/******************************************************************************
 * Spine Runtimes License Agreement
 * Last updated January 1, 2020. Replaces all prior versions.
 *
 * Copyright (c) 2013-2020, 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:
 * http://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.
 *****************************************************************************/

module spine {

	/** Applies animations over time, queues animations for later playback, mixes (crossfading) between animations, and applies
	 * multiple animations on top of each other (layering).
	 *
	 * See [Applying Animations](http://esotericsoftware.com/spine-applying-animations/) in the Spine Runtimes Guide. */
	export class AnimationState {
		private static emptyAnimation(): Animation {
			if (!_emptyAnimation) _emptyAnimation = new Animation("<empty>", [], 0);
			return _emptyAnimation;
		}

		/** The AnimationStateData to look up mix durations. */
		data: AnimationStateData;

		/** The list of tracks that currently have animations, which may contain null entries. */
		tracks = new Array<TrackEntry>();

		/** 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.
		 *
		 * See TrackEntry {@link TrackEntry#timeScale} for affecting a single animation. */
		timeScale = 1;
		unkeyedState = 0;

		events = new Array<Event>();
		listeners = new Array<AnimationStateListener>();
		queue = new EventQueue(this);
		propertyIDs = new StringSet();
		animationsChanged = false;

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

		constructor (data: AnimationStateData) {
			this.data = data;
		}

		/** Increments each track entry {@link TrackEntry#trackTime()}, setting queued animations as current if needed. */
		update (delta: number) {
			delta *= this.timeScale;
			let tracks = this.tracks;
			for (let i = 0, n = tracks.length; i < n; i++) {
				let current = tracks[i];
				if (!current) continue;

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

				let currentDelta = delta * current.timeScale;

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

				let next = current.next;
				if (next) {
					// When the next entry's delay is passed, change to the next entry, preserving leftover time.
					let 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;
						this.setCurrent(i, next, true);
						while (next.mixingFrom) {
							next.mixTime += delta;
							next = next.mixingFrom;
						}
						continue;
					}
				} else if (current.trackLast >= current.trackEnd && !current.mixingFrom) {
					tracks[i] = null;
					this.queue.end(current);
					this.disposeNext(current);
					continue;
				}
				if (current.mixingFrom && this.updateMixingFrom(current, delta)) {
					// End mixing from entries once all have completed.
					let from = current.mixingFrom;
					current.mixingFrom = null;
					if (from) from.mixingTo = null;
					while (from) {
						this.queue.end(from);
						from = from.mixingFrom;
					}
				}

				current.trackTime += currentDelta;
			}

			this.queue.drain();
		}

		/** Returns true when all mixing from entries are complete. */
		updateMixingFrom (to: TrackEntry, delta: number): boolean {
			let from = to.mixingFrom;
			if (!from) return true;

			let finished = this.updateMixingFrom(from, delta);

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

			// Require mixTime > 0 to ensure the mixing from entry was applied at least once.
			if (to.mixTime > 0 && to.mixTime >= to.mixDuration) {
				// Require totalAlpha == 0 to ensure mixing is complete, unless mixDuration == 0 (the transition is a single frame).
				if (from.totalAlpha == 0 || to.mixDuration == 0) {
					to.mixingFrom = from.mixingFrom;
					if (from.mixingFrom) from.mixingFrom.mixingTo = to;
					to.interruptAlpha = from.interruptAlpha;
					this.queue.end(from);
				}
				return finished;
			}

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

		/** Poses the skeleton using the track entry animations. There are no side effects other than invoking listeners, so the
		 * animation state can be applied to multiple skeletons to pose them identically.
		 * @returns True if any animations were applied. */
		apply (skeleton: Skeleton) : boolean {
			if (!skeleton) throw new Error("skeleton cannot be null.");
			if (this.animationsChanged) this._animationsChanged();

			let events = this.events;
			let tracks = this.tracks;
			let applied = false;

			for (let i = 0, n = tracks.length; i < n; i++) {
				let current = tracks[i];
				if (!current || current.delay > 0) continue;
				applied = true;
				let blend: MixBlend = i == 0 ? MixBlend.first : current.mixBlend;

				// Apply mixing from entries first.
				let mix = current.alpha;
				if (current.mixingFrom)
					mix *= this.applyMixingFrom(current, skeleton, blend);
				else if (current.trackTime >= current.trackEnd && !current.next)
					mix = 0;

				// Apply current entry.
				let animationLast = current.animationLast, animationTime = current.getAnimationTime(), applyTime = animationTime;
				let applyEvents = events;
				if (current.reverse) {
					applyTime = current.animation.duration - applyTime;
					applyEvents = null;
				}
				let timelineCount = current.animation.timelines.length;
				let timelines = current.animation.timelines;
				if ((i == 0 && mix == 1) || blend == MixBlend.add) {
					for (let ii = 0; ii < timelineCount; ii++) {
						// Fixes issue #302 on IOS9 where mix, blend sometimes became undefined and caused assets
						// to sometimes stop rendering when using color correction, as their RGBA values become NaN.
						// (https://github.com/pixijs/pixi-spine/issues/302)
						Utils.webkit602BugfixHelper(mix, blend);
						var timeline = timelines[ii];
						if (timeline instanceof AttachmentTimeline)
							this.applyAttachmentTimeline(timeline, skeleton, applyTime, blend, true);
						else
							timeline.apply(skeleton, animationLast, applyTime, applyEvents, mix, blend, MixDirection.mixIn);
					}
				} else {
					let timelineMode = current.timelineMode;

