#include <stdio.h>
#include <stdlib.h>
#define LEN sizeof(NODE)

typedef struct tagNode{
    int index;
    int value;
    struct tagNode * prev;
    struct tagNode * next;
} NODE;

NODE* insert(NODE* head, int index, int value);
NODE* delete_by_index(NODE* head, int index);
NODE* create(int index, int value);
void printOut(NODE* head);

int main() {
    char command;
    int index, value;
    NODE* head = NULL;
    while (1) {
        printf("Type a command. (P)rint, (I)nsert, (D)elete, (Q)uit: ");
        fflush(stdin);
        scanf("%c", &command);
        fflush(stdin);
        switch (command) {
            case 'P':
            case 'p':
                printOut(head);
                break;
            case 'I':
            case 'i':
                printf("Index and value: ");
                scanf("%d %d", &index, &value);
                if (head == NULL) {
                    head = create(index, value);
                }
                else {
                    insert(head, index, value);
                }
                break;
            case 'D':
            case 'd':
                printf("Index: ");
                scanf("%d", &index);
                head = delete_by_index(head, index);
                break;
            case 'Q':
            case 'q':
                return 0;
            default:
                printf("Unkown command.\n");
        }
    }
    return 0;
}

NODE* insert(NODE* head, int index, int value) {
    NODE* currentNode;
    NODE* newNodePtr;
    currentNode = head;
    if ((*currentNode).index > index) {
        newNodePtr = malloc(LEN);
        (*newNodePtr).index = index;
        (*newNodePtr).value = value;
        (*newNodePtr).prev = NULL;
        (*newNodePtr).next = currentNode;
        (*currentNode).prev = newNodePtr;
        return newNodePtr;
    }
    while((*currentNode).next != NULL) {
        if (index == (*currentNode).index) {
            (*currentNode).value = value;
            return currentNode;
        }
        if (index >= (*((*currentNode).next)).index) {
            currentNode = (*currentNode).next;
            continue;
        }
        newNodePtr = malloc(LEN);
        (*newNodePtr).index = index;
        (*newNodePtr).value = value;
        (*newNodePtr).prev = currentNode;
        (*newNodePtr).next = (*currentNode).next;
        (*(*currentNode).next).prev = newNodePtr;
        (*currentNode).next = newNodePtr;
        return newNodePtr;
    }
    newNodePtr = malloc(LEN);
    (*newNodePtr).index = index;
    (*newNodePtr).value = value;
    (*newNodePtr).prev = currentNode;
    (*newNodePtr).next = NULL;
    (*currentNode).next = newNodePtr;
    return newNodePtr;
}

NODE* create(int index, int value) {
    NODE* newNodePtr;
    newNodePtr = malloc(LEN);
    (*newNodePtr).index = index;
    (*newNodePtr).value = value;
    (*newNodePtr).prev = NULL;
    (*newNodePtr).next = NULL;
    return newNodePtr;
}

void printOut(NODE* head) {
    NODE current;
    if (head == NULL) {
        printf("(Empty list)\n");
        return;
    }
    current = *head;
    while (1) {
        printf("Index: %d Value: %d\n", current.index, current.value);
        if (current.next == NULL) {
            break;
        }
        current = *(current.next);
    }
}

NODE* delete_by_index(NODE* head, int index) {
    NODE* current = head;
    NODE* newHead;
    if ((*current).index == index) {
        if ((*current).next != NULL) {
            (*((*current).next)).prev = NULL;
        }
        newHead = (*current).next;
        free(current);
        return newHead;
    }
    while ((*current).next != NULL) {
        if ((*current).index == index) {
            (*((*current).prev)).next = (*current).next;
            (*((*current).next)).prev = (*current).prev;
            free(current);
            return head;
        }
        current = (*current).next;
    }
    if ((*current).index == index) {
        if (((*current).prev) != NULL) {
            (*((*current).prev)).next = NULL;
        }
        newHead = (*current).prev;
        free(current);
        return newHead;
    }
    printf("No such node whose index is %d!\n", index);
    return head;
}