libds/include/ht.h

#ifndef LIBDS_HT_HEADER
#define LIBDS_HT_HEADER

#define LIBDS_HT_SIZE 32

#include "libds.h"

/**
 * A linked list node used for hash table buckets.
 * Contains a copy of the key that was used to store the
 * data as to avoid conflicting hash functions.
 */
struct ht_node_s {
  /**
   * A copy of the key used to store this node's data.
   */
  void* key;
  /**
   * The data stored in this node.
   */
  void* data;
  /**
   * The next linked list node with the same hash.
   */
  struct ht_node_s* next;
};

/**
 * A hash table struct.
 * The struct contains function pointers to all necessary
 * internal functions so that it can be customized to work with
 * any kind of data. By default, it works with strings.
 *
 * The copy function, which is intended to use malloc(), should return
 * NULL if the allocation failed - otherwise, there is no way for the
 * hash table to know something went wrong.
 */
struct ht_s {
  /**
   * The buckets in this hash table.
   */
  struct ht_node_s* data[LIBDS_HT_SIZE];
  /**
   * Hash function used to store data.
   * @param input the data being hashed.
   * @return the data's hash.
   */
  unsigned long (*hash_func)(const void* input);
  /**
   * Function to compare two keys.
   * @param given_key the key being used to retrieve data
   * @param current_key the key of a hash table node
   * @return nonzero value if the keys match.
   */
  int (*cmp_func)(const void* given_key, const void* current_key);
  /**
   * Function used to duplicate the given key and
   * store it in a node.
   * @param key the key to copy
   * @return pointer to a new key.
   */
  void* (*copy_func)(const void* key);
  /**
   * Function used to free a previously copied key.
   * @param key the key to free.
   */
  void (*free_func)(void* key);
};

typedef struct ht_node_s ht_node;
typedef struct ht_s ht;

/**
 * The default hash function.
 * Uses FNV-1 hash, and assumes data is a string.
 * @param key the data to hash.
 * @return the produced hashed integer.
 */
unsigned long ht_default_hash_func(const void* key);
/**
 * The default key comparison function.
 * Assumes both keys are strings and uses strcmp.
 * @param a the key to compare
 * @param b the key compared against
 * @return true if the keys represent the same string.
 */
int ht_default_cmp_func(const void* a, const void* b);
/**
 * The default key copy function.
 * @param key the key being copied
 * @return a pointer to the copy of the key.
 */
void* ht_default_copy_func(const void* key);
/**
 * The default key free function. Simply calls free()
 * @param key the key to free.
 */
void ht_default_free_func(void* key);

/**
 * Initializes the hash table with default values.
 * @param ht the hash table to initialize.
 */
void ht_init(ht* ht);
/**
 * Frees the hash table and its internally allocated nodes.
 * The data itself is left intact - use ht_foreach to free it
 * if it is no longer used.
 * @param ht the hash table to free.
 */
void ht_free(ht* ht);

/**
 * Stores data into the hash table. Uses malloc for node allocation.
 * @param ht the hash table to store data into.
 * @param key the key to use to store the data.
 * @param value the value to store.
 * @return LIBDS_SUCCESS if all goes well, LIBDS_MALLOC if an allocation fails.
 */
libds_result ht_put(ht* ht, const void* key, void* value);
/**
 * Retrieves a value from the hash table.
 * @param ht the hash table to retrieve a value from.
 * @param key the key to use to find the data.
 * @return the data, or NULL if it is not found.
 */
void* ht_get(ht* ht, const void* key);
/**
 * Removes a value from the hash table.
 * @param ht the hash table to remove a value from.
 * @param key the key to use to find the data.
 */
void ht_remove(ht* ht, const void* key);

/**
 * Runs through every element in the hash table, and compares it against the
 * given data using the given comparison function. If the comparison function returns
 * true, calls the foreach function, passing it the element and the variable argument list.
 * Stops if any foreach function returns a nonzero code.
 * @param ht the hash table to perform the operation on.
 * @param data the data passed to the comparison function.
 * @param compare the comparison function operating on the data and each element in the list.
 * @param foreach the foreach function called on every element that is matched by the comparison function.
 * @param ... variable arguments to be passed to the foreach function.
 * @return the code returned by the foreach functions.
 */
int ht_foreach(ht* ht, void* data, compare_func compare, foreach_func foreach, ...);

#endif