namespace MrGameEng.Core;

/// <summary>
/// Engine time service: per-frame delta, total elapsed time, time scaling and frame counter.
/// Advanced once per frame (or per fixed tick) by the host.
/// </summary>
public sealed class GameClock
{
    /// <summary>Seconds elapsed since the previous frame, multiplied by <see cref="TimeScale"/>.</summary>
    public float DeltaTime { get; private set; }

    /// <summary>Seconds elapsed since the previous frame, unaffected by <see cref="TimeScale"/>.</summary>
    public float UnscaledDeltaTime { get; private set; }

    /// <summary>Total scaled time in seconds since the game started.</summary>
    public double TotalTime { get; private set; }

    /// <summary>Total unscaled time in seconds since the game started.</summary>
    public double UnscaledTotalTime { get; private set; }

    /// <summary>Multiplier applied to <see cref="DeltaTime"/>. 0 pauses gameplay, 1 is real time. Never negative.</summary>
    public float TimeScale
    {
        get => _timeScale;
        set => _timeScale = value < 0f ? 0f : value;
    }

    /// <summary>Number of completed frames since the game started.</summary>
    public long FrameCount { get; private set; }

    private float _timeScale = 1f;

    /// <summary>Advances the clock by one frame. Called by the host; games should not call this.</summary>
    public void Advance(float unscaledDeltaSeconds)
    {
        UnscaledDeltaTime = unscaledDeltaSeconds;
        DeltaTime = unscaledDeltaSeconds * _timeScale;
        UnscaledTotalTime += unscaledDeltaSeconds;
        TotalTime += DeltaTime;
        FrameCount++;
    }
}