// 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.Composition;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeFixes;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Diagnostics;
using Microsoft.CodeAnalysis.Editing;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.Shared.Extensions;

namespace Microsoft.CodeAnalysis.CSharp.MakeStructFieldsWritable
{
    [ExportCodeFixProvider(LanguageNames.CSharp, Name = PredefinedCodeFixProviderNames.MakeStructFieldsWritable), Shared]
    internal class CSharpMakeStructFieldsWritableCodeFixProvider : SyntaxEditorBasedCodeFixProvider
    {
        [ImportingConstructor]
        [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
        public CSharpMakeStructFieldsWritableCodeFixProvider()
        {
        }

        public override ImmutableArray<string> FixableDiagnosticIds
            => ImmutableArray.Create(IDEDiagnosticIds.MakeStructFieldsWritable);

        public override Task RegisterCodeFixesAsync(CodeFixContext context)
        {
            RegisterCodeFix(context, CSharpAnalyzersResources.Make_readonly_fields_writable, nameof(CSharpAnalyzersResources.Make_readonly_fields_writable));
            return Task.CompletedTask;
        }

        protected override Task FixAllAsync(
            Document document,
            ImmutableArray<Diagnostic> diagnostics,
            SyntaxEditor editor,
            CodeActionOptionsProvider fallbackOptions, CancellationToken cancellationToken)
        {
            foreach (var diagnostic in diagnostics)
            {
                var diagnosticNode = diagnostic.Location.FindNode(cancellationToken);

                if (diagnosticNode is not StructDeclarationSyntax structDeclaration)
                {
                    continue;
                }

                var fieldDeclarations = structDeclaration.Members
                    .OfType<FieldDeclarationSyntax>();

                foreach (var fieldDeclaration in fieldDeclarations)
                {
                    var fieldDeclarationModifiers = editor.Generator.GetModifiers(fieldDeclaration);
                    var containsReadonlyModifier =
                        (fieldDeclarationModifiers & DeclarationModifiers.ReadOnly) == DeclarationModifiers.ReadOnly;

                    if (containsReadonlyModifier)
                    {
                        editor.SetModifiers(fieldDeclaration, fieldDeclarationModifiers.WithIsReadOnly(false));
                    }
                }
            }

            return Task.CompletedTask;
        }
    }
}
