/******************************************************************************
 * Spine Runtimes License Agreement
 * Last updated April 5, 2025. Replaces all prior versions.
 *
 * Copyright (c) 2013-2026, Esoteric Software LLC
 *
 * Integration of the Spine Runtimes into software or otherwise creating
 * derivative works of the Spine Runtimes is permitted under the terms and
 * conditions of Section 2 of the Spine Editor License Agreement:
 * https://esotericsoftware.com/spine-editor-license
 *
 * Otherwise, it is permitted to integrate the Spine Runtimes into software
 * or otherwise create derivative works of the Spine Runtimes (collectively,
 * "Products"), provided that each user of the Products must obtain their own
 * Spine Editor license and redistribution of the Products in any form must
 * include this license and copyright notice.
 *
 * THE SPINE RUNTIMES ARE PROVIDED BY ESOTERIC SOFTWARE LLC "AS IS" AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL ESOTERIC SOFTWARE LLC BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES,
 * BUSINESS INTERRUPTION, OR LOSS OF USE, DATA, OR PROFITS) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THE SPINE RUNTIMES, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *****************************************************************************/

using System;
using System.Collections.Generic;

namespace Spine {

	/// <summary>
	/// <para>
	/// Applies animations over time, queues animations for later playback, mixes (crossfading) between animations, and applies
	/// multiple animations on top of each other (layering).</para>
	/// <para>
	/// See <see href='https://esotericsoftware.com/spine-applying-animations#AnimationState-API'>Applying Animations</see> in the Spine
	/// Runtimes Guide.</para>
	/// </summary>
	public class AnimationState {
		internal static readonly Animation EmptyAnimation = CreateEmptyAnimation();
		internal static Animation CreateEmptyAnimation () {
			var empty = new Animation("<empty>");
			empty.SetTimelines(new ExposedList<Timeline>(), new ExposedList<int>());
			return empty;
		}

		internal const int Subsequent = 0, First = 1, Hold = 2, HoldFirst = 3, Setup = 1, Retain = 2;

		protected AnimationStateData data;
		private readonly ExposedList<TrackEntry> tracks = new ExposedList<TrackEntry>();
		private readonly ExposedList<Event> events = new ExposedList<Event>();
		// difference to libgdx reference: delegates are used for event callbacks instead of 'final SnapshotArray<AnimationStateListener> listeners'.
		internal void OnStart (TrackEntry entry) { if (Start != null) Start(entry); }
		internal void OnInterrupt (TrackEntry entry) { if (Interrupt != null) Interrupt(entry); }
		internal void OnEnd (TrackEntry entry) { if (End != null) End(entry); }
		internal void OnDispose (TrackEntry entry) { if (Dispose != null) Dispose(entry); }
		internal void OnComplete (TrackEntry entry) { if (Complete != null) Complete(entry); }
		internal void OnEvent (TrackEntry entry, Event e) { if (Event != null) Event(entry, e); }

		public delegate void TrackEntryDelegate (TrackEntry trackEntry);
		/// <summary>See <see href="https://esotericsoftware.com/spine-api-reference#AnimationStateListener-Methods">
		/// API Reference documentation pages here</see> for details. Usage in C# and spine-unity is explained
		/// <see href="https://esotericsoftware.com/spine-unity-main-components#Processing-AnimationState-Events">here</see>
		/// on the spine-unity documentation pages.</summary>
		public event TrackEntryDelegate Start, Interrupt, End, Dispose, Complete;

		public delegate void TrackEntryEventDelegate (TrackEntry trackEntry, Event e);
		public event TrackEntryEventDelegate Event;

		public void AssignEventSubscribersFrom (AnimationState src) {
			Event = src.Event;
			Start = src.Start;
			Interrupt = src.Interrupt;
			End = src.End;
			Dispose = src.Dispose;
			Complete = src.Complete;
		}

		public void AddEventSubscribersFrom (AnimationState src) {
			Event += src.Event;
			Start += src.Start;
			Interrupt += src.Interrupt;
			End += src.End;
			Dispose += src.Dispose;
			Complete += src.Complete;
		}

		// end of difference
		private readonly EventQueue queue; // Initialized by constructor.
		private readonly HashSet<ulong> propertyIds = new HashSet<ulong>();
		private bool animationsChanged;
		private float timeScale = 1;
		private int unkeyedState;

		private readonly Pool<TrackEntry> trackEntryPool = new Pool<TrackEntry>();

		public AnimationState (AnimationStateData data) {
			if (data == null) throw new ArgumentNullException("data", "data cannot be null.");
			this.data = data;
			this.queue = new EventQueue(
				this,
				delegate { this.animationsChanged = true; },
				trackEntryPool
			);
		}

		/// <summary>
		/// Increments the track entry <see cref="TrackEntry.TrackTime"/>, setting queued animations as current if needed.</summary>
		/// <param name="delta">delta time</param>
		public void Update (float delta) {
			delta *= timeScale;
			TrackEntry[] tracksItems = tracks.Items;
			for (int i = 0, n = tracks.Count; i < n; i++) {
				TrackEntry current = tracksItems[i];
				if (current == null) continue;

				current.animationLast = current.nextAnimationLast;
				current.trackLast = current.nextTrackLast;

				float currentDelta = delta * current.timeScale;

				if (current.delay > 0) {
					current.delay -= currentDelta;
					if (current.delay > 0) continue;
					currentDelta = -current.delay;
					current.delay = 0;
				}

				TrackEntry next = current.next;
				if (next != null) {
					// When the next entry's delay is passed, change to the next entry, preserving leftover time.
					float nextTime = current.trackLast - next.delay;
					if (nextTime >= 0) {
						next.delay = 0;
						next.trackTime += current.timeScale == 0 ? 0 : (nextTime / current.timeScale + delta) * next.timeScale;
						current.trackTime += currentDelta;
						SetTrack(i, next, true);
						while (next.mixingFrom != null) {
							next.mixTime += delta;
							next = next.mixingFrom;
						}
						continue;
					}
				} else if (current.trackLast >= current.trackEnd && current.mixingFrom == null) {
					// Clear the track when there is no next entry, the track end time is reached, and there is no mixingFrom.
					tracksItems[i] = null;
					queue.End(current);
					ClearNext(current);
					continue;
				}
				if (current.mixingFrom != null && UpdateMixingFrom(current, delta)) {
					// End mixing from entries once all have completed.
					TrackEntry from = current.mixingFrom;
					current.mixingFrom = null;
					if (from != null) from.mixingTo = null;
					while (from != null) {
						queue.End(from);
						from = from.mixingFrom;
					}
				}

				current.trackTime += currentDelta;
			}

			queue.Drain();
		}

		/// <summary>Returns true when all mixing from entries are complete.</summary>
		private bool UpdateMixingFrom (TrackEntry to, float delta) {
			TrackEntry from = to.mixingFrom;
			if (from == null) return true;

			bool finished = UpdateMixingFrom(from, delta);

			from.animationLast = from.nextAnimationLast;
			from.trackLast = from.nextTrackLast;

			// The from entry was applied at least once and the mix is complete.
			if (to.nextTrackLast != -1 && to.mixTime >= to.mixDuration) {
				// Mixing is complete for all entries before the from entry or the mix is instantaneous.
				if (from.totalAlpha == 0 || to.mixDuration == 0) {
					to.mixingFrom = from.mixingFrom;
					if (from.mixingFrom != null) from.mixingFrom.mixingTo = to;
					if (from.totalAlpha == 0) {
						for (TrackEntry next = to; next.mixingTo != null; next = next.mixingTo)
							next.keepHold = true;
					}
					queue.End(from);
				}
				return finished;
			}

			from.trackTime += delta * from.timeScale;
			to.mixTime += delta;
			return false;
		}

		/// <summary>
		/// Poses the skeleton using the track entry animations.  The animation state is not changed, so can be applied to multiple
		/// skeletons to pose them identically.</summary>
		/// <returns>True if any animations were applied.</returns>
		public bool Apply (Skeleton skeleton) {
			if (skeleton == null) throw new ArgumentNullException("skeleton", "skeleton cannot be null.");
			if (animationsChanged) AnimationsChanged();

			ExposedList<Event> events = this.events;
			bool applied = false;
			TrackEntry[] tracksItems = tracks.Items;
			for (int i = 0, n = tracks.Count; i < n; i++) {
				TrackEntry current = tracksItems[i];
				if (current == null || current.delay > 0) continue;
				applied = true;

				// Apply mixing from entries first.
				float alpha = current.alpha;
				if (current.mixingFrom != null)
					alpha *= ApplyMixingFrom(current, skeleton);
				else if (current.trackTime >= current.trackEnd && current.next == null) //
					alpha = 0; // Set to setup pose the last time the entry will be applied.

