backend/app/controllers/gekanator_games_controller.rb

@@ -8,7 +8,7 @@ class GekanatorGamesController < ApplicationController
         user: current_user,
         guessed_post_id: params.require(:guessed_post_id),
         correct_post_id: params[:correct_post_id].presence,
-        won: bool?(:won),
+        won: params[:guessed_post_id].to_i == params[:correct_post_id].to_i,
         question_count: params.require(:question_count),
         answers:)
 

backend/app/models/gekanator_game.rb

@@ -4,15 +4,7 @@ class GekanatorGame < ApplicationRecord
   belongs_to :correct_post, class_name: 'Post', optional: true
 
   validates :answers, presence: true
+  validates :correct_post, presence: true
   validates :question_count, numericality: { greater_than_or_equal_to: 0 }
   validates :won, inclusion: { in: [true, false] }
-  validate :correct_post_required_when_lost
-
-  private
-
-  def correct_post_required_when_lost
-    return if won || correct_post_id.present?
-
-    errors.add(:correct_post_id, '外れた時は正解の投稿を指定してくださぃ．')
-  end
 end

backend/spec/requests/gekanator_games_spec.rb

@@ -11,7 +11,7 @@ RSpec.describe 'Gekanator games API', type: :request do
 
       post '/gekanator/games', params: {
           guessed_post_id: guessed_post.id,
-          won: true,
+          correct_post_id: guessed_post.id,
           question_count: 3,
           answers: [{ question_id: 'tag:1', answer: 'yes' }] }
 
@@ -19,7 +19,7 @@ RSpec.describe 'Gekanator games API', type: :request do
       game = GekanatorGame.find(json['id'])
       expect(game.user).to eq(user)
       expect(game.guessed_post).to eq(guessed_post)
-      expect(game.correct_post).to be_nil
+      expect(game.correct_post).to eq(guessed_post)
       expect(game.won).to eq(true)
       expect(game.answers).to eq([{ 'question_id' => 'tag:1', 'answer' => 'yes' }])
     end
@@ -30,20 +30,20 @@ RSpec.describe 'Gekanator games API', type: :request do
       post '/gekanator/games', params: {
           guessed_post_id: guessed_post.id,
           correct_post_id: correct_post.id,
-          won: false,
           question_count: 4,
           answers: [{ question_id: 'tag:1', answer: 'no' }] }
 
       expect(response).to have_http_status(:created)
-      expect(GekanatorGame.find(json['id']).correct_post).to eq(correct_post)
+      game = GekanatorGame.find(json['id'])
+      expect(game.correct_post).to eq(correct_post)
+      expect(game.won).to eq(false)
     end
 
-    it 'rejects a lost game without the correct post' do
+    it 'rejects a game without the correct post' do
       sign_in_as user
 
       post '/gekanator/games', params: {
           guessed_post_id: guessed_post.id,
-          won: false,
           question_count: 4,
           answers: [{ question_id: 'tag:1', answer: 'no' }] }
 
@@ -53,7 +53,7 @@ RSpec.describe 'Gekanator games API', type: :request do
     it 'requires a user' do
       post '/gekanator/games', params: {
           guessed_post_id: guessed_post.id,
-          won: true,
+          correct_post_id: guessed_post.id,
           question_count: 1,
           answers: [] }
 

frontend/src/lib/gekanator.ts

@@ -17,11 +17,9 @@ export type GekanatorAnswerLog = {
 
 export type GekanatorQuestionKind =
     | 'tag'
-    | 'title'
-    | 'date'
-    | 'media'
     | 'source'
-    | 'structure'
+    | 'title'
+    | 'original_date'
 
 export type GekanatorQuestion = {
     id:    string
@@ -54,6 +52,19 @@ const hostOf = (post: Post): string | null => {
 }
 
 
+const originalYearOf = (post: Post): number | null => {
+  const value = post.originalCreatedFrom || post.originalCreatedBefore
+  if (!(value))
+    return null
+
+  const date = new Date (value)
+  if (Number.isNaN (date.getTime ()))
+    return null
+
+  return date.getFullYear ()
+}
+
+
 const tagQuestionKey = ({ category, name }: { category: string; name: string }): string =>
     `${ category }:${ name }`
 
@@ -113,9 +124,11 @@ export const buildGekanatorQuestions = (posts: Post[]): GekanatorQuestion[] => {
 	  && !(tag.name.includes ('bot操作')))
       .map (tag => tagQuestionKey (tag))))
   const hosts = countBy (posts.map (hostOf).filter ((host): host is string => Boolean (host)))
-  const tagMedian = median (posts.map (post => post.tags.length))
+  const originalYears = countBy (
+      posts
+      .map (originalYearOf)
+      .filter ((year): year is number => year !== null))
   const titleLengthMedian = median (posts.map (post => post.title?.length ?? 0))
-  const currentYear = new Date ().getFullYear ()
 
   const usefulEntries = <T extends string | number> (counts: Map<T, number>) =>
       [...counts.entries ()]
@@ -144,63 +157,41 @@ export const buildGekanatorQuestions = (posts: Post[]): GekanatorQuestion[] => {
       .filter (([, count]) => count >= 2 && count <= Math.max (2, posts.length * .7))
       .slice (0, 20)
       .map (([host]) => ({
-      id:   `source:${ host }`,
-      text: `${ host } の投稿を思ひ浮かべてゐる?`,
-      kind: 'source' as const,
-      test: (post: Post) => hostOf (post) === host }))
+	  id:   `source:${ host }`,
+	  text: `${ host } の投稿を思ひ浮かべてゐる?`,
+	  kind: 'source' as const,
+	  test: (post: Post) => hostOf (post) === host }))
 
