backend/app/controllers/theatre_comments_controller.rb

@@ -0,0 +1,32 @@
+class TheatreCommentsController < ApplicationController
+  def index
+    no_gt = params[:no_gt].to_i
+    no_gt = 0 if no_gt.negative?
+
+    comments = TheatreComment
+               .where(theatre_id: params[:theatre_id])
+               .where('no > ?', no_gt)
+               .order(no: :desc)
+
+    render json: comments.as_json(include: { user: { only: [:id, :name] } })
+  end
+
+  def create
+    return head :unauthorized unless current_user
+
+    content = params[:content]
+    return head :unprocessable_entity if content.blank?
+
+    theatre = Theatre.find_by(id: params[:theatre_id])
+    return head :not_found unless theatre
+
+    comment = nil
+    theatre.with_lock do
+      no = theatre.next_comment_no
+      comment = TheatreComment.create!(theatre:, no:, user: current_user, content:)
+      theatre.update!(next_comment_no: no + 1)
+    end
+
+    render json: comment, status: :created
+  end
+end

backend/app/controllers/theatres_controller.rb

@@ -31,7 +31,9 @@ class TheatresController < ApplicationController
       post_started_at = theatre.current_post_started_at
     end
 
-    render json: { host_flg:, post_id:, post_started_at: }
+    render json: {
+        host_flg:, post_id:, post_started_at:,
+        watching_users: theatre.watching_users.as_json(only: [:id, :name]) }
   end
 
   def next_post

backend/app/models/theatre_comment.rb

@@ -1,8 +1,8 @@
 class TheatreComment < ApplicationRecord
-  include MyDiscard
+  include Discard::Model
 
   self.primary_key = :theatre_id, :no
 
   belongs_to :theatre
+  belongs_to :user
 end
-

backend/config/routes.rb

@@ -78,5 +78,7 @@ Rails.application.routes.draw do
       put :watching
       patch :next_post
     end
+
+    resources :comments, controller: :theatre_comments, only: [:index, :create]
   end
 end

backend/spec/factories/theatre_comments.rb

@@ -0,0 +1,8 @@
+FactoryBot.define do
+  factory :theatre_comment do
+    association :theatre
+    association :user
+    sequence (:no) { |n| n }
+    content { 'test comment' }
+  end
+end

backend/spec/factories/theatres.rb

@@ -0,0 +1,11 @@
+FactoryBot.define do
+  factory :theatre do
+    name { 'Test Theatre' }
+    kind { 1 }
+    opens_at { Time.current }
+    closes_at { 1.day.from_now }
+    next_comment_no { 1 }
+
+    association :created_by_user, factory: :user
+  end
+end

