diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6ac2f99..3124799 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.0 )
+cmake_minimum_required(VERSION 3.10 )
 set(CMAKE_C_STANDARD 11)
 project(wlgol
     VERSION 0.0.1
@@ -22,7 +22,6 @@ add_custom_command(
 )
 
 set(SOURCES
-    wlgol.c
     tkeyboard.c
     tpointer.c
 	hashtable.c
@@ -33,7 +32,7 @@ set(GENHEADERS
     ${CMAKE_CURRENT_BINARY_DIR}/include/xdg-shell.h
 )
 
-add_executable(wlgol ${SOURCES} ${GENHEADERS})
+add_executable(wlgol wlgol.c ${SOURCES} ${GENHEADERS})
 
 target_include_directories(wlgol
     PUBLIC ${CMAKE_CURRENT_BINARY_DIR}/include
@@ -44,3 +43,20 @@ target_link_libraries(wlgol
     wayland-client
     wayland-cursor
 )
+
+
+
+add_executable(test_hashtable tests/test_hashtable.c
+    ${SOURCES}
+)
+target_link_libraries(test_hashtable
+    wayland-client
+    wayland-cursor
+)
+target_include_directories(test_hashtable
+    PUBLIC ${CMAKE_CURRENT_BINARY_DIR}/include
+    PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include
+)
+
+enable_testing()
+add_test(NAME Hashtable COMMAND test_hashtable)
diff --git a/hashtable.c b/hashtable.c
index 4134e0c..24ce993 100644
--- a/hashtable.c
+++ b/hashtable.c
@@ -7,124 +7,193 @@
 #include "hashtable.h"
 
 
-/**
- * @brief Hash function for hashtable
- *
- * This function takes a string key and calculates a hash value.
- * The hash value is used to determine the index in the hashtable
- * where the key-value pair should be stored.
- *
- * @param key The string key to hash
- * @return The calculated hash value
- */
+
+// entry in the hashtable
+struct entry
+{
+	const char *key;
+  void *value;
+	struct entry *next;
+};
+
+struct htobj
+{
+	int size;
+	struct entry **table;
+};
+
+struct item {
+	struct entry *prev, *found;
+	int index;
+};
+
 static unsigned int hash(const char *key)
 {
-	unsigned int hash = 0; // Initialize hash value to 0
+	unsigned int hash = 0;
 
-	// Iterate over each character in the key string
 	while (*key)
 	{
-		// Calculate the hash value by multiplying the current hash value
-		// with 32 (2^5) and subtracting the current hash value. Then add the
-		// ASCII value of the current character.
 		hash = (hash << 5) - hash + *key++;
 	}
-
-	// Return the calculated hash value
 	return hash;
 }
 
-/**
- * @brief Create a new hashtable
- *
- * This function creates a new hashtable with the specified size.
- * It initializes the table with NULL entries.
- *
- * @param size The size of the hashtable
- * @return A pointer to the newly created hashtable
- */
-hashtable *hashtable_new(int size)
+hashtable hashtable_new(int size)
 {
 	// Allocate memory for the hashtable
-	hashtable *h = malloc(sizeof(hashtable));
+	hashtable h = malloc(sizeof(struct htobj));
 
 	// Set the size of the hashtable
 	h->size = size;
 
 	// Allocate memory for the entry pointers
-	h->table = malloc(sizeof(entry *) * size);
-
-	// Initialize all entries to NULL
-	for (int i = 0; i < size; i++)
-	{
-		h->table[i] = NULL;
-	}
+	h->table = calloc(size, sizeof(struct entry *));
 
 	// Return the newly created hashtable
 	return h;
 }
 
 
-// hashtable_insert
-void hashtable_insert(hashtable *h, const char *key, void *value) {
+struct item hashtable_lookup_item(hashtable h, const char *key)
+{
+	struct item result = {
+		.found = NULL,
+		.index = -1,
+	};
 
-	// Calculate the index using the hash function
 	int index = hash(key) % h->size;
+	struct entry *e = h->table[index];
+	struct entry *prev = NULL;
 