					let firstFrame = current.timelinesRotation.length != timelineCount << 1;
					if (firstFrame) current.timelinesRotation.length = timelineCount << 1;

					for (let ii = 0; ii < timelineCount; ii++) {
						let timeline = timelines[ii];
						let timelineBlend = timelineMode[ii] == SUBSEQUENT ? blend : MixBlend.setup;
						if (timeline instanceof RotateTimeline) {
							this.applyRotateTimeline(timeline, skeleton, applyTime, mix, timelineBlend, current.timelinesRotation, ii << 1, firstFrame);
						} else if (timeline instanceof AttachmentTimeline) {
							this.applyAttachmentTimeline(timeline, skeleton, applyTime, blend, true);
						} else {
							// This fixes the WebKit 602 specific issue described at http://esotericsoftware.com/forum/iOS-10-disappearing-graphics-10109
							Utils.webkit602BugfixHelper(mix, blend);
							timeline.apply(skeleton, animationLast, applyTime, applyEvents, mix, timelineBlend, MixDirection.mixIn);
						}
					}
				}
				this.queueEvents(current, animationTime);
				events.length = 0;
				current.nextAnimationLast = animationTime;
				current.nextTrackLast = current.trackTime;
			}

			// Set slots attachments to the setup pose, if needed. This occurs if an animation that is mixing out sets attachments so
			// subsequent timelines see any deform, but the subsequent timelines don't set an attachment (eg they are also mixing out or
			// the time is before the first key).
			var setupState = this.unkeyedState + SETUP;
			var slots = skeleton.slots;
			for (var i = 0, n = skeleton.slots.length; i < n; i++) {
				var slot = slots[i];
				if (slot.attachmentState == setupState) {
					var attachmentName = slot.data.attachmentName;
					slot.setAttachment(!attachmentName ? null : skeleton.getAttachment(slot.data.index, attachmentName));
				}
			}
			this.unkeyedState += 2; // Increasing after each use avoids the need to reset attachmentState for every slot.

			this.queue.drain();
			return applied;
		}

		applyMixingFrom (to: TrackEntry, skeleton: Skeleton, blend: MixBlend) {
			let from = to.mixingFrom;
			if (from.mixingFrom) this.applyMixingFrom(from, skeleton, blend);

			let mix = 0;
			if (to.mixDuration == 0) { // Single frame mix to undo mixingFrom changes.
				mix = 1;
				if (blend == MixBlend.first) blend = MixBlend.setup;
			} else {
				mix = to.mixTime / to.mixDuration;
				if (mix > 1) mix = 1;
				if (blend != MixBlend.first) blend = from.mixBlend;
			}

			let attachments = mix < from.attachmentThreshold, drawOrder = mix < from.drawOrderThreshold;
			let timelineCount = from.animation.timelines.length;
			let timelines = from.animation.timelines;
			let alphaHold = from.alpha * to.interruptAlpha, alphaMix = alphaHold * (1 - mix);
			let animationLast = from.animationLast, animationTime = from.getAnimationTime(), applyTime = animationTime;
			let events = null;
			if (from.reverse)
				applyTime = from.animation.duration - applyTime;
			else if (mix < from.eventThreshold)
				events = this.events;

			if (blend == MixBlend.add) {
				for (let i = 0; i < timelineCount; i++)
					timelines[i].apply(skeleton, animationLast, applyTime, events, alphaMix, blend, MixDirection.mixOut);
			} else {
				let timelineMode = from.timelineMode;
				let timelineHoldMix = from.timelineHoldMix;

				let firstFrame = from.timelinesRotation.length != timelineCount << 1;
				if (firstFrame) from.timelinesRotation.length = timelineCount << 1;

				from.totalAlpha = 0;
				for (let i = 0; i < timelineCount; i++) {
					let timeline = timelines[i];
					let direction = MixDirection.mixOut;
					let timelineBlend: MixBlend;
					let alpha = 0;
					switch (timelineMode[i]) {
					case SUBSEQUENT:
						if (!drawOrder && timeline instanceof DrawOrderTimeline) continue;
						timelineBlend = blend;
						alpha = alphaMix;
						break;
					case FIRST:
						timelineBlend = MixBlend.setup;
						alpha = alphaMix;
						break;
					case HOLD_SUBSEQUENT:
						timelineBlend = blend;
						alpha = alphaHold;
						break;
					case HOLD_FIRST:
						timelineBlend = MixBlend.setup;
						alpha = alphaHold;
						break;
					default:
						timelineBlend = MixBlend.setup;
						let holdMix = timelineHoldMix[i];
						alpha = alphaHold * Math.max(0, 1 - holdMix.mixTime / holdMix.mixDuration);
						break;
					}
					from.totalAlpha += alpha;

					if (timeline instanceof RotateTimeline)
						this.applyRotateTimeline(timeline, skeleton, applyTime, alpha, timelineBlend, from.timelinesRotation, i << 1, firstFrame);
					else if (timeline instanceof AttachmentTimeline)
						this.applyAttachmentTimeline(timeline, skeleton, applyTime, timelineBlend, attachments);
					else {
						// This fixes the WebKit 602 specific issue described at http://esotericsoftware.com/forum/iOS-10-disappearing-graphics-10109
						Utils.webkit602BugfixHelper(alpha, blend);
						if (drawOrder && timeline instanceof DrawOrderTimeline && timelineBlend == MixBlend.setup)
							direction = MixDirection.mixIn;
						timeline.apply(skeleton, animationLast, applyTime, events, alpha, timelineBlend, direction);
					}
				}
			}

