// 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.Diagnostics;
using System.Text;

namespace ICSharpCode.AvalonEdit.Document
{
	static class NewLineFinder
	{
		static readonly char[] newline = { '\r', '\n' };
		
		/// <summary>
		/// Gets the location of the next new line character, or SimpleSegment.Invalid
		/// if none is found.
		/// </summary>
		internal static SimpleSegment NextNewLine(string text, int offset)
		{
			int pos = text.IndexOfAny(newline, offset);
			if (pos >= 0) {
				if (text[pos] == '\r') {
					if (pos + 1 < text.Length && text[pos + 1] == '\n')
						return new SimpleSegment(pos, 2);
				}
				return new SimpleSegment(pos, 1);
			}
			return SimpleSegment.Invalid;
		}
		
		/// <summary>
		/// Gets the location of the next new line character, or SimpleSegment.Invalid
		/// if none is found.
		/// </summary>
		internal static SimpleSegment NextNewLine(ITextSource text, int offset)
		{
			int textLength = text.TextLength;
			int pos = text.IndexOfAny(newline, offset, textLength - offset);
			if (pos >= 0) {
				if (text.GetCharAt(pos) == '\r') {
					if (pos + 1 < textLength && text.GetCharAt(pos + 1) == '\n')
						return new SimpleSegment(pos, 2);
				}
				return new SimpleSegment(pos, 1);
			}
			return SimpleSegment.Invalid;
		}
	}
	
	partial class TextUtilities
	{
		/// <summary>
		/// Finds the next new line character starting at offset.
		/// </summary>
		/// <param name="text">The text source to search in.</param>
		/// <param name="offset">The starting offset for the search.</param>
		/// <param name="newLineType">The string representing the new line that was found, or null if no new line was found.</param>
		/// <returns>The position of the first new line starting at or after <paramref name="offset"/>,
		/// or -1 if no new line was found.</returns>
		public static int FindNextNewLine(ITextSource text, int offset, out string newLineType)
		{
			if (text == null)
				throw new ArgumentNullException("text");
			if (offset < 0 || offset > text.TextLength)
				throw new ArgumentOutOfRangeException("offset", offset, "offset is outside of text source");
			SimpleSegment s = NewLineFinder.NextNewLine(text, offset);
			if (s == SimpleSegment.Invalid) {
				newLineType = null;
				return -1;
			} else {
				if (s.Length == 2) {
					newLineType = "\r\n";
				} else if (text.GetCharAt(s.Offset) == '\n') {
					newLineType = "\n";
				} else {
					newLineType = "\r";
				}
				return s.Offset;
			}
		}
		
		/// <summary>
		/// Gets whether the specified string is a newline sequence.
		/// </summary>
		public static bool IsNewLine(string newLine)
		{
			return newLine == "\r\n" || newLine == "\n" || newLine == "\r";
		}
		
		/// <summary>
		/// Normalizes all new lines in <paramref name="input"/> to be <paramref name="newLine"/>.
		/// </summary>
		public static string NormalizeNewLines(string input, string newLine)
		{
			if (input == null)
				return null;
			if (!IsNewLine(newLine))
				throw new ArgumentException("newLine must be one of the known newline sequences");
			SimpleSegment ds = NewLineFinder.NextNewLine(input, 0);
			if (ds == SimpleSegment.Invalid) // text does not contain any new lines
				return input;
			StringBuilder b = new StringBuilder(input.Length);
			int lastEndOffset = 0;
			do {
				b.Append(input, lastEndOffset, ds.Offset - lastEndOffset);
				b.Append(newLine);
				lastEndOffset = ds.EndOffset;
				ds = NewLineFinder.NextNewLine(input, lastEndOffset);
			} while (ds != SimpleSegment.Invalid);
			// remaining string (after last newline)
			b.Append(input, lastEndOffset, input.Length - lastEndOffset);
			return b.ToString();
		}
		
		/// <summary>
		/// Gets the newline sequence used in the document at the specified line.
		/// </summary>
		public static string GetNewLineFromDocument(TextDocument document, int lineNumber)
		{
			DocumentLine line = document.GetLineByNumber(lineNumber);
			if (line.DelimiterLength == 0) {
				// at the end of the document, there's no line delimiter, so use the delimiter
				// from the previous line
				line = line.PreviousLine;
				if (line == null)
					return Environment.NewLine;
			}
			return document.GetText(line.Offset + line.Length, line.DelimiterLength);
		}
	}
}