import type { AnimationAsset, TextureAsset } from './Asset';
import { textOf } from './Properties';

export const PLAYBACKS = ['loop', 'once', 'pingpong'] as const;
export type Playback = (typeof PLAYBACKS)[number];

export interface FrameAt {
  /** -1 for an animation without frames. */
  index: number;
  /** Only `once` ever finishes; it then holds its last frame. */
  finished: boolean;
}

/** Slack for `time * fps`: six ticks of 1/60 s sum to 0.09999999999999999, which at 10 fps is frame 1. */
const STEP_EPSILON = 1e-6;

/** Which frame shows at `time` seconds after the animation started. */
export function frameAt(count: number, fps: number, playback: Playback, time: number): FrameAt {
  if (count <= 0) return { index: -1, finished: false };
  if (!Number.isFinite(fps) || fps <= 0 || !(time > 0)) return { index: 0, finished: false };
  const step = Math.floor(time * fps + STEP_EPSILON);
  switch (playback) {
    case 'loop':
      return { index: step % count, finished: false };
    case 'once':
      return step >= count ? { index: count - 1, finished: true } : { index: step, finished: false };
    case 'pingpong': {
      if (count === 1) return { index: 0, finished: false };
      const period = 2 * count - 2;
      const at = step % period;
      return { index: at < count ? at : period - at, finished: false };
    }
  }
}

export function playbackOf(asset: AnimationAsset): Playback {
  const value = textOf(asset.props.playback ?? 'loop');
  return (PLAYBACKS as readonly string[]).includes(value) ? (value as Playback) : 'loop';
}

export function fpsOf(asset: AnimationAsset): number {
  const fps = Number(asset.props.fps);
  return Number.isFinite(fps) && fps > 0 ? fps : 0;
}

export function animationFrameAt(asset: AnimationAsset, time: number): FrameAt {
  return frameAt(asset.frames.length, fpsOf(asset), playbackOf(asset), time);
}

/** Seconds for one pass through the frames. */
export function animationDuration(asset: AnimationAsset): number {
  const fps = fpsOf(asset);
  return fps > 0 ? asset.frames.length / fps : 0;
}

/** What an animation made from a texture plays: its frames in order, the whole picture when it has none. */
export function framesOfTexture(texture: TextureAsset): string[] {
  return texture.frames.length > 0 ? texture.frames.map((f) => f.id) : [texture.id];
}