-  return [
-      ...sourceQuestions,
-      {
-	  id:   'title:present',
-	  text: '題名が付いてゐる投稿?',
-	  kind: 'title',
-	  test: post => Boolean (post.title) },
+  const originalYearQuestions = usefulEntries (originalYears)
+      .filter (([, count]) => count >= 2 && count <= Math.max (2, posts.length * .7))
+      .slice (0, 20)
+      .map (([year]) => ({
+	  id:   `original-year:${ year }`,
+	  text: `オリジナルの投稿年は ${ year } 年?`,
+	  kind: 'original_date' as const,
+	  test: (post: Post) => originalYearOf (post) === year }))
+
+  const titleQuestions = [
       {
 	  id:   'title:long',
 	  text: '題名が長めの投稿?',
-	  kind: 'title',
-	  test: post => (post.title?.length ?? 0) > titleLengthMedian },
+	  kind: 'title' as const,
+	  test: (post: Post) => (post.title?.length ?? 0) > titleLengthMedian },
       {
 	  id:   'title:ascii',
 	  text: '題名に英数字が混じってゐる?',
-	  kind: 'title',
-	  test: post => /[A-Za-z0-9]/.test (post.title ?? '') },
-      {
-	  id:   'media:thumbnail',
-	  text: 'ぱっと見でサムネが付いてゐる投稿?',
-	  kind: 'media',
-	  test: post => Boolean (post.thumbnail || post.thumbnailBase) },
-      {
-	  id:   'media:video-source',
-	  text: '動画として見られる投稿?',
-	  kind: 'media',
-	  test: post => /nicovideo|youtube|youtu\.be/.test (post.url) },
-      {
-	  id:   'structure:many-tags',
-	  text: 'タグが多めに付いてゐる投稿?',
-	  kind: 'structure',
-	  test: post => post.tags.length > tagMedian },
-      {
-	  id:   'structure:no-title',
-	  text: '題名がまだ付いてゐない投稿?',
-	  kind: 'structure',
-	  test: post => !(post.title) },
-      {
-	  id:   'date:recent',
-	  text: '最近追加されたほうの投稿?',
-	  kind: 'date',
-	  test: post => new Date (post.createdAt).getFullYear () >= currentYear - 1 },
-      {
-	  id:   'date:old',
-	  text: 'むかし追加されたほうの投稿?',
-	  kind: 'date',
-	  test: post => new Date (post.createdAt).getFullYear () <= currentYear - 3 },
-      {
-	  id:   'date:original-known',
-	  text: 'オリジナルの投稿日時が分かってゐる投稿?',
-	  kind: 'date',
-	  test: post => Boolean (post.originalCreatedFrom || post.originalCreatedBefore) },
+	  kind: 'title' as const,
+	  test: (post: Post) => /[A-Za-z0-9]/.test (post.title ?? '') }]
+      .filter (question => {
+	const yes = posts.filter (post => question.test (post)).length
+	const no = posts.length - yes
+	return yes >= 2 && no >= 2 && yes <= posts.length * .7 && no <= posts.length * .7
+      })
+
+  return [
+      ...sourceQuestions,
+      ...originalYearQuestions,
+      ...titleQuestions,
       ...tagQuestions]
 }
 
@@ -208,18 +199,15 @@ export const buildGekanatorQuestions = (posts: Post[]): GekanatorQuestion[] => {
 export const saveGekanatorGame = async ({
     guessedPostId,
     correctPostId,
-    won,
     answers,
 }: {
     guessedPostId:  number
-    correctPostId:  number | null
-    won:            boolean
+    correctPostId:  number
     answers:        GekanatorAnswerLog[]
 }): Promise<{ id: number }> =>
     await apiPost ('/gekanator/games', {
 	guessed_post_id: guessedPostId,
 	correct_post_id: correctPostId,
-	won,
 	question_count: answers.length,
 	answers: answers.map (answer => ({
 	    question_id: answer.questionId,

frontend/src/pages/GekanatorPage.tsx

@@ -18,7 +18,7 @@ import type { GekanatorAnswerLog,
 	      GekanatorQuestion } from '@/lib/gekanator'
 import type { Post } from '@/types'
 
-type Phase = 'intro' | 'question' | 'guess' | 'continue' | 'learned'
+type Phase = 'intro' | 'question' | 'guess' | 'continue' | 'review' | 'learned'
 
 type AnswerOption = {
     label:  string
@@ -41,14 +41,16 @@ type GameSnapshot = {
     scores:                  Map<number, number>
     answers:                 GekanatorAnswerLog[]
     askedIds:                Set<string>
-    candidateIds:            Set<number> | null
     softenedQuestionIds:     Set<string>
-    questionBank:            GekanatorQuestion[]
+    askedQuestionBank:       GekanatorQuestion[]
     search:                  string
+    selectingCorrectPost:    boolean
     rejectedPostIds:         Set<number>
     lastGuessQuestionCount:  number
     lastRejectedGuessId:     number | null
-    activeGuessId:           number | null }
+    activeGuessId:           number | null
+    reviewGuessedPostId:     number | null
+    reviewCorrectPostId:     number | null }
 
