// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.IO;
using System.Text;
using Microsoft.Build.Shared.LanguageParser;

#nullable disable

namespace Microsoft.Build.Tasks
{
    /// <summary>
    /// Specific-purpose utility functions for parsing C#.
    /// </summary>
    internal static class CSharpParserUtilities
    {
        /// <summary>
        /// Parse a C# file and get the first class name, fully qualified with namespace.
        /// </summary>
        /// <param name="binaryStream"></param>
        /// <returns></returns>
        internal static ExtractedClassName GetFirstClassNameFullyQualified(Stream binaryStream)
        {
            try
            {
                var tokens = new CSharpTokenizer(binaryStream, /* forceANSI */ false);
                return Extract(tokens);
            }
            catch (DecoderFallbackException)
            {
                // There was no BOM and there are non UTF8 sequences. Fall back to ANSI.
                var tokens = new CSharpTokenizer(binaryStream, /* forceANSI */ true);
                return Extract(tokens);
            }
        }


        /// <summary>
        /// Extract the class name.
        /// </summary>
        private static ExtractedClassName Extract(CSharpTokenizer tokens)
        {
            var state = new ParseState();
            var result = new ExtractedClassName();

            foreach (Token t in tokens)
            {
                // Search first for the namespace keyword
                if (t is KeywordToken)
                {
                    state.Reset();

                    if (t.InnerText == "namespace")
                    {
                        state.ResolvingNamespace = true;
                        if (state.InsideConditionalDirective)
                        {
                            result.IsInsideConditionalBlock = true;
                        }
                    }
                    else if (t.InnerText == "class" || t.InnerText == "record")
                    {
                        state.ResolvingClass = true;
                        if (state.InsideConditionalDirective)
                        {
                            result.IsInsideConditionalBlock = true;
                        }
                    }
                }
                else if (t is CSharpTokenizer.OpenScopeToken)
                {
                    state.PushNamespacePart(state.Namespace);
                    state.Reset();
                }
                else if (t is CSharpTokenizer.CloseScopeToken)
                {
                    state.Reset();
                    state.PopNamespacePart();
                }
                else if (t is OperatorOrPunctuatorToken)
                {
                    if (state.ResolvingNamespace)
                    {
                        // If we see a ';' while resolving a namespace, we assume it's a file-scoped namespace
                        // namespace foo.bar; <- At this point in code, we're at the semicolon.
                        // class test { ... }
                        // https://github.com/dotnet/csharplang/blob/088f20b6f9b714a7b68f6d792d54def0f3b3057e/proposals/csharp-10.0/file-scoped-namespaces.md
                        if (t.InnerText == ";")
                        {
                            state.PushNamespacePart(state.Namespace);
                            state.Reset();
                        }
                        else if (t.InnerText == ".")
                        {
                            state.Namespace += ".";
                        }
                    }
                }
                else if (t is IdentifierToken)
                {
                    // If we're resolving a namespace, then this is part of the namespace.
                    if (state.ResolvingNamespace)
                    {
                        state.Namespace += t.InnerText;
                    }
                    // If we're resolving a class, then we're done. We found the class name.
                    else if (state.ResolvingClass)
                    {
                        // We're done.
                        result.Name = state.ComposeQualifiedClassName(t.InnerText);
                        return result;
                    }
                }
                else if (t is OpenConditionalDirectiveToken)
                {
                    state.OpenConditionalDirective();
                }
                else if (t is CloseConditionalDirectiveToken)
                {
                    state.CloseConditionalDirective();
                }
            }

            return result;
        }
    }
}