backend/spec/requests/theatre_comments_spec.rb

@@ -0,0 +1,150 @@
+require 'rails_helper'
+
+RSpec.describe 'TheatreComments', type: :request do
+  def sign_in_as(user)
+    allow_any_instance_of(ApplicationController).to receive(:current_user).and_return(user)
+  end
+
+  describe 'GET /theatres/:theatre_id/comments' do
+    let(:theatre) { create(:theatre) }
+    let(:other_theatre) { create(:theatre) }
+    let(:alice) { create(:user, name: 'Alice') }
+    let(:bob) { create(:user, name: 'Bob') }
+
+    let!(:comment_3) do
+      create(
+        :theatre_comment,
+        theatre: theatre,
+        no: 3,
+        user: alice,
+        content: 'third comment'
+      )
+    end
+
+    let!(:comment_1) do
+      create(
+        :theatre_comment,
+        theatre: theatre,
+        no: 1,
+        user: alice,
+        content: 'first comment'
+      )
+    end
+
+    let!(:comment_2) do
+      create(
+        :theatre_comment,
+        theatre: theatre,
+        no: 2,
+        user: bob,
+        content: 'second comment'
+      )
+    end
+
+    let!(:other_comment) do
+      create(
+        :theatre_comment,
+        theatre: other_theatre,
+        no: 1,
+        user: bob,
+        content: 'other theatre comment'
+      )
+    end
+
+    it 'theatre_id で絞り込み、no_gt より大きいものを no 降順で返す' do
+      get "/theatres/#{theatre.id}/comments", params: { no_gt: 1 }
+
+      expect(response).to have_http_status(:ok)
+      expect(response.parsed_body.map { |row| row['no'] }).to eq([3, 2])
+      expect(response.parsed_body.map { |row| row['content'] }).to eq([
+        'third comment',
+        'second comment'
+      ])
+    end
+
+    it 'user は id と name だけを含む' do
+      get "/theatres/#{theatre.id}/comments", params: { no_gt: 1 }
+
+      expect(response).to have_http_status(:ok)
+
+      expect(response.parsed_body.first['user']).to eq({
+        'id' => alice.id,
+        'name' => 'Alice'
+      })
+      expect(response.parsed_body.first['user'].keys).to contain_exactly('id', 'name')
+    end
+
+    it 'no_gt が負数なら 0 として扱う' do
+      get "/theatres/#{theatre.id}/comments", params: { no_gt: -100 }
+
+      expect(response).to have_http_status(:ok)
+      expect(response.parsed_body.map { |row| row['no'] }).to eq([3, 2, 1])
+    end
+  end
+
+  describe 'POST /theatres/:theatre_id/comments' do
+    let(:user) { create(:user, name: 'Alice') }
+    let(:theatre) { create(:theatre, next_comment_no: 2) }
+
+    before do
+      create(
+        :theatre_comment,
+        theatre: theatre,
+        no: 1,
+        user: user,
+        content: 'existing comment'
+      )
+    end
+
+    it '未ログインなら 401 を返す' do
+      expect {
+        post "/theatres/#{theatre.id}/comments", params: { content: 'hello' }
+      }.not_to change(TheatreComment, :count)
+
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it 'content が blank なら 422 を返す' do
+      sign_in_as(user)
+
+      expect {
+        post "/theatres/#{theatre.id}/comments", params: { content: '   ' }
+      }.not_to change(TheatreComment, :count)
+
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+
+    it 'theatre が存在しなければ 404 を返す' do
+      sign_in_as(user)
+
+      expect {
+        post '/theatres/999999/comments', params: { content: 'hello' }
+      }.not_to change(TheatreComment, :count)
+
+      expect(response).to have_http_status(:not_found)
+    end
+
+    it 'コメントを作成し、user を紐づけ、next_comment_no を進める' do
+      sign_in_as(user)
+
+      expect {
+        post "/theatres/#{theatre.id}/comments", params: { content: 'new comment' }
+      }.to change(TheatreComment, :count).by(1)
+
+      expect(response).to have_http_status(:created)
+
+      comment = TheatreComment.find_by!(theatre: theatre, no: 2)
+
+      expect(comment.user).to eq(user)
+      expect(comment.content).to eq('new comment')
+      expect(theatre.reload.next_comment_no).to eq(3)
+
+      expect(response.parsed_body.slice('theatre_id', 'no', 'user_id', 'content')).to eq({
+        'theatre_id' => theatre.id,
+        'no' => 2,
+        'user_id' => user.id,
+        'content' => 'new comment'
+      })
+    end
+  end
+end

backend/spec/requests/theatres_spec.rb

@@ -117,11 +117,18 @@ RSpec.describe 'Theatres API', type: :request do
         expect(theatre.host_user_id).to eq(member.id)
         expect(watch.expires_at).to be_within(1.second).of(30.seconds.from_now)
 
-        expect(json).to eq(
+        expect(json).to include(
           'host_flg' => true,
           'post_id' => nil,
           'post_started_at' => nil
         )
+
+        expect(json.fetch('watching_users')).to contain_exactly(
+          {
+            'id' => member.id,
+            'name' => 'member user'
+          }
+        )
       end
     end
 
@@ -167,11 +174,22 @@ RSpec.describe 'Theatres API', type: :request do
         expect(response).to have_http_status(:ok)
         expect(theatre.reload.host_user_id).to eq(other_user.id)
 