				// Apply current entry.
				float animationLast = current.animationLast, animationTime = current.AnimationTime, applyTime = animationTime;
				ExposedList<Event> applyEvents = events;
				if (current.reverse) {
					applyTime = current.animation.duration - applyTime;
					applyEvents = null;
				}

				int timelineCount = current.animation.timelines.Count;
				Timeline[] timelines = current.animation.timelines.Items;
				if (i == 0 && alpha == 1) {
					for (int ii = 0; ii < timelineCount; ii++) {
						Timeline timeline = timelines[ii];
						if (timeline is AttachmentTimeline)
							ApplyAttachmentTimeline((AttachmentTimeline)timeline, skeleton, applyTime, true, true);
						else {
							timeline.Apply(skeleton, animationLast, applyTime, applyEvents, alpha, true, false, false, false);
						}
					}
				} else {
					int[] timelineMode = current.timelineMode.Items;

					bool retainAttachments = alpha >= current.alphaAttachmentThreshold;
					bool add = current.additive, shortestRotation = add || current.shortestRotation;
					bool firstFrame = !shortestRotation && current.timelinesRotation.Count != timelineCount << 1;
					if (firstFrame) current.timelinesRotation.EnsureSize(timelineCount << 1);
					float[] timelinesRotation = current.timelinesRotation.Items;

					for (int ii = 0; ii < timelineCount; ii++) {
						Timeline timeline = timelines[ii];
						bool fromSetup = (timelineMode[ii] & AnimationState.First) != 0;
						RotateTimeline rotateTimeline = timeline as RotateTimeline;
						if (!shortestRotation && rotateTimeline != null)
							ApplyRotateTimeline(rotateTimeline, skeleton, applyTime, alpha, fromSetup, timelinesRotation,
												ii << 1, firstFrame);
						else if (timeline is AttachmentTimeline)
							ApplyAttachmentTimeline((AttachmentTimeline)timeline, skeleton, applyTime, fromSetup, retainAttachments);
						else
							timeline.Apply(skeleton, animationLast, applyTime, applyEvents, alpha, fromSetup, add, false, false);
					}
				}
				if (current.reverse) EventsReverse(current, animationLast, animationTime);
				QueueEvents(current, animationTime);
				events.Clear(false);
				current.nextAnimationLast = animationTime;
				current.nextTrackLast = current.trackTime;
			}

			// Set slot attachments to the setup pose if they were set temporarily to apply deform timelines.
			int setupState = unkeyedState + Setup;
			Slot[] slots = skeleton.slots.Items;
			for (int i = 0, n = skeleton.slots.Count; i < n; i++) {
				Slot slot = slots[i];
				if (slot.attachmentState == setupState) {
					string attachmentName = slot.data.attachmentName;
					slot.pose.Attachment = (attachmentName == null ? null : skeleton.GetAttachment(slot.data.index, attachmentName));
				}
			}
			unkeyedState += 2; // Reset.

			queue.Drain();
			return applied;
		}

		/// <summary>Version of <see cref="Apply"/> only applying and updating time at
		/// EventTimelines for lightweight off-screen updates.</summary>
		/// <param name="issueEvents">When set to false, only animation times of TrackEntries are updated.</param>
		// Note: This method is not part of the libgdx reference implementation.
		public bool ApplyEventTimelinesOnly (Skeleton skeleton, bool issueEvents = true) {
			if (skeleton == null) throw new ArgumentNullException("skeleton", "skeleton cannot be null.");

			ExposedList<Event> events = this.events;
			bool applied = false;
			TrackEntry[] tracksItems = tracks.Items;
			for (int i = 0, n = tracks.Count; i < n; i++) {
				TrackEntry current = tracksItems[i];
				if (current == null || current.delay > 0) continue;
				applied = true;

				// Apply mixing from entries first.
				if (current.mixingFrom != null) ApplyMixingFromEventTimelinesOnly(current, skeleton, issueEvents);

				// Apply current entry.
				float animationLast = current.animationLast, animationTime = current.AnimationTime, applyTime = animationTime;
				ExposedList<Event> applyEvents = events;
				if (current.reverse) {
					applyTime = current.animation.duration - applyTime;
					applyEvents = null;
				}

				if (issueEvents) {
					int timelineCount = current.animation.timelines.Count;
					Timeline[] timelines = current.animation.timelines.Items;
					for (int ii = 0; ii < timelineCount; ii++) {
						Timeline timeline = timelines[ii];
						if (timeline is EventTimeline)
							timeline.Apply(skeleton, animationLast, applyTime, applyEvents, 1.0f, true, false, false, false);
					}
					if (current.reverse) EventsReverse(current, animationLast, animationTime);
					QueueEvents(current, animationTime);
					events.Clear(false);
				}
				current.nextAnimationLast = animationTime;
				current.nextTrackLast = current.trackTime;
			}

			if (issueEvents)
				queue.Drain();
			return applied;
		}

		private float ApplyMixingFrom (TrackEntry to, Skeleton skeleton) {
			TrackEntry from = to.mixingFrom;
			float fromMix = from.mixingFrom != null ? ApplyMixingFrom(from, skeleton) : 1;
			float mix = to.Mix();

			float a = from.alpha * fromMix, keep = 1 - mix * to.alpha;
			float alphaMix = a * (1 - mix), alphaHold = keep > 0 ? alphaMix / keep : a;

			int timelineCount = from.animation.timelines.Count;
			Timeline[] timelines = from.animation.timelines.Items;
			int[] timelineMode = from.timelineMode.Items;
			TrackEntry[] timelineHoldMix = from.timelineHoldMix.Items;

			bool retainAttachments = mix < from.mixAttachmentThreshold, drawOrder = mix < from.mixDrawOrderThreshold;
			bool add = from.additive, shortestRotation = add || from.shortestRotation;
			bool firstFrame = !shortestRotation && from.timelinesRotation.Count != timelineCount << 1;
			if (firstFrame) from.timelinesRotation.EnsureSize(timelineCount << 1);
			float[] timelinesRotation = from.timelinesRotation.Items;

			float animationLast = from.animationLast, animationTime = from.AnimationTime, applyTime = animationTime;
			ExposedList<Event> events = null;
			if (from.reverse)
				applyTime = from.animation.duration - applyTime;
			else if (mix < from.eventThreshold)
				events = this.events;

			from.totalAlpha = 0;
			for (int i = 0; i < timelineCount; i++) {
				Timeline timeline = timelines[i];
				int mode = timelineMode[i];
				bool fromSetup = (mode & AnimationState.First) != 0;
				float alpha;
				if ((mode & AnimationState.Hold) != 0) {
					TrackEntry holdMix = timelineHoldMix[i];
					alpha = holdMix == null ? alphaHold : alphaHold * (1 - holdMix.Mix());
				} else {
					if (!drawOrder && timeline is DrawOrderTimeline && !fromSetup) continue;
					alpha = alphaMix;
				}

				from.totalAlpha += alpha;
				RotateTimeline rotateTimeline = timeline as RotateTimeline;
				if (!shortestRotation && rotateTimeline != null) {
					ApplyRotateTimeline(rotateTimeline, skeleton, applyTime, alpha, fromSetup, timelinesRotation, i << 1,
						firstFrame);
				} else if (timeline is AttachmentTimeline) {
					ApplyAttachmentTimeline((AttachmentTimeline)timeline, skeleton, applyTime, fromSetup,
						retainAttachments && alpha >= from.alphaAttachmentThreshold);
				} else {
					bool mixOut = !drawOrder || !(timeline is DrawOrderTimeline) || !fromSetup;
					timeline.Apply(skeleton, animationLast, applyTime, events, alpha, fromSetup, add, mixOut, false);
				}
			}

			if (from.reverse && mix < from.eventThreshold) EventsReverse(from, animationLast, animationTime);
			if (to.mixDuration > 0) QueueEvents(from, animationTime);
			this.events.Clear(false);

			from.nextAnimationLast = animationTime;
			from.nextTrackLast = from.trackTime;
			return mix;
		}

