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// The On Air frame director, reduced to its rules: signals in, one frame out.
type Mode = 'listening' | 'waiting' | 'speaking' | 'held';

const T = {
  hold: 1.2, blinkMin: 3, blinkMax: 6.5, blink: 0.14, nod: 0.9, smile: 1.6, laugh: 1.4,
  snapMs: 70, fadeMs: 350, maxStep: 0.1, laughOn: ['playful', 'happy', 'excited'],
};

/** A linear congruential generator: the same seed gives the same blinks everywhere. */
const nextSeed = (seed: number) => (Math.imul(seed, 1664525) + 1013904223) >>> 0;

export class Director {
  private t = 0;
  private mode: Mode | null = null;
  private since = 0;
  private nextBlink: number;
  private blinkUntil = -1;
  private reaction: { frame: string; until: number } | null = null;
  private reactions = 0;
  private pieces: number | null = null;
  private emotion: string | null = null;
  private current = '';

  constructor(private frames: Set<string>, private seed = 1) {
    this.nextBlink = this.drawBlink();
  }

  private random() { this.seed = nextSeed(this.seed); return this.seed / 2 ** 32; }
  private drawBlink() { return this.t + T.blinkMin + this.random() * (T.blinkMax - T.blinkMin); }
  private has(frame: string | null): frame is string { return !!frame && this.frames.has(frame); }

  step(mode: Mode, replyEmotion: string | null, heardPieces: number, dt: number) {
    this.t += Math.max(0, Math.min(dt, T.maxStep));        // a hidden tab is not a jump
    if (mode !== this.mode) { this.mode = mode; this.since = this.t; this.reaction = null; }
    if (mode === 'listening' && this.pieces !== null && heardPieces > this.pieces) {
      const frame = this.reactions++ % 2 === 0 ? 'nod' : 'smile';
      if (this.has(frame)) this.reaction = { frame, until: this.t + (frame === 'nod' ? T.nod : T.smile) };
    }
    this.pieces = heardPieces;
    if (mode === 'speaking' && replyEmotion && replyEmotion !== this.emotion
        && T.laughOn.includes(replyEmotion) && this.has('laugh')) {
      this.reaction = { frame: 'laugh', until: this.t + T.laugh };
    }
    this.emotion = replyEmotion;
    if (this.reaction && this.t >= this.reaction.until) this.reaction = null;

    const settled = this.t - this.since >= T.hold;
    let frame: string;
    if (this.reaction) frame = this.reaction.frame;
    else if (mode === 'waiting' && this.has('thinking')) frame = 'thinking';
    else if (mode === 'listening' && settled && this.has('listening')) frame = 'listening';
    else {
      const wanted = mode === 'waiting' || (mode === 'listening' && settled) ? 'warm' : replyEmotion ?? 'warm';
      frame = this.has(wanted) ? wanted : 'default';        // a frame the set lacks falls back
    }
    if (frame === 'listening' && this.has('blink')) {
      if (this.t >= this.nextBlink) { this.blinkUntil = this.t + T.blink; this.nextBlink = this.drawBlink(); }
      if (this.t < this.blinkUntil) frame = 'blink';
    }
    const fadeMs = frame === 'blink' || this.current === 'blink' ? T.snapMs : T.fadeMs;
    this.current = frame;
    return { frame, fadeMs };
  }
}

const set = new Set(['default', 'warm', 'happy', 'playful', 'listening', 'blink',
  'nod', 'smile', 'laugh', 'thinking']);
const director = new Director(set, 42);
let pieces = 0;
let shown = '';
for (let i = 0; i <= 200; i += 1) {                         // 20 seconds at 10 frames a second
  const t = i / 10;
  const mode: Mode = t < 12 ? 'listening' : t < 14 ? 'waiting' : 'speaking';
  if (i === 50 || i === 80) pieces += 1;                     // two pieces of his words land
  const out = director.step(mode, t < 14 ? 'happy' : 'playful', pieces, 0.1);
  if (out.frame !== shown) {
    console.log(`${t.toFixed(1).padStart(5)}s  ${mode.padEnd(9)} -> ${out.frame} (${out.fadeMs} ms)`);
    shown = out.frame;
  }
}