-        expect(json).to eq(
+        expect(json).to include(
           'host_flg' => false,
           'post_id' => nil,
           'post_started_at' => nil
         )
+
+        expect(json.fetch('watching_users')).to contain_exactly(
+          {
+            'id' => member.id,
+            'name' => 'member user'
+          },
+          {
+            'id' => other_user.id,
+            'name' => 'other user'
+          }
+        )
       end
     end
 

frontend/src/components/PrefetchLink.tsx

@@ -71,7 +71,8 @@ export default forwardRef<HTMLAnchorElement, Props> (({
 	  || ev.metaKey
 	  || ev.ctrlKey
 	  || ev.shiftKey
-	  || ev.altKey)
+	  || ev.altKey
+	  || (rest.target && rest.target !== '_self'))
 	return
 
       ev.preventDefault ()

frontend/src/components/TopNav.tsx

@@ -79,9 +79,11 @@ export default (({ user }: Props) => {
 	  { name: '上位タグ', to: '/tags/implications', visible: false },
 	  { name: 'ニコニコ連携', to: '/tags/nico' },
 	  { name: 'ヘルプ', to: '/wiki/ヘルプ:タグ' }] },
-      // TODO: 本実装時に消す．
-      // { name: '上映会', to: '/theatres/1', base: '/theatres', subMenu: [
-      //     { name: '一覧', to: '/theatres' }] },
+      { name: '上映会', to: '/theatres/1', base: '/theatres', subMenu: [
+          { name: <>第&thinsp;1&thinsp;会場</>, to: '/theatres/1' },
+          { name: 'CyTube', to: '//cytube.mm428.net/r/deernijika' },
+	  { name: <>ニジカ放送局第&thinsp;1&thinsp;チャンネル</>,
+	    to: '//www.youtube.com/watch?v=DCU3hL4Uu6A' }] },
       { name: 'Wiki', to: '/wiki/ヘルプ:ホーム', base: '/wiki', subMenu: [
 	  { name: '検索', to: '/wiki' },
 	  { name: '新規', to: '/wiki/new' },
@@ -92,7 +94,7 @@ export default (({ user }: Props) => {
 	    visible: wikiPageFlg },
 	  { name: '履歴', to: `/wiki/changes?id=${ wikiId }`, visible: wikiPageFlg },
 	  { name: '編輯', to: `/wiki/${ wikiId || wikiTitle }/edit`, visible: wikiPageFlg }] },
-      { name: 'ユーザ', to: '/users', subMenu: [
+      { name: 'ユーザ', to: '/users/settings', subMenu: [
 	  { name: '一覧', to: '/users', visible: false },
 	  { name: 'お前', to: `/users/${ user?.id }`, visible: false },
 	  { name: '設定', to: '/users/settings', visible: Boolean (user) }] }]
@@ -209,6 +211,7 @@ export default (({ user }: Props) => {
 		      <PrefetchLink
 			  key={`l-${ i }`}
 			  to={item.to}
+			  target={item.to.slice (0, 2) === '//' ? '_blank' : undefined}
 			  className="h-full flex items-center px-3">
 			{item.name}
 		      </PrefetchLink>)))}
@@ -275,6 +278,9 @@ export default (({ user }: Props) => {
 				      <PrefetchLink
 					  key={`sp-l-${ i }-${ j }`}
 					  to={subItem.to}
+					  target={subItem.to.slice (0, 2) === '//'
+						  ? '_blank'
+						  : undefined}
 					  className="w-full min-h-[36px] flex items-center pl-12">
 					{subItem.name}
 				      </PrefetchLink>)))}

frontend/src/pages/theatres/TheatreDetailPage.tsx

@@ -2,85 +2,225 @@ import { useEffect, useRef, useState } from 'react'
 import { Helmet } from 'react-helmet-async'
 import { useParams } from 'react-router-dom'
 
+import ErrorScreen from '@/components/ErrorScreen'
 import PostEmbed from '@/components/PostEmbed'
+import PrefetchLink from '@/components/PrefetchLink'
+import TagDetailSidebar from '@/components/TagDetailSidebar'
 import MainArea from '@/components/layout/MainArea'
+import SidebarComponent from '@/components/layout/SidebarComponent'
 import { SITE_TITLE } from '@/config'
-import { apiGet, apiPatch, apiPut } from '@/lib/api'
+import { apiGet, apiPatch, apiPost, apiPut } from '@/lib/api'
 import { fetchPost } from '@/lib/posts'
+import { dateString } from '@/lib/utils'
 
 import type { FC } from 'react'
 
