namespace codelanguage;

/// <summary>Structural checks shared by IDE compilation and artifact builds.</summary>
public static class SyntaxValidation
{
    public static List<ParseError> ValidateTokens(IReadOnlyList<Token> tokens)
    {
        var strictErrors = tokens
            .Where(t => t.Type == TokenType.Error)
            .Select(t => new ParseError(t.Value, t.Line, t.Column, t.File))
            .ToList();
        var delimiters = new Stack<Token>();
        foreach (var token in tokens)
        {
            if (token.IsIndentation) continue;
            if (token.Type is TokenType.LeftBrace or TokenType.LeftParen or TokenType.LeftBracket or TokenType.QuestionLeftBracket)
            {
                delimiters.Push(token);
                continue;
            }
            TokenType? expected = token.Type switch
            {
                TokenType.RightBrace => TokenType.LeftBrace,
                TokenType.RightParen => TokenType.LeftParen,
                TokenType.RightBracket => TokenType.LeftBracket,
                _ => null
            };
            if (expected == null) continue;
            if (delimiters.Count == 0)
                strictErrors.Add(new ParseError($"Unexpected closing delimiter '{token.Value}'.", token.Line, token.Column));
            else
            {
                var opening = delimiters.Pop();
                if (opening.Type != expected && !(expected == TokenType.LeftBracket && opening.Type == TokenType.QuestionLeftBracket))
                    strictErrors.Add(new ParseError($"Closing delimiter '{token.Value}' does not match '{opening.Value}'.", token.Line, token.Column));
            }
        }
        foreach (var opening in delimiters)
            strictErrors.Add(new ParseError($"Unclosed delimiter '{opening.Value}'.", opening.Line, opening.Column));

        // The parser supports both same-line statements and indented bodies.
        // Keep validation structural and let the parser diagnose empty bodies.
        return strictErrors;
    }
}