using System;
using System.Collections.Generic;
using JD.Kernel.StaticHelpers;

namespace JD.Collections
{
    /// <summary>
    /// TreeNode
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public class TreeNode<T> : IEnumerable<TreeNode<T>>
    {
        #region Variables

        private T m_data;
        private TreeNode<T> m_parent;
        private TreeNode<T> m_child;
        private TreeNode<T> m_sibling;
        private TreeNode<T> m_lastChild;

        #endregion

        #region Constructor

        /// <summary>
        /// Default constructor.
        /// </summary>
        public TreeNode()
        {
            m_data = default(T);
        }

        /// <summary>
        /// Alternative constructor.
        /// </summary>
        /// <param name="data">Node's data.</param>
        public TreeNode(T data)
        {
            m_data = data;
        }

        #endregion

        #region Properties

        /// <summary>
        /// Is root.
        /// </summary>
        public bool IsRoot
        {
            get
            {
                return m_parent == null;
            }
        }

        /// <summary>
        /// Is leaf.
        /// </summary>
        public bool IsLeaf
        {
            get
            {
                return m_child == null;
            }
        }

        /// <summary>
        /// Is isolated.
        /// </summary>
        public bool IsIsolated
        {
            get
            {
                return IsRoot && IsLeaf;
            }
        }

        /// <summary>
        /// Data.
        /// </summary>
        public T Data
        {
            get
            {
                return m_data;
            }
            set
            {
                m_data = value;
            }
        }

        /// <summary>
        /// Parent.
        /// </summary>
        public TreeNode<T> Parent
        {
            get
            {
                return m_parent;
            }
        }

        #endregion

        /// <summary>
        /// Children.
        /// </summary>
        public IEnumerable<TreeNode<T>> Children
        {
            get
            {
                TreeNode<T> child = m_child;
                while (child != null)
                {
                    yield return child;
                    child = child.m_sibling;
                }
            }
        }

        /// <summary>
        /// Enumerate directly through children data.
        /// </summary>
        public IEnumerable<T> ChildrenData
        {
            get
            {
                foreach (TreeNode<T> child in Children)
                {
                    yield return child.Data;
                }
            }
        }

        /// <summary>
        /// Descendants.
        /// </summary>
        public IEnumerable<TreeNode<T>> Descendants
        {
            get
            {
                foreach (TreeNode<T> child in Children)
                {
                    yield return child;
                    foreach (TreeNode<T> descendant in child.Descendants)
                    {
                        yield return descendant;
                    }
                }
            }
        }

        public IEnumerable<TreeNode<T>> AllNodes
        {
            get
            {
                yield return this;

                foreach (TreeNode<T> child in Descendants)
                {
                    yield return child;
                }
            }
        }

        public IEnumerable<T> AllNodesData
        {
            get
            {
                yield return m_data;

                foreach (TreeNode<T> child in Descendants)
                {
                    yield return child.Data;
                }
            }
        }

        #region Methods

        /// <summary>
        /// Adds a new node with data as value.
        /// </summary>
        /// <param name="data">Data of the new child.</param>
        /// <returns>The created node.</returns>
        public TreeNode<T> Add(T data)
        {
            TreeNode<T> newChild = new TreeNode<T>(data);
            AttachChild(newChild);
            return newChild;
        }

        /// <summary>
        /// Attach <paramref name="newChild"/> as a child.
        /// </summary>
        /// <remarks>The TreeNode <paramref name="newChild"/> will be detach from its current parent if it's not a root.</remarks>
        /// <param name="newChild"></param>
        public void AttachChild(TreeNode<T> newChild)
        {
            Throw.IfNull(newChild, "newChild");
            Throw.InvalidOperationIf(newChild == this, "Trying to attach a node to itself.");
            Throw.InvalidOperationIf(IsDescendantOf(newChild), "Try to attach a node to one of its descendants.");

            if (newChild.Parent != null)
            {
                newChild.Detach();
            }

            if (m_child == null)
            {
                m_child = newChild;
            }
            else
            {
                m_lastChild.m_sibling = newChild;
            }

