#define DEBUG
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics;

namespace AspClassic.Parser;

/// <summary>
/// The root class of all trees.
/// </summary>
public abstract class Tree
{
	private readonly TreeType _Type;

	private readonly Span _Span;

	private Tree _Parent;

	private ReadOnlyCollection<Tree> _Children;

	/// <summary>
	/// The type of the tree.
	/// </summary>
	public TreeType Type => _Type;

	/// <summary>
	/// The location of the tree.
	/// </summary>
	/// <remarks>
	/// The span ends at the first character beyond the tree
	/// </remarks>
	public Span Span => _Span;

	/// <summary>
	/// The parent of the tree. Nothing if the root tree.
	/// </summary>
	public Tree Parent => _Parent;

	/// <summary>
	/// The children of the tree.
	/// </summary>
	public ReadOnlyCollection<Tree> Children
	{
		get
		{
			if (_Children == null)
			{
				List<Tree> ChildList = new List<Tree>();
				GetChildTrees(ChildList);
				_Children = new ReadOnlyCollection<Tree>(ChildList);
			}
			return _Children;
		}
	}

	/// <summary>
	/// Whether the tree is 'bad'.
	/// </summary>
	public virtual bool IsBad => false;

	protected Tree(TreeType type, Span span)
	{
		Debug.Assert(type >= TreeType.SyntaxError && type <= TreeType.File);
		_Type = type;
		_Span = span;
	}

	protected void SetParent(Tree child)
	{
		if (child != null)
		{
			child._Parent = this;
		}
	}

	protected void SetParents<T>(IList<T> children) where T : Tree
	{
		if (children == null)
		{
			return;
		}
		foreach (Tree Child in children)
		{
			SetParent(Child);
		}
	}

	protected static void AddChild(IList<Tree> childList, Tree child)
	{
		if (child != null)
		{
			childList.Add(child);
		}
	}

	protected static void AddChildren<T>(IList<Tree> childList, ReadOnlyCollection<T> children) where T : Tree
	{
		if (children == null)
		{
			return;
		}
		foreach (Tree Child in children)
		{
			childList.Add(Child);
		}
	}

	protected virtual void GetChildTrees(IList<Tree> childList)
	{
	}
}