// avatar/facade.js
//
// THIS IS THE ONLY FILE IN avatar/ THAT ASSIGNS window.Avatar.
// tests/test_transport_seam.py::test_only_facade_assigns_window_avatar fails if any
// other module does.
//
// Why one builder rather than one per transport: the naive design has each transport
// build its own window.Avatar, and then every later plan must remember to update both.
// That seam rots silently - a method added to the inline transport and forgotten in the
// fallback is invisible until the day the fallback is needed. Here the method list is
// DATA (AVATAR_SURFACE), the object is built by iterating it, and an unresolved name
// throws at boot with the missing name rather than being quietly absent.
//
// This module knows nothing about any host framework and nothing about the renderer.
// It reaches the renderer only through the six-method stagePort it is handed.

/**
 * The transport contract. The single source of truth for the method list.
 * Tests parse this array out of this file rather than duplicating it, so it cannot drift.
 *
 * mount           (vrmUrl) -> Promise, resolves once the VRM is ready
 * speak           ({audioUrl, timeline, expression, subtitle}) -> Promise, resolves at speech end
 * replay          re-plays the cached directive, no network
 * setListening    (bool)
 * setThinking     (bool)
 * on              (event, cb) where event is one of:
 *                 ready, speech-start, speech-end, error, asr-tier, transcript
 * getDebug        -> Promise<debug>, async so a message-passing transport can answer
 * startListening  push-to-talk down     - body wired in plan 01-07
 * stopListening   push-to-talk up       - body wired in plan 01-07
 * dispatchTurn    (text, {speed})       - body wired in plan 01-08
 * requestSlower   re-synthesise the last utterance slower - plan 01-08
 */
export const AVATAR_SURFACE = [
  'mount',
  'speak',
  'replay',
  'setListening',
  'setThinking',
  'on',
  'getDebug',
  'startListening',
  'stopListening',
  'dispatchTurn',
  'requestSlower',
];

/**
 * Build window.Avatar out of a stagePort and a turn loop.
 *
 * @param {object}   opts
 * @param {string}   opts.transport      'inline' | 'iframe', recorded in __debug
 * @param {object}   opts.stagePort      mount, speak, replayCached, setThinking, setListening, getDebug
 * @param {object}   opts.turnLoop       the result of createTurnLoop()
 * @param {Function} [opts.onEmit]       optional hook so a transport can forward events onward
 * @returns {{avatar: object, emit: Function, debug: object}}
 */
export function installFacade({ transport, stagePort, turnLoop, onEmit }) {
  if (!stagePort) throw new Error('installFacade: a stagePort is required');
  if (!turnLoop) throw new Error('installFacade: a turnLoop is required');

  const listeners = new Map();

  const debug = {
    ready: false,
    mountCount: 0,
    vrmMetaTitle: '',
    vrmMeta: null,
    threeInstanceCount: 0,
    currentVisemes: { aa: 0, ih: 0, ou: 0, ee: 0, oh: 0 },
    blinkValue: 0,
    breathValue: 0,
    clockOffset: 0,
    thinking: false,
    listening: false,
    lastTurnId: null,
    transport: transport || 'inline',
  };

  function emit(name, data) {
    if (name === 'ready') debug.ready = true;
    const subs = listeners.get(name);
    if (subs) {
      for (const cb of [...subs]) {
        try {
          cb(data);
        } catch (err) {
          console.error(`Avatar listener for ${name} failed`, err);
        }
      }
    }
    if (typeof onEmit === 'function') {
      try {
        onEmit(name, data);
      } catch (err) {
        console.error('Avatar onEmit hook failed', err);
      }
    }
  }

  // The members the facade itself owns: the event bus, the mount counter, and the
  // merge that turns three independent debug sources into one readable object.
  const local = {
    on(event, cb) {
      if (typeof cb !== 'function') return () => {};
      if (!listeners.has(event)) listeners.set(event, new Set());
      listeners.get(event).add(cb);
      return () => listeners.get(event)?.delete(cb);
    },

    async mount(a, b) {
      // The canvas belongs to the transport, so a URL is the only thing that has to
      // cross this boundary. Accept mount(url) and mount(canvas, url) alike.
      const vrmUrl = b === undefined ? a : b;
      debug.mountCount += 1;
      await stagePort.mount(vrmUrl);
      debug.ready = true;
      return local.getDebug();
    },

    async getDebug() {
      let stageDebug = null;
      try {
        stageDebug = await stagePort.getDebug();
      } catch {
        stageDebug = null; // not mounted yet, or the far side has not answered
      }
      Object.assign(debug, turnLoop.state || {}, stageDebug || {});
      return debug;
    },
  };

  // Build by ITERATING the surface list. This loop, and the throw under it, are what
  // make "both transports expose the same methods" a guarantee instead of a habit.
  const avatar = {};
  const unresolved = [];
  for (const name of AVATAR_SURFACE) {
    let owner = null;
    if (typeof local[name] === 'function') owner = local;
    else if (typeof turnLoop[name] === 'function') owner = turnLoop;
    else if (typeof stagePort[name] === 'function') owner = stagePort;

    if (!owner) {
      unresolved.push(name);
      continue;
    }
    avatar[name] = (...args) => owner[name](...args);
  }

  if (unresolved.length > 0) {
    throw new Error(
      `installFacade: nothing implements ${unresolved.join(', ')} - every name in ` +
        'AVATAR_SURFACE must resolve to a turn-loop method or a stagePort method'
    );
  }

  avatar.__debug = debug;
  window.Avatar = avatar;
  return { avatar, emit, debug };
}