// Copyright (c) AlphaSierraPapa for the SharpDevelop Team (for details please see \doc\copyright.txt)
// This code is distributed under the GNU LGPL (for details please see \doc\license.txt)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;

using Tango.Scripting.Editors.Document;

namespace Tango.Scripting.Editors.Folding
{
	/// <summary>
	/// Holds information about the start of a fold in an xml string.
	/// </summary>
	sealed class XmlFoldStart : NewFolding
	{
		internal int StartLine;
	}
	
	/// <summary>
	/// Determines folds for an xml string in the editor.
	/// </summary>
	public class XmlFoldingStrategy : AbstractFoldingStrategy
	{
		/// <summary>
		/// Flag indicating whether attributes should be displayed on folded
		/// elements.
		/// </summary>
		public bool ShowAttributesWhenFolded { get; set; }
		
		/// <summary>
		/// Create <see cref="NewFolding"/>s for the specified document.
		/// </summary>
		public override IEnumerable<NewFolding> CreateNewFoldings(TextDocument document, out int firstErrorOffset)
		{
			try {
				XmlTextReader reader = new XmlTextReader(document.CreateReader());
				reader.XmlResolver = null; // don't resolve DTDs
				return CreateNewFoldings(document, reader, out firstErrorOffset);
			} catch (XmlException) {
				firstErrorOffset = 0;
				return Enumerable.Empty<NewFolding>();
			}
		}
		
		/// <summary>
		/// Create <see cref="NewFolding"/>s for the specified document.
		/// </summary>
		public IEnumerable<NewFolding> CreateNewFoldings(TextDocument document, XmlReader reader, out int firstErrorOffset)
		{
			Stack<XmlFoldStart> stack = new Stack<XmlFoldStart>();
			List<NewFolding> foldMarkers = new List<NewFolding>();
			try {
				while (reader.Read()) {
					switch (reader.NodeType) {
						case XmlNodeType.Element:
							if (!reader.IsEmptyElement) {
								XmlFoldStart newFoldStart = CreateElementFoldStart(document, reader);
								stack.Push(newFoldStart);
							}
							break;
							
						case XmlNodeType.EndElement:
							XmlFoldStart foldStart = stack.Pop();
							CreateElementFold(document, foldMarkers, reader, foldStart);
							break;
							
						case XmlNodeType.Comment:
							CreateCommentFold(document, foldMarkers, reader);
							break;
					}
				}
				firstErrorOffset = -1;
			} catch (XmlException ex) {
				// ignore errors at invalid positions (prevent ArgumentOutOfRangeException)
				if (ex.LineNumber >= 1 && ex.LineNumber <= document.LineCount)
					firstErrorOffset = document.GetOffset(ex.LineNumber, ex.LinePosition);
				else
					firstErrorOffset = 0;
			}
			foldMarkers.Sort((a,b) => a.StartOffset.CompareTo(b.StartOffset));
			return foldMarkers;
		}
		
		static int GetOffset(TextDocument document, XmlReader reader)
		{
			IXmlLineInfo info = reader as IXmlLineInfo;
			if (info != null && info.HasLineInfo()) {
				return document.GetOffset(info.LineNumber, info.LinePosition);
			} else {
				throw new ArgumentException("XmlReader does not have positioning information.");
			}
		}
		
		/// <summary>
		/// Creates a comment fold if the comment spans more than one line.
		/// </summary>
		/// <remarks>The text displayed when the comment is folded is the first
		/// line of the comment.</remarks>
		static void CreateCommentFold(TextDocument document, List<NewFolding> foldMarkers, XmlReader reader)
		{
			string comment = reader.Value;
			if (comment != null) {
				int firstNewLine = comment.IndexOf('\n');
				if (firstNewLine >= 0) {
					
					// Take off 4 chars to get the actual comment start (takes
					// into account the <!-- chars.
					
