#include <stdio.h>
#include <stdlib.h>

#define INITIAL_CAPACITY 4

typedef struct elem_s // for example purspose
{
    int data;
} elem_t;

typedef struct arr_s // to define in .c file - no direct access from outside this file
{
    elem_t** elems_arr;
    int size;
    int capacity;
} arr_t;

void init_arr(arr_t* arr)  // private - not to declare in header file
{
    arr->elems_arr = malloc(INITIAL_CAPACITY*sizeof(elem_t*));

    for (int i=0; i<INITIAL_CAPACITY; i++)
    {
        arr->elems_arr[i] = NULL;
    }

    arr->size = 0;
    arr->capacity = INITIAL_CAPACITY;
}

void increase_capacity(arr_t* arr) // private - not to declare in header file
{
    int new_capacity = 2*arr->capacity;
    arr->elems_arr = realloc(arr->elems_arr, new_capacity*sizeof(elem_t*));

    for (int i=(arr->capacity); i<new_capacity; i++)
    {
        arr->elems_arr[i] = NULL;
    }

    arr->capacity = new_capacity;
}

void push(arr_t* arr, elem_t* elem)
{
    if (arr->elems_arr == NULL)
    {
        init_arr(arr);
    }

    int* capacity_ptr = &(arr->capacity);
    int* size_ptr = &(arr->size);

    if (*size_ptr == *capacity_ptr)
    {
        increase_capacity(arr);
    }

    arr->elems_arr[*size_ptr] = elem;
    (*size_ptr)++;
}

void clear (arr_t* arr)
{
    for (int i=0; i<(arr->size); i++)
    {
        if(arr->elems_arr[i] != NULL)
        {
            free(arr->elems_arr[i]);
            arr->elems_arr[i] = NULL;
        }
    }
    free(arr->elems_arr);
}

void print_data (const arr_t* arr) // for example pursposes
{
    for (int i=0; i<(arr->size); i++)
    {
        printf("%d ", (arr->elems_arr[i])->data);
    }
    printf("\n");
}

elem_t* create_elem (int data) // for example purposes
{
    elem_t* elem = malloc(sizeof(elem_t));
    elem->data = data;

    return elem;
}

int main()
{
    arr_t* arr = malloc(sizeof(arr_t));

    elem_t* first_el = create_elem(1);
    push(arr, first_el);

    elem_t* second_el = create_elem(5);
    push(arr, second_el);

    elem_t* third_el = create_elem(3);
    push(arr, third_el);

    elem_t* fourth_el = create_elem(4);
    push(arr, fourth_el);

    elem_t* fifth_el = create_elem(6);
    push(arr, fifth_el);

    print_data(arr);
    clear(arr);
    free(arr);

    return 0;
}