// 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.Generic;
using System.Collections.Immutable;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeFixes;
using Microsoft.CodeAnalysis.Diagnostics;
using Microsoft.CodeAnalysis.Editing;
using Microsoft.CodeAnalysis.Formatting;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.MakeFieldReadonly
{
    internal abstract class AbstractMakeFieldReadonlyCodeFixProvider<TSymbolSyntax, TFieldDeclarationSyntax>
        : SyntaxEditorBasedCodeFixProvider
        where TSymbolSyntax : SyntaxNode
        where TFieldDeclarationSyntax : SyntaxNode
    {
        public override ImmutableArray<string> FixableDiagnosticIds
            => ImmutableArray.Create(IDEDiagnosticIds.MakeFieldReadonlyDiagnosticId);
 
        protected abstract SyntaxNode? GetInitializerNode(TSymbolSyntax declaration);
        protected abstract ImmutableList<TSymbolSyntax> GetVariableDeclarators(TFieldDeclarationSyntax declaration);
 
        public override Task RegisterCodeFixesAsync(CodeFixContext context)
        {
            RegisterCodeFix(context, AnalyzersResources.Add_readonly_modifier, nameof(AnalyzersResources.Add_readonly_modifier));
            return Task.CompletedTask;
        }
 
        protected override async Task FixAllAsync(
            Document document,
            ImmutableArray<Diagnostic> diagnostics,
            SyntaxEditor editor,
            CodeActionOptionsProvider fallbackOptions, CancellationToken cancellationToken)
        {
            var declarators = new List<TSymbolSyntax>();
            var root = await document.GetRequiredSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
            foreach (var diagnostic in diagnostics)
            {
                var diagnosticSpan = diagnostic.Location.SourceSpan;
 
                declarators.Add(root.FindNode(diagnosticSpan, getInnermostNodeForTie: true).FirstAncestorOrSelf<TSymbolSyntax>()!);
            }
 
            await MakeFieldReadonlyAsync(document, editor, declarators, cancellationToken).ConfigureAwait(false);
        }
 
        private async Task MakeFieldReadonlyAsync(
            Document document, SyntaxEditor editor, List<TSymbolSyntax> declarators, CancellationToken cancellationToken)
        {
            var generator = editor.Generator;
            var declaratorsByField = declarators.GroupBy(g => g.FirstAncestorOrSelf<TFieldDeclarationSyntax>()!);
 
            foreach (var fieldDeclarators in declaratorsByField)
            {
                var fieldDeclaration = fieldDeclarators.Key;
                var declarationDeclarators = GetVariableDeclarators(fieldDeclaration);
 
                if (declarationDeclarators.Count == fieldDeclarators.Count())
                {
                    var modifiers = WithReadOnly(editor.Generator.GetModifiers(fieldDeclaration));
                    editor.ReplaceNode(
                        fieldDeclaration,
                        generator.WithModifiers(fieldDeclaration.WithoutTrivia(), modifiers).WithTriviaFrom(fieldDeclaration));
                }
                else
                {
                    var model = await document.GetRequiredSemanticModelAsync(cancellationToken).ConfigureAwait(false);
 
                    foreach (var declarator in declarationDeclarators.Reverse())
                    {
                        var symbol = (IFieldSymbol?)model.GetDeclaredSymbol(declarator, cancellationToken);
                        Contract.ThrowIfNull(symbol);
                        var modifiers = generator.GetModifiers(fieldDeclaration);
 
                        var newDeclaration = generator
                            .FieldDeclaration(
                                symbol.Name,
                                generator.TypeExpression(symbol.Type),
                                Accessibility.Private,
                                fieldDeclarators.Contains(declarator)
                                    ? WithReadOnly(modifiers)
                                    : modifiers,
                                GetInitializerNode(declarator))
                            .WithAdditionalAnnotations(Formatter.Annotation);
 
                        editor.InsertAfter(fieldDeclaration, newDeclaration);
                    }
 
                    editor.RemoveNode(fieldDeclaration, SyntaxRemoveOptions.KeepLeadingTrivia);
                }
            }
        }
 
        private static DeclarationModifiers WithReadOnly(DeclarationModifiers modifiers)
            => (modifiers - DeclarationModifiers.Volatile) | DeclarationModifiers.ReadOnly;
    }
}