			if (to.mixDuration > 0) this.queueEvents(from, animationTime);
			this.events.length = 0;
			from.nextAnimationLast = animationTime;
			from.nextTrackLast = from.trackTime;

			return mix;
		}

		applyAttachmentTimeline (timeline: AttachmentTimeline, skeleton: Skeleton, time: number, blend: MixBlend, attachments: boolean) {
			var slot = skeleton.slots[timeline.slotIndex];
			if (!slot.bone.active) return;

			var frames = timeline.frames;
			if (time < frames[0]) { // Time is before first frame.
				if (blend == MixBlend.setup || blend == MixBlend.first)
					this.setAttachment(skeleton, slot, slot.data.attachmentName, attachments);
			} else
				this.setAttachment(skeleton, slot, timeline.attachmentNames[Timeline.search1(frames, time)], attachments);

			// If an attachment wasn't set (ie before the first frame or attachments is false), set the setup attachment later.
			if (slot.attachmentState <= this.unkeyedState) slot.attachmentState = this.unkeyedState + SETUP;
		}

		setAttachment (skeleton: Skeleton, slot: Slot, attachmentName: string, attachments: boolean) {
			slot.setAttachment(!attachmentName ? null : skeleton.getAttachment(slot.data.index, attachmentName));
			if (attachments) slot.attachmentState = this.unkeyedState + CURRENT;
		}

		applyRotateTimeline (timeline: Timeline, skeleton: Skeleton, time: number, alpha: number, blend: MixBlend,
			timelinesRotation: Array<number>, i: number, firstFrame: boolean) {

			if (firstFrame) timelinesRotation[i] = 0;

			if (alpha == 1) {
				timeline.apply(skeleton, 0, time, null, 1, blend, MixDirection.mixIn);
				return;
			}

			let rotateTimeline = timeline as RotateTimeline;
			let bone = skeleton.bones[rotateTimeline.boneIndex];
			if (!bone.active) return;
			let frames = rotateTimeline.frames;
			let r1 = 0, r2 = 0;
			if (time < frames[0]) {
				switch (blend) {
					case MixBlend.setup:
						bone.rotation = bone.data.rotation;
					default:
						return;
					case MixBlend.first:
						r1 = bone.rotation;
						r2 = bone.data.rotation;
				}
			} else {
				r1 = blend == MixBlend.setup ? bone.data.rotation : bone.rotation;
				r2 = bone.data.rotation + rotateTimeline.getCurveValue(time);
			}

			// Mix between rotations using the direction of the shortest route on the first frame while detecting crosses.
			let total = 0, diff = r2 - r1;
			diff -= (16384 - ((16384.499999999996 - diff / 360) | 0)) * 360;
			if (diff == 0) {
				total = timelinesRotation[i];
			} else {
				let lastTotal = 0, lastDiff = 0;
				if (firstFrame) {
					lastTotal = 0;
					lastDiff = diff;
				} else {
					lastTotal = timelinesRotation[i]; // Angle and direction of mix, including loops.
					lastDiff = timelinesRotation[i + 1]; // Difference between bones.
				}
				let current = diff > 0, dir = lastTotal >= 0;
				// Detect cross at 0 (not 180).
				if (MathUtils.signum(lastDiff) != MathUtils.signum(diff) && Math.abs(lastDiff) <= 90) {
					// A cross after a 360 rotation is a loop.
					if (Math.abs(lastTotal) > 180) lastTotal += 360 * MathUtils.signum(lastTotal);
					dir = current;
				}
				total = diff + lastTotal - lastTotal % 360; // Store loops as part of lastTotal.
				if (dir != current) total += 360 * MathUtils.signum(lastTotal);
				timelinesRotation[i] = total;
			}
			timelinesRotation[i + 1] = diff;
			bone.rotation = r1 + total * alpha;
		}

		queueEvents (entry: TrackEntry, animationTime: number) {
			let animationStart = entry.animationStart, animationEnd = entry.animationEnd;
			let duration = animationEnd - animationStart;
			let trackLastWrapped = entry.trackLast % duration;

			// Queue events before complete.
			let events = this.events;
			let i = 0, n = events.length;
			for (; i < n; i++) {
				let event = events[i];
				if (event.time < trackLastWrapped) break;
				if (event.time > animationEnd) continue; // Discard events outside animation start/end.
				this.queue.event(entry, event);
			}

			// Queue complete if completed a loop iteration or the animation.
			let complete = false;
			if (entry.loop)
				complete = duration == 0 || trackLastWrapped > entry.trackTime % duration;
			else
				complete = animationTime >= animationEnd && entry.animationLast < animationEnd;
			if (complete) this.queue.complete(entry);

			// Queue events after complete.
			for (; i < n; i++) {
				let event = events[i];
				if (event.time < animationStart) continue; // Discard events outside animation start/end.
				this.queue.event(entry, event);
			}
		}

		/** Removes all animations from all tracks, leaving skeletons in their current pose.
		 *
		 * It may be desired to use {@link AnimationState#setEmptyAnimation()} to mix the skeletons back to the setup pose,
		 * rather than leaving them in their current pose. */
		clearTracks () {
			let oldDrainDisabled = this.queue.drainDisabled;
			this.queue.drainDisabled = true;
			for (let i = 0, n = this.tracks.length; i < n; i++)
				this.clearTrack(i);
			this.tracks.length = 0;
			this.queue.drainDisabled = oldDrainDisabled;
			this.queue.drain();
		}

