using System;

namespace Luneraria.View
{
    /// <summary>
    /// Fixed simulation tick (U2C): frame time goes into an accumulator, and whole steps of
    /// LuneBalance.SimStep (0.05 s) come out. The frame rate only decides how many steps run in a
    /// frame, never what a step does, so every frame rate produces the same sequence of steps.
    /// Alpha is the fraction of the next step already elapsed; views interpolate with it.
    /// </summary>
    public sealed class LuneClock
    {
        public readonly double Step;
        /// <summary>Upper bound per frame; a stalled frame is caught up over the next frames.</summary>
        public int MaxStepsPerFrame = 200;
        double _accumulator;

        public LuneClock(double step)
        {
            Step = step;
        }

        public double Alpha { get { return Math.Min(1.0, _accumulator / Step); } }

        public void Reset()
        {
            _accumulator = 0.0;
        }

        /// <summary>Adds frame time and runs whole steps; step returns false when it has to stop.</summary>
        public int Advance(double seconds, Func<bool> step)
        {
            if (seconds > 0.0)
                _accumulator += seconds;
            int count = 0;
            while (_accumulator >= Step && count < MaxStepsPerFrame)
            {
                _accumulator -= Step;
                count++;
                if (!step())
                {
                    _accumulator = 0.0;
                    break;
                }
            }
            return count;
        }
    }
}