 const answerOptions: AnswerOption[] = [
     { label: 'はい', value: 'yes' },
@@ -58,6 +60,9 @@ const answerOptions: AnswerOption[] = [
     { label: 'わからない', value: 'unknown' }]
 
 const questionsBetweenGuesses = 25
+const minQuestionsBeforeCertainGuess = 5
+const certainGuessPercent = 99.5
+const runnerUpMaxPercent = .5
 const hardMaxQuestions = 80
 const softenedAnswerWeight = .35
 const confidenceTemperature = 6
@@ -87,18 +92,14 @@ const answerWeightFor = (
 
 
 const questionDifficulty = (question: GekanatorQuestion): number => {
-  if (question.id === 'structure:many-tags')
-    return 6
-  if (question.id.startsWith ('date:'))
-    return 5
-  if (question.id === 'title:long' || question.id === 'title:ascii')
-    return 4
   if (question.kind === 'source')
     return 4
+  if (question.kind === 'original_date')
+    return 4
+  if (question.kind === 'title')
+    return 4
   if (question.kind === 'tag')
     return 3
-  if (question.kind === 'title' || question.kind === 'structure')
-    return 2
 
   return 1
 }
@@ -136,6 +137,47 @@ const recalculateScores = ({
 }
 
 
+const candidatePostsFor = ({
+    posts,
+    questions,
+    answers,
+    softenedQuestionIds,
+    rejectedPostIds,
+}: {
+    posts:                Post[]
+    questions:            GekanatorQuestion[]
+    answers:              GekanatorAnswerLog[]
+    softenedQuestionIds:  Set<string>
+    rejectedPostIds:      Set<number>
+}): Post[] => {
+  const questionById = new Map (questions.map (question => [question.id, question]))
+
+  return posts.filter (post => {
+    if (rejectedPostIds.has (post.id))
+      return false
+
+    return answers.every (answer => {
+      if (softenedQuestionIds.has (answer.questionId))
+	return true
+
+      const question = questionById.get (answer.questionId)
+      if (!(question))
+	return true
+
+      switch (answer.answer)
+      {
+      case 'yes':
+	return question.test (post)
+      case 'no':
+	return !(question.test (post))
+      default:
+	return true
+      }
+    })
+  })
+}
+
+
 const confidencesFor = (posts: Post[], scores: Map<number, number>): Confidence[] => {
   if (posts.length === 0)
     return []
@@ -306,26 +348,12 @@ const chooseQuestion = ({
 	  return null
 
 	const splitScore = Math.abs (candidates.length / 2 - yes)
-	const answerPreviews = answerOptions.map (option =>
-	    previewAnswer ({
-		posts: candidates.map (({ post }) => post),
-		scores,
-		question,
-		answer: option.value }))
-	const expectedEntropy =
-	    answerPreviews.reduce ((sum, preview) => sum + preview.entropy, 0)
-	    / answerPreviews.length
-	const expectedCandidateCount =
-	    answerPreviews.reduce ((sum, preview) => sum + preview.candidateCount, 0)
-	    / answerPreviews.length
-	const kindPenalty = askedIds.has (question.kind) ? 2 : 0
-	const tagPenalty = question.kind === 'tag' ? 0 : 10
+	const tagPenalty = question.kind === 'tag' ? 0 : 20
 	const minSide = candidates.length < 10 ? 1 : Math.max (3, candidates.length * .08)
 	const narrowPenalty = yes < minSide || no < minSide ? candidates.length : 0
 
 	return { question,
-		 score: splitScore + expectedEntropy + expectedCandidateCount / 8
-			+ kindPenalty + tagPenalty + narrowPenalty,
+		 score: splitScore + tagPenalty + narrowPenalty,
 		 narrow: narrowPenalty > 0 }
       })
       .filter ((item): item is {
@@ -373,34 +401,47 @@ const GekanatorPage: FC = () => {
   const [scores, setScores] = useState<Map<number, number>> (new Map ())
   const [answers, setAnswers] = useState<GekanatorAnswerLog[]> ([])
   const [askedIds, setAskedIds] = useState<Set<string>> (new Set ())
-  const [candidateIds, setCandidateIds] = useState<Set<number> | null> (null)
   const [softenedQuestionIds, setSoftenedQuestionIds] = useState<Set<string>> (new Set ())
-  const [questionBank, setQuestionBank] = useState<GekanatorQuestion[]> ([])
+  const [askedQuestionBank, setAskedQuestionBank] = useState<GekanatorQuestion[]> ([])
   const [search, setSearch] = useState ('')
+  const [selectingCorrectPost, setSelectingCorrectPost] = useState (false)
   const [saved, setSaved] = useState (false)
   const [resultWon, setResultWon] = useState<boolean | null> (null)
   const [rejectedPostIds, setRejectedPostIds] = useState<Set<number>> (new Set ())
   const [lastGuessQuestionCount, setLastGuessQuestionCount] = useState (0)
   const [lastRejectedGuessId, setLastRejectedGuessId] = useState<number | null> (null)
   const [activeGuessId, setActiveGuessId] = useState<number | null> (null)
+  const [reviewGuessedPostId, setReviewGuessedPostId] = useState<number | null> (null)
+  const [reviewCorrectPostId, setReviewCorrectPostId] = useState<number | null> (null)
   const [history, setHistory] = useState<GameSnapshot[]> ([])
 
   const { data: posts = [], isLoading, error } = useQuery ({
       queryKey: gekanatorKeys.posts (),
       queryFn: fetchGekanatorPosts })
 
