// 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.Globalization;
using System.Threading;

namespace Microsoft.CodeAnalysis;

/// <summary>
/// The documentation provider used to lookup xml docs for any metadata reference we pass out.  They'll
/// all get the same xml doc comment provider (as different references to the same compilation don't
/// see the xml docs any differently).  This provider does root a Compilation around.  However, this should
/// not be an issue in practice as the compilation we are rooting is a clone of the acutal compilation of
/// project, and not the compilation itself.  This clone doesn't share any symbols/semantics with the main
/// compilation, and it can dump syntax trees whenever necessary.  What is does store is the compact
/// decl-table which is safe and cheap to hold onto long term.  When some downstream consumer of this
/// metadata-reference then needs to get xml-doc comments, it will resolve a doc-comment-id against this
/// decl-only-compilation.  Resolution is very cheap, only causing the necessary symbols referenced directly
/// in the ID to be created.  As downstream consumers are only likely to resolve a small handful of these 
/// symbols in practice, this should not be expensive to hold onto.  Importantly, semantic models and 
/// complex method binding/caching should never really happen with this compilation.
/// </summary>
internal sealed class DeferredDocumentationProvider(Compilation compilation) : DocumentationProvider
{
    private readonly Compilation _compilation = compilation.Clone();

    protected override string? GetDocumentationForSymbol(string documentationMemberID, CultureInfo preferredCulture, CancellationToken cancellationToken = default)
    {
        if (documentationMemberID is null)
            return null;

        var symbol = DocumentationCommentId.GetFirstSymbolForDeclarationId(documentationMemberID, _compilation);
        return symbol == null
            ? string.Empty
            : symbol.GetDocumentationCommentXml(preferredCulture, cancellationToken: cancellationToken);
    }

    public override bool Equals(object? obj)
        => object.ReferenceEquals(this, obj);

    public override int GetHashCode()
        => _compilation.GetHashCode();
}