// 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
// without restriction, including without limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// 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
// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

using System;
using System.Collections.Generic;

using UyghurEditPP.Document;

namespace UyghurEditPP.Editing
{
	/// <summary>
	/// Implementation for <see cref="IReadOnlySectionProvider"/> that stores the segments
	/// in a <see cref="TextSegmentCollection{T}"/>.
	/// </summary>
	public class TextSegmentReadOnlySectionProvider<T> : IReadOnlySectionProvider where T : TextSegment
	{
		readonly TextSegmentCollection<T> segments;

		/// <summary>
		/// Gets the collection storing the read-only segments.
		/// </summary>
		public TextSegmentCollection<T> Segments {
			get { return segments; }
		}

		/// <summary>
		/// Creates a new TextSegmentReadOnlySectionProvider instance for the specified document.
		/// </summary>
		public TextSegmentReadOnlySectionProvider(TextDocument textDocument)
		{
			segments = new TextSegmentCollection<T>(textDocument);
		}

		/// <summary>
		/// Creates a new TextSegmentReadOnlySectionProvider instance using the specified TextSegmentCollection.
		/// </summary>
		public TextSegmentReadOnlySectionProvider(TextSegmentCollection<T> segments)
		{
			if (segments == null)
				throw new ArgumentNullException("segments");
			this.segments = segments;
		}

		/// <summary>
		/// Gets whether insertion is possible at the specified offset.
		/// </summary>
		public virtual bool CanInsert(int offset)
		{
			foreach (TextSegment segment in segments.FindSegmentsContaining(offset)) {
				if (segment.StartOffset < offset && offset < segment.EndOffset)
					return false;
			}
			return true;
		}

		/// <summary>
		/// Gets the deletable segments inside the given segment.
		/// </summary>
		public virtual IEnumerable<ISegment> GetDeletableSegments(ISegment segment)
		{
			if (segment == null)
				throw new ArgumentNullException("segment");

			if (segment.Length == 0 && CanInsert(segment.Offset)) {
				yield return segment;
				yield break;
			}

			int readonlyUntil = segment.Offset;
			foreach (TextSegment ts in segments.FindOverlappingSegments(segment)) {
				int start = ts.StartOffset;
				int end = start + ts.Length;
				if (start > readonlyUntil) {
					yield return new SimpleSegment(readonlyUntil, start - readonlyUntil);
				}
				if (end > readonlyUntil) {
					readonlyUntil = end;
				}
			}
			int endOffset = segment.EndOffset;
			if (readonlyUntil < endOffset) {
				yield return new SimpleSegment(readonlyUntil, endOffset - readonlyUntil);
			}
		}
	}
}
