SameRhythmHitObjectGrouping.cs

// Copyright (c) ppy Pty Ltd <[email protected]>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.

using System;
using System.Collections.Generic;
using System.Linq;
using osu.Game.Rulesets.Difficulty.Preprocessing;
using osu.Game.Rulesets.Taiko.Difficulty.Utils;

namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Rhythm.Data
{
    /// <summary>
    /// Represents a group of <see cref="TaikoDifficultyHitObject"/>s with no rhythm variation.
    /// </summary>
    public class SameRhythmHitObjectGrouping : IHasInterval
    {
        public readonly List<TaikoDifficultyHitObject> HitObjects;

        public TaikoDifficultyHitObject FirstHitObject => HitObjects[0];

        public readonly SameRhythmHitObjectGrouping? Previous;

        private const double snap_tolerance = IntervalGroupingUtils.MARGIN_OF_ERROR;

        /// <summary>
        /// <see cref="DifficultyHitObject.StartTime"/> of the first hit object.
        /// </summary>
        public double StartTime => HitObjects[0].StartTime;

        /// <summary>
        /// The interval between the first and final hit object within this group.
        /// </summary>
        public double Duration => HitObjects[^1].StartTime - HitObjects[0].StartTime;

        /// <summary>
        /// The normalised interval in ms of each hit object in this <see cref="SameRhythmHitObjectGrouping"/>. This is only defined if there is
        /// more than two hit objects in this <see cref="SameRhythmHitObjectGrouping"/>.
        /// </summary>
        public readonly double? HitObjectInterval;

        /// <summary>
        /// The normalised ratio of <see cref="HitObjectInterval"/> between this and the previous <see cref="SameRhythmHitObjectGrouping"/>. In the
        /// case where one or both of the <see cref="HitObjectInterval"/> is undefined, this will have a value of 1.
        /// </summary>
        public readonly double HitObjectIntervalRatio;

        /// <inheritdoc/>
        public double Interval { get; } = double.PositiveInfinity;

        public SameRhythmHitObjectGrouping(SameRhythmHitObjectGrouping? previous, List<TaikoDifficultyHitObject> hitObjects)
        {
            Previous = previous;
            HitObjects = hitObjects;

            // Cluster and normalise each hitobjects delta-time.
            var normaliseHitObjects = DeltaTimeNormaliser.Normalise(hitObjects, snap_tolerance);

            var normalisedHitObjectDeltaTime = hitObjects
                                               .Skip(1)
                                               .Select(hitObject => normaliseHitObjects[hitObject])
                                               .ToList();

            // Secondary check to ensure there isn't any 'noise' or outliers by taking the modal delta time.
            double modalDelta = normalisedHitObjectDeltaTime.Count > 0
                ? Math.Round(normalisedHitObjectDeltaTime[0])
                : 0;

            // Calculate the average interval between hitobjects.
            if (normalisedHitObjectDeltaTime.Count > 0)
            {
                if (previous?.HitObjectInterval is double previousDelta && Math.Abs(modalDelta - previousDelta) <= snap_tolerance)
                    HitObjectInterval = previousDelta;
                else
                    HitObjectInterval = modalDelta;
            }

            // Calculate the ratio between this group's interval and the previous group's interval
            HitObjectIntervalRatio = previous?.HitObjectInterval is double previousInterval && HitObjectInterval is double currentInterval
                ? currentInterval / previousInterval
                : 1.0;

            // Calculate the interval from the previous group's start time
            if (previous != null)
            {
                if (Math.Abs(StartTime - previous.StartTime) <= snap_tolerance)
                    Interval = 0;
                else
                    Interval = StartTime - previous.StartTime;
            }
        }
    }
}