					int startOffset = GetOffset(document, reader) - 4;
					int endOffset = startOffset + comment.Length + 7;
					
					string foldText = String.Concat("<!--", comment.Substring(0, firstNewLine).TrimEnd('\r') , "-->");
					foldMarkers.Add(new NewFolding(startOffset, endOffset) { Name = foldText } );
				}
			}
		}
		
		/// <summary>
		/// Creates an XmlFoldStart for the start tag of an element.
		/// </summary>
		XmlFoldStart CreateElementFoldStart(TextDocument document, XmlReader reader)
		{
			// Take off 1 from the offset returned
			// from the xml since it points to the start
			// of the element name and not the beginning
			// tag.
			//XmlFoldStart newFoldStart = new XmlFoldStart(reader.Prefix, reader.LocalName, reader.LineNumber - 1, reader.LinePosition - 2);
			XmlFoldStart newFoldStart = new XmlFoldStart();
			
			IXmlLineInfo lineInfo = (IXmlLineInfo)reader;
			newFoldStart.StartLine = lineInfo.LineNumber;
			newFoldStart.StartOffset = document.GetOffset(newFoldStart.StartLine, lineInfo.LinePosition - 1);
			
			if (this.ShowAttributesWhenFolded && reader.HasAttributes) {
				newFoldStart.Name = String.Concat("<", reader.Name, " ", GetAttributeFoldText(reader), ">");
			} else {
				newFoldStart.Name = String.Concat("<", reader.Name, ">");
			}
			
			return newFoldStart;
		}
		
		/// <summary>
		/// Create an element fold if the start and end tag are on
		/// different lines.
		/// </summary>
		static void CreateElementFold(TextDocument document, List<NewFolding> foldMarkers, XmlReader reader, XmlFoldStart foldStart)
		{
			IXmlLineInfo lineInfo = (IXmlLineInfo)reader;
			int endLine = lineInfo.LineNumber;
			if (endLine > foldStart.StartLine) {
				int endCol = lineInfo.LinePosition + reader.Name.Length + 1;
				foldStart.EndOffset = document.GetOffset(endLine, endCol);
				foldMarkers.Add(foldStart);
			}
		}
		
		/// <summary>
		/// Gets the element's attributes as a string on one line that will
		/// be displayed when the element is folded.
		/// </summary>
		/// <remarks>
		/// Currently this puts all attributes from an element on the same
		/// line of the start tag.  It does not cater for elements where attributes
		/// are not on the same line as the start tag.
		/// </remarks>
		static string GetAttributeFoldText(XmlReader reader)
		{
			StringBuilder text = new StringBuilder();
			
			for (int i = 0; i < reader.AttributeCount; ++i) {
				reader.MoveToAttribute(i);
				
				text.Append(reader.Name);
				text.Append("=");
				text.Append(reader.QuoteChar.ToString());
				text.Append(XmlEncodeAttributeValue(reader.Value, reader.QuoteChar));
				text.Append(reader.QuoteChar.ToString());
				
				// Append a space if this is not the
				// last attribute.
				if (i < reader.AttributeCount - 1) {
					text.Append(" ");
				}
			}
			
			return text.ToString();
		}
		
		/// <summary>
		/// Xml encode the attribute string since the string returned from
		/// the XmlTextReader is the plain unencoded string and .NET
		/// does not provide us with an xml encode method.
		/// </summary>
		static string XmlEncodeAttributeValue(string attributeValue, char quoteChar)
		{
			StringBuilder encodedValue = new StringBuilder(attributeValue);
			
			encodedValue.Replace("&", "&amp;");
			encodedValue.Replace("<", "&lt;");
			encodedValue.Replace(">", "&gt;");
			
			if (quoteChar == '"') {
				encodedValue.Replace("\"", "&quot;");
			} else {
				encodedValue.Replace("'", "&apos;");
			}
			
			return encodedValue.ToString();
		}
	}
}