namespace Svrnty.CQRS.Altcha.Abstractions;

/// <summary>
/// Server-issued Altcha challenge. Shape matches what the
/// <a href="https://altcha.org/docs/v2/widget-v3/">altcha widget v3</a>
/// expects from its <c>challengeurl</c>.
/// </summary>
public sealed class AltchaChallenge
{
    /// <summary>Hashing algorithm name (e.g. <c>SHA-256</c>).</summary>
    public required string Algorithm { get; init; }

    /// <summary>Hex-encoded hash the client must find a preimage for.</summary>
    public required string Challenge { get; init; }

    /// <summary>Hex-encoded salt (embeds an expiry timestamp).</summary>
    public required string Salt { get; init; }

    /// <summary>
    /// HMAC-SHA256 of <c>algorithm|challenge|salt|maxnumber</c> using the
    /// server's signing secret. Lets the verify step trust the issued
    /// challenge without keeping per-challenge state.
    /// </summary>
    public required string Signature { get; init; }

    /// <summary>Upper bound of the PoW search space (equals the requested complexity).</summary>
    public required uint MaxNumber { get; init; }
}