typedef struct {
    struct list *prev;
    struct list *next;
    struct list *undop;
    struct list *redop;
    char val;
    }list;

void copy(list *first, int n, list *clipboard, int cursor)
{
    int i;
    list *current, *currentclip, *p;
    current = first;
    for (i=0; i<cursor; i++)
    {
        current = current->next;
    }

    if(clipboard!=NULL)
    {
        currentclip=clipboard;
        while(clipboard->next != NULL)
        {
            currentclip=clipboard;
            clipboard=clipboard->next;
            free(currentclip);
        }
        free(clipboard);
    }
    clipboard = (list*)malloc(sizeof(list));
    clipboard -> prev = NULL;
    clipboard -> next = NULL;
    clipboard -> val = current -> val;
    currentclip = clipboard;
    current=current->next;

    for (i=0; i<n-1; i++)
    {
        p = (list*)malloc(sizeof(list));
        p -> prev = currentclip;
        p -> next = NULL;
        p -> val = current -> val;
        currentclip -> next = p;
        currentclip = p;
        current = current -> next;
    }
}

void paste(list *first, list *clipboard, int *cursor)
{
    int i;
    list *current, *currentclip, *p, *currentnext;
    current = first;
    for (i=0; i<(*cursor); i++)
    {
        current = current->next;
    }

    if(clipboard!=NULL)
    {
        currentclip = clipboard;
        currentnext = current->next;
        while (currentclip!=NULL)
        {
            p=(list*)malloc(sizeof(list));
            current->next = p;
            currentnext->prev = p;
            p->next = currentnext;
            p->prev = current;
            p->val = currentclip->val;
            (*cursor)++;
        }
    }
}

void del(list *first, int cursor, int n)
{
    int i;
    list *current, *currentprev, *currentnext;
    current = first;
    for (i=0; i<cursor; i++)
    {
        current = current->next;
    }
    for (i=0; i<n; i++)
    {
        currentprev = current->prev;
        currentnext = current->next;
        currentnext -> prev = currentprev;
        if (currentprev!=NULL)
        {
            currentprev->next = currentnext;
        }
        free(current);
        current=currentnext;
    }
}

void insert(list *first, int *cursor, char* stringtoinsert)
{
    list *toinsert, *p, *prevp;
    int i;
    toinsert = (list*)malloc(sizeof(list));
    toinsert ->next = NULL;
    toinsert -> prev = NULL;
    toinsert -> val = stringtoinsert[0];
    prevp = toinsert;
    for (i=1; i<strlen(stringtoinsert); i++)
    {
        p = (list*)malloc(sizeof(list));
        p ->next = NULL;
        p -> prev = prevp;
        p -> val = stringtoinsert[i];
        prevp->next = p;
        prevp = p;
    }
    paste(first, toinsert, cursor);
}

void move(int *cursor, int n)
{
    (*cursor) += n;
}

void backspace(int *cursor, list *first)
{
    (*cursor) --;
    del(first, cursor, 1);
}

void backup(list *first)
{
    list *newfirst, *current, *currentprev, *oldcurrent;
    newfirst = (list*)malloc(sizeof(list));
    newfirst->undop = first;
    first->redop = newfirst;
    newfirst->val = first -> val;
    currentprev = newfirst;
    oldcurrent = first->next;
    while(oldcurrent!=NULL)
    {
        current = (list*)malloc(sizeof (list));
        current -> val = oldcurrent -> val;
        current -> prev = currentprev;
        currentprev -> next = current;
        current->next = NULL;
        currentprev = current;
        oldcurrent = oldcurrent->next;
    }
    first = newfirst;
}

void undo(list *first)
{
    first = first -> undop;
}

void redo (list *first)
{
    first = first -> redop;
}