── list.c
 │    ├── hashtable.h
 │    ├── hashtable.c
 │    ├── trie.h
 │    ├── trie.c
 │    ├── util.h
 │    ├── util.c
 │    ├── pack.h
 │    └── pack.c
 ├── CHANGELOG
 ├── CMakeLists.txt
 ├── COPYING
 └── README.md