Fix SEO and refactor HTML pages generation

* Split methods in multiple classes
 * Add JSONLD tags in embed too
 * Index embeds but use a canonical URL tag (targeting the watch page)
 * Remote objects don't include a canonical URL tag anymore. Instead we
   forbid indexation
 * Canonical URLs now use the official short URL (/w/, /w/p, /a, /c
   etc.)

server/core/lib/html/client-html.ts

@@ -0,0 +1,95 @@
+import { HttpStatusCode } from '@peertube/peertube-models'
+import express from 'express'
+import { logger } from '../../helpers/logger.js'
+import { ACCEPT_HEADERS } from '../../initializers/constants.js'
+import { VideoHtml } from './shared/video-html.js'
+import { PlaylistHtml } from './shared/playlist-html.js'
+import { ActorHtml } from './shared/actor-html.js'
+import { PageHtml } from './shared/page-html.js'
+
+class ClientHtml {
+
+  static invalidateCache () {
+    PageHtml.invalidateCache()
+  }
+
+  static getDefaultHTMLPage (req: express.Request, res: express.Response, paramLang?: string) {
+    return PageHtml.getDefaultHTML(req, res, paramLang)
+  }
+
+  // ---------------------------------------------------------------------------
+
+  static getWatchHTMLPage (videoIdArg: string, req: express.Request, res: express.Response) {
+    return VideoHtml.getWatchVideoHTML(videoIdArg, req, res)
+  }
+
+  static getVideoEmbedHTML (videoIdArg: string) {
+    return VideoHtml.getEmbedVideoHTML(videoIdArg)
+  }
+
+  // ---------------------------------------------------------------------------
+
+  static getWatchPlaylistHTMLPage (videoPlaylistIdArg: string, req: express.Request, res: express.Response) {
+    return PlaylistHtml.getWatchPlaylistHTML(videoPlaylistIdArg, req, res)
+  }
+
+  static getVideoPlaylistEmbedHTML (playlistIdArg: string) {
+    return PlaylistHtml.getEmbedPlaylistHTML(playlistIdArg)
+  }
+
+  // ---------------------------------------------------------------------------
+
+  static getAccountHTMLPage (nameWithHost: string, req: express.Request, res: express.Response) {
+    return ActorHtml.getAccountHTMLPage(nameWithHost, req, res)
+  }
+
+  static getVideoChannelHTMLPage (nameWithHost: string, req: express.Request, res: express.Response) {
+    return ActorHtml.getVideoChannelHTMLPage(nameWithHost, req, res)
+  }
+
+  static getActorHTMLPage (nameWithHost: string, req: express.Request, res: express.Response) {
+    return ActorHtml.getActorHTMLPage(nameWithHost, req, res)
+  }
+}
+
+function sendHTML (html: string, res: express.Response, localizedHTML: boolean = false) {
+  res.set('Content-Type', 'text/html; charset=UTF-8')
+
+  if (localizedHTML) {
+    res.set('Vary', 'Accept-Language')
+  }
+
+  return res.send(html)
+}
+
+async function serveIndexHTML (req: express.Request, res: express.Response) {
+  if (req.accepts(ACCEPT_HEADERS) === 'html' || !req.headers.accept) {
+    try {
+      await generateHTMLPage(req, res, req.params.language)
+      return
+    } catch (err) {
+      logger.error('Cannot generate HTML page.', { err })
+      return res.status(HttpStatusCode.INTERNAL_SERVER_ERROR_500).end()
+    }
+  }
+
+  return res.status(HttpStatusCode.NOT_ACCEPTABLE_406).end()
+}
+
+// ---------------------------------------------------------------------------
+
+export {
+  ClientHtml,
+  sendHTML,
+  serveIndexHTML
+}
+
+// ---------------------------------------------------------------------------
+// Private
+// ---------------------------------------------------------------------------
+
+async function generateHTMLPage (req: express.Request, res: express.Response, paramLang?: string) {
+  const html = await ClientHtml.getDefaultHTMLPage(req, res, paramLang)
+
+  return sendHTML(html, res, true)
+}