// 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.
 
using System;
using System.Collections.Immutable;
using System.Linq;
using System.Runtime.CompilerServices;
using Microsoft.VisualStudio.Text;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.Text;
 
public static partial class Extensions
{
    /// <summary>
    /// ITextBuffer implementation of SourceTextContainer
    /// </summary>
    internal sealed class TextBufferContainer : SourceTextContainer
    {
        private readonly WeakReference<ITextBuffer> _weakEditorBuffer;
        private readonly object _gate = new object();
        private readonly ITextBufferCloneService? _textBufferCloneService;
 
        private event EventHandler<TextChangeEventArgs>? EtextChanged;
        private SourceText _currentText;
 
        private TextBufferContainer(ITextBuffer editorBuffer)
        {
            Contract.ThrowIfNull(editorBuffer);
 
            _weakEditorBuffer = new WeakReference<ITextBuffer>(editorBuffer);
            editorBuffer.Properties.TryGetProperty(typeof(ITextBufferCloneService), out _textBufferCloneService);
            _currentText = SnapshotSourceText.From(_textBufferCloneService, editorBuffer.CurrentSnapshot, this);
        }
 
        /// <summary>
        /// A weak map of all Editor ITextBuffers and their associated SourceTextContainer
        /// </summary>
        private static readonly ConditionalWeakTable<ITextBuffer, TextBufferContainer> s_textContainerMap = new();
 
        public static TextBufferContainer From(ITextBuffer buffer)
        {
            if (buffer == null)
            {
                throw new ArgumentNullException(nameof(buffer));
            }
 
            return s_textContainerMap.GetValue(buffer, static buffer => new TextBufferContainer(buffer));
        }
 
        public ITextBuffer? TryFindEditorTextBuffer()
            => _weakEditorBuffer.GetTarget();
 
        public override SourceText CurrentText
        {
            get
            {
                var editorBuffer = this.TryFindEditorTextBuffer();
                return editorBuffer != null
                    ? editorBuffer.CurrentSnapshot.AsText()
                    : _currentText;
            }
        }
 
        public override event EventHandler<TextChangeEventArgs> TextChanged
        {
            add
            {
                lock (_gate)
                {
                    var textBuffer = this.TryFindEditorTextBuffer();
                    if (this.EtextChanged == null && textBuffer != null)
                    {
                        textBuffer.ChangedHighPriority += this.OnTextContentChanged;
                    }
 
                    this.EtextChanged += value;
                }
            }
 
            remove
            {
                lock (_gate)
                {
                    this.EtextChanged -= value;
 
                    var textBuffer = this.TryFindEditorTextBuffer();
                    if (this.EtextChanged == null && textBuffer != null)
                    {
                        textBuffer.ChangedHighPriority -= this.OnTextContentChanged;
                    }
                }
            }
        }
 
        private void OnTextContentChanged(object? sender, TextContentChangedEventArgs args)
        {
            var changed = this.EtextChanged;
            if (changed == null)
            {
                return;
            }
 
            // we should process all changes even though there is no text changes
            // otherwise, Workspace.CurrentSolution won't move forward to latest ITextSnapshot
 
            // this should convert given editor snapshots to roslyn forked snapshots
            var oldText = (SnapshotSourceText)args.Before.AsText();
            var newText = SnapshotSourceText.From(_textBufferCloneService, args.After);
            _currentText = newText;
 
            var changes = ImmutableArray.CreateRange(args.Changes.Select(c => new TextChangeRange(new TextSpan(c.OldSpan.Start, c.OldSpan.Length), c.NewLength)));
            var eventArgs = new TextChangeEventArgs(oldText, newText, changes);
 
            this.LastEventArgs = eventArgs;
            changed(sender, eventArgs);
        }
 
        // These are the event args that were last sent from this text container when the text
        // content may have changed.
        public TextChangeEventArgs? LastEventArgs { get; private set; }
    }
}