import { AnimationClip } from "./AnimationClip.ts";
import type { Track } from "./Track.ts";

/** Extracts a portion of a clip between startFrame and endFrame. */
function subclip(
	clip: AnimationClip,
	name: string,
	startFrame: number,
	endFrame: number,
	fps = 30,
): AnimationClip {
	const startTime = startFrame / fps;
	const endTime = endFrame / fps;
	const duration = endTime - startTime;

	const newTracks: Track[] = [];
	for (const track of clip.tracks) {
		const times = track.times;
		const values = track.values;
		const size = track.itemSize;

		const newTimes: number[] = [];
		const newValues: number[] = [];

		for (let i = 0; i < times.length; i++) {
			const t = times[i];
			if (t < startTime || t > endTime) continue;
			newTimes.push(t - startTime);
			for (let j = 0; j < size; j++) newValues.push(values[i * size + j]);
		}

		if (newTimes.length === 0) continue;

		const TrackCtor = track.constructor as new (
			name: string,
			times: Float32Array,
			values: Float32Array,
		) => Track;
		newTracks.push(
			new TrackCtor(
				track.name,
				new Float32Array(newTimes),
				new Float32Array(newValues),
			),
		);
	}

	return new AnimationClip(name, duration, newTracks);
}

/** Converts a clip to additive form by subtracting the reference pose. */
function makeClipAdditive(
	clip: AnimationClip,
	referenceFrame = 0,
	referenceClip: AnimationClip = clip,
): AnimationClip {
	const fps = 30;
	const referenceTime = referenceFrame / fps;

	for (const track of clip.tracks) {
		const refTrack = referenceClip.tracks.find((t) => t.name === track.name);
		if (!refTrack) continue;

		const refValues = refTrack.getValueAtTime(referenceTime);
		const values = track.values;
		const size = track.itemSize;

		for (let i = 0; i < track.times.length; i++) {
			for (let j = 0; j < size; j++) {
				values[i * size + j] -= refValues[j];
			}
		}
	}

	return clip;
}

/** Utility functions for clipping and modifying AnimationClips. */
export interface AnimationUtilsType {
	subclip(
		clip: AnimationClip,
		name: string,
		startFrame: number,
		endFrame: number,
		fps?: number,
	): AnimationClip;
	makeClipAdditive(
		clip: AnimationClip,
		referenceFrame?: number,
		referenceClip?: AnimationClip,
	): AnimationClip;
}

export const AnimationUtils: AnimationUtilsType = { subclip, makeClipAdditive };