		/// <summary>Version of <see cref="ApplyMixingFrom"/> only applying and updating time at
		/// EventTimelines for lightweight off-screen updates.</summary>
		/// <param name="issueEvents">When set to false, only animation times of TrackEntries are updated.</param>
		// Note: This method is not part of the libgdx reference implementation.
		private float ApplyMixingFromEventTimelinesOnly (TrackEntry to, Skeleton skeleton, bool issueEvents) {
			TrackEntry from = to.mixingFrom;
			if (from.mixingFrom != null) ApplyMixingFromEventTimelinesOnly(from, skeleton, issueEvents);

			float mix = to.Mix();

			float animationLast = from.animationLast, animationTime = from.AnimationTime, applyTime = animationTime;
			ExposedList<Event> events = this.events;
			if (from.reverse) {
				applyTime = from.animation.duration - applyTime;
				events = null;
			}

			if (issueEvents) {
				if (mix < from.eventThreshold) {
					int timelineCount = from.animation.timelines.Count;
					Timeline[] timelines = from.animation.timelines.Items;
					for (int i = 0; i < timelineCount; i++) {
						Timeline timeline = timelines[i];
						if (timeline is EventTimeline)
							timeline.Apply(skeleton, animationLast, applyTime, events, 0, true, false, true, false);
					}
					if (from.reverse) EventsReverse(from, animationLast, animationTime);
				}
				if (to.mixDuration > 0) QueueEvents(from, animationTime);
				this.events.Clear(false);
			}
			from.nextAnimationLast = animationTime;
			from.nextTrackLast = from.trackTime;

			return mix;
		}

		/// <summary> Applies the attachment timeline and sets <see cref="Slot.attachmentState"/>.</summary>
		/// <param name="retain">True if the attachment remains after apply, false if temporary for deform timelines.</param>
		private void ApplyAttachmentTimeline (AttachmentTimeline timeline, Skeleton skeleton, float time, bool fromSetup,
			bool retain) {

			Slot slot = skeleton.slots.Items[timeline.SlotIndex];
			if (!slot.bone.active) return;
			if (!retain && slot.attachmentState == unkeyedState + Retain) return;

			bool setup = time < timeline.frames[0];
			string name = null;
			if (!setup) {
				name = timeline.AttachmentNames[Timeline.Search(timeline.frames, time)];
				setup = !retain && name == null;
			}
			if (setup) {
				if (!fromSetup) return;
				name = slot.data.attachmentName;
			}
			slot.pose.Attachment = name == null ? null : skeleton.GetAttachment(slot.data.index, name);
			if (retain)
				slot.attachmentState = unkeyedState + Retain;
			else if (!setup) //
				slot.attachmentState = unkeyedState + Setup;
		}

		/// <summary>
		/// Applies the rotate timeline, mixing with the current pose while keeping the same rotation direction chosen as the shortest
		/// the first time the mixing was applied.</summary>
		static private void ApplyRotateTimeline (RotateTimeline timeline, Skeleton skeleton, float time, float alpha, bool fromSetup,
			float[] timelinesRotation, int i, bool firstFrame) {

			if (firstFrame) timelinesRotation[i] = 0;

			if (alpha == 1) {
				timeline.Apply(skeleton, 0, time, null, 1, fromSetup, false, false, false);
				return;
			}

			Bone bone = skeleton.bones.Items[timeline.BoneIndex];
			if (!bone.active) return;
			BonePose pose = bone.pose, setup = bone.data.setupPose;
			float[] frames = timeline.frames;
			if (time < frames[0]) { // Time is before first frame.
				if (fromSetup) pose.rotation = setup.rotation;
				return;
			}
			float r1 = fromSetup ? setup.rotation : pose.rotation;
			float r2 = setup.rotation + timeline.GetCurveValue(time);

			// Mix between rotations using the direction of the shortest route on the first frame.
			float total, diff = r2 - r1;
			diff -= (float)Math.Ceiling(diff / 360 - 0.5f) * 360;
			if (diff == 0) {
				total = timelinesRotation[i];
			} else {
				float lastTotal, lastDiff;
				if (firstFrame) {
					lastTotal = 0;
					lastDiff = diff;
				} else {
					lastTotal = timelinesRotation[i];
					lastDiff = timelinesRotation[i + 1];
				}
				float loops = lastTotal - lastTotal % 360;
				total = diff + loops;
				bool current = diff >= 0, dir = lastTotal >= 0;
				if (Math.Abs(lastDiff) <= 90 && Math.Sign(lastDiff) != Math.Sign(diff)) {
					if (Math.Abs(lastTotal - loops) > 180) {
						total += 360 * Math.Sign(lastTotal);
						dir = current;
					} else if (loops != 0)
						total -= 360 * Math.Sign(lastTotal);
					else
						dir = current;
				}
				if (dir != current) total += 360 * Math.Sign(lastTotal);
				timelinesRotation[i] = total;
			}
			timelinesRotation[i + 1] = diff;
			pose.rotation = r1 + total * alpha;
		}

		private void QueueEvents (TrackEntry entry, float animationTime) {
			float animationStart = entry.animationStart, animationEnd = entry.animationEnd, duration = animationEnd - animationStart;
			bool reverse = entry.reverse;
			float split = entry.trackLast % duration;
			if (reverse) split = duration - split;

			// Queue events before complete.
			Event[] eventsItems = this.events.Items;
			int i = 0, n = events.Count;
			for (; i < n; i++) {
				Event e = eventsItems[i];
				if ((e.time < split) ^ reverse) break;
				if (e.time >= animationStart && e.time <= animationEnd) queue.Event(entry, e);
			}

			// Queue complete if completed a loop iteration or the animation.
			bool complete = false;
			if (entry.loop) {
				if (duration == 0)
					complete = true;
				else {
					int cycles = (int)(entry.trackTime / duration);
					complete = cycles > 0 && cycles > (int)(entry.trackLast / duration);
				}
			} else
				complete = animationTime >= animationEnd && entry.animationLast < animationEnd;
			if (complete) queue.Complete(entry);

			// Queue events after complete.
			for (; i < n; i++) {
				Event e = eventsItems[i];
				if (e.time >= animationStart && e.time <= animationEnd) queue.Event(entry, e);
			}
		}

		private void EventsReverse (TrackEntry entry, float animationLast, float animationTime) {
			float duration = entry.animation.duration, from = duration - animationLast, to = duration - animationTime;
			Timeline[] timelines = entry.animation.timelines.Items;
			for (int i = 0, n = entry.animation.timelines.Count; i < n; i++) {
				EventTimeline eventTimeline = timelines[i] as EventTimeline;
				if (eventTimeline == null) continue;
				Event[] timelineEvents = eventTimeline.Events;
				float[] frames = eventTimeline.frames;
				int frameCount = frames.Length;
				if (from >= to) { // from -> to
					for (int ii = 0; ii < frameCount; ii++) {
						if (frames[ii] < to) continue;
						if (frames[ii] >= from) break;
						events.Add(timelineEvents[ii]);
					}
				} else {
					int ii = 0;
					for (; ii < frameCount; ii++) { // from -> 0
						if (frames[ii] >= from) break;
						events.Add(timelineEvents[ii]);
					}
					ii = 0; // end -> to
					for (; ii < frameCount; ii++)
						if (frames[ii] >= to) break;
					for (; ii < frameCount; ii++)
						events.Add(timelineEvents[ii]);
				}
			}
		}

		/// <summary>
		/// <para>Removes all animations from all tracks, leaving skeletons in their current pose.</para>
		/// <para>
		/// Usually you want to use <see cref="SetEmptyAnimations(float)"/> to mix the skeletons back to the setup pose, rather than leaving
		/// them in their current pose.</para>
		/// </summary>
		public void ClearTracks () {
			bool oldDrainDisabled = queue.drainDisabled;
			queue.drainDisabled = true;
			for (int i = 0, n = tracks.Count; i < n; i++) {
				ClearTrack(i);
			}
			tracks.Clear();
			queue.drainDisabled = oldDrainDisabled;
			queue.Drain();
		}

		/// <summary>
		/// <para>Removes all animations from the track, leaving skeletons in their current pose.</para>
		/// <para>
		/// Usually you want to use <see cref="SetEmptyAnimation(int, float)"/> to mix the skeletons back to the setup pose, rather than
		/// leaving them in their current pose.</para>
		/// </summary>
		public void ClearTrack (int trackIndex) {
			if (trackIndex < 0) throw new ArgumentException("trackIndex must be >= 0.", "trackIndex");
			if (trackIndex >= tracks.Count) return;
			TrackEntry current = tracks.Items[trackIndex];
			if (current == null) return;

			queue.End(current);

