// 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 System.Runtime.CompilerServices;
using Unity.CodeEditor.Document;
using Unity.CodeEditor.Utils;

namespace Unity.CodeEditor.Editing
{
    sealed class EmptySelection : Selection
    {
        internal EmptySelection(TextArea textArea) : base(textArea)
        {
        }

        internal override Selection UpdateOnDocumentChange(DocumentChangeEventArgs e)
        {
            return this;
        }

        internal override TextViewPosition StartPosition => new TextViewPosition(TextLocation.Empty);

        internal override TextViewPosition EndPosition => new TextViewPosition(TextLocation.Empty);

        internal override ISegment SurroundingSegment => null;

        internal override Selection SetEndpoint(TextViewPosition endPosition)
        {
            throw new NotSupportedException();
        }

        internal override Selection StartSelectionOrSetEndpoint(TextViewPosition startPosition, TextViewPosition endPosition)
        {
            var document = TextArea.Document;
            if (document == null)
                throw ThrowUtil.NoDocumentAssigned();
            return Create(TextArea, startPosition, endPosition);
        }

        internal override IEnumerable<SelectionSegment> Segments => Empty<SelectionSegment>.Array;

        internal override string GetText()
        {
            return string.Empty;
        }

        internal override void ReplaceSelectionWithText(string newText)
        {
            if (newText == null)
                throw new ArgumentNullException(nameof(newText));
            newText = AddSpacesIfRequired(newText, TextArea.Caret.Position, TextArea.Caret.Position);
            if (newText.Length > 0)
            {
                if (TextArea.ReadOnlySectionProvider.CanInsert(TextArea.Caret.Offset))
                {
                    TextArea.Document.Insert(TextArea.Caret.Offset, newText);
                }
            }
            TextArea.Caret.VisualColumn = -1;
        }

        internal override int Length => 0;

        // Use reference equality because there's only one EmptySelection per text area.
        public override int GetHashCode()
        {
            return RuntimeHelpers.GetHashCode(this);
        }

        public override bool Equals(object obj)
        {
            return this == obj;
        }
    }
}