// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
#nullable disable
 
using System.Collections.Generic;
using System.Composition;
using Microsoft.CodeAnalysis.Editor.Shared.Utilities;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.Text;
using Microsoft.VisualStudio.Text.Operations;
using Microsoft.VisualStudio.Text;
using System;
 
namespace Microsoft.CodeAnalysis.Editor.Undo
{
    [ExportWorkspaceService(typeof(ISourceTextUndoService), ServiceLayer.Editor), Shared]
    internal sealed class EditorSourceTextUndoService : ISourceTextUndoService
    {
        private readonly Dictionary<SourceText, SourceTextUndoTransaction> _transactions = new();
 
        private readonly ITextUndoHistoryRegistry _undoHistoryRegistry;
 
        [ImportingConstructor]
        [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
        public EditorSourceTextUndoService(ITextUndoHistoryRegistry undoHistoryRegistry)
            => _undoHistoryRegistry = undoHistoryRegistry;
 
        public ISourceTextUndoTransaction RegisterUndoTransaction(SourceText sourceText, string description)
        {
            if (sourceText != null && !string.IsNullOrWhiteSpace(description))
            {
                var transaction = new SourceTextUndoTransaction(this, sourceText, description);
                _transactions.Add(sourceText, transaction);
                return transaction;
            }
 
            return null;
        }
 
        public bool BeginUndoTransaction(ITextSnapshot snapshot)
        {
            var sourceText = snapshot?.AsText();
            if (sourceText != null)
            {
                _transactions.TryGetValue(sourceText, out var transaction);
                if (transaction != null)
                {
                    return transaction.Begin(_undoHistoryRegistry?.GetHistory(snapshot.TextBuffer));
                }
            }
 
            return false;
        }
 
        public bool EndUndoTransaction(ISourceTextUndoTransaction transaction)
        {
            if (transaction != null && _transactions.ContainsKey(transaction.SourceText))
            {
                _transactions.Remove(transaction.SourceText);
                return true;
            }
 
            return false;
        }
 
        private sealed class SourceTextUndoTransaction : ISourceTextUndoTransaction
        {
            private readonly ISourceTextUndoService _service;
            public SourceText SourceText { get; }
            public string Description { get; }
 
            private ITextUndoTransaction _transaction;
 
            public SourceTextUndoTransaction(ISourceTextUndoService service, SourceText sourceText, string description)
            {
                _service = service;
                SourceText = sourceText;
                Description = description;
            }
 
            internal bool Begin(ITextUndoHistory undoHistory)
            {
                if (undoHistory != null)
                {
                    _transaction = new HACK_TextUndoTransactionThatRollsBackProperly(undoHistory.CreateTransaction(Description));
                    return true;
                }
 
                return false;
            }
 
            public void Dispose()
            {
                _transaction?.Complete();
 
                _service.EndUndoTransaction(this);
            }
        }
    }
}