			ClearNext(current);

			TrackEntry entry = current;
			while (true) {
				TrackEntry from = entry.mixingFrom;
				if (from == null) break;
				queue.End(from);
				entry.mixingFrom = null;
				entry.mixingTo = null;
				entry = from;
			}

			tracks.Items[current.trackIndex] = null;

			queue.Drain();
		}

		/// <summary>Sets the active TrackEntry for a given track number.</summary>
		private void SetTrack (int index, TrackEntry current, bool interrupt) {
			TrackEntry from = ExpandToIndex(index);
			tracks.Items[index] = current;
			current.previous = null;

			if (from != null) {
				from.next = null;
				if (interrupt) queue.Interrupt(from);
				current.mixingFrom = from;
				from.mixingTo = current;
				current.mixTime = 0;
				from.timelinesRotation.Clear(); // Reset rotation for mixing out, in case entry was mixed in.
			}

			queue.Start(current); // triggers AnimationsChanged
		}

		/// <summary>Sets an animation by name. <seealso cref="SetAnimation(int, Animation, bool)" /></summary>
		public TrackEntry SetAnimation (int trackIndex, string animationName, bool loop) {
			Animation animation = data.skeletonData.FindAnimation(animationName);
			if (animation == null) throw new ArgumentException("Animation not found: " + animationName, "animationName");
			return SetAnimation(trackIndex, animation, loop);
		}

		/// <summary><para>
		/// Sets the current animation for a track, discarding any queued animations.</para>
		/// <para>
		/// If the formerly current track entry is for the same animation and was never applied to a skeleton, it is replaced (not mixed
		/// from).
		/// </para></summary>
		/// <param name="loop">If true, the animation will repeat. If false it will not, instead its last frame is applied if played beyond its
		///          duration. In either case <see cref="TrackEntry.TrackEnd"/> determines when the track is cleared.</param>
		/// <returns> A track entry to allow further customization of animation playback. References to the track entry must not be kept
		///          after the <see cref="AnimationState.Dispose"/> event occurs.</returns>
		public TrackEntry SetAnimation (int trackIndex, Animation animation, bool loop) {
			if (trackIndex < 0) throw new ArgumentException("trackIndex must be >= 0.", "trackIndex");
			if (animation == null) throw new ArgumentNullException("animation", "animation cannot be null.");
			bool interrupt = true;
			TrackEntry current = ExpandToIndex(trackIndex);
			if (current != null) {
				if (current.nextTrackLast == -1 && current.animation == animation) {
					// Don't mix from an entry that was never applied.
					tracks.Items[trackIndex] = current.mixingFrom;
					queue.Interrupt(current);
					queue.End(current);
					ClearNext(current);
					current = current.mixingFrom;
					interrupt = false; // mixingFrom is current again, but don't interrupt it twice.
				} else
					ClearNext(current);
			}
			TrackEntry entry = NewTrackEntry(trackIndex, animation, loop, current);
			SetTrack(trackIndex, entry, interrupt);
			queue.Drain();
			return entry;
		}

		/// <summary>Queues an animation by name.</summary>
		/// <seealso cref="AddAnimation(int, Animation, bool, float)" />
		public TrackEntry AddAnimation (int trackIndex, string animationName, bool loop, float delay) {
			Animation animation = data.skeletonData.FindAnimation(animationName);
			if (animation == null) throw new ArgumentException("Animation not found: " + animationName, "animationName");
			return AddAnimation(trackIndex, animation, loop, delay);
		}

		/// <summary>Adds an animation to be played after the current or last queued animation for a track. If the track has no entries, this is
		/// equivalent to calling <see cref="SetAnimation(int, Animation, bool)"/>.</summary>
		/// <param name="delay">
		/// If &gt; 0, sets <see cref="TrackEntry.Delay"/>. If &lt;= 0, the delay set is the duration of the previous track entry
		/// minus any mix duration (from <see cref="Data"/>) plus the specified <c>Delay</c> (ie the mix ends at (when
		/// <c>Delay</c> = 0) or before (when <c>Delay</c> &lt; 0) the previous track entry duration). If the
		/// previous entry is looping, its next loop completion is used instead of its duration.
		/// </param>
		/// <returns>A track entry to allow further customization of animation playback. References to the track entry must not be kept
		/// after the <see cref="AnimationState.Dispose"/> event occurs.</returns>
		public TrackEntry AddAnimation (int trackIndex, Animation animation, bool loop, float delay) {
			if (trackIndex < 0) throw new ArgumentException("trackIndex must be >= 0.", "trackIndex");
			if (animation == null) throw new ArgumentNullException("animation", "animation cannot be null.");

			TrackEntry last = ExpandToIndex(trackIndex);
			if (last != null) {
				while (last.next != null)
					last = last.next;
			}

			TrackEntry entry = NewTrackEntry(trackIndex, animation, loop, last);

			if (last == null) {
				SetTrack(trackIndex, entry, true);
				queue.Drain();
				if (delay < 0) delay = 0;
			} else {
				last.next = entry;
				entry.previous = last;
				if (delay <= 0) delay = Math.Max(delay + last.TrackComplete - entry.mixDuration, 0);
			}

			entry.delay = delay;
			return entry;
		}

		/// <summary>
		/// <para>Sets an empty animation for a track, discarding any queued animations, and sets the track entry's
		/// <see cref="TrackEntry.MixDuration"/>. An empty animation has no timelines and serves as a placeholder for mixing in or out.</para>
		/// <para>
		/// Mixing out is done by setting an empty animation with a mix duration using either <see cref="AnimationState.SetEmptyAnimation(int, float)"/>,
		/// <see cref="AnimationState.SetEmptyAnimations(float)"/>, or <see cref="AnimationState.AddEmptyAnimation(int, float, float)"/>. Mixing to an empty animation causes
		/// the previous animation to be applied less and less over the mix duration. Properties keyed in the previous animation
		/// transition to the value from lower tracks or to the setup pose value if no lower tracks key the property. A mix duration of
		/// 0 still needs to be applied one more time to mix out, so the properties it was animating are reverted.</para>
		/// <para>
		/// Mixing in is done by first setting an empty animation, then adding an animation using
		/// <see cref="AnimationState.AddAnimation(int, Animation, bool, float)"/> with the desired delay (an empty animation has a duration of 0) and on
		/// the returned track entry set <see cref="TrackEntry.MixDuration"/>. Mixing from an empty animation causes the new
		/// animation to be applied more and more over the mix duration. Properties keyed in the new animation transition from the value
		/// from lower tracks or from the setup pose value if no lower tracks key the property to the value keyed in the new animation.</para>
		/// <para>
		/// See <see href='https://esotericsoftware.com/spine-applying-animations#Empty-animations'>Empty animations</see> in the Spine
		/// Runtimes Guide.</para></summary>
		public TrackEntry SetEmptyAnimation (int trackIndex, float mixDuration) {
			TrackEntry entry = SetAnimation(trackIndex, AnimationState.EmptyAnimation, false);
			entry.mixDuration = mixDuration;
			entry.trackEnd = mixDuration;
			return entry;
		}

		/// <summary>
		/// Adds an empty animation to be played after the current or last queued animation for a track, and sets the track entry's
		/// <see cref="TrackEntry.MixDuration"/>. If the track has no entries, this is equivalent to calling
		/// <see cref="AnimationState.SetEmptyAnimation(int, float)"/>.</summary>
		/// <seealso cref="AnimationState.SetEmptyAnimation(int, float)"/>
		/// <param name="trackIndex">Track number.</param>
		/// <param name="mixDuration">Mix duration.</param>
		/// <param name="delay">If &gt; 0, sets <see cref="TrackEntry.Delay"/>. If &lt;= 0, the delay set is the duration of the previous track entry
		/// minus any mix duration plus the specified <c>Delay</c> (ie the mix ends at (when <c>Delay</c> = 0) or
		/// before (when <c>Delay</c> &lt; 0) the previous track entry duration). If the previous entry is looping, its
		/// next loop completion is used instead of its duration.</param>
		/// <returns> A track entry to allow further customization of animation playback. References to the track entry must not be kept
		/// after the <see cref="AnimationState.Dispose"/> event occurs.
		/// </returns>
		public TrackEntry AddEmptyAnimation (int trackIndex, float mixDuration, float delay) {
			TrackEntry entry = AddAnimation(trackIndex, AnimationState.EmptyAnimation, false, delay);
			if (delay <= 0) entry.delay = Math.Max(entry.delay + entry.mixDuration - mixDuration, 0);
			entry.mixDuration = mixDuration;
			entry.trackEnd = mixDuration;
			return entry;
		}

