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


typedef struct node {
    void* data;
    void* next;
    struct node* previous;
} node;

typedef struct double_linked_list {
    node* start;
    node* end;
    size_t size;
    size_t objsize;
} double_linked_list;

void create_list(double_linked_list* list, size_t objsize) {
    list->start = NULL;
    list->objsize = objsize;
}

bool get_next(node** node) {
    if(!(*node)->next) {
        *node = NULL;
        return false;
    }
    *node = (*node)->next;
    return true;
}

bool get_previous(node** node) {
    if(!(*node)->previous) {
        *node = NULL;
        return false;
    }
    *node = (*node)->previous;
    return true;
}

node* push_front(double_linked_list* list, void* obj) {
    node* prev = list->start;
    list->start = malloc(sizeof(node));
    list->start->data = malloc(list->objsize);
    memcpy(list->start->data, obj, list->objsize);
    list->start->next = prev;
    list->start->previous = NULL;
    if(prev != NULL) {
        prev->previous = list->start;
    } else {
        list->end = list->start;
    }
    return list->start;
}

node* push_back(double_linked_list* list, void* obj) {
    node* prev = list->end;
    list->end = malloc(sizeof(node));
    list->end->data = malloc(list->objsize);
    memcpy(list->end->data, obj, list->objsize);
    list->end->next = NULL;
    list->end->previous = prev;
    if(prev != NULL) {
        prev->next = list->end;
    } else {
        list->start = list->end;
    }
    return list->end;
}

void free_list(double_linked_list* list) {
    node* iterator = list->start;
    while(iterator) {
        node* cur = iterator;
        free(cur->data);
        get_next(&iterator);
        free(cur);
    }
}


int main() {
    double_linked_list list;
    create_list(&list, sizeof(int));
    int vals[] = { 1, 2, 3, 4, 5 };
    for(int i = sizeof(vals) / sizeof(int) - 1; i >= 0; i--) {
        push_back(&list, &vals[i]);
    }

    node* iterator = list.start;
    while(iterator) {
        printf("%d\n", *(int*)iterator->data);
        get_next(&iterator);
    }

    iterator = list.end;
    while(iterator) {
        printf("%d\n", *(int*)iterator->data);
        get_previous(&iterator);
    }
    free_list(&list);
}