-import type { NiconicoMetadata, NiconicoViewerHandle, Post, Theatre } from '@/types'
+import type { NiconicoMetadata,
+	      NiconicoViewerHandle,
+	      Post,
+	      Theatre,
+	      TheatreComment } from '@/types'
 
 type TheatreInfo = {
     hostFlg:        boolean
     postId:         number | null
-    postStartedAt:  string | null }
+    postStartedAt:  string | null
+    watchingUsers:  { id: number; name: string }[] }
+
+const INITIAL_THEATRE_INFO =
+    { hostFlg: false,
+      postId: null,
+      postStartedAt: null,
+      watchingUsers: [] as { id: number; name: string }[] } as const
 
 
 export default (() => {
   const { id } = useParams ()
 
+  const commentsRef = useRef<HTMLDivElement> (null)
   const embedRef = useRef<NiconicoViewerHandle> (null)
+  const theatreInfoRef = useRef<TheatreInfo> (INITIAL_THEATRE_INFO)
+  const videoLengthRef = useRef (0)
+  const lastCommentNoRef = useRef (0)
 
+  const [comments, setComments] = useState<TheatreComment[]> ([])
+  const [content, setContent] = useState ('')
   const [loading, setLoading] = useState (false)
+  const [sending, setSending] = useState (false)
+  const [status, setStatus] = useState (200)
   const [theatre, setTheatre] = useState<Theatre | null> (null)
-  const [theatreInfo, setTheatreInfo] =
-      useState<TheatreInfo> ({ hostFlg: false, postId: null, postStartedAt: null })
+  const [theatreInfo, setTheatreInfo] = useState<TheatreInfo> (INITIAL_THEATRE_INFO)
   const [post, setPost] = useState<Post | null> (null)
-  const [videoLength, setVideoLength] = useState (9_999_999_999)
+  const [videoLength, setVideoLength] = useState (0)
+
+  useEffect (() => {
+    theatreInfoRef.current = theatreInfo
+  }, [theatreInfo])
+
+  useEffect (() => {
+    videoLengthRef.current = videoLength
+  }, [videoLength])
+
+  useEffect (() => {
+    lastCommentNoRef.current = comments[0]?.no ?? 0
+  }, [comments])
 
   useEffect (() => {
     if (!(id))
       return
 
+    let cancelled = false
+
+    setComments ([])
+    setTheatre (null)
+    setPost (null)
+    setTheatreInfo (INITIAL_THEATRE_INFO)
+    setVideoLength (0)
+    lastCommentNoRef.current = 0
+
     void (async () => {
-      setTheatre (await apiGet<Theatre> (`/theatres/${ id }`))
+      try
+      {
+	const data = await apiGet<Theatre> (`/theatres/${ id }`)
+	if (!(cancelled))
+	  setTheatre (data)
+      }
+      catch (error)
+      {
+	setStatus ((error as any)?.response.status ?? 200)
+      }
     }) ()
 
-    const interval = setInterval (async () => {
-      if (theatreInfo.hostFlg
-	  && theatreInfo.postStartedAt
-	  && ((new Date).getTime () - (new Date (theatreInfo.postStartedAt)).getTime ()
-	      > videoLength))
-	setTheatreInfo ({ hostFlg: true, postId: null, postStartedAt: null })
-      else
-	setTheatreInfo (await apiPut<TheatreInfo> (`/theatres/${ id }/watching`))
-    }, 1_000)
+    return () => {
+      cancelled = true
+    }
+  }, [id])
 
