spectre.console/src/Spectre.Console.Cli/Internal/Configuration/TemplateTokenizer.cs

namespace Spectre.Console.Cli;

internal static class TemplateTokenizer
{
    public static IReadOnlyList<TemplateToken> Tokenize(string template)
    {
        using var buffer = new TextBuffer(template);
        var result = new List<TemplateToken>();

        while (!buffer.ReachedEnd)
        {
            EatWhitespace(buffer);

            if (!buffer.TryPeek(out var character))
            {
                break;
            }

            if (character == '-')
            {
                result.Add(ReadOption(buffer));
            }
            else if (character == '|')
            {
                buffer.Consume('|');
            }
            else if (character == '<')
            {
                result.Add(ReadValue(buffer, true));
            }
            else if (character == '[')
            {
                result.Add(ReadValue(buffer, false));
            }
            else
            {
                throw CommandTemplateException.UnexpectedCharacter(buffer.Original, buffer.Position, character);
            }
        }

        return result;
    }

    private static void EatWhitespace(TextBuffer buffer)
    {
        while (!buffer.ReachedEnd)
        {
            var character = buffer.Peek();
            if (!char.IsWhiteSpace(character))
            {
                break;
            }

            buffer.Read();
        }
    }

    private static TemplateToken ReadOption(TextBuffer buffer)
    {
        var position = buffer.Position;

        buffer.Consume('-');
        if (buffer.IsNext('-'))
        {
            buffer.Consume('-');
            var longValue = ReadOptionName(buffer);
            return new TemplateToken(TemplateToken.Kind.LongName, position, longValue, $"--{longValue}");
        }

        var shortValue = ReadOptionName(buffer);
        return new TemplateToken(TemplateToken.Kind.ShortName, position, shortValue, $"-{shortValue}");
    }

    private static string ReadOptionName(TextBuffer buffer)
    {
        var builder = new StringBuilder();
        while (!buffer.ReachedEnd)
        {
            var character = buffer.Peek();
            if (char.IsWhiteSpace(character) || character == '|')
            {
                break;
            }

            builder.Append(buffer.Read());
        }

        return builder.ToString();
    }

    private static TemplateToken ReadValue(TextBuffer buffer, bool required)
    {
        var start = required ? '<' : '[';
        var end = required ? '>' : ']';

        var position = buffer.Position;
        var kind = required ? TemplateToken.Kind.RequiredValue : TemplateToken.Kind.OptionalValue;

        // Consume start of value character (< or [).
        buffer.Consume(start);

        var builder = new StringBuilder();
        while (!buffer.ReachedEnd)
        {
            var character = buffer.Peek();
            if (character == end)
            {
                break;
            }

            buffer.Read();
            builder.Append(character);
        }

        if (buffer.ReachedEnd)
        {
            var name = builder.ToString();
            var token = new TemplateToken(kind, position, name, $"{start}{name}");
            throw CommandTemplateException.UnterminatedValueName(buffer.Original, token);
        }

        // Consume end of value character (> or ]).
        buffer.Consume(end);

        // Get the value (the text within the brackets).
        var value = builder.ToString();

        // Create a token and return it.
        return new TemplateToken(kind, position, value, required ? $"<{value}>" : $"[{value}]");
    }
}