-  const candidatePosts = useMemo (
-      () => posts.filter (post => candidateIds === null || candidateIds.has (post.id)),
-      [posts, candidateIds])
   const eligiblePosts = useMemo (
-      () => candidatePosts.filter (post => !(rejectedPostIds.has (post.id))),
-      [candidatePosts, rejectedPostIds])
+      () => candidatePostsFor ({
+	  posts,
+	  questions: askedQuestionBank,
+	  answers,
+	  softenedQuestionIds,
+	  rejectedPostIds }),
+      [posts, askedQuestionBank, answers, softenedQuestionIds, rejectedPostIds])
   const questions = useMemo (
       () => buildGekanatorQuestions (eligiblePosts.length > 1 ? eligiblePosts : posts),
       [eligiblePosts, posts])
   const scoringQuestions = useMemo (() => {
-    return mergeQuestions ([...questions, ...questionBank])
-  }, [questions, questionBank])
+    return mergeQuestions ([...questions, ...askedQuestionBank])
+  }, [questions, askedQuestionBank])
+  const questionsSinceLastGuess = answers.length - lastGuessQuestionCount
+  const nonRejectedPosts = useMemo (
+      () => posts.filter (post => !(rejectedPostIds.has (post.id))),
+      [posts, rejectedPostIds])
+  const questionPosts =
+      eligiblePosts.length > 1
+	|| questionsSinceLastGuess >= minQuestionsBeforeCertainGuess
+	  ? eligiblePosts
+	  : nonRejectedPosts
   const topScoredPosts = useMemo (
       () => eligiblePosts
       .map (post => ({ post, score: scores.get (post.id) ?? 0 }))
@@ -408,7 +449,7 @@ const GekanatorPage: FC = () => {
       .slice (0, 3),
       [eligiblePosts, scores])
   const currentQuestion = chooseQuestion ({
-      posts: eligiblePosts, questions: scoringQuestions, scores, askedIds })
+      posts: questionPosts, questions: scoringQuestions, scores, askedIds })
   const answerPreviews = useMemo (
       () => currentQuestion
 	  ? answerOptions.map (option => previewAnswer ({
@@ -418,29 +459,122 @@ const GekanatorPage: FC = () => {
 	      answer: option.value }))
 	  : [],
       [currentQuestion, eligiblePosts, scores])
-  const guess = bestPost (eligiblePosts, scores)
+  const guessablePosts =
+      eligiblePosts.length > 0
+	? eligiblePosts
+	: nonRejectedPosts
+  const guess = bestPost (guessablePosts, scores)
   const displayedGuess =
       posts.find (post => post.id === activeGuessId) ?? guess
-  const saveMutation = useMutation ({ mutationFn: saveGekanatorGame })
+  const reviewGuessedPost =
+      posts.find (post => post.id === reviewGuessedPostId) ?? null
+  const reviewCorrectPost =
+      posts.find (post => post.id === reviewCorrectPostId) ?? null
+  const saveMutation = useMutation ({
+      mutationFn: saveGekanatorGame,
+      onSuccess: () => {
+	setSaved (true)
+	setResultWon (reviewGuessedPostId === reviewCorrectPostId)
+	setPhase ('learned')
+      }})
 
   const reset = () => {
+    saveMutation.reset ()
     setPhase ('intro')
     setScores (new Map ())
     setAnswers ([])
     setAskedIds (new Set ())
-    setCandidateIds (null)
     setSoftenedQuestionIds (new Set ())
-    setQuestionBank ([])
+    setAskedQuestionBank ([])
     setSearch ('')
+    setSelectingCorrectPost (false)
     setSaved (false)
     setResultWon (null)
     setRejectedPostIds (new Set ())
     setLastGuessQuestionCount (0)
     setLastRejectedGuessId (null)
     setActiveGuessId (null)
+    setReviewGuessedPostId (null)
+    setReviewCorrectPostId (null)
     setHistory ([])
   }
 