		/// <summary>
		/// Sets an empty animation for every track, discarding any queued animations, and mixes to it over the specified mix
		/// duration.</summary>
		public void SetEmptyAnimations (float mixDuration) {
			bool oldDrainDisabled = queue.drainDisabled;
			queue.drainDisabled = true;
			TrackEntry[] tracksItems = tracks.Items;
			for (int i = 0, n = tracks.Count; i < n; i++) {
				TrackEntry current = tracksItems[i];
				if (current != null) SetEmptyAnimation(current.trackIndex, mixDuration);
			}
			queue.drainDisabled = oldDrainDisabled;
			queue.Drain();
		}

		private TrackEntry ExpandToIndex (int index) {
			if (index < tracks.Count) return tracks.Items[index];
			tracks.EnsureSize(index + 1);
			return null;
		}

		/// <summary>Object-pooling version of new TrackEntry. Obtain an unused TrackEntry from the pool and clear/initialize its values.</summary>
		/// <param name="last">May be null.</param>
		private TrackEntry NewTrackEntry (int trackIndex, Animation animation, bool loop, TrackEntry last) {
			TrackEntry entry = trackEntryPool.Obtain();
			entry.trackIndex = trackIndex;
			entry.animation = animation;
			entry.loop = loop;

			entry.additive = false;
			entry.reverse = false;
			entry.shortestRotation = false;

			entry.eventThreshold = 0;
			entry.alphaAttachmentThreshold = 0;
			entry.mixAttachmentThreshold = 0;
			entry.mixDrawOrderThreshold = 0;

			entry.animationStart = 0;
			entry.animationEnd = animation.Duration;
			entry.animationLast = -1;
			entry.nextAnimationLast = -1;

			entry.delay = 0;
			entry.trackTime = 0;
			entry.trackLast = -1;
			entry.nextTrackLast = -1;
			entry.trackEnd = float.MaxValue;
			entry.timeScale = 1;

			entry.alpha = 1;
			entry.mixTime = 0;
			entry.mixDuration = last == null ? 0 : data.GetMix(last.animation, animation);
			entry.mixInterpolation = Interpolation.Linear;
			entry.totalAlpha = 0;
			entry.keepHold = false;
			return entry;
		}

		/// <summary>Removes <see cref="TrackEntry.Next"/> and all entries after it for the specified entry.</summary>
		public void ClearNext (TrackEntry entry) {
			TrackEntry next = entry.next;
			while (next != null) {
				queue.Dispose(next);
				next = next.next;
			}
			entry.next = null;
		}

		private void AnimationsChanged () {
			animationsChanged = false;

			// Process in the order that animations are applied.
			int n = tracks.Count;
			TrackEntry[] tracksItems = tracks.Items;
			for (int i = 0; i < n; i++) {
				TrackEntry entry = tracksItems[i];
				if (entry == null) continue;
				while (entry.mixingFrom != null) // Move to last entry, then iterate in reverse.
					entry = entry.mixingFrom;
				do {
					ComputeHold(entry);
					entry = entry.mixingTo;
				} while (entry != null);
			}
			propertyIds.Clear();
		}

		private void ComputeHold (TrackEntry entry) {
			Timeline[] timelines = entry.animation.timelines.Items;
			int timelinesCount = entry.animation.timelines.Count;
			int[] timelineMode = entry.timelineMode.EnsureSize(timelinesCount).Items;
			entry.timelineHoldMix.Clear();
			TrackEntry[] timelineHoldMix = entry.timelineHoldMix.Resize(timelinesCount).Items;
			HashSet<ulong> propertyIds = this.propertyIds;

			bool add = entry.additive, keepHold = entry.keepHold;
			TrackEntry to = entry.mixingTo;

			// outer:
			for (int i = 0; i < timelinesCount; i++) {
				Timeline timeline = timelines[i];
				ulong[] ids = timeline.propertyIds;
				bool first = propertyIds.AddAll(ids)
						&& !(timeline is DrawOrderFolderTimeline && propertyIds.Contains(DrawOrderTimeline.propertyID));
				if (add && timeline.additive) {
					timelineMode[i] = first ? AnimationState.First : AnimationState.Subsequent;
					continue;
				}

				for (TrackEntry from = entry.mixingFrom; from != null; from = from.mixingFrom) {
					if (from.animation.HasTimeline(ids)) {
						// An earlier entry on this track keys this property, isolating it from lower tracks.
						timelineMode[i] = AnimationState.Subsequent;
						goto continue_outer; // continue outer;
					}
				}

				// Hold if the next entry will overwrite this property.
				int mode;
				if (to == null || timeline.instant || (to.additive && timeline.additive) || !to.animation.HasTimeline(ids))
					mode = first ? AnimationState.First : AnimationState.Subsequent;
				else {
					mode = first ? AnimationState.HoldFirst : AnimationState.Hold;
					// Find next entry that doesn't overwrite this property. Its mix fades out the hold, instead of it ending abruptly.
					for (TrackEntry next = to.mixingTo; next != null; next = next.mixingTo) {
						if ((next.additive && timeline.additive) || !next.animation.HasTimeline(ids)) {
							if (next.mixDuration > 0) timelineHoldMix[i] = next;
							break;
						}
					}
				}
				if (keepHold) mode = (mode & ~AnimationState.Hold) | (timelineMode[i] & AnimationState.Hold);
				timelineMode[i] = mode;
				continue_outer: { }
			}
		}

		/// <summary>Returns the track entry for the animation currently playing on the track, or null if no animation is currently playing.</summary>
		public TrackEntry GetTrack (int trackIndex) {
			if (trackIndex < 0) throw new ArgumentException("trackIndex must be >= 0.", "trackIndex");
			if (trackIndex >= tracks.Count) return null;
			return tracks.Items[trackIndex];
		}

		/// <summary> Discards all listener notifications that have not yet been delivered. This can be useful to call from an
		/// AnimationState event subscriber when it is known that further notifications that may have been already queued for delivery
		/// are not wanted because new animations are being set.
		/// </summary>
		public void ClearListenerNotifications () {
			queue.Clear();
		}

		public void DelayListenerNotifications () {
			queue.drainDisabled = true;
		}

		public void IssueDelayedListenerNotifications () {
			queue.drainDisabled = false;
			queue.Drain();
		}

		/// <summary>
		/// <para>Multiplier for the delta time when the animation state is updated, causing time for all animations and mixes to play slower
		/// or faster. Defaults to 1.</para>
		/// <para>
		/// See <see cref="TrackEntry.TimeScale"/> to affect a single animation.</para>
		/// </summary>
		public float TimeScale { get { return timeScale; } set { timeScale = value; } }

		/// <summary>The <see cref="AnimationStateData"/> to look up mix durations.</summary>
		public AnimationStateData Data {
			get {
				return data;
			}
			set {
				if (value == null) throw new ArgumentNullException("data", "data cannot be null.");
				this.data = value;
			}
		}

		/// <summary>The list of tracks that have had animations. May contain null entries for tracks that currently have no animation.</summary>
		public ExposedList<TrackEntry> Tracks { get { return tracks; } }

		override public string ToString () {
			var buffer = new System.Text.StringBuilder();
			TrackEntry[] tracksItems = tracks.Items;
			for (int i = 0, n = tracks.Count; i < n; i++) {
				TrackEntry entry = tracksItems[i];
				if (entry == null) continue;
				if (buffer.Length > 0) buffer.Append(", ");
				buffer.Append(entry.ToString());
			}
			if (buffer.Length == 0) return "<none>";
			return buffer.ToString();
		}
	}

