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

using System.Diagnostics;
using Microsoft.AspNetCore.Razor.Language.Syntax.InternalSyntax;

namespace Microsoft.AspNetCore.Razor.Language.Legacy
{
	internal class DirectiveHtmlTokenizer : HtmlTokenizer
	{
		private bool _visitedFirstTokenStart;
		private SourceLocation _firstTokenVisitLocation = SourceLocation.Undefined;

		public DirectiveHtmlTokenizer( ITextDocument source ) : base( source )
		{
		}

		protected override StateResult Dispatch()
		{
			var location = CurrentLocation;
			var result = base.Dispatch();
			if ( result.Result != null && IsValidTokenType( result.Result.Kind ) )
			{
				_visitedFirstTokenStart = true;
				_firstTokenVisitLocation = location;
			}

			return result;
		}

		public override SyntaxToken NextToken()
		{
			// Post-Condition: Buffer should be empty at the start of Next()
			Debug.Assert( Buffer.Length == 0 );
			StartToken();

			if ( EndOfFile || (_visitedFirstTokenStart && _firstTokenVisitLocation != CurrentLocation) )
			{
				// We also need to make sure we are currently past the position where we found the first token.
				// If the position is equal, that means the parser put the token back for later parsing.
				return null;
			}

			var token = Turn();

			// Post-Condition: Buffer should be empty at the end of Next()
			Debug.Assert( Buffer.Length == 0 );

			return token;
		}

		private bool IsValidTokenType( SyntaxKind kind )
		{
			return kind != SyntaxKind.Whitespace &&
				kind != SyntaxKind.NewLine &&
				kind != SyntaxKind.RazorCommentLiteral &&
				kind != SyntaxKind.RazorCommentStar &&
				kind != SyntaxKind.RazorCommentTransition &&
				kind != SyntaxKind.Transition;
		}
	}
}