+  const recoverQuestionState = ({
+      nextAnswers,
+      nextAskedIds,
+      nextAskedQuestionBank,
+      nextSoftenedQuestionIds,
+      nextRejectedPostIds,
+  }: {
+      nextAnswers:              GekanatorAnswerLog[]
+      nextAskedIds:             Set<string>
+      nextAskedQuestionBank:    GekanatorQuestion[]
+      nextSoftenedQuestionIds:  Set<string>
+      nextRejectedPostIds:      Set<number>
+  }) => {
+    let recoveredSoftenedQuestionIds = new Set (nextSoftenedQuestionIds)
+    let recoveredScores = recalculateScores ({
+	posts,
+	questions: nextAskedQuestionBank,
+	answers: nextAnswers,
+	softenedQuestionIds: recoveredSoftenedQuestionIds })
+    let recoveredEligiblePosts = candidatePostsFor ({
+	posts,
+	questions: nextAskedQuestionBank,
+	answers: nextAnswers,
+	softenedQuestionIds: recoveredSoftenedQuestionIds,
+	rejectedPostIds: nextRejectedPostIds })
+    let recoveredScoringQuestions = mergeQuestions ([
+	...buildGekanatorQuestions (
+	    recoveredEligiblePosts.length > 1 ? recoveredEligiblePosts : posts),
+	...nextAskedQuestionBank])
+
+    while (
+	recoveredEligiblePosts.length === 0
+	|| (
+	    recoveredEligiblePosts.length !== 1
+	    && !(chooseQuestion ({
+		posts: recoveredEligiblePosts,
+		questions: recoveredScoringQuestions,
+		scores: recoveredScores,
+		askedIds: nextAskedIds })))
+    )
+      {
+	if (nextAnswers.length >= hardMaxQuestions)
+	  break
+
+	const softened = softenNextQuestionIds ({
+	    questions: nextAskedQuestionBank,
+	    answers: nextAnswers,
+	    softenedQuestionIds: recoveredSoftenedQuestionIds })
+	if (!(softened))
+	  break
+
+	recoveredSoftenedQuestionIds = softened
+	recoveredScores = recalculateScores ({
+	    posts,
+	    questions: nextAskedQuestionBank,
+	    answers: nextAnswers,
+	    softenedQuestionIds: recoveredSoftenedQuestionIds })
+	recoveredEligiblePosts = candidatePostsFor ({
+	    posts,
+	    questions: nextAskedQuestionBank,
+	    answers: nextAnswers,
+	    softenedQuestionIds: recoveredSoftenedQuestionIds,
+	    rejectedPostIds: nextRejectedPostIds })
+	recoveredScoringQuestions = mergeQuestions ([
+	    ...buildGekanatorQuestions (
+		recoveredEligiblePosts.length > 1 ? recoveredEligiblePosts : posts),
+	    ...nextAskedQuestionBank])
+      }
+
+    return {
+	softenedQuestionIds: recoveredSoftenedQuestionIds,
+	scores: recoveredScores,
+	eligiblePosts: recoveredEligiblePosts,
+	scoringQuestions: recoveredScoringQuestions }
+  }
+
   const answer = (value: GekanatorAnswerValue) => {
     if (!(currentQuestion))
       {
@@ -454,92 +588,66 @@ const GekanatorPage: FC = () => {
 	scores: new Map (scores),
 	answers: [...answers],
 	askedIds: new Set (askedIds),
-	candidateIds: candidateIds === null ? null : new Set (candidateIds),
 	softenedQuestionIds: new Set (softenedQuestionIds),
-	questionBank: [...questionBank],
+	askedQuestionBank: [...askedQuestionBank],
 	search,
+	selectingCorrectPost,
 	rejectedPostIds: new Set (rejectedPostIds),
 	lastGuessQuestionCount,
 	lastRejectedGuessId,
-	activeGuessId }])
+	activeGuessId,
+	reviewGuessedPostId,
+	reviewCorrectPostId }])
     const nextAnswers = [...answers, {
 	questionId:    currentQuestion.id,
 	questionText:  currentQuestion.text,
 	answer:        value }]
     const nextAskedIds = new Set ([...askedIds, currentQuestion.id])
-    const nextQuestionBank = [
-	...questionBank.filter (question => question.id !== currentQuestion.id),
+    const nextAskedQuestionBank = [
+	...askedQuestionBank.filter (question => question.id !== currentQuestion.id),
 	currentQuestion]
-    const hardFilteredPosts =
-	value === 'yes'
-	  ? eligiblePosts.filter (post => currentQuestion.test (post))
-	  : value === 'no'
-	    ? eligiblePosts.filter (post => !(currentQuestion.test (post)))
-	    : eligiblePosts
-    let nextCandidateIds =
-	(value === 'yes' || value === 'no') && hardFilteredPosts.length > 0
-	  ? new Set (hardFilteredPosts.map (post => post.id))
-	  : candidateIds
-    let nextSoftenedQuestionIds = new Set (softenedQuestionIds)
-    let nextScores = recalculateScores ({
-	posts,
-	questions: nextQuestionBank,
-	answers: nextAnswers,
-	softenedQuestionIds: nextSoftenedQuestionIds })
-
-    let nextEligiblePosts =
-	posts.filter (post =>
-	    (nextCandidateIds === null || nextCandidateIds.has (post.id))
-	    && !(rejectedPostIds.has (post.id)))
-    let nextScoringQuestions = mergeQuestions ([
-	...buildGekanatorQuestions (nextEligiblePosts.length > 1 ? nextEligiblePosts : posts),
-	...nextQuestionBank])
-    while (
-	nextAnswers.length < hardMaxQuestions
-	&& nextEligiblePosts.length > 1
-	&& !(chooseQuestion ({
-	    posts: nextEligiblePosts,
-	    questions: nextScoringQuestions,
-	    scores: nextScores,
-	    askedIds: nextAskedIds }))
-    )
-      {
-	const softened = softenNextQuestionIds ({
-	    questions: nextQuestionBank,
-	    answers: nextAnswers,
-	    softenedQuestionIds: nextSoftenedQuestionIds })
-	if (!(softened))
-	  break
-
-	nextSoftenedQuestionIds = softened
-	nextCandidateIds = null
-	nextEligiblePosts = posts.filter (post => !(rejectedPostIds.has (post.id)))
-	nextScoringQuestions = mergeQuestions ([
-	    ...buildGekanatorQuestions (nextEligiblePosts),
-	    ...nextQuestionBank])
-	nextScores = recalculateScores ({
-	    posts,
-	    questions: nextQuestionBank,
-	    answers: nextAnswers,
-	    softenedQuestionIds: nextSoftenedQuestionIds })
-      }
+    const recovered = recoverQuestionState ({
+	nextAnswers,
+	nextAskedIds,
+	nextAskedQuestionBank,
+	nextSoftenedQuestionIds: softenedQuestionIds,
+	nextRejectedPostIds: rejectedPostIds })
+    const nextSoftenedQuestionIds = recovered.softenedQuestionIds
+    const nextScores = recovered.scores
+    const nextEligiblePosts = recovered.eligiblePosts
 
