// 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 Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeFixes;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Editing;
using Microsoft.CodeAnalysis.Host.Mef;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.CSharp.AssignOutParameters;
 
[ExportCodeFixProvider(LanguageNames.CSharp, Name = PredefinedCodeFixProviderNames.AssignOutParametersAtStart), Shared]
[method: ImportingConstructor]
[method: Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
internal sealed class AssignOutParametersAtStartCodeFixProvider() : AbstractAssignOutParametersCodeFixProvider
{
    protected override void TryRegisterFix(CodeFixContext context, Document document, SyntaxNode container, SyntaxNode location)
    {
        // Don't offer if we're already the starting statement of the container. This case will
        // be handled by the AssignOutParametersAboveReturnCodeFixProvider class.
        if (location is ExpressionSyntax)
        {
            return;
        }
 
        if (location is LocalFunctionStatementSyntax { ExpressionBody: { } })
        {
            // This is an expression-bodied local function, which is also handled by the other code fix.
            return;
        }
 
        if (location is StatementSyntax statement &&
            statement.Parent is BlockSyntax block &&
            block.Statements[0] == statement &&
            block.Parent == container)
        {
            return;
        }
 
        context.RegisterCodeFix(
            CodeAction.Create(
                CSharpCodeFixesResources.Assign_out_parameters_at_start,
                GetDocumentUpdater(context),
                nameof(CSharpCodeFixesResources.Assign_out_parameters_at_start)),
            context.Diagnostics);
    }
 
    protected override void AssignOutParameters(
        SyntaxEditor editor, SyntaxNode container,
        MultiDictionary<SyntaxNode, (SyntaxNode exprOrStatement, ImmutableArray<IParameterSymbol> unassignedParameters)>.ValueSet values,
        CancellationToken cancellationToken)
    {
        var generator = editor.Generator;
        var unassignedParameters =
            values.SelectMany(t => t.unassignedParameters)
                  .Distinct()
                  .OrderBy(p => p.DeclaringSyntaxReferences[0].GetSyntax(cancellationToken).SpanStart)
                  .ToImmutableArray();
 
        var statements = GenerateAssignmentStatements(generator, unassignedParameters);
        var originalStatements = generator.GetStatements(container).ToImmutableArray();
 
        var finalStatements = statements.AddRange(originalStatements);
        var updatedContainer = generator.WithStatements(container, finalStatements);
 
        editor.ReplaceNode(container, updatedContainer);
    }
}