namespace ytLive.Models;

/// <summary>Owns the session's <see cref="ScoreboardState"/> and the one lifecycle rule that
/// matters: a new session starts from zero.
///
/// <para>Kept separate from the view-model so the rule is testable without a window, and so the
/// scoreboard layer has exactly one place that decides when counting begins.</para></summary>
public sealed class ScoreboardRecorder
{
    public ScoreboardState State { get; private set; } = new();

    /// <summary>Called when a session starts (go-live, test, or a local recording). Every start
    /// clears the tallies — "session" is the only scope the numbers promise.</summary>
    public void StartSession()
    {
        State = new ScoreboardState();
        IsRunning = true;
        RaiseChanged();
    }

    /// <summary>Folds a chat event in. Outside a session nothing is counted: a stale tally left over
    /// from the last stream would be the "today" lie this design exists to avoid.</summary>
    public void Record(ChatMessage message)
    {
        if (!IsRunning) return;
        var before = Fingerprint(State);
        State.Apply(message);
        if (Fingerprint(State) != before) RaiseChanged();
    }

    /// <summary>True while the tallies are live.</summary>
    public bool IsRunning { get; private set; }

    /// <summary>Marks the session finished. The tallies stay visible (the End screen may show
    /// them) but stop moving.</summary>
    public void EndSession()
    {
        IsRunning = false;
        RaiseChanged();
    }

    public event System.Action? Changed;

    private void RaiseChanged() => Changed?.Invoke();

    /// <summary>Cheap change detector: only re-render the strip when a displayed value moved.</summary>
    private static string Fingerprint(ScoreboardState state) =>
        $"{state.NewMembers}|{state.MilestoneCount}|{state.LastMemberName}|{state.LastGifterName}|" +
        $"{state.LastGiftCount}|{state.LastSuperChatAuthor}|{state.LastSuperChatDisplay}|" +
        $"{state.SessionTotal.Currency}|{state.SessionTotal.Total:0.######}";
}