	/// <summary>
	/// <para>
	/// Stores settings and other state for the playback of an animation on an <see cref="AnimationState"/> track.</para>
	/// <para>
	/// References to a track entry must not be kept after the <see cref="AnimationState.Dispose"/> event occurs</para>
	/// </summary>
	public class TrackEntry : Pool<TrackEntry>.IPoolable {
		internal Animation animation;

		internal TrackEntry previous, next, mixingFrom, mixingTo;
		// difference to libgdx reference: delegates are used for event callbacks instead of 'AnimationStateListener listener'.
		/// <summary>See <see href="https://esotericsoftware.com/spine-api-reference#AnimationStateListener-Methods">
		/// API Reference documentation pages here</see> for details. Usage in C# and spine-unity is explained
		/// <see href="https://esotericsoftware.com/spine-unity-main-components#Processing-AnimationState-Events">here</see>
		/// on the spine-unity documentation pages.
		/// <para>A track entry returned from <see cref="AnimationState.SetAnimation(int, Animation, bool)"/> is already the current
		/// animation for the track, so the <see cref="Start"/> callback will not be called for subscribers added afterward.</para></summary>
		public event AnimationState.TrackEntryDelegate Start, Interrupt, End, Dispose, Complete;
		public event AnimationState.TrackEntryEventDelegate Event;
		internal void OnStart () { if (Start != null) Start(this); }
		internal void OnInterrupt () { if (Interrupt != null) Interrupt(this); }
		internal void OnEnd () { if (End != null) End(this); }
		internal void OnDispose () { if (Dispose != null) Dispose(this); }
		internal void OnComplete () { if (Complete != null) Complete(this); }
		internal void OnEvent (Event e) { if (Event != null) Event(this, e); }

		internal int trackIndex;

		internal bool loop, additive, reverse, shortestRotation, keepHold;
		internal float eventThreshold, mixAttachmentThreshold, alphaAttachmentThreshold, mixDrawOrderThreshold;
		internal float animationStart, animationEnd, animationLast, nextAnimationLast;
		internal float delay, trackTime, trackLast, nextTrackLast, trackEnd, timeScale = 1f;
		internal float alpha, mixTime, mixDuration, totalAlpha;
		internal Interpolation mixInterpolation = Interpolation.Linear;

		/// <summary>
		/// For each timeline:
		/// <list type="bullet">
		/// <item>Bit 0, First: 0 = mix from current pose, 1 = mix from setup pose. Timeline is first to set the property.</item>
		/// <item>Bit 1, Hold: 0 = mix out using alphaMix, 1 = apply full alpha to prevent dipping. Timeline is first on its track to
		/// set the property and the next entry (mixingTo) also sets it. When held, timelineHoldMix's mix controls how the hold fades
		/// out (for 3+ entry chains where the chain eventually stops setting the property).</item>
		/// </list>
		/// </summary>
		internal readonly ExposedList<int> timelineMode = new ExposedList<int>();
		internal readonly ExposedList<TrackEntry> timelineHoldMix = new ExposedList<TrackEntry>();
		internal readonly ExposedList<float> timelinesRotation = new ExposedList<float>();

		// IPoolable.Reset()
		public void Reset () {
			previous = null;
			next = null;
			mixingFrom = null;
			mixingTo = null;
			mixInterpolation = Interpolation.Linear;
			animation = null;
			// replaces 'listener = null;' since delegates are used for event callbacks
			Start = null;
			Interrupt = null;
			End = null;
			Dispose = null;
			Complete = null;
			Event = null;
			timelineMode.Clear();
			timelineHoldMix.Clear();
			timelinesRotation.Clear();
		}

		/// <summary>The index of the track where this track entry is either current or queued.</summary>
		/// <seealso cref="AnimationState.GetTrack(int)"/>
		public int TrackIndex { get { return trackIndex; } }

		/// <summary>The animation to apply for this track entry.</summary>
		public Animation Animation {
			get { return animation; }
			set {
				if (value == null) throw new ArgumentNullException("animation", "animation cannot be null.");
				animation = value;
			}
		}

		/// <summary>
		/// If true, the animation will repeat. If false it will not, instead its last frame is applied if played beyond its
		/// duration.</summary>
		public bool Loop { get { return loop; } set { loop = value; } }

		/// <summary>
		/// <para>
		/// Seconds to postpone playing the animation. Must be >= 0. When this track entry is the current track entry,
		/// <c>Delay</c> postpones incrementing the <see cref="TrackEntry.TrackTime"/>. When this track entry is queued,
		/// <c>Delay</c> is the time from the start of the previous animation to when this track entry will become the current
		/// track entry (ie when the previous track entry <see cref="TrackTime"/> &gt;= this track entry's
		/// <c>Delay</c>).</para>
		/// <para>
		/// <see cref="TrackEntry.TimeScale"/> affects the delay.</para>
		/// <para>
		/// When passing <c>delay</c> &lt;= 0 to <see cref="AnimationState.AddAnimation(int, Animation, bool, float)"/>, this
		/// <c>delay</c> is set using a mix duration from the <see cref="AnimationStateData"/>. To change the <see cref="MixDuration"/>
		/// afterward, use <see cref="SetMixDuration(float, float)"/> so this <c>delay</c> is adjusted.</para></summary>
		public float Delay {
			get { return delay; }
			set {
				if (value < 0) throw new ArgumentException("delay must be >= 0.", "delay");
				delay = value;
			}
		}

		/// <summary>
		/// The time in seconds this track entry has been the current track entry, starting at 0 and increasing forever. Compare to
		/// <see cref="TrackEntry.AnimationTime"/>, which is always between <see cref="TrackEntry.AnimationStart"/> and
		/// <see cref="TrackEntry.AnimationEnd"/>.
		/// <para>
		/// The track time can be set to start the animation at a time other than 0, without affecting looping. When doing so,
		/// <see cref="TrackEntry.AnimationLast"/> can be set to the same value to avoid firing events from the start of the animation.</para>
		/// <para>
		/// To set the time an animation starts and loops, use <see cref="TrackEntry.AnimationStart"/> and
		/// <see cref="TrackEntry.AnimationEnd"/>.</para></summary>
		public float TrackTime { get { return trackTime; } set { trackTime = value; } }

		/// <summary>
		/// <para>
		/// The track time in seconds when this animation will be removed from the track. Defaults to the highest possible float
		/// value, meaning the animation will be applied until a new animation is set or the track is cleared. If the track end time
		/// is reached, no other animations are queued for playback, and mixing from any previous animations is complete, then the
		/// properties keyed by the animation are set to the setup pose and the track is cleared.</para>
		/// <para>
		/// Usually you want to use <see cref="AnimationState.AddEmptyAnimation(int, float, float)"/> rather than have the animation
		/// abruptly cease being applied.</para>
		/// </summary>
		public float TrackEnd { get { return trackEnd; } set { trackEnd = value; } }

		/// <summary>
		/// <para>If this track entry is non-looping, this is the track time in seconds when <see cref="AnimationEnd"/> is reached, or the
		/// current <see cref="TrackTime"/> if it has already been reached.</para>
		/// <para>If this track entry is looping, this is the track time when this animation will reach its next
		/// <see cref="AnimationEnd"/> (the next loop completion).</para></summary>
		public float TrackComplete {
			get {
				float duration = animationEnd - animationStart;
				if (duration != 0) {
					if (loop) return duration * (1 + (int)(trackTime / duration)); // Completion of next loop.
					if (trackTime < duration) return duration; // Before duration.
				}
				return trackTime; // Next update.
			}
		}

		/// <summary>
		/// <para>
		/// The time in seconds for the first frame of this animation, both initially and after looping. Defaults to 0.</para>
		/// <para>
		/// When setting the <c>AnimationStart</c> time, <see cref="TrackEntry.AnimationLast"/> can be set to the same value to avoid
		/// firing events from the start of the animation.</para>
		/// </summary>
		public float AnimationStart { get { return animationStart; } set { animationStart = value; } }

		/// <summary>
		/// The time in seconds for the last frame of this animation. Past this time, non-looping animations hold the pose at this
		/// time while looping animations will loop back to <see cref="TrackEntry.AnimationStart"/>. Defaults to the
		/// <see cref="Animation.Duration"/>.
		/// </summary>
		public float AnimationEnd { get { return animationEnd; } set { animationEnd = value; } }

		/// <summary>
		/// The time in seconds this animation was last applied. Some timelines use this for one-time triggers. For example, when
		/// this animation is applied, event timelines will fire all events between the <c>AnimationLast</c> time (exclusive) and
		/// <c>AnimationTime</c> (inclusive). Defaults to -1 to ensure triggers on frame 0 happen the first time this animation
		/// is applied.</summary>
		public float AnimationLast {
			get { return animationLast; }
			set {
				animationLast = value;
				nextAnimationLast = value;
			}
		}

