// 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.Immutable;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeFixes;
using Microsoft.CodeAnalysis.CodeRefactorings;
using Microsoft.CodeAnalysis.Editing;
using Microsoft.CodeAnalysis.Formatting;
using Microsoft.CodeAnalysis.LanguageService;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Shared.Utilities;
using Microsoft.CodeAnalysis.Text;
using Roslyn.Utilities;

namespace Microsoft.CodeAnalysis.AddFileBanner;

internal abstract class AbstractAddFileBannerCodeRefactoringProvider : SyntaxEditorBasedCodeRefactoringProvider
{
    private const string BannerFileNamePlaceholder = "{filename}";

    protected abstract bool IsCommentStartCharacter(char ch);

    protected sealed override ImmutableArray<RefactorAllScope> SupportedRefactorAllScopes { get; }
        = [RefactorAllScope.Project, RefactorAllScope.Solution];

    public override async Task ComputeRefactoringsAsync(CodeRefactoringContext context)
    {
        var (document, span, cancellationToken) = context;
        if (!span.IsEmpty)
        {
            return;
        }

        var formattingOptions = await document.GetDocumentFormattingOptionsAsync(cancellationToken).ConfigureAwait(false);
        if (!string.IsNullOrEmpty(formattingOptions.FileHeaderTemplate))
        {
            // If we have a defined file header template, allow the analyzer and code fix to handle it
            return;
        }

        var tree = await document.GetRequiredSyntaxTreeAsync(cancellationToken).ConfigureAwait(false);
        var root = await tree.GetRootAsync(cancellationToken).ConfigureAwait(false);

        var position = span.Start;
        var firstToken = root.GetFirstToken();
        if (!firstToken.FullSpan.IntersectsWith(position))
            return;

        if (HasExistingBanner(document, root))
            return;

        // Process the other documents in this document's project.  Look at the
        // ones that we can get a root from (without having to parse).  Then
        // look at the ones we'd need to parse.
        var siblingDocumentsAndRoots =
            document.Project.Documents
                    .Where(d => d != document)
                    .Select(d =>
                    {
                        d.TryGetSyntaxRoot(out var siblingRoot);
                        return (document: d, root: siblingRoot);
                    })
                    .OrderBy((t1, t2) => (t1.root != null) == (t2.root != null) ? 0 : t1.root != null ? -1 : 1);

        foreach (var (siblingDocument, siblingRoot) in siblingDocumentsAndRoots)
        {
            cancellationToken.ThrowIfCancellationRequested();

            var siblingBanner = await TryGetBannerAsync(siblingDocument, siblingRoot, cancellationToken).ConfigureAwait(false);
            if (siblingBanner.Length > 0 && !siblingDocument.IsGeneratedCode(cancellationToken))
            {
                context.RegisterRefactoring(
                    CodeAction.Create(
                        CodeFixesResources.Add_file_header,
                        cancellationToken => AddFileBannerHelpers.CopyBannerAsync(
                            destinationDocument: document, document.FilePath, sourceDocument: siblingDocument, cancellationToken),
                        equivalenceKey: GetEquivalenceKey(siblingDocument, siblingBanner)),
                    new TextSpan(position, length: 0));
                return;
            }
        }
    }

    private static bool HasExistingBanner(Document document, SyntaxNode root)
    {
        var bannerService = document.GetRequiredLanguageService<IFileBannerFactsService>();
        var banner = bannerService.GetFileBanner(root);
        return banner.Length > 0;
    }

    private static string GetEquivalenceKey(Document document, ImmutableArray<SyntaxTrivia> banner)
    {
        var bannerText = banner.Select(trivia => trivia.ToFullString()).Join(string.Empty);

        var fileName = IOUtilities.PerformIO(() => Path.GetFileName(document.FilePath));
        if (!string.IsNullOrEmpty(fileName))
            bannerText = bannerText.Replace(fileName, BannerFileNamePlaceholder);

        return bannerText;
    }

    private static ImmutableArray<SyntaxTrivia> GetBannerFromEquivalenceKey(string equivalenceKey, Document document)
    {
        var fileName = IOUtilities.PerformIO(() => Path.GetFileName(document.FilePath));
        if (!string.IsNullOrEmpty(fileName))
            equivalenceKey = equivalenceKey.Replace(BannerFileNamePlaceholder, fileName);

        var syntaxFacts = document.GetRequiredLanguageService<ISyntaxFactsService>();
        var token = syntaxFacts.ParseToken(equivalenceKey);

        var bannerService = document.GetRequiredLanguageService<IFileBannerFactsService>();
        return bannerService.GetFileBanner(token);
    }

    private async Task<ImmutableArray<SyntaxTrivia>> TryGetBannerAsync(
        Document document, SyntaxNode? root, CancellationToken cancellationToken)
    {
        var bannerService = document.GetRequiredLanguageService<IFileBannerFactsService>();
        var syntaxFacts = document.GetRequiredLanguageService<ISyntaxFactsService>();

        // If we have a tree already for this document, then just check to see
        // if it has a banner.
        if (root != null)
        {
            return bannerService.GetFileBanner(root);
        }

        // Didn't have a tree.  Don't want to parse the file if we can avoid it.
        var text = await document.GetValueTextAsync(cancellationToken).ConfigureAwait(false);
        if (text.Length == 0 || !IsCommentStartCharacter(text[0]))
        {
            // Didn't start with a comment character, don't bother looking at 
            // this file.
            return [];
        }

        var token = syntaxFacts.ParseToken(text.ToString());
        return bannerService.GetFileBanner(token);
    }

    protected sealed override async Task RefactorAllAsync(
        Document document,
        ImmutableArray<TextSpan> fixAllSpans,
        SyntaxEditor editor,
        string? equivalenceKey,
        CancellationToken cancellationToken)
    {
        Debug.Assert(equivalenceKey != null);

        // Bail out if the document to fix already has an existing banner.
        var root = await document.GetRequiredSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
        if (HasExistingBanner(document, root))
            return;

        // Get banner from the equivalence key.
        var banner = GetBannerFromEquivalenceKey(equivalenceKey, document);
        Debug.Assert(banner.Length > 0);

        // Finally add the banner to the document to be fixed.
        var newRoot = root.WithPrependedLeadingTrivia(new SyntaxTriviaList(banner));
        editor.ReplaceNode(editor.OriginalRoot, newRoot);
    }
}