// 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.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeFixes;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.LanguageService;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Editing;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Simplification;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.CSharp.DisambiguateSameVariable
{
    using static SyntaxFactory;
 
    [ExportCodeFixProvider(LanguageNames.CSharp, Name = PredefinedCodeFixProviderNames.DisambiguateSameVariable), Shared]
    internal class CSharpDisambiguateSameVariableCodeFixProvider : SyntaxEditorBasedCodeFixProvider
    {
        private const string CS1717 = nameof(CS1717); // Assignment made to same variable; did you mean to assign something else?
        private const string CS1718 = nameof(CS1718); // Comparison made to same variable; did you mean to compare something else?
 
        [ImportingConstructor]
        [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
        public CSharpDisambiguateSameVariableCodeFixProvider()
        {
        }
 
        public override ImmutableArray<string> FixableDiagnosticIds { get; }
            = ImmutableArray.Create(CS1717, CS1718);
 
        public override async Task RegisterCodeFixesAsync(CodeFixContext context)
        {
            var document = context.Document;
            var diagnostic = context.Diagnostics.First();
            var cancellationToken = context.CancellationToken;
 
            var semanticModel = await document.GetRequiredSemanticModelAsync(cancellationToken).ConfigureAwait(false);
            if (CanFix(semanticModel, diagnostic, cancellationToken, out _, out _, out var title))
            {
                RegisterCodeFix(context, title, nameof(CSharpDisambiguateSameVariableCodeFixProvider));
            }
        }
 
        private static bool CanFix(
            SemanticModel semanticModel, Diagnostic diagnostic, CancellationToken cancellationToken,
            [NotNullWhen(true)] out SimpleNameSyntax? leftName,
            [NotNullWhen(true)] out ISymbol? matchingMember,
            [NotNullWhen(true)] out string? title)
        {
            leftName = null;
            matchingMember = null;
            title = null;
 
            var span = diagnostic.Location.SourceSpan;
            var node = diagnostic.Location.FindNode(getInnermostNodeForTie: true, cancellationToken);
            var (left, right, titleFormat) = node switch
            {
                BinaryExpressionSyntax binary => (binary.Left, binary.Right, CSharpCodeFixesResources.Compare_to_0),
                AssignmentExpressionSyntax assignment => (assignment.Left, assignment.Right, CSharpCodeFixesResources.Assign_to_0),
                _ => default,
            };
 
            if (left == null || right == null)
                return false;
 
            if (left is not IdentifierNameSyntax and not MemberAccessExpressionSyntax)
                return false;
 
            var leftSymbol = semanticModel.GetSymbolInfo(left, cancellationToken).GetAnySymbol();
            var rightSymbol = semanticModel.GetSymbolInfo(right, cancellationToken).GetAnySymbol();
 
            if (leftSymbol == null || rightSymbol == null)
                return false;
 
            // Since this is a self assignment/compare, these symbols should be the same.
            Debug.Assert(leftSymbol.Equals(rightSymbol));
 
            if (leftSymbol.Kind is not SymbolKind.Local and
                not SymbolKind.Parameter and
                not SymbolKind.Field and
                not SymbolKind.Property)
            {
                return false;
            }
 
            var localOrParamName = leftSymbol.Name;
            if (string.IsNullOrWhiteSpace(localOrParamName))
                return false;
 
            var enclosingType = semanticModel.GetEnclosingNamedType(span.Start, cancellationToken);
            if (enclosingType == null)
                return false;
 
            // Given a local/param called 'x' See if we have an instance field or prop in the containing type
            // called 'x' or 'X' or '_x'.
 
            var pascalName = localOrParamName.ToPascalCase();
            var camelName = localOrParamName.ToCamelCase();
            var underscoreName = "_" + localOrParamName;
            var members = from t in enclosingType.GetBaseTypesAndThis()
                          from m in t.GetMembers()
                          where !m.IsStatic
                          where m is IFieldSymbol or IPropertySymbol
                          where !m.Equals(leftSymbol)
                          where m.Name == localOrParamName ||
                                m.Name == pascalName ||
                                m.Name == camelName ||
                                m.Name == underscoreName
                          where m.IsAccessibleWithin(enclosingType)
                          select m;
 
            matchingMember = members.FirstOrDefault();
            if (matchingMember == null)
                return false;
 
            var memberContainer = matchingMember.ContainingType.ToMinimalDisplayString(semanticModel, span.Start);
            title = string.Format(titleFormat, $"{memberContainer}.{matchingMember.Name}");
 
            leftName = left is MemberAccessExpressionSyntax memberAccess
                ? memberAccess.Name
                : (IdentifierNameSyntax)left;
 
            return true;
        }
 
        protected override async Task FixAllAsync(
            Document document, ImmutableArray<Diagnostic> diagnostics,
            SyntaxEditor editor, CodeActionOptionsProvider fallbackOptions, CancellationToken cancellationToken)
        {
            var syntaxFacts = CSharpSyntaxFacts.Instance;
            var semanticModel = await document.GetRequiredSemanticModelAsync(cancellationToken).ConfigureAwait(false);
 
            foreach (var diagnostic in diagnostics)
            {
                if (!CanFix(semanticModel, diagnostic, cancellationToken,
                        out var nameNode, out var matchingMember, out _))
                {
                    continue;
                }
 
                var newNameNode = matchingMember.Name.ToIdentifierName();
                var newExpr = (ExpressionSyntax)newNameNode;
                if (!syntaxFacts.IsNameOfSimpleMemberAccessExpression(nameNode) &&
                    !syntaxFacts.IsNameOfMemberBindingExpression(nameNode))
                {
                    newExpr = MemberAccessExpression(
                        SyntaxKind.SimpleMemberAccessExpression, ThisExpression(), newNameNode).WithAdditionalAnnotations(Simplifier.Annotation);
                }
 
                newExpr = newExpr.WithTriviaFrom(nameNode);
                editor.ReplaceNode(nameNode, newExpr);
            }
        }
    }
}