addition: insert, push_back and push_front

Decided that push front and insert will be O(n) because it moves
everything one space ahead, could do something like a buffer ring but i
think is too much, maybe in the future i do change it but i'm not sure,
for now it just moves everything, also, i havne't tested them and i'm
not sure the for loop meant for moving everything actually works.

src/arraylist.c

@@ -1,11 +1,11 @@
 #include "arraylist.h"
-#include <stdatomic.h>
 #include <stdbool.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 
 struct ArrayList{
-    void *data;
+    uint8_t *buffer;
     size_t capacity;
     size_t len;
     size_t elem_size;
@@ -33,8 +33,8 @@ ArrayList *arraylist_init(size_t capacity, size_t elem_size) {
     arr->capacity = capacity;
     arr->elem_size = elem_size;
     arr->len = 0;
-    arr->data = malloc(capacity * elem_size);
+    arr->buffer = malloc(capacity * elem_size);
-    if (arr->data == NULL) {
+    if (arr->buffer == NULL) {
         free(arr);
         return NULL;
     }
@@ -50,8 +50,8 @@ ArrayListErr arraylist_destroy(ArrayList *arr) {
     arr->capacity = 0;
     arr->elem_size = 0;
     arr->len = 0;
-    free(arr->data);
+    free(arr->buffer);
-    arr->data = NULL;
+    arr->buffer = NULL;
     free(arr);
     return ARRLIST_OK;
 }
@@ -61,7 +61,7 @@ ArrayListErr arraylist_clear(ArrayList *arr) {
         return ARRLIST_NULL_ARG;
     }
 
-    memset(arr->data, 0, arr->capacity * arr->elem_size);
+    memset(arr->buffer, 0, arr->capacity * arr->elem_size);
     arr->capacity = 0;
     arr->elem_size = 0;
     arr->len = 0;
@@ -94,22 +94,98 @@ static ArrayListErr arraylist_grow(ArrayList *arr) {
     // and only used by funtions that already verified
     // arr is not null, same with shrink.
     size_t new_capacity = arr->capacity * 2;
-    void *tmp = realloc(arr->data, new_capacity * arr->elem_size);
+    void *tmp = realloc(arr->buffer, new_capacity * arr->elem_size);
     if (tmp == NULL) {
         return ARRLIST_BAD_ALLOC;
     }
     arr->capacity = new_capacity;
-    arr->data = tmp;
+    arr->buffer = tmp;
     return ARRLIST_OK;
 }
 
 static ArrayListErr arraylist_shrink(ArrayList *arr) {
     size_t new_capacity = arr->capacity / 2;
-    void *tmp = realloc(arr->data, new_capacity *arr->elem_size);
+    void *tmp = realloc(arr->buffer, new_capacity *arr->elem_size);
     if (tmp == NULL) {
         return ARRLIST_BAD_ALLOC;
     }
     arr->capacity = new_capacity;
-    arr->data = tmp;
+    arr->buffer = tmp;
     return ARRLIST_OK;
 }
+
+ArrayListErr arraylist_push_back(ArrayList *arr, void *data) {
+    if (arr == NULL || data == NULL) {
+        return ARRLIST_NULL_ARG;
+    }
+
+    if (arr->len >= arr->capacity) {
+        ArrayListErr err = arraylist_grow(arr);
+
+        if (err != ARRLIST_OK) {
+            return err;
+        }
+    }
+
+    memcpy(arr->buffer, data, arr->elem_size);
+    arr->len++;
+    return ARRLIST_OK;
+}
+
+ArrayListErr arraylist_push_front(ArrayList *arr, void *data) {
+    if (arr == NULL || data == NULL) {
+        return ARRLIST_NULL_ARG;
+    }
+
+    if (arr->len >= arr->capacity) {
+        ArrayListErr err = arraylist_grow(arr);
+
+        if (err != ARRLIST_OK) {
+            return err;
+        }
+    }
+
+    // No problem if array is full because  it grows if it's full
+    for (size_t i = arr->len - 1; i >= 0; i--) {
+        memcpy(
+            arr->buffer + ((i + 1) * arr->elem_size),
+            arr->buffer + (i * arr->elem_size),
+            arr->elem_size);
+    }
+
+    memcpy(arr->buffer, data, arr->elem_size);
+    arr->len++;
+
+    return ARRLIST_OK;
+}
+
+ArrayListErr arraylist_insert(ArrayList *arr, size_t index, void *data) {
+    if (arr == NULL || data == NULL) {
+        return ARRLIST_NULL_ARG;
+    }
+
+    if (index >= arr->len) {
+        return ARRLIST_OUT_OF_BOUNDS;
+    }
+
+    if (arr->len >= arr->capacity) {
+        ArrayListErr err = arraylist_grow(arr);
+        if (err != ARRLIST_OK) {
+            return err;
+        }
+    }
+
+    for (size_t i = arr->len - 1; i >= index; i--) {
+        memcpy(
+            arr->buffer + ((i + 1) * arr->elem_size),
+            arr->buffer + (i * arr->elem_size),
+            arr->elem_size);
+    }
+
+    memcpy(arr->buffer + (index * arr->elem_size), data, arr->elem_size);
+    arr->len++;
+
+    return ARRLIST_OK;
+}
+
+