refactor: rewrite Live Chat logic (#85)

* dev: start LiveChat refactor

* dev: implement simple module system to separate classes

+ add a few Live Chat actions

* dev: add fundamental Live Chat classes

* chore: update type declarations

* feat: finalize Live Chat

Now supporting almost all kinds of messages! Next up: add a ability to send messages.

* chore: update type declarations

* chore: update contributors list

* feat(livechat): add `sendMessage()` method

* chore: remove unneeded files

* style: format code

* chore: remove outdated examples

* chore: update tests

* chore: remove trailing spaces

* chore: remove trailing spaces x2

lib/parser/youtube/LiveChat.js

@@ -0,0 +1,164 @@
+'use strict';
+
+const Parser = require('../contents');
+const EventEmitter = require('events');
+
+class LiveChat {
+  ev;
+
+  #actions;
+  #video_info;
+  #continuation;
+  #mcontinuation;
+
+  #lc_polling_interval_ms = 1000;
+  #md_polling_interval_ms = 5000;
+
+  initial_info;
+  live_metadata;
+
+  running = false;
+  is_replay = false;
+
+  /**
+   * @param {import('./VideoInfo')} video_info
+   */
+  constructor(video_info) {
+    this.#video_info = video_info;
+    this.#actions = video_info.actions;
+    this.#continuation = this.#video_info.livechat.continuation;
+    this.is_replay = this.#video_info.livechat.is_replay;
+
+    this.live_metadata = {
+      /** @type {import('../contents/classes/livechat/metadata/UpdateTitleAction')} */
+      title: null,
+      /** @type {import('../contents/classes/livechat/metadata/UpdateDescriptionAction')} */
+      description: null,
+      /** @type {import('../contents/classes/livechat/metadata/UpdateViewershipAction')} */
+      views: null,
+      /** @type {import('../contents/classes/livechat/metadata/UpdateTitleAction')} */
+      likes: null,
+      /** @type {import('../contents/classes/livechat/metadata/UpdateDateTextAction')} */
+      date: null
+    };
+
+    this.ev = new EventEmitter();
+  }
+
+  start() {
+    if (!this.running) {
+      this.running = true;
+      this.#pollLivechat();
+      this.#pollMetadata();
+    }
+  }
+
+  stop() {
+    this.running = false;
+  }
+
+  #pollLivechat() {
+    const lc_poller = setTimeout(() => {
+      (async () => {
+        const endpoint = this.is_replay ? 'live_chat/get_live_chat_replay': 'live_chat/get_live_chat';
+        const response = await this.#actions.livechat(endpoint, { ctoken: this.#continuation });
+
+        const data = Parser.parseResponse(response.data);
+        const contents = data.continuation_contents;
+
+        this.#continuation = contents.continuation.token;
+        this.#lc_polling_interval_ms = contents.continuation.timeout_ms;
+
+        // Header only exists in the first request
+        if (contents.header) {
+          this.initial_info = contents;
+          this.ev.emit('start', contents);
+        } else {
+          await this.#emitSmoothedActions(contents.actions);
+        }
+
+        clearTimeout(lc_poller);
+
+        this.running && this.#pollLivechat();
+      })().catch((err) => Promise.reject(err));
+    }, this.#lc_polling_interval_ms);
+  }
+
+  /**
+   * Ensures actions are emitted at the right speed.
+   * This was adapted from YouTube's compiled code (Android).
+   * @param {object} actions
+   */
+  async #emitSmoothedActions(actions) {
+    let base = 1E4;
+    let delay = actions.length < base / 80 ? 1: 0;
+
+    const emit_delay_ms =
+      delay == 1 ? (
+        delay = base / actions.length,
+        delay *= Math.random() + 0.5,
+        delay = Math.min(1E3, delay),
+        delay = Math.max(80, delay)
+      ): delay = 80;
+
+    for (const action of actions) {
+      await this.#wait(emit_delay_ms);
+      this.ev.emit('chat-update', action);
+    }
+  }
+
+  #pollMetadata() {
+    const md_poller = setTimeout(() => {
+      (async () => {
+        const payload = { video_id: this.#video_info.basic_info.id };
+
+        this.#mcontinuation &&
+          (payload.ctoken = this.#mcontinuation);
+
+        const response = await this.#actions.livechat('updated_metadata', payload);
+        const data = Parser.parseResponse(response.data);
+
+        this.#mcontinuation = data.continuation.token;
+        this.#md_polling_interval_ms = data.continuation.timeout_ms;
+
+        this.metadata = {
+          title: data.actions.get({ type: 'UpdateTitleAction' }) || this.metadata?.title,
+          description: data.actions.get({ type: 'UpdateDescriptionAction' }) || this.metadata?.description,
+          views: data.actions.get({ type: 'UpdateViewershipAction' }) || this.metadata?.views,
+          likes: data.actions.get({ type: 'UpdateToggleButtonTextAction' }) || this.metadata?.likes,
+          date: data.actions.get({ type: 'UpdateDateTextAction' }) || this.metadata?.date
+        };
+
+        this.ev.emit('metadata-update', this.metadata);
+
+        clearTimeout(md_poller);
+
+        this.running && this.#pollMetadata();
+      })().catch((err) => Promise.reject(err));
+    }, this.#md_polling_interval_ms);
+  }
+
+  /**
+   * Sends a message.
+   * @param {string} text
+   * @returns {Promise.<import('../contents/classes/livechat/AddChatItemAction')[]>}
+   */
+  async sendMessage(text) {
+    const response = await this.#actions.livechat('live_chat/send_message', {
+      text,
+      ... {
+        video_id: this.#video_info.basic_info.id,
+        channel_id: this.#video_info.basic_info.channel_id
+      }
+    });
+
+    const data = Parser.parseResponse(response.data);
+    return data.actions;
+  }
+
+  async #wait(ms) {
+    return new Promise((resolve) => setTimeout(() => resolve(), ms));
+  }
+}
+
+module.exports = LiveChat;