            newChild.m_parent = this;
            m_lastChild = newChild;
        }

        /// <summary>
        /// Detach from parent.
        /// </summary>
        public void Detach()
        {
            Throw.InvalidOperationIf(IsRoot, "Unable to detach a root node.");

            if (m_parent.m_child == this)
            {
                //Parent's first child is us:
                //Set the parent's new child as our sibling.
                m_parent.m_child = m_sibling;

                if (m_parent.m_lastChild == this)
                {
                    m_parent.m_lastChild = null;
                }
            }
            else
            {
                //Parent's first child is not us:
                //Iterate in the children of the parent until a child's sibling is us
                TreeNode<T> childIter = m_parent.m_child;
                while (childIter != null && childIter.m_sibling != this)
                {
                    childIter = childIter.m_sibling;
                }

                System.Diagnostics.Debug.Assert(childIter != null, "Unable to find node in parent's child.");
                if (m_parent.m_lastChild == this)
                {
                    m_parent.m_lastChild = childIter;
                }

                childIter.m_sibling = m_sibling;
            }

            m_parent = null;
            m_sibling = null;
        }

        /// <summary>
        /// Is parent of <paramref name="node"/>.
        /// </summary>
        /// <param name="node"></param>
        /// <returns></returns>
        public bool IsParentOf(TreeNode<T> node)
        {
            Throw.IfNull(node, "node");
            return node.Parent == this;
        }

        /// <summary>
        /// Is ancestor of <paramref name="node"/>.
        /// </summary>
        /// <param name="node"></param>
        /// <returns></returns>
        public bool IsAncestorOf(TreeNode<T> node)
        {
            Throw.IfNull(node, "node");
            return node.IsDescendantOf(this);
        }

        /// <summary>
        /// Is decendant of <paramref name="node"/>.
        /// </summary>
        /// <param name="node"></param>
        /// <returns></returns>
        public bool IsDescendantOf(TreeNode<T> node)
        {
            Throw.IfNull(node, "node");
            TreeNode<T> parent = m_parent;
            while(parent != null && parent != node)
            {
                parent = parent.Parent;
            }

            return parent != null;
        }

        /// <summary>
        /// Perform <paramref name="action"/> for all children.
        /// </summary>
        /// <param name="action"></param>
        public void ForEachChildren(Action<TreeNode<T>> action)
        {
            Throw.IfNull(action, "action");

            TreeNode<T> child = m_child;
            while(child != null)
            {
                //Cache the next child in case the child pointer gets 
                //invalidated in the action. This happens if, for example, you 
                //delete an item in the sibling chain while iterating. In this
                //case, the pointer to m_sibling might be deleted, resulting in
                //loosing items.
                TreeNode<T> nextChild = child.m_sibling;
                action(child);
                child = nextChild;
            }
        }

        /// <summary>
        /// Perform <paramref name="action"/> for all ancestor.
        /// </summary>
        /// <param name="action"></param>
        public void ForEachAncestor(Action<TreeNode<T>> action)
        {
            Throw.IfNull(action, "action");

            TreeNode<T> parent = m_parent;
            while(parent != null)
            {
                //Cache the next parent. See reason in ForEachChildren
                TreeNode<T> nextParent = parent.Parent;
                action(parent);
                parent = nextParent;
            }
        }

        /// <summary>
        /// Perform <paramref name="action"/> for all descendant.
        /// </summary>
        /// <remarks>Action application is done before calling the child.
        /// DO NOT MODIFY THE HIERARCHY STRUCTURE FROM THE GIVEN ACTION.</remarks>
        /// <param name="action"></param>
        public void ForEachDescendant(Action<TreeNode<T>> action)
        {
            Throw.IfNull(action, "action");

            TreeNode<T> child = m_child;
            while(child != null)
            {
                action(child);
                child.ForEachDescendant(action);
                child = child.m_sibling;
            }
        }

        #endregion

        #region IEnumerable<T> Members

        public IEnumerator<TreeNode<T>> GetEnumerator()
        {
            return AllNodes.GetEnumerator();
        }

        #endregion

        #region IEnumerable Members

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            return AllNodes.GetEnumerator();
        }

        #endregion
    }
}