// Runs ATL timelines (see backend/app/converter/atl.py) on the properties of one shown image.

export type AtlProps = Record<string, any>;

export interface AtlBlock {
  steps: AtlStep[];
  repeat: null | true | number;
}

export type AtlStep =
  | { op: "set"; props: AtlProps }
  | { op: "move"; warp: "linear" | "ease" | "easein" | "easeout"; t: number; props: AtlProps }
  | { op: "pause"; t: number }
  | { op: "parallel"; blocks: AtlBlock[] }
  | { op: "choice"; blocks: { w: number; block: AtlBlock }[] }
  | { op: "block"; block: AtlBlock }
  | { op: "on"; events: string[]; block: AtlBlock }
  | { op: "use"; name: string };

export interface AtlHost {
  /** Timeline of a named animated transform. */
  block(name: string): AtlBlock | null;
  /** Properties of a named static transform. */
  props(name: string): AtlProps | null;
  /** Called after every change of the working properties. */
  apply(props: AtlProps): void;
}

const SHOW_EVENTS = new Set(["show", "appear", "default", "start", "update", "replace"]);
const HIDE_EVENTS = new Set(["hide", "replaced"]);
const NEUTRAL: AtlProps = {
  alpha: 1, zoom: 1, xzoom: 1, yzoom: 1, rotate: 0, xoffset: 0, yoffset: 0,
  xpos: 0, ypos: 0, xanchor: 0, yanchor: 0, xalign: 0, yalign: 0, xcenter: 0, ycenter: 0,
};
const MAX_DEPTH = 16;

class Stopped extends Error {}

const curves = {
  linear: (t: number) => t,
  ease: (t: number) => 0.5 - Math.cos(Math.PI * t) / 2,
  easein: (t: number) => Math.cos((1 - t) * Math.PI / 2),
  easeout: (t: number) => 1 - Math.cos(t * Math.PI / 2),
};

function nextFrame() {
  return new Promise<number>((resolve) => requestAnimationFrame(resolve));
}

export class AtlRunner {
  private token = 0;

  constructor(private host: AtlHost, private props: AtlProps) {}

  /** Start the timeline; resolves when it ends (never, for endless loops) or is stopped. */
  async start(block: AtlBlock): Promise<void> {
    const token = ++this.token;
    try {
      await this.run(block, token, 0, "show");
    } catch (err) {
      if (!(err instanceof Stopped)) throw err;
    }
  }

  stop() {
    this.token++;
  }

  /** Run the `on hide` handler of the block, if any; resolves once it has finished. */
  async hide(block: AtlBlock): Promise<void> {
    const handler = this.handlers(block, HIDE_EVENTS);
    this.stop();
    if (!handler.length) return;
    const token = ++this.token;
    try {
      for (const b of handler) await this.run(b, token, 0, "hide");
    } catch (err) {
      if (!(err instanceof Stopped)) throw err;
    }
  }

  hasHideHandler(block: AtlBlock): boolean {
    return this.handlers(block, HIDE_EVENTS).length > 0;
  }

  private handlers(block: AtlBlock, events: Set<string>, depth = 0): AtlBlock[] {
    if (depth > MAX_DEPTH) return [];
    const out: AtlBlock[] = [];
    for (const step of block.steps) {
      if (step.op === "on" && step.events.some((e) => events.has(e))) out.push(step.block);
      else if (step.op === "parallel") for (const b of step.blocks) out.push(...this.handlers(b, events, depth + 1));
      else if (step.op === "block") out.push(...this.handlers(step.block, events, depth + 1));
      else if (step.op === "use") {
        const named = this.host.block(step.name);
        if (named) out.push(...this.handlers(named, events, depth + 1));
      }
    }
    return out;
  }

  private alive(token: number) {
    if (token !== this.token) throw new Stopped();
  }

