RtB/src/HashTable.hpp

/* ================================================================ 
HashTable
````````````````
HashTable is a template class for storing the provided data type T along with an identifier key as a char*. Values are stored in the predefined HashTable with a hash of their key used as the position offset. Data collisions are handled by storing data in a HashEntry object and checking if the key itself does not match a stored copy. If the key does not match, the HashEntry provides a pointer to the next HashEntry. This continues on as a linked list until a match is or is not found.

If a match is not found, the HashTable returns a special user-defined "null" variable that should match the provided data type to be stored.

A HashTable may be resized, but it should _ONLY_ be resized if there is _NO_ data in the table. Future iterations of this template may allow for resizing by creating a new table, copying over the old stored data into their new positions, then replacing the old table with the new one.
================================================================ */
#ifndef HASHTABLE_HPP
#define HASHTABLE_HPP
#include <stdlib.h> // malloc
#include <string.h> // strlen
#include <limits.h> // INT_MAX
#include <iostream>

template<class T> class HashEntry {
  public:
    HashEntry(const char *key_, T data_) {
      int key_len = strlen(key_)+1;
      key = (char*)malloc(key_len*sizeof(char));
      memcpy(key, key_, key_len*sizeof(char));
      data = data_;
      next = NULL;
    };
    ~HashEntry() {
      free(key);
    };
    char *key;
    T data;
    HashEntry *next;
};

template<class T> class HashTable {
  public:
    HashTable() { HashTable<T>(128); };
    HashTable(int hash_size) {
      pos = 0; // iterator pos
      size = hash_size;
      iter = NULL;
      last_iter = NULL;
      table = (HashEntry<T>**)malloc(sizeof(HashEntry<T>*)*size);
      for (int i = 0; i < size; i++) {
        table[i] = NULL;
      }
    };
    ~HashTable() {
     for (int i = 0; i < size; i++) {
       if (table[i] != NULL) delete table[i];
     }
     free(table);
    };
    // resize should _only_ be called when the HashTable has _no_ data!
    void resize(int hash_size) {
      size = hash_size;
      table = (HashEntry<T>**)realloc(table, sizeof(HashEntry<T>*)*size);
      for (int i = 0; i < size; i++) {
        table[i] = NULL;
      }
    };
    void setnull(T null_value) {
      null = null_value;
    }
    //
    T get(const char* key) {
      int key_hash = getHash(key);
      // find our hash if it exists
      HashEntry<T> *entry = table[key_hash];
      while (entry != NULL) {
        if (strcmp(entry->key, key) == 0) {
          return entry->data;
        }
        entry = entry->next;
      }
      // doesn't exist, return the user's null value
      return null;
    };
    bool exists(const char *key) {
      int key_hash = getHash(key);
      // find our hash if it exists
      HashEntry<T> *entry = table[key_hash];
      while (entry != NULL) {
        if (strcmp(entry->key, key) == 0) {
          return true;
        }
        entry = entry->next;
      }
      // doesn't exist, return the user's null value
      return false;
    }
    T set(const char *key, T value) {
      int key_hash = getHash(key);
      // find our hash if it exists
      HashEntry<T> *entry = table[key_hash];
      if (entry == NULL) {
        table[key_hash] = new HashEntry<T>(key, value);
        return table[key_hash]->data;
      }
      while (entry->next != NULL) {
        if (strcmp(entry->key, key) == 0) {
          entry->data = value;
          return entry->data;
        }
        entry = entry->next;
      }
      entry->next = new HashEntry<T>(key, value);
      return entry->next->data;
    };
    void del(const char *key) {
      int key_hash = getHash(key);
      HashEntry<T> *entry = table[key_hash];
      HashEntry<T> *last_entry = NULL;
      if (entry != NULL) {
        if (strcmp(entry->key, key) == 0) {
          table[key_hash] = entry->next;
          delete entry;
          return;
        }
        entry = entry->next;
      }
      while (entry != NULL) {
        if (strcmp(entry->key, key) == 0) {
          if (last_entry != NULL) last_entry->next = entry->next;
          delete entry;
          return;
        }
        last_entry = entry;
        entry = entry->next;
      }
    }
    int getHash(const char *key) {
      int key_hash = 0;
      int key_len = strlen(key);
      // generate our hash
      for (int i = 0; key_hash < INT_MAX && i < key_len; i++) {
        key_hash += key[i];
      }
      // limit hash to the HashTable's size and return
      return (key_hash % size);
    }
    /*T iterate() {
      int i = 1;
      while(i) {
        if (iter == NULL) {
          if (pos > size) {
            iter = NULL;
            pos = 0;
            return null;
          }
          iter = table[pos++];
        } else {
          if (iter->data != null) {
            std::cout << "found one at" << i-1 << std::endl;
            HashEntry *ret = iter;
            iter = iter->next;
            return ret->data;
          }
        }
      }
      return iter->data;
    }*/
    T operator[](char* key) {
      int key_hash = 0;
      int key_len = strlen(key);
      // get our key hash
      for (int i = 0; key_hash < INT_MAX && i < key_len; i++) {
        key_hash += key[i];
      }
      // limit it to our HashTable's size
      key_hash = key_hash % size;
      // find our hash if it exists
      HashEntry<T> *entry = table[key_hash];
      while (entry != NULL) {
        if (strcmp(entry->key, key) == 0) {
          return entry->data;
        }
        entry = entry->next;
      }
      // doesn't exist, return the user's null value
      return null;
    }
    T& operator[](char *key) const {
      int key_hash = 0;
      int key_len = strlen(key);
      // get our key hash
      for (int i = 0; key_hash < INT_MAX && i < key_len; i++) {
        key_hash += key[i];
      }
      // limit it to our HashTable's size
      key_hash = key_hash % size;
      // find our hash if it exists
      HashEntry<T> *last_entry, *entry = table[key_hash];
      if (entry == NULL) {
        table[key_hash] = new HashEntry<T>(key, null);
        return entry->data;
      }
      while (entry->next != NULL) {
        if (strcmp(entry->key, key) == 0) {
          return entry->data;
        }
        last_entry = entry;
        entry = entry->next;
      }
      entry->next = new HashEntry<T>(key, null);
      return entry->next;
    }
    HashEntry<T> *iterate() {
      int i = 1;
      while(i) {
        if (iter == NULL) {
          if (pos >= size) {
            iter = NULL;
            pos = 0;
            return NULL;
          }
          iter = table[pos++];
        } else {
          HashEntry<T> *ret = iter;
          iter = iter->next;
          return ret;
        }
      }
      return NULL;
    }
  private:
    int size;
    T null; // user defined "null" value
    HashEntry<T> **table;
    int pos;
    HashEntry<T> *iter;
    HashEntry<T> *last_iter;
};
#endif