		/** Removes all animations from the track, leaving skeletons in their current pose.
		 *
		 * It may be desired to use {@link AnimationState#setEmptyAnimation()} to mix the skeletons back to the setup pose,
		 * rather than leaving them in their current pose. */
		clearTrack (trackIndex: number) {
			if (trackIndex >= this.tracks.length) return;
			let current = this.tracks[trackIndex];
			if (!current) return;

			this.queue.end(current);

			this.disposeNext(current);

			let entry = current;
			while (true) {
				let from = entry.mixingFrom;
				if (!from) break;
				this.queue.end(from);
				entry.mixingFrom = null;
				entry.mixingTo = null;
				entry = from;
			}

			this.tracks[current.trackIndex] = null;

			this.queue.drain();
		}

		/** Removes the {@link TrackEntry#getNext() next entry} and all entries after it for the specified entry. */
		clearNext(entry: TrackEntry) {
			this.disposeNext(entry.next);
		}

		setCurrent (index: number, current: TrackEntry, interrupt: boolean) {
			let from = this.expandToIndex(index);
			this.tracks[index] = current;
			current.previous = null;

			if (from) {
				if (interrupt) this.queue.interrupt(from);
				current.mixingFrom = from;
				from.mixingTo = current;
				current.mixTime = 0;

				// Store the interrupted mix percentage.
				if (from.mixingFrom && from.mixDuration > 0)
					current.interruptAlpha *= Math.min(1, from.mixTime / from.mixDuration);

				from.timelinesRotation.length = 0; // Reset rotation for mixing out, in case entry was mixed in.
			}

			this.queue.start(current);
		}

		/** Sets an animation by name.
	 	*
	 	* See {@link #setAnimationWith()}. */
		setAnimation (trackIndex: number, animationName: string, loop: boolean) {
			let animation = this.data.skeletonData.findAnimation(animationName);
			if (!animation) throw new Error("Animation not found: " + animationName);
			return this.setAnimationWith(trackIndex, animation, loop);
		}

		/** Sets the current animation for a track, discarding any queued animations. If the formerly current track entry was never
		 * applied to a skeleton, it is replaced (not mixed from).
		 * @param 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 {@link TrackEntry#trackEnd} determines when the track is cleared.
		 * @returns A track entry to allow further customization of animation playback. References to the track entry must not be kept
		 *         after the {@link AnimationStateListener#dispose()} event occurs. */
		setAnimationWith (trackIndex: number, animation: Animation, loop: boolean) {
			if (!animation) throw new Error("animation cannot be null.");
			let interrupt = true;
			let current = this.expandToIndex(trackIndex);
			if (current) {
				if (current.nextTrackLast == -1) {
					// Don't mix from an entry that was never applied.
					this.tracks[trackIndex] = current.mixingFrom;
					this.queue.interrupt(current);
					this.queue.end(current);
					this.disposeNext(current);
					current = current.mixingFrom;
					interrupt = false;
				} else
					this.disposeNext(current);
			}
			let entry = this.trackEntry(trackIndex, animation, loop, current);
			this.setCurrent(trackIndex, entry, interrupt);
			this.queue.drain();
			return entry;
		}

		/** Queues an animation by name.
		 *
		 * See {@link #addAnimationWith()}. */
		addAnimation (trackIndex: number, animationName: string, loop: boolean, delay: number) {
			let animation = this.data.skeletonData.findAnimation(animationName);
			if (!animation) throw new Error("Animation not found: " + animationName);
			return this.addAnimationWith(trackIndex, animation, loop, delay);
		}

		/** Adds an animation to be played after the current or last queued animation for a track. If the track is empty, it is
		 * equivalent to calling {@link #setAnimationWith()}.
		 * @param delay If > 0, sets {@link TrackEntry#delay}. If <= 0, the delay set is the duration of the previous track entry
		 *           minus any mix duration (from the {@link AnimationStateData}) plus the specified `delay` (ie the mix
		 *           ends at (`delay` = 0) or before (`delay` < 0) the previous track entry duration). If the
		 *           previous entry is looping, its next loop completion is used instead of its duration.
		 * @returns A track entry to allow further customization of animation playback. References to the track entry must not be kept
		 *         after the {@link AnimationStateListener#dispose()} event occurs. */
		addAnimationWith (trackIndex: number, animation: Animation, loop: boolean, delay: number) {
			if (!animation) throw new Error("animation cannot be null.");

			let last = this.expandToIndex(trackIndex);
			if (last) {
				while (last.next)
					last = last.next;
			}

			let entry = this.trackEntry(trackIndex, animation, loop, last);

			if (!last) {
				this.setCurrent(trackIndex, entry, true);
				this.queue.drain();
			} else {
				last.next = entry;
				entry.previous = last;
				if (delay <= 0) delay += last.getTrackComplete() - entry.mixDuration;
			}

			entry.delay = delay;
			return entry;
		}

		/** Sets an empty animation for a track, discarding any queued animations, and sets the track entry's
		 * {@link TrackEntry#mixduration}. An empty animation has no timelines and serves as a placeholder for mixing in or out.
		 *
		 * Mixing out is done by setting an empty animation with a mix duration using either {@link #setEmptyAnimation()},
		 * {@link #setEmptyAnimations()}, or {@link #addEmptyAnimation()}. 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 mixes out over one frame.
		 *
		 * Mixing in is done by first setting an empty animation, then adding an animation using
		 * {@link #addAnimation()} and on the returned track entry, set the
		 * {@link TrackEntry#setMixDuration()}. 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. */
		setEmptyAnimation (trackIndex: number, mixDuration: number) {
			let entry = this.setAnimationWith(trackIndex, AnimationState.emptyAnimation(), false);
			entry.mixDuration = mixDuration;
			entry.trackEnd = mixDuration;
			return entry;
		}