-	// Create a new entry
-	entry *e = malloc(sizeof(entry));
-	e->key = key;
-	e->value = value;
-	e->next = NULL;
-
-	// Insert the entry at the beginning of the linked list
-	e->next = h->table[index];
-	h->table[index] = e;
-
-	return;
-}
-
-
-// hashtable_lookup
-void *hashtable_lookup(hashtable *h, const char *key) {
-
-	// Calculate the index using the hash function
-	int index = hash(key) % h->size;
-
-	// Traverse the linked list at the index
-	entry *e = h->table[index];
 	while (e != NULL) {
 		if (strcmp(e->key, key) == 0) {
-			return e->value;
-		}
-		e = e->next;
-	}
-
-	// Return NULL if the key is not found
-	return NULL;
-}
-
-
-// hashtable_remove
-void hashtable_remove(hashtable *h, const char *key) {
-
-	// Calculate the index using the hash function
-	int index = hash(key) % h->size;
-
-	// Traverse the linked list at the index
-	entry *e = h->table[index];
-	entry *prev = NULL;
-	while (e != NULL) {
-		if (strcmp(e->key, key) == 0) {
-			if (prev == NULL) {
-				h->table[index] = e->next;
-			} else {
-				prev->next = e->next;
-			}
-			free(e);
-			return;
+			result.index = index;
+			result.found = e;
+			result.prev = prev;
+			return result;
 		}
 		prev = e;
 		e = e->next;
 	}
+	return result; // empty in this case
+}
+
+void *hashtable_set(hashtable h, const char *key, void *value)
+{
+
+	struct item item = hashtable_lookup_item(h, key);
+	// not found - insert new
+	if (item.found == NULL) {
+		int index = hash(key) % h->size;
+
+		// Create a new entry
+		struct entry *e = malloc(sizeof(struct entry));
+		e->key = strdup(key); // key is the copy
+		e->value = value;
+		e->next = NULL;
+
+		// Insert the entry at the beginning of the linked list
+		e->next = h->table[index];
+		h->table[index] = e;
+		return NULL;
+	}
+	// found replace the value
+	void *old_value = item.found->value;
+	item.found-> value = value;
+
+	return old_value;
+}
+
+void *hashtable_lookup(hashtable h, const char *key)
+{
+	struct item item = hashtable_lookup_item(h, key);
+	if (item.found != NULL) {
+		return item.found->value;
+	}
+	return NULL;
+}
+
+void *hashtable_remove(hashtable h, const char *key)
+{
+	struct item item = hashtable_lookup_item(h, key);
+	if (item.found == NULL) {
+		return NULL;
+	}
+	// found, so detete it
+  if (item.prev != NULL) {
+  	item.prev->next = item.found->next;
+  } else {
+  	h->table[item.index] = item.found->next;
+  }
+  // free unused memory
+  void *value = item.found->value; // remember value
+  free((void*) item.found->key); // free key
+  free((void*) item.found); // free entry
+
+  return value;
+}
+
+void hashtable_destroy_bucket(hashtable h, int i)
+{
+	struct entry *e = h->table[i];
+	while (e != NULL) {
+		free((void*)e->key);
+		e = e->next;
+		free(e);
+	}
+}
+
+void hashtable_destroy(hashtable h)
+{
+	if (h==NULL) return;
+	for (int i = 0; i < h->size; i++) {
+		hashtable_destroy_bucket(h, i);
+	}
+	free (h->table);
+	free(h);
+}
+
+ht_iterator hashtable_iter(hashtable h)
+{
+	ht_iterator iter = {
+		.h = h,
+		.index = -1,
+	  .entry = NULL,
+	};
+
+	return iter;
+}
+
+bool ht_iter_next(ht_iterator *iter)
+{
+	if (iter == NULL) {
+		return false;
+	}
+	hashtable h = iter->h;
+
+	while(true)	{
+		if (iter->index >= h->size) {
+			return false;
+		}
+		if (iter->entry == NULL) {
+			iter->index++;
+			iter->entry = h->table[iter->index];
+		} else {
+			iter->entry = iter->entry->next;
+		}
+		if (iter->entry != NULL) return true;
+	}
+
+}
+
+const char *ht_iter_key(ht_iterator *iter)
+{
+	if (iter == NULL || iter->entry == NULL) return NULL;
+	return iter->entry->key;
+}
+
+void *ht_iter_value(ht_iterator *iter)
+{
+	if (iter == NULL || iter->entry == NULL) return NULL;
+	return iter->entry->value;
 }
diff --git a/include/hashtable.h b/include/hashtable.h
index 2fc59ea..7e374a2 100644
--- a/include/hashtable.h
+++ b/include/hashtable.h
@@ -1,23 +1,16 @@
 #ifndef HASHTABLE_H
 #define HASHTABLE_H
 
-#include <stdlib.h>
-#include <string.h>
+#include <stdbool.h>
 
-// entry in the hashtable
-typedef struct entry
-{
-	const char *key;
-	void *value;
-	struct entry *next;
-} entry;
+struct htobj;
+typedef struct htobj *hashtable;
 
-// hashtable
-typedef struct
-{
-	int size;
-	entry **table;
-} hashtable;
+typedef struct {
+	struct htobj *h;
+	struct entry *entry;
+	int index;
+} ht_iterator;
 
 /**
  * @brief Create a new hashtable
@@ -28,7 +21,7 @@ typedef struct
  * @param size The size of the hashtable
  * @return A pointer to the newly created hashtable
  */
-hashtable *hashtable_new(int size);
+hashtable hashtable_new(int size);
 
