// Copyright (c) 2014 AlphaSierraPapa for the SharpDevelop Team
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
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// to whom the Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
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using System;
using Unity.CodeEditor.Utils;

namespace Unity.CodeEditor.Document
{
	/// <summary>
	/// The TextAnchor class references an offset (a position between two characters).
	/// It automatically updates the offset when text is inserted/removed in front of the anchor.
	/// </summary>
	/// <remarks>
	/// <para>Use the <see cref="Offset"/> property to get the offset from a text anchor.
	/// Use the <see cref="TextDocument.CreateAnchor"/> method to create an anchor from an offset.
	/// </para>
	/// <para>
	/// The document will automatically update all text anchors; and because it uses weak references to do so,
	/// the garbage collector can simply collect the anchor object when you don't need it anymore.
	/// </para>
	/// <para>Moreover, the document is able to efficiently update a large number of anchors without having to look
	/// at each anchor object individually. Updating the offsets of all anchors usually only takes time logarithmic
	/// to the number of anchors. Retrieving the <see cref="Offset"/> property also runs in O(lg N).</para>
	/// <inheritdoc cref="IsDeleted" />
	/// <inheritdoc cref="MovementType" />
	/// <para>If you want to track a segment, you can use the <see cref="AnchorSegment"/> class which
	/// implements <see cref="ISegment"/> using two text anchors.</para>
	/// </remarks>
	/// <example>
	/// Usage:
	/// <code>TextAnchor anchor = document.CreateAnchor(offset);
	/// ChangeMyDocument();
	/// int newOffset = anchor.Offset;
	/// </code>
	/// </example>
	internal sealed class TextAnchor : ITextAnchor
	{
	    internal TextAnchorNode Node { get; set; }
		
		internal TextAnchor(TextDocument document)
		{
			Document = document;
		}
		
		/// <summary>
		/// Gets the document owning the anchor.
		/// </summary>
		internal TextDocument Document { get; }

	    /// <inheritdoc/>
		public AnchorMovementType MovementType { get; set; }
		
		/// <inheritdoc/>
		public bool SurviveDeletion { get; set; }
		
		/// <inheritdoc/>
		public bool IsDeleted {
			get {
				Document.DebugVerifyAccess();
				return Node == null;
			}
		}
		
		/// <inheritdoc/>
		public event EventHandler Deleted;
		
		internal void OnDeleted(DelayedEvents delayedEvents)
		{
			Node = null;
			delayedEvents.DelayedRaise(Deleted, this, EventArgs.Empty);
		}
		
		/// <summary>
		/// Gets the offset of the text anchor.
		/// </summary>
		/// <exception cref="InvalidOperationException">Thrown when trying to get the Offset from a deleted anchor.</exception>
		public int Offset {
			get {
				Document.DebugVerifyAccess();
				
				var n = Node;
				if (n == null)
					throw new InvalidOperationException();
				
				var offset = n.Length;
				if (n.Left != null)
					offset += n.Left.TotalLength;
				while (n.Parent != null) {
					if (n == n.Parent.Right) {
						if (n.Parent.Left != null)
							offset += n.Parent.Left.TotalLength;
						offset += n.Parent.Length;
					}
					n = n.Parent;
				}
				return offset;
			}
		}
		
		/// <summary>
		/// Gets the line number of the anchor.
		/// </summary>
		/// <exception cref="InvalidOperationException">Thrown when trying to get the Offset from a deleted anchor.</exception>
		public int Line => Document.GetLineByOffset(Offset).LineNumber;

	    /// <summary>
		/// Gets the column number of this anchor.
		/// </summary>
		/// <exception cref="InvalidOperationException">Thrown when trying to get the Offset from a deleted anchor.</exception>
		public int Column {
			get {
				var offset = Offset;
				return offset - Document.GetLineByOffset(offset).Offset + 1;
			}
		}
		
		/// <summary>
		/// Gets the text location of this anchor.
		/// </summary>
		/// <exception cref="InvalidOperationException">Thrown when trying to get the Offset from a deleted anchor.</exception>
		public TextLocation Location => Document.GetLocation(Offset);

	    /// <inheritdoc/>
		public override string ToString()
		{
			return "[TextAnchor Offset=" + Offset + "]";
		}
	}
}