// 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.Collections.Generic;
using System.Collections.Immutable;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeGeneration;
using Microsoft.CodeAnalysis.LanguageService;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Text;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.CodeFixes.GenerateMember;
 
internal abstract class AbstractGenerateMemberCodeFixProvider : CodeFixProvider
{
    public override FixAllProvider? GetFixAllProvider()
    {
        // Fix All is not supported by this code fix
        return null;
    }
 
    protected abstract Task<ImmutableArray<CodeAction>> GetCodeActionsAsync(Document document, SyntaxNode node, CancellationToken cancellationToken);
    protected abstract bool IsCandidate(SyntaxNode node, SyntaxToken token, Diagnostic diagnostic);
 
    public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
    {
        // TODO: https://github.com/dotnet/roslyn/issues/5777
        // Not supported in REPL for now.
        if (context.Document.Project.IsSubmission)
        {
            return;
        }
 
        var diagnostic = context.Diagnostics.First();
        var document = context.Document;
        var syntaxFacts = document.GetRequiredLanguageService<ISyntaxFactsService>();
 
        var root = await document.GetRequiredSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
        var names = GetTargetNodes(syntaxFacts, root, context.Span, diagnostic);
        foreach (var name in names)
        {
            var codeActions = await GetCodeActionsAsync(context.Document, name, context.CancellationToken).ConfigureAwait(false);
            if (codeActions.IsDefaultOrEmpty)
            {
                continue;
            }
 
            context.RegisterFixes(codeActions, context.Diagnostics);
            return;
        }
    }
 
    protected virtual SyntaxNode? GetTargetNode(SyntaxNode node)
        => node;
 
    private IEnumerable<SyntaxNode> GetTargetNodes(
        ISyntaxFactsService syntaxFacts, SyntaxNode root,
        TextSpan span, Diagnostic diagnostic)
    {
        var token = root.FindToken(span.Start);
        if (token.Span.IntersectsWith(span))
        {
            var first = true;
            foreach (var ancestor in token.GetAncestors<SyntaxNode>())
            {
                // If we're crossing a local function/lambda point then stop looking higher. We've clearly gone past
                // the point of the original diagnostic and should not consider this node as something to consider.
                //
                // Note: it's ok if we are on a lambda that was the direct node with the diagnostic (i.e. if the
                // compiler was reporting a diagnostic on a lambda itself).  However, once we start walking upwards,
                // we don't want to cross a lambda.
                if (!first &&
                    syntaxFacts.IsAnonymousOrLocalFunction(ancestor) &&
                    ancestor.SpanStart < token.SpanStart)
                {
                    break;
                }
 
                first = false;
                if (!IsCandidate(ancestor, token, diagnostic))
                    continue;
 
                var name = GetTargetNode(ancestor);
 
                if (name != null)
                    yield return name;
            }
        }
    }
}