using C_.Datastructures.Nodes;

namespace C_.Datastructures
{
    internal class LinkedList<T>
    {
        internal LinkedListNode<T>? Head { get; set; } = default;
        private int Count { get; set; } = 0;

        public static LinkedList<T> Create(){
            //Create a new empty list
            return new LinkedList<T>();
        }

        public static LinkedList<T> Create(T value){
            //Create a new Class with a single item
            return new LinkedList<T>(){
                Head = LinkedListNode<T>.Create(value, null),
                Count = 1
            };
        }

        public static LinkedList<T> Create(LinkedList<T> list1, LinkedList<T> list2){
            //Append a previous list to a new List
            LinkedList<T> list;
            
            list = list1;
            if (list == null || list.Count == 0)
            {
                //If list 2 is the only list present
                return list2;
            }

            //Find end of list and append fist item of next list
            if (list2 == null || list.Count == 0) return list;

            LinkedListNode<T>? end = list.Traverse();
            end!.Next = list2!.Head;
            list.Count += list2!.Count;

            return list;
        }

        public T? this[int i]
        {
            get
            {
                //Check Range
                if (i >= Count) throw new System.Exception("Error! Index out of Bounds");

                //Return Value
                LinkedListNode<T>? node = Traverse(i);
                if (node != null) return node.Value;
                return default;
            }
            set
            {
                //Check Range
                if (i >= Count) throw new System.Exception("Error! Index out of Bounds");

                //Change Value
                LinkedListNode<T>? node = Traverse(i);
                node!.Value = value;
            }
        }

        public void Append(T value){
            LinkedListNode<T> newItem = LinkedListNode<T>.Create(value, default);
            Count++;

            //Set head to new item if list is empty
            if (Head == null) 
            {
                Head = newItem;
                return;
            }

            //Find last item in list
            LinkedListNode<T>? end = Head;
            if (end != null)
            {
                end = Traverse();
            }
            
            //Append item to end
            end!.Next = new LinkedListNode<T>{
                Value = value,
                Next = default
            };
        }

        public void Insert(int index, T value)
        {
            if (index > Count) throw new System.Exception("Error! Index outside of Bounds");

            //Fetch point in list at which item will be added
            LinkedListNode<T>? node = Traverse(index - 1);
            node!.Next = new LinkedListNode<T> { 
                Value = value, 
                Next = node.Next 
            };
            Count++;
        }

        public void Delete(int index)
        {
            //Check if we are trying to reference the first item
            if (index == 0 && Head != null)
            {
                Head = (LinkedListNode<T>?)Head!.Next;
                return;
            }

            //Find node we are trying to delete and then remove / relink
            LinkedListNode<T>? node = Traverse(index - 1);

            if (node == null || node.Next == null) throw new System.Exception("Error! Index outside of Bounds");

            node.Next = node.Next.Next;
            Count--;
        }

        private LinkedListNode<T>? Traverse(){
            //Start at Head of list
            LinkedListNode<T>? node = Head;
            if (node != null)
            {   
                //continue to end of list
                while (node!.Next != default)
                {
                    node = (LinkedListNode<T>)node.Next;
                }
            }
            return node;
        }

        //private static LinkedListNode<T>? Traverse(LinkedListNode<T> start){
        //    //Start at given point in list
        //    LinkedListNode<T>? node = start;
        //    if (node != null)
        //    {
        //        //Continue to end of list
        //        while (node!.Next != default)
        //        {
        //            node = (LinkedListNode<T>)node.Next;
        //        }
        //    }
        //    return node;
        //}

        private LinkedListNode<T>? Traverse(int n)
        {
            //Start at given point in list
            LinkedListNode<T>? node = Head;
            if (node != null || n == 0)
            {
                //Continue to end of list
                for (int i = 0; i < n; i++)
                {
                    if (node!.Next == null) return null;
                    node = (LinkedListNode<T>)node.Next;
                }
            }
            return node;
        }
    }
}