     setScores (nextScores)
     setAskedIds (nextAskedIds)
-    setCandidateIds (nextCandidateIds)
     setSoftenedQuestionIds (nextSoftenedQuestionIds)
-    setQuestionBank (nextQuestionBank)
+    setAskedQuestionBank (nextAskedQuestionBank)
     setAnswers (nextAnswers)
 
-    const nextGuess = bestPost (nextEligiblePosts, nextScores)
+    const nextGuessablePosts =
+	nextEligiblePosts.length > 0
+	  ? nextEligiblePosts
+	  : nonRejectedPosts
+    const nextGuess = bestPost (nextGuessablePosts, nextScores)
     const nextQuestionCount = answers.length + 1
-    const definitelyKnown = nextEligiblePosts.length === 1
-    const enoughQuestions =
-	nextQuestionCount - lastGuessQuestionCount >= questionsBetweenGuesses
+    const nextQuestionsSinceLastGuess =
+	nextQuestionCount - lastGuessQuestionCount
+    const nextConfidences = confidencesFor (nextGuessablePosts, nextScores)
+    const topConfidence = nextConfidences[0] ?? null
+    const runnerUpConfidence = nextConfidences[1] ?? null
+    const structurallyCertain = nextEligiblePosts.length === 1
+    const statisticallyCertain =
+	topConfidence !== null
+	&& topConfidence.percent >= certainGuessPercent
+	&& (runnerUpConfidence === null
+	    || runnerUpConfidence.percent <= runnerUpMaxPercent)
+    const canGuessByQuestionCount =
+	nextQuestionsSinceLastGuess >= questionsBetweenGuesses
+    const canGuessEarlyByConfidence =
+	nextQuestionsSinceLastGuess >= minQuestionsBeforeCertainGuess
+	&& (structurallyCertain || statisticallyCertain)
     const shouldGuess =
 	nextQuestionCount >= hardMaxQuestions
-	|| definitelyKnown
-	|| enoughQuestions
+	|| canGuessByQuestionCount
+	|| canGuessEarlyByConfidence
     if (shouldGuess)
       {
 	setActiveGuessId (nextGuess?.id ?? null)
@@ -548,20 +656,35 @@ const GekanatorPage: FC = () => {
       }
   }
 
-  const saveResult = (won: boolean, correctPostId: number | null) => {
+  const startReview = (correctPostId: number) => {
     const guessedPostId =
-	won ? displayedGuess?.id : lastRejectedGuessId ?? displayedGuess?.id
-    if (!(guessedPostId) || saved)
+	phase === 'continue'
+	  ? lastRejectedGuessId ?? displayedGuess?.id
+	  : displayedGuess?.id ?? lastRejectedGuessId
+    if (!(guessedPostId))
+      return
+
+    saveMutation.reset ()
+    setReviewGuessedPostId (guessedPostId)
+    setReviewCorrectPostId (correctPostId)
+    setSearch ('')
+    setSelectingCorrectPost (false)
+    setPhase ('review')
+  }
+
+  const saveReviewedResult = () => {
+    if (
+	reviewGuessedPostId === null
+	|| reviewCorrectPostId === null
+	|| saveMutation.isPending
+	|| saved
+    )
       return
 
-    setSaved (true)
-    setResultWon (won)
     saveMutation.mutate ({
-	guessedPostId,
-	correctPostId,
-	won,
+	guessedPostId: reviewGuessedPostId,
+	correctPostId: reviewCorrectPostId,
 	answers })
-    setPhase ('learned')
   }
 
   const rejectGuess = () => {
@@ -571,13 +694,14 @@ const GekanatorPage: FC = () => {
     setLastRejectedGuessId (displayedGuess.id)
     if (answers.length >= hardMaxQuestions)
       {
-	setSearch (' ')
+	setSelectingCorrectPost (true)
 	return
       }
 
     setRejectedPostIds (new Set ([...rejectedPostIds, displayedGuess.id]))
     setActiveGuessId (null)
     setSearch ('')
+    setSelectingCorrectPost (false)
     setLastGuessQuestionCount (answers.length)
     setPhase ('continue')
   }
@@ -591,30 +715,66 @@ const GekanatorPage: FC = () => {
     setScores (snapshot.scores)
     setAnswers (snapshot.answers)
     setAskedIds (snapshot.askedIds)
-    setCandidateIds (snapshot.candidateIds)
     setSoftenedQuestionIds (snapshot.softenedQuestionIds)
-    setQuestionBank (snapshot.questionBank)
+    setAskedQuestionBank (snapshot.askedQuestionBank)
     setSearch (snapshot.search)
+    setSelectingCorrectPost (snapshot.selectingCorrectPost)
     setRejectedPostIds (snapshot.rejectedPostIds)
     setLastGuessQuestionCount (snapshot.lastGuessQuestionCount)
     setLastRejectedGuessId (snapshot.lastRejectedGuessId)
     setActiveGuessId (snapshot.activeGuessId)
+    setReviewGuessedPostId (snapshot.reviewGuessedPostId)
+    setReviewCorrectPostId (snapshot.reviewCorrectPostId)
     setHistory (history.slice (0, -1))
   }
 
