// 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.Generic;
using System.Collections.Immutable;
using System.Composition;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeFixes;
using Microsoft.CodeAnalysis.Diagnostics;
using Microsoft.CodeAnalysis.Editing;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.Shared.Collections;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Text;
 
namespace Microsoft.CodeAnalysis.CSharp.RemoveUnnecessaryUnsafeModifier;
 
[ExportCodeFixProvider(LanguageNames.CSharp, Name = PredefinedCodeFixProviderNames.RemoveUnnecessaryUnsafeModifier), Shared]
[method: ImportingConstructor]
[method: Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
internal sealed class CSharpRemoveUnnecessaryUnsafeModifierCodeFixProvider() : CodeFixProvider
{
    public override ImmutableArray<string> FixableDiagnosticIds => [IDEDiagnosticIds.RemoveUnnecessaryUnsafeModifier];
 
    public sealed override Task RegisterCodeFixesAsync(CodeFixContext context)
    {
        context.RegisterCodeFix(CodeAction.Create(
            AnalyzersResources.Remove_unnecessary_unsafe_modifier,
            cancellationToken => FixAllAsync(context.Document, context.Diagnostics, cancellationToken),
            nameof(AnalyzersResources.Remove_unnecessary_unsafe_modifier)),
            context.Diagnostics);
 
        return Task.CompletedTask;
    }
 
    private static async Task<Document> FixAllAsync(Document document, ImmutableArray<Diagnostic> diagnostics, CancellationToken cancellationToken)
    {
        var root = await document.GetRequiredSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
 
        var editor = new SyntaxEditor(root, document.Project.Solution.Services);
 
        FixAll(editor, diagnostics.Select(static d => d.AdditionalLocations[0].SourceSpan));
 
        return document.WithSyntaxRoot(editor.GetChangedRoot());
    }
 
    private static void FixAll(SyntaxEditor editor, IEnumerable<TextSpan> spans)
    {
        var root = editor.OriginalRoot;
 
        // Process from inside out.  Don't remove unsafe modifiers on containing nodes if we removed it from an inner
        // node. The inner removal may make the outer one necessary.
 
        var intervalTree = new TextSpanMutableIntervalTree();
 
        foreach (var span in spans.OrderByDescending(d => d.Start))
        {
            if (intervalTree.HasIntervalThatIntersectsWith(span))
                continue;
 
            intervalTree.AddIntervalInPlace(span);
 
            var node = root.FindNode(span, getInnermostNodeForTie: true);
            editor.ReplaceNode(
                node,
                static (current, generator) => generator.WithModifiers(current, generator.GetModifiers(current).WithIsUnsafe(false)));
        }
    }
 
    public override FixAllProvider? GetFixAllProvider()
        => new RemoveUnnecessaryUnsafeModifierSuppressionsFixAllProvider();
 
    /// <summary>
    /// Fix-all for removing unnecessary `unsafe` modifiers works in a fairly specialized fashion.  The core problem is
    /// that it's normal to have situations where a `unsafe` operator is unnecessary in one linked document in one
    /// project, but necessary in another.  Consider cases where some projects have access to modern C# with 'ref', while
    /// others may fall back to pointers.  Removing for the 'ref' case would break the pointer case.
    ///
    /// To deal with this, we consider all linked documents together.  If an `unsafe` modifier is unnecessary in *all*
    /// linked documents, then we can remove it.  Otherwise, we must keep it.
    /// </summary>
    private sealed class RemoveUnnecessaryUnsafeModifierSuppressionsFixAllProvider : MultiProjectSafeFixAllProvider
    {
#if !CODE_STYLE
        internal override CodeActionCleanup Cleanup => CodeActionCleanup.SyntaxOnly;
#endif
 
        protected override void FixAll(SyntaxEditor editor, IEnumerable<TextSpan> commonSpans)
            => CSharpRemoveUnnecessaryUnsafeModifierCodeFixProvider.FixAll(editor, commonSpans);
    }
}