function lerp(start: number, end: number, t: number): number {
	return start + (end - start) * t
}

export interface AnimationLoop {
	/** User callback to be called on each animation frame. */
	callback: FrameRequestCallback
	/** {@link loopFrame} bound to this loop. */
	frame: FrameRequestCallback
	/** The current frame id returned by {@link requestAnimationFrame}. */
	frame_id: number
}

export function animationLoop(callback: FrameRequestCallback): AnimationLoop {
	const loop: AnimationLoop = {
		callback: callback,
		frame: t => loopFrame(loop, t),
		frame_id: 0,
	}
	return loop
}
export function loopFrame(loop: AnimationLoop, time: number): void {
	loop.frame_id = requestAnimationFrame(loop.frame)
	loop.callback(time)
}
export function loopStart(loop: AnimationLoop): void {
	loop.frame_id ||= requestAnimationFrame(loop.frame)
}
export function loopClear(loop: AnimationLoop): void {
	cancelAnimationFrame(loop.frame_id)
	loop.frame_id = 0
}

export const DEFAULT_TARGET_FPS = 44

export interface FrameIterationsLimit {
	target_fps: number
	last_timestamp: number
}

export function frameIterationsLimit(
	target_fps: number = DEFAULT_TARGET_FPS,
): FrameIterationsLimit {
	return {
		target_fps,
		last_timestamp: performance.now(),
	}
}
export function calcIterations(limit: FrameIterationsLimit, current_time: number): number {
	let target_ms  = 1000 / limit.target_fps
	let delta_time = current_time - limit.last_timestamp
	let times      = Math.floor(delta_time / target_ms)
	limit.last_timestamp += times * target_ms
	return times
}

export interface AlphaUpdateSteps {
	increment: number
	decrement: number
}
export const DEFAULT_ALPHA_UPDATE_STEPS: AlphaUpdateSteps = {
	increment: 0.03,
	decrement: 0.005,
}
export const updateAlpha = (
	alpha: number,
	is_playing: boolean,
	update_steps = DEFAULT_ALPHA_UPDATE_STEPS,
): number => {
	return is_playing
		? lerp(alpha, 1, update_steps.increment)
		: lerp(alpha, 0, update_steps.decrement)
}

export const DEFAULT_BUMP_TIMEOUT_DURATION = 2000

export const bump = (
	bump_end: number,
	duration: number = DEFAULT_BUMP_TIMEOUT_DURATION,
): number => {
	const start = performance.now()
	const end = start + duration
	return end > bump_end ? end : bump_end
}