-    return () => clearInterval (interval)
-  }, [id, theatreInfo.hostFlg, theatreInfo.postStartedAt, videoLength])
+  useEffect (() => {
+    if (!(id))
+      return
+
+    let cancelled = false
+    let running = false
+
+    const tick = async () => {
+      if (running)
+	return
+
+      running = true
+
+      try
+      {
+	const newComments = await apiGet<TheatreComment[]> (
+	    `/theatres/${ id }/comments`,
+	    { params: { no_gt: lastCommentNoRef.current } })
+
+	if (!(cancelled) && newComments.length > 0)
+	  {
+	    lastCommentNoRef.current = newComments[newComments.length - 1].no
+	    setComments (prev => [...newComments, ...prev])
+	  }
+
+	const currentInfo = theatreInfoRef.current
+	const ended =
+	    currentInfo.hostFlg
+	    && currentInfo.postStartedAt
+	    && ((Date.now () - (new Date (currentInfo.postStartedAt)).getTime ())
+	        > videoLengthRef.current + 3_000)
+
+	if (ended)
+	  {
+	    if (!(cancelled))
+	      setTheatreInfo (prev => ({ ...prev, postId: null, postStartedAt: null }))
+
+	    return
+	  }
+
+	const nextInfo = await apiPut<TheatreInfo> (`/theatres/${ id }/watching`)
+	if (!(cancelled))
+	  setTheatreInfo (nextInfo)
+      }
+      catch (error)
+      {
+	console.error (error)
+      }
+      finally
+      {
+	running = false
+      }
+    }
+
+    tick ()
+    const interval = setInterval (() => tick (), 1_500)
+
+    return () => {
+      cancelled = true
+      clearInterval (interval)
+    }
+  }, [id])
 
   useEffect (() => {
-    if (!(theatreInfo.hostFlg) || loading)
+    if (!(id) || !(theatreInfo.hostFlg) || loading || theatreInfo.postId != null)
       return
 
-    if (theatreInfo.postId == null)
+    let cancelled = false
+
+    void (async () => {
+      setLoading (true)
+
+      try
       {
-	void (async () => {
-	  setLoading (true)
-	  await apiPatch<void> (`/theatres/${ id }/next_post`)
+	await apiPatch<void> (`/theatres/${ id }/next_post`)
+      }
+      catch (error)
+      {
+	console.error (error)
+      }
+      finally
+      {
+	if (!(cancelled))
 	  setLoading (false)
-	}) ()
-	return
       }
-  }, [id, loading, theatreInfo.hostFlg, theatreInfo.postId])
+    }) ()
+
+    return () => {
+      cancelled = true
+    }
+  }, [id, theatreInfo.hostFlg, theatreInfo.postId])
 
   useEffect (() => {
+    setVideoLength (0)
+
     if (theatreInfo.postId == null)
       return
 
+    let cancelled = false
+
     void (async () => {
-      setPost (await fetchPost (String (theatreInfo.postId)))
+      try
+      {
+	const nextPost = await fetchPost (String (theatreInfo.postId))
+	if (!(cancelled))
+	  setPost (nextPost)
+      }
+      catch (error)
+      {
+	console.error (error)
+      }
     }) ()
-  }, [theatreInfo.postId, theatreInfo.postStartedAt])
+
+    return () => {
+      cancelled = true
+    }
+  }, [theatreInfo.postId])
 
   const syncPlayback = (meta: NiconicoMetadata) => {
     if (!(theatreInfo.postStartedAt))
       return
 
-    const targetTime =
-	((new Date).getTime () - (new Date (theatreInfo.postStartedAt)).getTime ())
+    const targetTime = Math.min (
+	Math.max (0, Date.now () - (new Date (theatreInfo.postStartedAt)).getTime ()),
+	videoLength)
 
     const drift = Math.abs (meta.currentTime - targetTime)
 
@@ -88,8 +228,11 @@ export default (() => {
       embedRef.current?.seek (targetTime)
   }
 
+  if (status >= 400)
+    return <ErrorScreen status={status}/>
+
   return (
-      <MainArea>
+      <div className="md:flex md:flex-1">
 	<Helmet>
 	  {theatre && (
 	      <title>
@@ -99,16 +242,100 @@ export default (() => {
 	      </title>)}
 	</Helmet>
 
