// 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.Formatting;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Roslyn.Utilities;

namespace Microsoft.CodeAnalysis.CSharp.SimplifyPropertyPattern
{
    using static SyntaxFactory;

    [ExportCodeFixProvider(LanguageNames.CSharp, Name = PredefinedCodeFixProviderNames.SimplifyPropertyPattern), Shared]
    internal class CSharpSimplifyPropertyPatternCodeFixProvider : SyntaxEditorBasedCodeFixProvider
    {
        [ImportingConstructor]
        [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
        public CSharpSimplifyPropertyPatternCodeFixProvider()
        {
        }

        public override ImmutableArray<string> FixableDiagnosticIds { get; } =
            ImmutableArray.Create(IDEDiagnosticIds.SimplifyPropertyPatternDiagnosticId);

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

        protected override Task FixAllAsync(
            Document document, ImmutableArray<Diagnostic> diagnostics,
            SyntaxEditor editor, CodeActionOptionsProvider fallbackOptions, CancellationToken cancellationToken)
        {
            // Process subpatterns in reverse order so we rewrite from inside-to-outside with nested
            // patterns.
            var subpatterns = diagnostics.Select(d => (SubpatternSyntax)d.AdditionalLocations[0].FindNode(cancellationToken))
                                         .OrderByDescending(s => s.SpanStart)
                                         .ToImmutableArray();

            foreach (var subpattern in subpatterns)
            {
                editor.ReplaceNode(
                    subpattern,
                    (current, _) =>
                    {
                        var currentSubpattern = (SubpatternSyntax)current;
                        var simplified = TrySimplify(currentSubpattern);
                        return simplified ?? currentSubpattern;
                    });
            }

            return Task.CompletedTask;
        }

        private static SubpatternSyntax? TrySimplify(SubpatternSyntax currentSubpattern)
        {
            if (!SimplifyPropertyPatternHelpers.IsSimplifiable(currentSubpattern, out var innerSubpattern, out var outerExpressionColon))
                return null;

            // attempt to simplify the inner pattern we're pointing at as well (that way if the user
            // invokes the fix on a top level property, we collapse as far inwards as possible).
            innerSubpattern = TrySimplify(innerSubpattern) ?? innerSubpattern;

            var innerExpressionColon = innerSubpattern.ExpressionColon;

            if (!SimplifyPropertyPatternHelpers.IsMergable(outerExpressionColon.Expression) ||
                !SimplifyPropertyPatternHelpers.IsMergable(innerExpressionColon?.Expression))
            {
                return null;
            }

            var merged = Merge(outerExpressionColon, innerExpressionColon);
            if (merged == null)
                return null;

            return currentSubpattern.WithExpressionColon(merged)
                                    .WithPattern(innerSubpattern.Pattern)
                                    .WithAdditionalAnnotations(Formatter.Annotation);
        }

        private static BaseExpressionColonSyntax? Merge(BaseExpressionColonSyntax outerExpressionColon, BaseExpressionColonSyntax innerExpressionColon)
        {
            var merged = Merge(outerExpressionColon.Expression, innerExpressionColon.Expression);
            if (merged == null)
                return null;

            return outerExpressionColon.WithExpression(merged);
        }

        private static MemberAccessExpressionSyntax? Merge(ExpressionSyntax? outerExpression, ExpressionSyntax? innerExpression)
        {
            if (outerExpression == null || innerExpression == null)
                return null;

            // if the inner name is simple (i.e. just 'X') we can trivially form the final member
            // access by joining the two names together.
            if (innerExpression is SimpleNameSyntax innerName)
                return MemberAccessExpression(SyntaxKind.SimpleMemberAccessExpression, outerExpression, innerName);

            if (innerExpression is not MemberAccessExpressionSyntax innerMemberAccess)
                return null;

            // otherwise, attempt to decompose the inner expression, joining that with the outer until we get
            // the result.
            return Merge(Merge(outerExpression, innerMemberAccess.Expression), innerMemberAccess.Name);
        }
    }
}