		/** Adds an empty animation to be played after the current or last queued animation for a track, and sets the track entry's
		 * {@link TrackEntry#mixDuration}. If the track is empty, it is equivalent to calling
		 * {@link #setEmptyAnimation()}.
		 *
		 * See {@link #setEmptyAnimation()}.
		 * @param delay If > 0, sets {@link TrackEntry#delay}. If <= 0, the delay set is the duration of the previous track entry
		 *           minus any mix duration plus the specified `delay` (ie the mix ends at (`delay` = 0) or
		 *           before (`delay` < 0) the previous track entry duration). If the previous entry is looping, its next
		 *           loop completion is used instead of its duration.
		 * @return A track entry to allow further customization of animation playback. References to the track entry must not be kept
		 *         after the {@link AnimationStateListener#dispose()} event occurs. */
		addEmptyAnimation (trackIndex: number, mixDuration: number, delay: number) {
			let entry = this.addAnimationWith(trackIndex, AnimationState.emptyAnimation(), false, delay <= 0 ? 1 : delay);
			entry.mixDuration = mixDuration;
			entry.trackEnd = mixDuration;
			if (delay <= 0 && entry.previous) entry.delay = entry.previous.getTrackComplete() - entry.mixDuration;
			return entry;
		}

		/** Sets an empty animation for every track, discarding any queued animations, and mixes to it over the specified mix
	 	* duration. */
		setEmptyAnimations (mixDuration: number) {
			let oldDrainDisabled = this.queue.drainDisabled;
			this.queue.drainDisabled = true;
			for (let i = 0, n = this.tracks.length; i < n; i++) {
				let current = this.tracks[i];
				if (current) this.setEmptyAnimation(current.trackIndex, mixDuration);
			}
			this.queue.drainDisabled = oldDrainDisabled;
			this.queue.drain();
		}

		expandToIndex (index: number) {
			if (index < this.tracks.length) return this.tracks[index];
			Utils.ensureArrayCapacity(this.tracks, index + 1, null);
			this.tracks.length = index + 1;
			return null;
		}

		/** @param last May be null. */
		trackEntry (trackIndex: number, animation: Animation, loop: boolean, last: TrackEntry) {
			let entry = this.trackEntryPool.obtain();
			entry.trackIndex = trackIndex;
			entry.animation = animation;
			entry.loop = loop;
			entry.holdPrevious = false;

			entry.eventThreshold = 0;
			entry.attachmentThreshold = 0;
			entry.drawOrderThreshold = 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 = Number.MAX_VALUE;
			entry.timeScale = 1;

			entry.alpha = 1;
			entry.interruptAlpha = 1;
			entry.mixTime = 0;
			entry.mixDuration = !last ? 0 : this.data.getMix(last.animation, animation);
			entry.mixBlend = MixBlend.replace;
			return entry;
		}

		disposeNext (entry: TrackEntry) {
			let next = entry.next;
			while (next) {
				this.queue.dispose(next);
				next = next.next;
			}
			entry.next = null;
		}

		_animationsChanged () {
			this.animationsChanged = false;

			this.propertyIDs.clear();

			for (let i = 0, n = this.tracks.length; i < n; i++) {
				let entry = this.tracks[i];
				if (!entry) continue;
				while (entry.mixingFrom)
					entry = entry.mixingFrom;

				do {
					if (!entry.mixingFrom || entry.mixBlend != MixBlend.add) this.computeHold(entry);
					entry = entry.mixingTo;
				} while (entry)
			}
		}

		computeHold (entry: TrackEntry) {
			let to = entry.mixingTo;
			let timelines = entry.animation.timelines;
			let timelinesCount = entry.animation.timelines.length;
			let timelineMode = entry.timelineMode;
			timelineMode.length = timelinesCount;
			let timelineHoldMix = entry.timelineHoldMix;
			timelineHoldMix.length = 0;
			let propertyIDs = this.propertyIDs;

			if (to && to.holdPrevious) {
				for (let i = 0; i < timelinesCount; i++)
					timelineMode[i] = propertyIDs.addAll(timelines[i].getPropertyIds()) ? HOLD_FIRST : HOLD_SUBSEQUENT;
				return;
			}

			outer:
			for (let i = 0; i < timelinesCount; i++) {
				let timeline = timelines[i];
				let ids = timeline.getPropertyIds();
				if (!propertyIDs.addAll(ids))
					timelineMode[i] = SUBSEQUENT;
				else if (!to || timeline instanceof AttachmentTimeline || timeline instanceof DrawOrderTimeline
					|| timeline instanceof EventTimeline || !to.animation.hasTimeline(ids)) {
					timelineMode[i] = FIRST;
				} else {
					for (let next = to.mixingTo; next; next = next.mixingTo) {
						if (next.animation.hasTimeline(ids)) continue;
						if (entry.mixDuration > 0) {
							timelineMode[i] = HOLD_MIX;
							timelineHoldMix[i] = next;
							continue outer;
						}
						break;
					}
					timelineMode[i] = HOLD_FIRST;
				}
			}
		}

		/** Returns the track entry for the animation currently playing on the track, or null if no animation is currently playing. */
		getCurrent (trackIndex: number) {
			if (trackIndex >= this.tracks.length) return null;
			return this.tracks[trackIndex];
		}