		/// <summary>
		/// Uses <see cref="TrackEntry.TrackTime"/> to compute the <c>AnimationTime</c>, which is always between
		/// <see cref="TrackEntry.AnimationStart"/> and <see cref="TrackEntry.AnimationEnd"/>. When <c>TrackTime</c> is 0,
		/// <c>AnimationTime</c> is equal to the <c>AnimationStart</c> time.
		/// </summary>
		public float AnimationTime {
			get {
				if (!loop) return Math.Min(trackTime + animationStart, animationEnd);
				float duration = animationEnd - animationStart;
				if (duration == 0) return animationStart;
				return (trackTime % duration) + animationStart;
			}
		}

		/// <summary>
		/// <para>
		/// Multiplier for the delta time when this track entry is updated, causing time for this animation to pass slower or
		/// faster. Defaults to 1.</para>
		/// <para>
		/// Values &lt; 0 are not supported. To play an animation in reverse, use <see cref="Reverse"/>.</para>
		/// <para>
		/// <see cref="TrackEntry.MixTime"/> is not affected by track entry time scale, so <see cref="TrackEntry.MixDuration"/> may need to be adjusted to
		/// match the animation speed.</para>
		/// <para>
		/// When using <see cref="AnimationState.AddAnimation(int, Animation, bool, float)"/> with a <c>Delay</c> &lt;= 0, the
		/// <see cref="TrackEntry.Delay"/> is set using the mix duration from <see cref="AnimationState.Data"/>, assuming time scale to be 1. If the
		/// time scale is not 1, the delay may need to be adjusted.</para>
		/// <para>
		/// See <see cref="AnimationState.TimeScale"/> to affect all animations.</para>
		/// </summary>
		public float TimeScale { get { return timeScale; } set { timeScale = value; } }

		/// <summary>
		/// <para>
		/// Values &lt; 1 mix this animation with the skeleton's current pose (either the setup pose or the pose from lower tracks).
		/// Defaults to 1, which overwrites the skeleton's current pose with this animation.</para>
		/// <para>
		/// Alpha should be 1 on track 0.</para>
		/// <para>
		/// See <see cref="AlphaAttachmentThreshold"/>.</para>
		/// </summary>
		public float Alpha { get { return alpha; } set { alpha = value; } }

		/// <summary>
		/// When the interpolated mix percentage is less than the <c>EventThreshold</c>, event timelines are applied while
		/// this animation is being mixed out. Defaults to 0, so event timelines are not applied while this animation is being mixed
		/// out.
		/// </summary>
		public float EventThreshold { get { return eventThreshold; } set { eventThreshold = value; } }

		/// <summary>
		/// When the computed alpha is greater than <c>AlphaAttachmentThreshold</c>, attachment timelines are applied. The
		/// computed alpha includes <see cref="Alpha"/> and the interpolated mix percentage. Defaults to 0, so attachment timelines are
		/// always applied.
		/// </summary>
		public float AlphaAttachmentThreshold { get { return alphaAttachmentThreshold; } set { alphaAttachmentThreshold = value; } }

		/// <summary>
		/// When the interpolated mix percentage is less than the <c>MixAttachmentThreshold</c>, attachment timelines are
		/// applied while this animation is being mixed out. Defaults to 0, so attachment timelines are not applied while this
		/// animation is being mixed out.
		/// </summary>
		public float MixAttachmentThreshold { get { return mixAttachmentThreshold; } set { mixAttachmentThreshold = value; } }

		/// <summary>
		/// When the interpolated mix percentage is less than the <c>MixDrawOrderThreshold</c>, draw order timelines are
		/// applied while this animation is being mixed out. Defaults to 0, so draw order timelines are not applied while this
		/// animation is being mixed out.
		/// </summary>
		public float MixDrawOrderThreshold { get { return mixDrawOrderThreshold; } set { mixDrawOrderThreshold = value; } }

		/// <summary>
		/// The interpolation to apply to the mix percentage <see cref="MixTime"/> / <see cref="MixDuration"/> when mixing from the previous
		/// animation to this animation. Defaults to linear.
		/// </summary>
		public Interpolation MixInterpolation {
			get {
				return mixInterpolation;
			}
			set {
				if (value == null) throw new ArgumentNullException("MixInterpolation", "MixInterpolation value cannot be null.");
				this.mixInterpolation = value;
			}
		}

		internal float Mix () {
			if (mixDuration == 0) return 1;
			float mix = mixTime / mixDuration;
			if (mix >= 1) return 1;
			if (mixInterpolation == Interpolation.Linear) return mix;
			mix = mixInterpolation.Apply(mix);
			if (mix < 0) return 0;
			if (mix > 1) return 1;
			return mix;
		}

		/// <summary>
		/// The animation queued to start after this animation, or null if there is none. <c>next</c> makes up a doubly linked
		/// list.
		/// <para>
		/// See <see cref="AnimationState.ClearNext(TrackEntry)"/> to truncate the list.</para></summary>
		public TrackEntry Next { get { return next; } }

		/// <summary>
		/// The animation queued to play before this animation, or null. <c>previous</c> makes up a doubly linked list.</summary>
		public TrackEntry Previous { get { return previous; } }

		/// <summary>Returns true if this track entry has been applied at least once.</summary>
		/// <seealso cref="AnimationState.Apply(Skeleton)"/>
		public bool WasApplied {
			get { return nextTrackLast != -1; }
		}

		/// <summary>Returns true if there is a <see cref="Next"/> track entry that will become the current track entry during the
		/// next <see cref="AnimationState.Update(float)"/>.</summary>
		public bool IsNextReady {
			get {
				return (next != null) && (nextTrackLast - next.delay >= 0);
			}
		}

		/// <summary>
		/// Returns true if at least one loop has been completed.</summary>
		/// <seealso cref="TrackEntry.Complete"/>
		public bool IsComplete {
			get { return trackTime >= animationEnd - animationStart; }
		}

		/// <summary>
		/// Seconds elapsed from 0 to the <see cref="TrackEntry.MixDuration"/> when mixing from the previous animation to this animation. May
		/// be slightly more than <c>MixDuration</c> when the mix is complete.</summary>
		public float MixTime { get { return mixTime; } set { mixTime = value; } }

		/// <summary>
		/// <para>
		/// Seconds for mixing from the previous animation to this animation. Defaults to the value provided by
		/// <see cref="AnimationStateData.GetMix(Animation, Animation)"/> based on the animation before this animation (if any).
		/// </para><para>
		/// A mix duration of 0 still needs to be applied one more time to mix out, so the properties it was animating are reverted.
		/// A mix duration of 0 can be set at any time to end the mix on the next <see cref="AnimationState.Update(float)">update</see>.
		/// </para><para>
		/// The <c>MixDuration</c> can be set manually rather than use the value from
		/// <see cref="AnimationStateData.GetMix(Animation, Animation)"/>. In that case, the <c>MixDuration</c> can be set for a new
		/// track entry only before <see cref="AnimationState.Update(float)"/> is next called.
		/// </para><para>
		/// When using <seealso cref="AnimationState.AddAnimation(int, Animation, bool, float)"/> with a <c>Delay</c> &lt;= 0, the
		/// <see cref="TrackEntry.Delay"/> is set using the mix duration from <see cref="AnimationState.Data"/>. If <c>MixDuration</c> is set
		/// afterward, the delay needs to be adjusted:
		/// </para>
		/// <code>
		/// entry.MixDuration = 0.25f;
		/// entry.Delay = entry.Previous.TrackComplete - entry.MixDuration + 0;
		/// </code>
		/// <para>Alternatively, use <see cref="SetMixDuration(float, float)"/> to set both the mix duration and recompute the delay:</para>
		/// <code>entry.SetMixDuration(0.25f, 0); // mixDuration, delay</code>
		/// </summary>
		public float MixDuration { get { return mixDuration; } set { mixDuration = value; } }

		/// <summary>Sets both <see cref="MixDuration"/> and <see cref="Delay"/>.</summary>
		/// <param name="delay">If > 0, sets <see cref="Delay"/>. If &lt;= 0, the delay set is the duration of the previous track
		///		entry minus the specified mix duration plus the specified <c>delay</c> (ie the mix ends at (when <c>delay</c>
		///		= 0) or before (when <c>delay</c> &lt; 0) the previous track entry duration). If the previous entry is
		///		looping, its next loop completion is used instead of its duration.</param>
		public void SetMixDuration (float mixDuration, float delay) {
			this.mixDuration = mixDuration;
			if (delay <= 0) delay = previous == null ? 0 : Math.Max(delay + previous.TrackComplete - mixDuration, 0);
			this.delay = delay;
		}