-	{post && (
-	    <PostEmbed
-		ref={embedRef}
-		post={post}
-		onLoadComplete={info => {
-		  embedRef.current?.play ()
-		  setVideoLength (info.lengthInSeconds * 1_000)
-		}}
-		onMetadataChange={meta => {
-		  syncPlayback (meta)
-		}}/>)}
-      </MainArea>)
+	<div className="hidden md:block">
+	  {post && <TagDetailSidebar post={post}/>}
+	</div>
+
+	<MainArea>
+	  {post ? (
+	      <>
+		<PostEmbed
+		    key={post.id}
+		    ref={embedRef}
+		    post={post}
+		    onLoadComplete={info => {
+		      embedRef.current?.play ()
+		      setVideoLength (info.lengthInSeconds * 1_000)
+		    }}
+		    onMetadataChange={syncPlayback}/>
+		<div className="m-2">
+		  <>再生中：</>
+		  <PrefetchLink to={`/posts/${ post.id }`} className="font-bold">
+		    {post.title || post.url}
+		  </PrefetchLink>
+		</div>
+	      </>) : 'Loading...'}
+	</MainArea>
+
+	<SidebarComponent>
+	  <form
+	      className="w-auto h-auto border border-black dark:border-white rounded mx-2"
+	      onSubmit={async e => {
+		e.preventDefault ()
+
+		if (!(content))
+		  return
+
+		try
+		{
+		  setSending (true)
+		  await apiPost (`/theatres/${ id }/comments`, { content })
+		  setContent ('')
+		  commentsRef.current?.scrollTo ({ top: 0, behavior: 'smooth' })
+		}
+		finally
+		{
+		  setSending (false)
+		}
+	      }}>
+	    <input
+		className="w-full p-2 border rounded"
+		type="text"
+		placeholder="ここにコメントを入力"
+		value={content}
+		onChange={e => setContent (e.target.value)}
+		disabled={sending}/>
+
+	    <div
+		ref={commentsRef}
+		className="overflow-x-hidden overflow-y-scroll text-wrap w-full
+			   h-[32vh] md:h-[64vh] border rounded">
+	      {comments.map (comment => (
+		  <div key={comment.no} className="p-2">
+		    <div className="w-full">
+		      {comment.content}
+		    </div>
+		    <div className="w-full text-sm text-right">
+		      by {comment.user
+			  ? (comment.user.name || `名もなきニジラー（#${ comment.user.id }）`)
+			  : '運営'}
+		    </div>
+		    <div className="w-full text-sm text-right">
+		      {dateString (comment.createdAt)}
+		    </div>
+		  </div>))}
+	    </div>
+	  </form>
+
+	  <div className="w-auto h-auto border border-black dark:border-white rounded mx-2 mt-4">
+	    <div className="p-2">
+		現在の同接数：{theatreInfo.watchingUsers.length}
+	    </div>
+
+	    <div className="overflow-x-hidden overflow-y-scroll text-wrap w-full h-32
+			    border rounded">
+	      <ul className="list-inside list-disc">
+		{theatreInfo.watchingUsers.map (user => (
+		    <li key={user.id} className="px-4 py-1 text-sm">
+		      {user.name || `名もなきニジラー（#${ user.id }）`}
+		    </li>))}
+	      </ul>
+	    </div>
+	  </div>
+	</SidebarComponent>
+
+	<div className="md:hidden">
+	  {post && <TagDetailSidebar post={post} sp/>}
+	</div>
+      </div>)
 }) satisfies FC

frontend/src/types.ts

@@ -52,7 +52,7 @@ export type FetchTagsParams = {
 export type Menu = MenuItem[]
 
 export type MenuItem = {
-    name:     string
+    name:     ReactNode
     to:       string
     base?:    string
     subMenu:  SubMenuItem[] }
@@ -117,7 +117,7 @@ export type PostTagChange = {
 export type SubMenuItem =
     | { component:  ReactNode
 	visible:    boolean }
-    | { name:     string
+    | { name:     ReactNode
 	to:       string
 	visible?: boolean }
 
@@ -141,6 +141,13 @@ export type Theatre = {
     createdAt:      string
     updatedAt:      string }
 
+export type TheatreComment = {
+    theatreId:  number,
+    no:         number,
+    user:       { id: number, name: string } | null
+    content:    string
+    createdAt:  string }
+
 export type User = {
     id:               number
     name:             string | null