		/** Adds a listener to receive events for all track entries. */
		addListener (listener: AnimationStateListener) {
			if (!listener) throw new Error("listener cannot be null.");
			this.listeners.push(listener);
		}

		/** Removes the listener added with {@link #addListener()}. */
		removeListener (listener: AnimationStateListener) {
			let index = this.listeners.indexOf(listener);
			if (index >= 0) this.listeners.splice(index, 1);
		}

		/** Removes all listeners added with {@link #addListener()}. */
		clearListeners () {
			this.listeners.length = 0;
		}

		/** Discards all listener notifications that have not yet been delivered. This can be useful to call from an
		 * {@link AnimationStateListener} when it is known that further notifications that may have been already queued for delivery
		 * are not wanted because new animations are being set. */
		clearListenerNotifications () {
			this.queue.clear();
		}
	}

	/** Stores settings and other state for the playback of an animation on an {@link AnimationState} track.
	 *
	 * References to a track entry must not be kept after the {@link AnimationStateListener#dispose()} event occurs. */
	export class TrackEntry {
		/** The animation to apply for this track entry. */
		animation: Animation;

		previous: TrackEntry;

		/** The animation queued to start after this animation, or null. `next` makes up a linked list. */
		next: TrackEntry;

		/** The track entry for the previous animation when mixing from the previous animation to this animation, or null if no
		 * mixing is currently occuring. When mixing from multiple animations, `mixingFrom` makes up a linked list. */
		mixingFrom: TrackEntry;

		/** The track entry for the next animation when mixing from this animation to the next animation, or null if no mixing is
		 * currently occuring. When mixing to multiple animations, `mixingTo` makes up a linked list. */
		mixingTo: TrackEntry;

		/** The listener for events generated by this track entry, or null.
		 *
		 * A track entry returned from {@link AnimationState#setAnimation()} is already the current animation
		 * for the track, so the track entry listener {@link AnimationStateListener#start()} will not be called. */
		listener: AnimationStateListener;

		/** The index of the track where this track entry is either current or queued.
		 *
		 * See {@link AnimationState#getCurrent()}. */
		trackIndex: number;

		/** If true, the animation will repeat. If false it will not, instead its last frame is applied if played beyond its
		 * duration. */
		loop: boolean;

		/** If true, when mixing from the previous animation to this animation, the previous animation is applied as normal instead
		 * of being mixed out.
		 *
		 * When mixing between animations that key the same property, if a lower track also keys that property then the value will
		 * briefly dip toward the lower track value during the mix. This happens because the first animation mixes from 100% to 0%
		 * while the second animation mixes from 0% to 100%. Setting `holdPrevious` to true applies the first animation
		 * at 100% during the mix so the lower track value is overwritten. Such dipping does not occur on the lowest track which
		 * keys the property, only when a higher track also keys the property.
		 *
		 * Snapping will occur if `holdPrevious` is true and this animation does not key all the same properties as the
		 * previous animation. */
		holdPrevious: boolean;

		reverse: boolean;

		/** When the mix percentage ({@link #mixTime} / {@link #mixDuration}) is less than the
		 * `eventThreshold`, 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. */
		eventThreshold: number;

		/** When the mix percentage ({@link #mixtime} / {@link #mixDuration}) is less than the
		 * `attachmentThreshold`, 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. */
		attachmentThreshold: number;

		/** When the mix percentage ({@link #mixTime} / {@link #mixDuration}) is less than the
		 * `drawOrderThreshold`, 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. */
		drawOrderThreshold: number;

		/** Seconds when this animation starts, both initially and after looping. Defaults to 0.
		 *
		 * When changing the `animationStart` time, it often makes sense to set {@link #animationLast} to the same
		 * value to prevent timeline keys before the start time from triggering. */
		animationStart: number;

		/** Seconds for the last frame of this animation. Non-looping animations won't play past this time. Looping animations will
		 * loop back to {@link #animationStart} at this time. Defaults to the animation {@link Animation#duration}. */
		animationEnd: number;


		/** The time in seconds this animation was last applied. Some timelines use this for one-time triggers. Eg, when this
		 * animation is applied, event timelines will fire all events between the `animationLast` time (exclusive) and
		 * `animationTime` (inclusive). Defaults to -1 to ensure triggers on frame 0 happen the first time this animation
		 * is applied. */
		animationLast: number;

		nextAnimationLast: number;

		/** Seconds to postpone playing the animation. When this track entry is the current track entry, `delay`
		 * postpones incrementing the {@link #trackTime}. When this track entry is queued, `delay` 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 {@link TrackEntry#trackTime} >= this track entry's `delay`).
		 *
		 * {@link #timeScale} affects the delay. */
		delay: number;

		/** Current time in seconds this track entry has been the current track entry. The track time determines
		 * {@link #animationTime}. The track time can be set to start the animation at a time other than 0, without affecting
		 * looping. */
		trackTime: number;

		trackLast: number; nextTrackLast: number;

		/** 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.
		 *
		 * It may be desired to use {@link AnimationState#addEmptyAnimation()} rather than have the animation
		 * abruptly cease being applied. */
		trackEnd: number;

		/** Multiplier for the delta time when this track entry is updated, causing time for this animation to pass slower or
		 * faster. Defaults to 1.
		 *
		 * {@link #mixTime} is not affected by track entry time scale, so {@link #mixDuration} may need to be adjusted to
		 * match the animation speed.
		 *
		 * When using {@link AnimationState#addAnimation()} with a `delay` <= 0, note the
		 * {@link #delay} is set using the mix duration from the {@link AnimationStateData}, assuming time scale to be 1. If
		 * the time scale is not 1, the delay may need to be adjusted.
		 *
		 * See AnimationState {@link AnimationState#timeScale} for affecting all animations. */
		timeScale: number;