 /**
  * @brief Insert a new key-value pair into the hashtable
@@ -40,8 +33,9 @@ hashtable *hashtable_new(int size);
  * @param h Pointer to the hashtable
  * @param key Pointer to the key
  * @param value Pointer to the value
+ * @return null or pointer to the previous value of the key
  */
-void hashtable_insert(hashtable *h, const char *key, void *value);
+void *hashtable_set(hashtable h, const char *key, void *value);
 
 /**
  * @brief Get the value associated with a key from the hashtable
@@ -54,7 +48,7 @@ void hashtable_insert(hashtable *h, const char *key, void *value);
  * @param key Pointer to the key
  * @return Pointer to the value associated with the key, or NULL if not found
  */
-void *hashtable_lookup(hashtable *h, const char *key);
+void *hashtable_lookup(hashtable h, const char *key);
 
 /**
  * @brief Remove a key-value pair from the hashtable
@@ -66,6 +60,57 @@ void *hashtable_lookup(hashtable *h, const char *key);
  *
  * @param h Pointer to the hashtable
  * @param key Pointer to the key to remove
+ * @return null or value associated with the removed key.
  */
-void hashtable_remove(hashtable *h, const char *key);
+void *hashtable_remove(hashtable h, const char *key);
+
+/**
+ * @brief Destroy hashtable.
+ *
+ * Values must be destroyed by the caller earlier.
+ *
+ * @param h Reference to the hastable.
+ */
+void hashtable_destroy(hashtable h);
+
+/**
+ * @brief Get the iterator of key-value pairs in the hashtable
+ *
+ * This function returns the iterator of key-value pairs in the hashtable.
+ *
+ * @param h Pointer to the hashtable
+ * @return The iterator of key-value pairs in the hashtable
+ */
+ht_iterator hashtable_iter(hashtable h);
+
+/**
+ * @brief Get the next key-value pair from the iterator
+ *
+ * This function returns the next key-value pair from the iterator.
+ *
+ * @param iter Pointer to the iterator
+ * @return true if there is a next key-value pair, false otherwise
+ */
+bool ht_iter_next(ht_iterator *iter);
+
+/**
+ * @brief Get the key from the iterator
+ *
+ * This function returns the key from the iterator.
+ *
+ * @param iter Pointer to the iterator
+ * @return The key from the iterator
+ */
+const char *ht_iter_key(ht_iterator *iter);
+
+/**
+ * @brief Get the value from the iterator
+ *
+ * This function returns the value from the iterator.
+ *
+ * @param iter Pointer to the iterator
+ * @return The value from the iterator
+ */
+void *ht_iter_value(ht_iterator *iter);
+
 #endif
diff --git a/tests/test_hashtable.c b/tests/test_hashtable.c
new file mode 100644
index 0000000..286bf67
--- /dev/null
+++ b/tests/test_hashtable.c
@@ -0,0 +1,63 @@
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include <stdio.h>
+
+#include <hashtable.h>
+
+void test_hashtable(int size) {
+	hashtable h =  hashtable_new(size);
+	void *value1 = "to jest jakaś tam wartość";
+	void *value2 = "I inna";
+	void *value3 = "trzecia";
+	void *value4 = "Czwarta";
+	void *value5 = "Piąta";
+
+	void *retval = hashtable_set(h, "jeden", value1);
+	assert(retval == NULL);
+
+	void *found = hashtable_lookup(h, "jeden");
+	assert(found != NULL && !strcmp(value1, found));
+
+	retval = hashtable_set(h, "dwa", value2);
+	assert(retval == NULL);
+
+	retval = hashtable_set(h, "trzy", value3);
+	assert(retval == NULL);
+
+	retval = hashtable_set(h, "cztery", value4);
+	assert(retval == NULL);
+
+	retval = hashtable_set(h, "jeden", value5);
+	assert(retval != NULL);
+	assert (retval == value1);
+
+	retval = hashtable_lookup(h, "niema");
+	assert(retval == NULL);
+
+	retval = hashtable_lookup(h, "jeden");
+	assert(retval == value5);
+
+	ht_iterator iter = hashtable_iter(h);
+
+	while (ht_iter_next(&iter)) {
+		printf("Key %s, value: %s\n", ht_iter_key(&iter), (const char*) ht_iter_value(&iter));
+	}
+	
+	
+	retval = hashtable_remove(h, "cztery");
+	assert (retval == value4);
+	retval = hashtable_remove(h, "trzy");
+	assert(retval == value3);
+	retval = hashtable_remove(h, "dwa");
+	assert(retval == value2);
+	retval = hashtable_remove(h, "jeden");
+	assert(retval == value5);
+
+	hashtable_destroy(h);
+}
+
+int main() {
+   test_hashtable(2);
+   test_hashtable(10);
+}