		/// <summary>
		/// When true, timelines in this animation that support additive have their values added to the setup or current pose values
		/// instead of replacing them. Additive can be set for a new track entry only before <see cref="AnimationState.Apply(Skeleton)"/>
		/// is next called.
		/// </summary>
		public bool Additive { get { return additive; } set { additive = value; } }

		/// <summary>
		/// The track entry for the previous animation when mixing to this animation, or null if no mixing is currently occurring.
		/// When mixing from multiple animations, <c>MixingFrom</c> makes up a doubly linked list.</summary>
		public TrackEntry MixingFrom { get { return mixingFrom; } }

		/// <summary>
		/// The track entry for the next animation when mixing from this animation, or null if no mixing is currently occurring.
		/// When mixing to multiple animations, <c>MixingTo</c> makes up a doubly linked list.</summary>
		public TrackEntry MixingTo { get { return mixingTo; } }

		/// <summary>
		/// If true, the animation will be applied in reverse.</summary>
		public bool Reverse { get { return reverse; } set { reverse = value; } }

		/// <summary><para>
		/// If true, mixing rotation between tracks always uses the shortest rotation direction. If the rotation is animated, the
		/// shortest rotation direction may change during the mix.
		/// </para><para>
		/// If false, the shortest rotation direction is remembered when the mix starts and the same direction is used for the rest
		/// of the mix. Defaults to false.</para>
		/// <para>See <see cref="ResetRotationDirections"/>.</para></summary>
		public bool ShortestRotation { get { return shortestRotation; } set { shortestRotation = value; } }

		/// <summary>Returns true if this entry is for the empty animation. See <see cref="AnimationState.SetEmptyAnimation(int, float)"/>,
		/// <see cref="AnimationState.AddEmptyAnimation(int, float, float)"/>, and <see cref="AnimationState.SetEmptyAnimations(float)"/>.
		/// </summary>
		public bool IsEmptyAnimation { get { return animation == AnimationState.EmptyAnimation; } }

		/// <summary>
		/// <para>
		/// When <see cref="ShortestRotation"/> is false, this clears the directions for mixing this entry's rotation. This can be useful
		/// to avoid bones rotating the long way around when using <see cref="Alpha"/> and starting animations on other tracks.</para>
		/// <para>
		/// Mixing involves finding a rotation between two others. There are two possible solutions: the short or the long way
		/// around. When the two rotations change over time, which direction is the short or long way can also change. If the short
		/// way was always chosen, bones flip to the other side when that direction became the long way. TrackEntry chooses the short
		/// way the first time it is applied and remembers that direction. Resetting that direction makes it choose a new short way
		/// on the next apply.</para>
		/// </summary>
		public void ResetRotationDirections () {
			timelinesRotation.Clear();
		}

		override public string ToString () {
			return animation == null ? "<none>" : animation.name;
		}

		// Note: This method is required by SpineAnimationStateMixerBehaviour,
		// which is part of the timeline extension package. Thus the internal member variable
		// nextTrackLast is not accessible. We favor providing this method
		// over exposing nextTrackLast as public property, which would rather confuse users.
		public void AllowImmediateQueue () {
			if (nextTrackLast < 0) nextTrackLast = 0;
		}
	}

	class EventQueue {
		private readonly List<EventQueueEntry> eventQueueEntries = new List<EventQueueEntry>();
		internal bool drainDisabled;

		private readonly AnimationState state;
		private readonly Pool<TrackEntry> trackEntryPool;
		internal event Action AnimationsChanged;

		internal EventQueue (AnimationState state, Action HandleAnimationsChanged, Pool<TrackEntry> trackEntryPool) {
			this.state = state;
			this.AnimationsChanged += HandleAnimationsChanged;
			this.trackEntryPool = trackEntryPool;
		}

		internal void Start (TrackEntry entry) {
			eventQueueEntries.Add(new EventQueueEntry(EventType.Start, entry));
			if (AnimationsChanged != null) AnimationsChanged();
		}

		internal void Interrupt (TrackEntry entry) {
			eventQueueEntries.Add(new EventQueueEntry(EventType.Interrupt, entry));
		}

		internal void End (TrackEntry entry) {
			eventQueueEntries.Add(new EventQueueEntry(EventType.End, entry));
			if (AnimationsChanged != null) AnimationsChanged();
		}

		internal void Dispose (TrackEntry entry) {
			eventQueueEntries.Add(new EventQueueEntry(EventType.Dispose, entry));
		}

		internal void Complete (TrackEntry entry) {
			eventQueueEntries.Add(new EventQueueEntry(EventType.Complete, entry));
		}

		internal void Event (TrackEntry entry, Event e) {
			eventQueueEntries.Add(new EventQueueEntry(EventType.Event, entry, e));
		}

		/// <summary>Raises all events in the queue and drains the queue.</summary>
		internal void Drain () {
			if (drainDisabled) return;
			drainDisabled = true;

			List<EventQueueEntry> eventQueueEntries = this.eventQueueEntries;
			AnimationState state = this.state;

			// Don't cache eventQueueEntries.Count so callbacks can queue their own events (eg, call SetAnimation in AnimationState_Complete).
			for (int i = 0; i < eventQueueEntries.Count; i++) {
				EventQueueEntry queueEntry = eventQueueEntries[i];
				TrackEntry trackEntry = queueEntry.entry;

				switch (queueEntry.type) {
				case EventType.Start:
					trackEntry.OnStart();
					state.OnStart(trackEntry);
					break;
				case EventType.Interrupt:
					trackEntry.OnInterrupt();
					state.OnInterrupt(trackEntry);
					break;
				case EventType.End:
					trackEntry.OnEnd();
					state.OnEnd(trackEntry);
					goto case EventType.Dispose; // Fall through. (C#)
				case EventType.Dispose:
					trackEntry.OnDispose();
					state.OnDispose(trackEntry);
					trackEntryPool.Free(trackEntry);
					break;
				case EventType.Complete:
					trackEntry.OnComplete();
					state.OnComplete(trackEntry);
					break;
				case EventType.Event:
					trackEntry.OnEvent(queueEntry.e);
					state.OnEvent(trackEntry, queueEntry.e);
					break;
				}
			}
			eventQueueEntries.Clear();

			drainDisabled = false;
		}

		internal void Clear () {
			eventQueueEntries.Clear();
		}

		struct EventQueueEntry {
			public EventType type;
			public TrackEntry entry;
			public Event e;

			public EventQueueEntry (EventType eventType, TrackEntry trackEntry, Event e = null) {
				this.type = eventType;
				this.entry = trackEntry;
				this.e = e;
			}
		}

		enum EventType {
			Start, Interrupt, End, Dispose, Complete, Event
		}
	}

	class Pool<T> where T : class, new() {
		public readonly int max;
		readonly Stack<T> freeObjects;

		public int Count { get { return freeObjects.Count; } }
		public int Peak { get; private set; }

		public Pool (int initialCapacity = 16, int max = int.MaxValue) {
			freeObjects = new Stack<T>(initialCapacity);
			this.max = max;
		}

		public T Obtain () {
			return freeObjects.Count == 0 ? new T() : freeObjects.Pop();
		}

		public void Free (T obj) {
			if (obj == null) throw new ArgumentNullException("obj", "obj cannot be null");
			if (freeObjects.Count < max) {
				freeObjects.Push(obj);
				Peak = Math.Max(Peak, freeObjects.Count);
			}
			Reset(obj);
		}

		public void Clear () {
			freeObjects.Clear();
		}

		protected void Reset (T obj) {
			IPoolable poolable = obj as IPoolable;
			if (poolable != null) poolable.Reset();
		}

		public interface IPoolable {
			void Reset ();
		}
	}

	public static class HashSetExtensions {
		public static bool AddAll<T> (this HashSet<T> set, T[] addSet) {
			bool anyItemAdded = false;
			for (int i = 0, n = addSet.Length; i < n; ++i) {
				T item = addSet[i];
				anyItemAdded |= set.Add(item);
			}
			return anyItemAdded;
		}
	}
}