		/** Values < 1 mix this animation with the skeleton's current pose (usually the pose resulting from lower tracks). Defaults
		 * to 1, which overwrites the skeleton's current pose with this animation.
		 *
		 * Typically track 0 is used to completely pose the skeleton, then alpha is used on higher tracks. It doesn't make sense to
		 * use alpha on track 0 if the skeleton pose is from the last frame render. */
		alpha: number;

		/** Seconds from 0 to the {@link #getMixDuration()} when mixing from the previous animation to this animation. May be
		 * slightly more than `mixDuration` when the mix is complete. */
		mixTime: number;

		/** Seconds for mixing from the previous animation to this animation. Defaults to the value provided by AnimationStateData
		 * {@link AnimationStateData#getMix()} based on the animation before this animation (if any).
		 *
		 * A mix duration of 0 still mixes out over one frame to provide the track entry being mixed out a chance to revert the
		 * properties it was animating.
		 *
		 * The `mixDuration` can be set manually rather than use the value from
		 * {@link AnimationStateData#getMix()}. In that case, the `mixDuration` can be set for a new
		 * track entry only before {@link AnimationState#update(float)} is first called.
		 *
		 * When using {@link AnimationState#addAnimation()} with a `delay` <= 0, note the
		 * {@link #delay} is set using the mix duration from the {@link AnimationStateData}, not a mix duration set
		 * afterward. */
		mixDuration: number; interruptAlpha: number; totalAlpha: number;

		/** Controls how properties keyed in the animation are mixed with lower tracks. Defaults to {@link MixBlend#replace}, which
		 * replaces the values from the lower tracks with the animation values. {@link MixBlend#add} adds the animation values to
		 * the values from the lower tracks.
		 *
		 * The `mixBlend` can be set for a new track entry only before {@link AnimationState#apply()} is first
		 * called. */
		mixBlend = MixBlend.replace;
		timelineMode = new Array<number>();
		timelineHoldMix = new Array<TrackEntry>();
		timelinesRotation = new Array<number>();

		reset () {
			this.next = null;
			this.previous = null;
			this.mixingFrom = null;
			this.mixingTo = null;
			this.animation = null;
			this.listener = null;
			this.timelineMode.length = 0;
			this.timelineHoldMix.length = 0;
			this.timelinesRotation.length = 0;
		}

		/** Uses {@link #trackTime} to compute the `animationTime`, which is between {@link #animationStart}
		 * and {@link #animationEnd}. When the `trackTime` is 0, the `animationTime` is equal to the
		 * `animationStart` time. */
		getAnimationTime () {
			if (this.loop) {
				let duration = this.animationEnd - this.animationStart;
				if (duration == 0) return this.animationStart;
				return (this.trackTime % duration) + this.animationStart;
			}
			return Math.min(this.trackTime + this.animationStart, this.animationEnd);
		}

		setAnimationLast(animationLast: number) {
			this.animationLast = animationLast;
			this.nextAnimationLast = animationLast;
		}

		/** Returns true if at least one loop has been completed.
		 *
		 * See {@link AnimationStateListener#complete()}. */
		isComplete () {
			return this.trackTime >= this.animationEnd - this.animationStart;
		}

		/** Resets the rotation directions for mixing this entry's rotate timelines. This can be useful to avoid bones rotating the
		 * long way around when using {@link #alpha} and starting animations on other tracks.
		 *
		 * Mixing with {@link MixBlend#replace} involves finding a rotation between two others, which has two possible solutions:
		 * the short way or the long way around. The two rotations likely change over time, so which direction is the short or long
		 * way also changes. If the short way was always chosen, bones would 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. */
		resetRotationDirections () {
			this.timelinesRotation.length = 0;
		}

		getTrackComplete() {
			let duration = this.animationEnd - this.animationStart;
			if (duration != 0) {
				if (this.loop) return duration * (1 + ((this.trackTime / duration) | 0)); // Completion of next loop.
				if (this.trackTime < duration) return duration; // Before duration.
			}
			return this.trackTime; // Next update.
		}
	}

	export class EventQueue {
		objects: Array<any> = [];
		drainDisabled = false;
		animState: AnimationState;

		constructor(animState: AnimationState) {
			this.animState = animState;
		}

		start (entry: TrackEntry) {
			this.objects.push(EventType.start);
			this.objects.push(entry);
			this.animState.animationsChanged = true;
		}

		interrupt (entry: TrackEntry) {
			this.objects.push(EventType.interrupt);
			this.objects.push(entry);
		}

		end (entry: TrackEntry) {
			this.objects.push(EventType.end);
			this.objects.push(entry);
			this.animState.animationsChanged = true;
		}

		dispose (entry: TrackEntry) {
			this.objects.push(EventType.dispose);
			this.objects.push(entry);
		}

		complete (entry: TrackEntry) {
			this.objects.push(EventType.complete);
			this.objects.push(entry);
		}

		event (entry: TrackEntry, event: Event) {
			this.objects.push(EventType.event);
			this.objects.push(entry);
			this.objects.push(event);
		}

		drain () {
			if (this.drainDisabled) return;
			this.drainDisabled = true;

			let objects = this.objects;
			let listeners = this.animState.listeners;

