using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;

namespace DictionaryWorkshop.Implementation
{
    public class MyLinkedList<TKey, TValue> : IEnumerable<MyKeyValuePair<TKey,TValue>>
    {
        public MyKeyValuePair<TKey, TValue> Head { get; private set; }
        public MyKeyValuePair<TKey, TValue> Tail { get; private set; }

        public MyLinkedList(TKey key, TValue value)
        {
            this.Head = new MyKeyValuePair<TKey, TValue>(key, value);
            this.Tail = this.Head;
            this.Count++;
        }

        public int Count { get; set; }

        public bool Add(TKey key, TValue value)
        {
            var oldTail = this.Tail;
            var  newNode = new MyKeyValuePair<TKey, TValue>(key, value);

            if (this.Count == 0 && this.Contains(key)==false)
            {
                this.Tail = newNode;
                this.Head = this.Tail;
                this.Count++;
                return true;
            }
            else if (this.Contains(key) == false)
            {
                oldTail.Next = newNode;
                this.Tail = newNode;
                this.Count++;
                return true;
            }
            return false;
        }
        public bool Remove(TKey key)
        {
            MyKeyValuePair<TKey, TValue> current = this.Head;
            if (this.Count == 0)
            {
                throw new InvalidOperationException();
            }
            if (this.Contains(key)==false )
            {
                return false;
            }
            if (this.Head.Key.Equals(key) && this.Tail.Key.Equals(key))
            {
                this.Head = null;
                this.Tail = null;
                this.Count--;
                return true;
            }
            else if (this.Tail.Key.Equals(key))
            {
                var currentNode = this.Head;

                while (currentNode !=null)
                {
                    if (currentNode.Next == this.Tail)
                    {
                        currentNode.Next = null;
                        currentNode = this.Tail;
                        this.Count--;
                        return true;
                    }
                    currentNode = currentNode.Next;
                }
            }
            while (current !=null)
            {
                if (current.Next.Key.Equals(key))
                {
                    var previous = current;
                    previous.Next = previous.Next.Next;
                    this.Count--;
                    return true;
                }
                current = current.Next;
            }
            return false;
        }
        public bool Contains(TKey key)
        {
            MyKeyValuePair<TKey, TValue> current = this.Head;

            while (current !=null)
            {
                if (current.Key.Equals(key))
                {
                    return true;
                }
                current = current.Next;
            }
            return false;
        }

        public IEnumerator<MyKeyValuePair<TKey, TValue>> GetEnumerator()
        {
            MyKeyValuePair<TKey, TValue> current = this.Head;

            while (current != null)
            {
                yield return current;
                current = current.Next;
            }
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }
        public override string ToString()
        {
            var sb = new StringBuilder();
            var temp = this.Head;
            while (temp !=null)
            {
                sb.AppendLine(temp.ToString());
                temp = temp.Next;
            }
            return sb.ToString();
        }
    }
}