-  const softenAndContinue = () => {
-    const softened = softenNextQuestionIds ({
-	questions: scoringQuestions, answers, softenedQuestionIds })
-    if (!(softened))
-      return
+  const continueGame = () => {
+    setSearch ('')
+    setSelectingCorrectPost (false)
 
-    setSoftenedQuestionIds (softened)
-    setCandidateIds (null)
-    setScores (
-	recalculateScores ({ posts,
-			     questions: scoringQuestions,
-			     answers,
-			     softenedQuestionIds: softened }))
+    const recovered = recoverQuestionState ({
+	nextAnswers: answers,
+	nextAskedIds: askedIds,
+	nextAskedQuestionBank: askedQuestionBank,
+	nextSoftenedQuestionIds: softenedQuestionIds,
+	nextRejectedPostIds: rejectedPostIds })
+
+    setSoftenedQuestionIds (recovered.softenedQuestionIds)
+    setScores (recovered.scores)
+
+    const nextQuestion = chooseQuestion ({
+	posts: recovered.eligiblePosts.length > 1
+	    ? recovered.eligiblePosts
+	    : nonRejectedPosts,
+	questions: recovered.scoringQuestions,
+	scores: recovered.scores,
+	askedIds })
+
+    if (nextQuestion)
+      {
+	setPhase ('question')
+	return
+      }
+
+    setActiveGuessId (guess?.id ?? null)
+    setPhase ('guess')
+  }
+
+  const correctAnswerAt = (index: number, value: GekanatorAnswerValue) => {
+    setAnswers (answers.map ((answer, i) =>
+	i === index ? { ...answer, answer: value } : answer))
+  }
+
+  const selectCorrectPost = (post: Post) => {
+    if (phase === 'review')
+      {
+	setReviewCorrectPostId (post.id)
+	setSelectingCorrectPost (false)
+	setSearch ('')
+	return
+      }
+
+    startReview (post.id)
   }
 
   const filteredPosts = posts
@@ -646,6 +806,7 @@ const GekanatorPage: FC = () => {
   return (
       <MainArea className="bg-yellow-50 dark:bg-red-975">
 	<Helmet>
+	  <meta name="robots" content="noindex"/>
 	  <title>{`グカネータ | ${ SITE_TITLE }`}</title>
 	</Helmet>
 
@@ -745,29 +906,19 @@ const GekanatorPage: FC = () => {
 		{phase === 'question' && !(currentQuestion) && (
 		    <div className="space-y-4">
 		      <p className="text-xl font-bold">
-			さっきまでの答へを少し疑って考へ直すよ．
+			もう十分わかった。
 		      </p>
-		      {answers.length >= hardMaxQuestions || eligiblePosts.length <= 1
-		       ? (
-			  <button
-			      type="button"
-			      className="rounded border border-yellow-300 px-4 py-2
-					 hover:bg-yellow-100 dark:border-red-700
-					 dark:hover:bg-red-900"
-			      onClick={() => {
-				setActiveGuessId (guess?.id ?? null)
-				setPhase ('guess')
-			      }}>
-			    推測へ
-			  </button>)
-		       : (
-			  <button
-			      type="button"
-			      className="rounded bg-pink-600 px-4 py-2 font-bold text-white
-					 hover:bg-pink-500"
-			      onClick={softenAndContinue}>
-			    考へ直す
-			  </button>)}
+		      <button
+			  type="button"
+			  className="rounded border border-yellow-300 px-4 py-2
+				     hover:bg-yellow-100 dark:border-red-700
+				     dark:hover:bg-red-900"
+			  onClick={() => {
+			    setActiveGuessId (guess?.id ?? null)
+			    setPhase ('guess')
+			  }}>
+			答える
+		      </button>
 		    </div>)}
 
 		{phase === 'guess' && displayedGuess && (
@@ -779,7 +930,10 @@ const GekanatorPage: FC = () => {
 			    type="button"
 			    className="rounded bg-pink-600 px-4 py-2 font-bold text-white
 				       hover:bg-pink-500"
-			    onClick={() => saveResult (true, null)}>
+			    onClick={() => {
+			      if (displayedGuess)
+				startReview (displayedGuess.id)
+			    }}>
 			  当たり
 			</button>
 			<button
@@ -800,6 +954,10 @@ const GekanatorPage: FC = () => {
 			      戻る
 			    </button>)}
 		      </div>
+		      {saveMutation.isError && (
+			  <p className="text-sm text-red-600">
+			    学習ログの保存に失敗しました。もう一度試せます。
+			  </p>)}
 		    </div>)}
 
 		{phase === 'continue' && (
@@ -810,7 +968,7 @@ const GekanatorPage: FC = () => {
 			    type="button"
 			    className="rounded bg-pink-600 px-4 py-2 font-bold text-white
 				       hover:bg-pink-500"
-			    onClick={() => setPhase ('question')}>
+			    onClick={continueGame}>
 			  はい
 			</button>
 			<button
@@ -818,7 +976,7 @@ const GekanatorPage: FC = () => {
 			    className="rounded border border-yellow-300 px-4 py-2
 				       hover:bg-yellow-100 dark:border-red-700
 				       dark:hover:bg-red-900"
-			    onClick={() => setSearch (' ')}>
+			    onClick={() => setSelectingCorrectPost (true)}>
 			  いいえ
 			</button>
 			{history.length > 0 && (
@@ -833,13 +991,98 @@ const GekanatorPage: FC = () => {
 		      </div>
 		    </div>)}
 
