// 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.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]
[method: ImportingConstructor]
[method: Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
internal sealed 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?
 
    public override ImmutableArray<string> FixableDiagnosticIds { get; } = [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, 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);
        }
    }
}