  private apply() {
    this.host.apply(this.props);
  }

  private async run(block: AtlBlock, token: number, depth: number, event: string): Promise<void> {
    if (depth > MAX_DEPTH) throw new Error("ATL: слишком глубокая вложенность");
    let loops = 0;
    for (;;) {
      const startedAt = performance.now();
      let waited = false;
      for (let i = 0; i < block.steps.length; i++) {
        this.alive(token);
        const step = block.steps[i];
        if (step.op === "on") {
          // `on` statements form an event loop: run the show-time handler, then wait for hide
          const matching = block.steps.filter((s) => s.op === "on" && s.events.some((e) => (event === "hide" ? HIDE_EVENTS : SHOW_EVENTS).has(e)));
          for (const handler of matching) await this.run((handler as { block: AtlBlock }).block, token, depth + 1, event);
          if (event === "hide") return;
          await new Promise<void>(() => {}); // idle until stopped
        }
        if (await this.step(step, token, depth, event)) waited = true;
      }
      loops++;
      if (block.repeat === null) return;
      if (block.repeat !== true && loops >= block.repeat) return;
      // a loop without any waiting step would freeze the page: yield one frame per turn
      if (!waited && performance.now() - startedAt < 1) await nextFrame();
    }
  }

  /** Returns true when the step took time. */
  private async step(step: AtlStep, token: number, depth: number, event: string): Promise<boolean> {
    switch (step.op) {
      case "set":
        Object.assign(this.props, step.props);
        this.apply();
        return false;
      case "pause":
        await this.sleep(step.t, token);
        return step.t > 0;
      case "move":
        await this.move(step, token);
        return step.t > 0;
      case "parallel":
        await Promise.all(step.blocks.map((b) => this.run(b, token, depth + 1, event)));
        return true;
      case "choice": {
        const total = step.blocks.reduce((s, b) => s + b.w, 0);
        let pick = Math.random() * total;
        const chosen = step.blocks.find((b) => (pick -= b.w) < 0) ?? step.blocks[step.blocks.length - 1];
        if (chosen) await this.run(chosen.block, token, depth + 1, event);
        return true;
      }
      case "block":
        await this.run(step.block, token, depth + 1, event);
        return true;
      case "use": {
        const named = this.host.block(step.name);
        if (named) await this.run(named, token, depth + 1, event);
        else {
          const props = this.host.props(step.name);
          if (props) {
            Object.assign(this.props, props);
            this.apply();
          }
        }
        return true;
      }
      case "on":
        return false;
    }
  }

  private async sleep(seconds: number, token: number) {
    const end = performance.now() + seconds * 1000;
    while (performance.now() < end) {
      await nextFrame();
      this.alive(token);
    }
  }

  /** Value a property has right now, including values implied by its aliases (xalign <- xpos). */
  private current(key: string): any {
    const p = this.props;
    const pair = (a: string, b: string, fa = 0, fb = 0) => [p[a] ?? fa, p[b] ?? fb];
    switch (key) {
      case "xalign": return p.xalign ?? p.xpos ?? 0;
      case "yalign": return p.yalign ?? p.ypos ?? 0;
      case "xcenter": return p.xcenter ?? p.xpos ?? 0;
      case "ycenter": return p.ycenter ?? p.ypos ?? 0;
      case "pos": return p.pos ?? pair("xpos", "ypos");
      case "align": return p.align ?? [p.xalign ?? p.xpos ?? 0, p.yalign ?? p.ypos ?? 0];
      case "anchor": return p.anchor ?? pair("xanchor", "yanchor");
      default: return p[key] ?? NEUTRAL[key] ?? 0;
    }
  }

  private async move(step: Extract<AtlStep, { op: "move" }>, token: number) {
    const from: AtlProps = {};
    for (const key of Object.keys(step.props)) from[key] = this.current(key);
    const curve = curves[step.warp] ?? curves.linear;
    const start = performance.now();
    const duration = step.t * 1000;
    while (duration > 0) {
      await nextFrame();
      this.alive(token);
      const raw = Math.min(1, (performance.now() - start) / duration);
      const k = curve(raw);
      for (const [key, to] of Object.entries(step.props)) this.props[key] = mix(from[key], to, k);
      this.apply();
      if (raw >= 1) return;
    }
    Object.assign(this.props, step.props);
    this.apply();
  }
}

function mix(a: any, b: any, k: number): any {
  if (typeof a === "number" && typeof b === "number") return a + (b - a) * k;
  if (Array.isArray(a) && Array.isArray(b) && a.length === b.length) return a.map((x, i) => mix(x, b[i], k));
  return k >= 1 ? b : a;
}