+		{phase === 'review' && (
+		    <div className="space-y-4">
+		      <div>
+			<p className="text-sm text-neutral-500">保存前確認</p>
+			<p className="text-xl font-bold">今回の結果を確認してね。</p>
+		      </div>
+
+		      {reviewGuessedPost && (
+			  <div className="space-y-2">
+			    <div className="font-bold">推測した投稿</div>
+			    <PostMiniCard post={reviewGuessedPost}/>
+			  </div>)}
+
+		      <div className="space-y-2">
+			<div className="font-bold">正解の投稿</div>
+			{reviewCorrectPost
+			 ? <PostMiniCard post={reviewCorrectPost}/>
+			 : <p className="text-sm text-red-600">正解投稿を選んでください。</p>}
+			<button
+			    type="button"
+			    className="rounded border border-yellow-300 px-3 py-2
+				       hover:bg-yellow-100 dark:border-red-700
+				       dark:hover:bg-red-900"
+			    onClick={() => setSelectingCorrectPost (true)}>
+			  正解投稿を変更
+			</button>
+		      </div>
+
+		      <div className="space-y-2">
+			<div className="font-bold">質問と回答</div>
+			<div className="space-y-2">
+			  {answers.map ((answer, index) => (
+			      <div
+				  key={`${ answer.questionId }:${ index }`}
+				  className="rounded border border-yellow-100 p-3
+					     dark:border-red-900">
+				<div className="text-sm text-neutral-600 dark:text-neutral-300">
+				  質問 {index + 1}
+				</div>
+				<div className="font-bold">{answer.questionText}</div>
+				<select
+				    value={answer.answer}
+				    className="mt-2 rounded border border-yellow-300 bg-white px-2 py-1
+					       dark:border-red-700 dark:bg-red-950"
+				    onChange={ev =>
+				      correctAnswerAt (
+					  index,
+					  ev.target.value as GekanatorAnswerValue)}>
+				  {answerOptions.map (option => (
+				      <option key={option.value} value={option.value}>
+					{option.label}
+				      </option>))}
+				</select>
+			      </div>))}
+			</div>
+		      </div>
+
+		      {reviewGuessedPostId !== null && reviewCorrectPostId !== null && (
+			  <p className="text-sm text-neutral-600 dark:text-neutral-300">
+			    判定: {reviewGuessedPostId === reviewCorrectPostId ? '当たり' : '違ひ'}
+			  </p>)}
+
+		      {saveMutation.isError && (
+			  <p className="text-sm text-red-600">
+			    学習ログの保存に失敗しました。もう一度試せます。
+			  </p>)}
+
+		      <div className="flex flex-wrap gap-2">
+			<button
+			    type="button"
+			    className="rounded bg-pink-600 px-4 py-2 font-bold text-white
+				       hover:bg-pink-500 disabled:opacity-50"
+			    disabled={
+			      reviewCorrectPostId === null || saveMutation.isPending || saved
+			    }
+			    onClick={saveReviewedResult}>
+			  保存
+			</button>
+			<button
+			    type="button"
+			    className="rounded border border-neutral-300 px-4 py-2
+				       hover:bg-neutral-100 dark:border-neutral-700
+				       dark:hover:bg-red-900"
+			    onClick={() => setPhase ('guess')}>
+			  戻る
+			</button>
+		      </div>
+		    </div>)}
+
 		{phase === 'learned' && (
 		    <div className="space-y-3">
 		      <p>覚えたよ．次はもっと見通す．</p>
-		      {saveMutation.isError && (
-			  <p className="text-sm text-red-600">
-			    ただし学習ログの保存には失敗しました．
-			  </p>)}
 		      <button
 			  type="button"
 			  className="rounded bg-pink-600 px-4 py-2 font-bold text-white
@@ -852,7 +1095,8 @@ const GekanatorPage: FC = () => {
 	    </div>
 	  </section>
 
-	  {['guess', 'continue', 'question'].includes (phase) && search !== '' && (
+	  {['guess', 'continue', 'question', 'review'].includes (phase)
+	   && selectingCorrectPost && (
 	      <section className="rounded-lg border border-yellow-300 bg-white p-4
 				  dark:border-red-800 dark:bg-red-950">
 		<label className="block space-y-2">
@@ -872,10 +1116,14 @@ const GekanatorPage: FC = () => {
 			  className={cn ('block w-full rounded border border-yellow-200 p-3',
 					 'text-left hover:bg-yellow-100',
 					 'dark:border-red-800 dark:hover:bg-red-900')}
-			  onClick={() => saveResult (false, post.id)}>
+			  onClick={() => selectCorrectPost (post)}>
 			<PostMiniCard post={post}/>
 		      </button>))}
 		  {search.trim () && filteredPosts.length === 0 && '見つかりません．'}
+		  {saveMutation.isError && (
+		      <p className="text-sm text-red-600">
+			学習ログの保存に失敗しました。もう一度試せます。
+		      </p>)}
 		</div>
 	      </section>)}
 	</div>