/* =====================================================================
   아바타 v3 반응 클립 재생기 — 결정문 §6.1 키프레임 보간·엔벨로프·합성.
   순수 함수뿐이다. 시간은 인자로만 받는다.
   ===================================================================== */

import { mirrorDelta, type ChannelDelta, type ChannelId } from "./channels";
import type { ClipEase, Keyframe, ReactionClip } from "./clipCatalog";

function ease(kind: ClipEase, t: number): number {
  switch (kind) {
    case "in":
      return t * t;
    case "out":
      return 1 - (1 - t) * (1 - t);
    case "inOut":
      return 3 * t * t - 2 * t * t * t;
    case "hold":
      return t >= 1 ? 1 : 0;
    case "linear":
    default:
      return t;
  }
}

function sampleTrack(frames: readonly Keyframe[], tMs: number): number {
  const first = frames[0];
  if (tMs <= first[0]) return first[1];
  const last = frames[frames.length - 1];
  if (tMs >= last[0]) return last[1];
  for (let i = 1; i < frames.length; i++) {
    const [t1, v1, arrivalEase] = frames[i];
    if (tMs > t1) continue;
    const [t0, v0] = frames[i - 1];
    const span = t1 - t0;
    const localT = span <= 0 ? 1 : (tMs - t0) / span;
    const eased = ease(arrivalEase ?? "linear", localT);
    return v0 + (v1 - v0) * eased;
  }
  return last[1];
}

/** 클립의 tMs 시점 채널 delta(가산값). t가 구간 밖이면 빈 delta. */
export function sampleClip(clip: ReactionClip, tMs: number): ChannelDelta {
  if (tMs < 0 || tMs > clip.durationMs) return {};
  const out: ChannelDelta = {};
  for (const id of Object.keys(clip.tracks) as ChannelId[]) {
    const frames = clip.tracks[id];
    if (!frames || frames.length === 0) continue;
    out[id] = sampleTrack(frames, tMs);
  }
  return out;
}

/** fadeIn→hold→fadeOut 엔벨로프(0..1). 구간 밖은 0. */
export function envelope(clip: ReactionClip, tMs: number): number {
  if (tMs < 0 || tMs > clip.durationMs) return 0;
  const { fadeInMs, fadeOutMs, durationMs } = clip;
  if (fadeInMs > 0 && tMs < fadeInMs) return tMs / fadeInMs;
  const fadeOutStart = durationMs - fadeOutMs;
  if (fadeOutMs > 0 && tMs > fadeOutStart) return (durationMs - tMs) / fadeOutMs;
  return 1;
}

export interface ResolveClipOptions {
  weight?: number;
  mirror?: boolean;
}

/** sampleClip × envelope × weight, mirror면 좌우 반전까지 적용한 최종 delta. */
export function resolveClipDelta(clip: ReactionClip, tMs: number, opts: ResolveClipOptions = {}): ChannelDelta {
  const raw = sampleClip(clip, tMs);
  const scale = envelope(clip, tMs) * (opts.weight ?? 1);
  const out: ChannelDelta = {};
  for (const id of Object.keys(raw) as ChannelId[]) {
    out[id] = (raw[id] as number) * scale;
  }
  return opts.mirror ? mirrorDelta(out) : out;
}