namespace Jtr.Parsing;

public abstract class ParsableStream<T>
{
    private readonly ReadOnlyMemory<T> _tokens;

    protected ReadOnlySpan<T> Tokens => _tokens.Span;

    protected int Position { get; set; }

    public T Current => Position < Tokens.Length ? Tokens[Position] : default!;

    protected ParsableStream(ReadOnlyMemory<T> tokens)
    {
        _tokens = tokens;
    }

    public virtual T Advance()
    {
        return Position + 1 <= Tokens.Length ? Tokens[++Position - 1] : default!;
    }

    public virtual T Peek(int offset = 0)
    {
        return Position + offset < Tokens.Length ? Tokens[Position + offset] : default!;
    }

    public virtual bool Ended()
    {
        return Position >= Tokens.Length;
    }
}