using System.Collections.Generic;

namespace Spectre.Console
{
    internal sealed class ListPromptItem<T> : IMultiSelectionItem<T>
        where T : notnull
    {
        public T Data { get; }
        public ListPromptItem<T>? Parent { get; }
        public List<ListPromptItem<T>> Children { get; }
        public int Depth { get; }
        public bool IsSelected { get; set; }

        public bool IsGroup => Children.Count > 0;

        public ListPromptItem(T data, ListPromptItem<T>? parent = null)
        {
            Data = data;
            Parent = parent;
            Children = new List<ListPromptItem<T>>();
            Depth = CalculateDepth(parent);
        }

        public IMultiSelectionItem<T> Select()
        {
            IsSelected = true;
            return this;
        }

        public ISelectionItem<T> AddChild(T item)
        {
            var node = new ListPromptItem<T>(item, this);
            Children.Add(node);
            return node;
        }

        public IEnumerable<ListPromptItem<T>> Traverse(bool includeSelf)
        {
            var stack = new Stack<ListPromptItem<T>>();

            if (includeSelf)
            {
                stack.Push(this);
            }
            else
            {
                foreach (var child in Children)
                {
                    stack.Push(child);
                }
            }

            while (stack.Count > 0)
            {
                var current = stack.Pop();
                yield return current;

                if (current.Children.Count > 0)
                {
                    foreach (var child in current.Children.ReverseEnumerable())
                    {
                        stack.Push(child);
                    }
                }
            }
        }

        private static int CalculateDepth(ListPromptItem<T>? parent)
        {
            var level = 0;
            while (parent != null)
            {
                level++;
                parent = parent.Parent;
            }

            return level;
        }
    }
}