			for (let i = 0; i < objects.length; i += 2) {
				let type = objects[i] as EventType;
				let entry = objects[i + 1] as TrackEntry;
				switch (type) {
				case EventType.start:
					if (entry.listener && entry.listener.start) entry.listener.start(entry);
					for (let ii = 0; ii < listeners.length; ii++)
						if (listeners[ii].start) listeners[ii].start(entry);
					break;
				case EventType.interrupt:
					if (entry.listener && entry.listener.interrupt) entry.listener.interrupt(entry);
					for (let ii = 0; ii < listeners.length; ii++)
						if (listeners[ii].interrupt) listeners[ii].interrupt(entry);
					break;
				case EventType.end:
					if (entry.listener && entry.listener.end) entry.listener.end(entry);
					for (let ii = 0; ii < listeners.length; ii++)
						if (listeners[ii].end) listeners[ii].end(entry);
					// Fall through.
				case EventType.dispose:
					if (entry.listener && entry.listener.dispose) entry.listener.dispose(entry);
					for (let ii = 0; ii < listeners.length; ii++)
						if (listeners[ii].dispose) listeners[ii].dispose(entry);
					this.animState.trackEntryPool.free(entry);
					break;
				case EventType.complete:
					if (entry.listener && entry.listener.complete) entry.listener.complete(entry);
					for (let ii = 0; ii < listeners.length; ii++)
						if (listeners[ii].complete) listeners[ii].complete(entry);
					break;
				case EventType.event:
					let event = objects[i++ + 2] as Event;
					if (entry.listener && entry.listener.event) entry.listener.event(entry, event);
					for (let ii = 0; ii < listeners.length; ii++)
						if (listeners[ii].event) listeners[ii].event(entry, event);
					break;
				}
			}
			this.clear();

			this.drainDisabled = false;
		}

		clear () {
			this.objects.length = 0;
		}
	}

	export enum EventType {
		start, interrupt, end, dispose, complete, event
	}

	/** The interface to implement for receiving TrackEntry events. It is always safe to call AnimationState methods when receiving
	 * events.
	 *
	 * See TrackEntry {@link TrackEntry#listener} and AnimationState
	 * {@link AnimationState#addListener()}. */
	export interface AnimationStateListener {
		/** Invoked when this entry has been set as the current entry. */
		start (entry: TrackEntry): void;

		/** Invoked when another entry has replaced this entry as the current entry. This entry may continue being applied for
		 * mixing. */
		interrupt (entry: TrackEntry): void;

		/** Invoked when this entry is no longer the current entry and will never be applied again. */
		end (entry: TrackEntry): void;

		/** Invoked when this entry will be disposed. This may occur without the entry ever being set as the current entry.
		 * References to the entry should not be kept after dispose is called, as it may be destroyed or reused. */
		dispose (entry: TrackEntry): void;

		/** Invoked every time this entry's animation completes a loop. */
		complete (entry: TrackEntry): void;

		/** Invoked when this entry's animation triggers an event. */
		event (entry: TrackEntry, event: Event): void;
	}

	export abstract class AnimationStateAdapter implements AnimationStateListener {
		start (entry: TrackEntry) {
		}

		interrupt (entry: TrackEntry) {
		}

		end (entry: TrackEntry) {
		}

		dispose (entry: TrackEntry) {
		}

		complete (entry: TrackEntry) {
		}

		event (entry: TrackEntry, event: Event) {
		}
	}

	/** 1. A previously applied timeline has set this property.
	 *
	 * Result: Mix from the current pose to the timeline pose. */
	const SUBSEQUENT = 0;
	/** 1. This is the first timeline to set this property.
	 * 2. The next track entry applied after this one does not have a timeline to set this property.
	 *
	 * Result: Mix from the setup pose to the timeline pose. */
	const FIRST = 1;
	/** 1) A previously applied timeline has set this property.<br>
	 * 2) The next track entry to be applied does have a timeline to set this property.<br>
	 * 3) The next track entry after that one does not have a timeline to set this property.<br>
	 * Result: Mix from the current pose to the timeline pose, but do not mix out. This avoids "dipping" when crossfading
	 * animations that key the same property. A subsequent timeline will set this property using a mix. */
	const HOLD_SUBSEQUENT = 2;
	/** 1) This is the first timeline to set this property.<br>
	 * 2) The next track entry to be applied does have a timeline to set this property.<br>
	 * 3) The next track entry after that one does not have a timeline to set this property.<br>
	 * Result: Mix from the setup pose to the timeline pose, but do not mix out. This avoids "dipping" when crossfading animations
	 * that key the same property. A subsequent timeline will set this property using a mix. */
	const HOLD_FIRST = 3;
	/** 1. This is the first timeline to set this property.
	 * 2. The next track entry to be applied does have a timeline to set this property.
	 * 3. The next track entry after that one does have a timeline to set this property.
	 * 4. timelineHoldMix stores the first subsequent track entry that does not have a timeline to set this property.
	 *
	 * Result: The same as HOLD except the mix percentage from the timelineHoldMix track entry is used. This handles when more than
	 * 2 track entries in a row have a timeline that sets the same property.
	 *
	 * Eg, A -> B -> C -> D where A, B, and C have a timeline setting same property, but D does not. When A is applied, to avoid
	 * "dipping" A is not mixed out, however D (the first entry that doesn't set the property) mixing in is used to mix out A
	 * (which affects B and C). Without using D to mix out, A would be applied fully until mixing completes, then snap into
	 * place. */
	const HOLD_MIX = 4;

	const SETUP = 1;
	const CURRENT = 2;

	let _emptyAnimation: Animation = null;
}