// avatar/avatar.js
//
// THE INLINE TRANSPORT: the renderer lives in the same document as the host component.
//
// Its ONLY job is to build a six-method stagePort and hand it to the shared
// installFacade. It implements no turn behaviour and it never assigns window.Avatar.
// tests/test_transport_seam.py fails if either rule is broken here.

import { getLastDecoded, playBuffer } from './audio-queue.js';
import { installFacade } from './facade.js';
import { makePlayer } from './lipsync.js';
import { createTurnLoop } from './turn-loop.js';
import { mountStage } from './vrm-stage.js';

/**
 * A bus that exists before the real one does.
 *
 * mountStage() needs an emit callback, but the facade's event bus is only created
 * once installFacade() runs - which is after the stage is mounted. Anything emitted
 * during mount (notably the 'error' raised when a VRM has no expressionManager, the
 * exact symptom of a double three.js instance) would otherwise be dropped on the
 * floor. This buffers until connect() and then replays in order.
 */
function deferredBus() {
  let sink = null;
  const queued = [];
  const emit = (name, data) => {
    if (sink) sink(name, data);
    else queued.push([name, data]);
  };
  emit.connect = (real) => {
    sink = real;
    while (queued.length > 0) {
      const [name, data] = queued.shift();
      sink(name, data);
    }
  };
  return emit;
}

/**
 * @param {HTMLElement} element the host-provided mount point
 * @param {object}      props   at minimum { vrmUrl }
 * @param {Function}    [trigger] host event sink, so the backend also sees avatar events
 * @param {object}      [server]  host bridge, handed to the turn loop as a getter
 */
export async function boot(element, props = {}, trigger = null, server = null) {
  // Re-entry guard. key="vrm-stage" should stop the host re-running js_on_load at all,
  // but if it ever does, returning the live object without remounting is what holds
  // mountCount at 1 across 20 interactions (AVTR-01).
  if (window.Avatar && window.Avatar.__debug && window.Avatar.__debug.ready) {
    return window.Avatar;
  }

  const canvas = element.querySelector('#vrm-canvas');
  if (!canvas) throw new Error('boot: no #vrm-canvas inside the mounted element');

  const AudioCtor = window.AudioContext || window.webkitAudioContext;
  const audioCtx = new AudioCtor();
  const emit = deferredBus();

  let stage = null;
  let player = null;
  let mounting = null;
  let cached = null;

  // Memoised: the stage is mounted exactly once no matter how many callers ask.
  function ensureStage(vrmUrl) {
    if (!mounting) {
      mounting = (async () => {
        stage = await mountStage(canvas, vrmUrl || props.vrmUrl, emit);
        player = makePlayer(stage);
        stage.setOnTick((dt) => player.tick(dt));
        return stage;
      })();
    }
    return mounting;
  }

  await ensureStage(props.vrmUrl);

  // The stagePort is the ONLY thing that differs between transports. Here every
  // method is a direct call; in the iframe transport every method is a round trip.
  const stagePort = {
    mount: (vrmUrl) => ensureStage(vrmUrl),

    async speak(payload = {}) {
      await ensureStage();
      cached = payload;
      return playBuffer(audioCtx, payload.audioUrl, emit, (when) =>
        player.start(payload.timeline, audioCtx, when)
      );
    },

    async replayCached() {
      // The decoded buffer, not the URL: zero network requests, which is what
      // plan 01-09's test_replay asserts with a browser request listener.
      const buffer = getLastDecoded();
      if (!buffer) throw new Error('nothing cached to re-play');
      return playBuffer(audioCtx, buffer, emit, (when) =>
        player.start(cached && cached.timeline, audioCtx, when)
      );
    },

    setThinking: (value) => (stage ? stage.setThinking(value) : undefined),
    setListening: (value) => (stage ? stage.setListening(value) : undefined),
    getDebug: async () => (stage ? stage.getDebug() : {}),
  };

  const turnLoop = createTurnLoop({ stagePort, emit, getServer: () => server });

  const installed = installFacade({
    transport: 'inline',
    stagePort,
    turnLoop,
    // The one host-aware line in the file: mirror avatar events onto the host's own
    // event system so backend listeners see them too.
    onEmit: (name, data) => {
      if (typeof trigger === 'function') trigger(name, data);
    },
  });

  emit.connect(installed.emit);
  await installed.avatar.mount(props.vrmUrl);
  return installed.avatar;
}

/**
 * What the host's watch('value', ...) calls. Tolerates null, '' and already-parsed
 * objects, because a component's initial value is empty and must not throw.
 */
export function onDirective(value) {
  if (value === null || value === undefined || value === '') return null;
  let directive = value;
  if (typeof value === 'string') {
    try {
      directive = JSON.parse(value);
    } catch {
      return null;
    }
  }
  if (!directive || typeof directive !== 'object') return null;
  if (!window.Avatar) throw new Error('onDirective called before boot()');
  return window.Avatar.speak(directive);
}