math_cms/app/Services/QuestionLocalService.php

<?php

namespace App\Services;

use App\Models\KnowledgePoint;
use App\Models\Question;
use App\Services\KnowledgeServiceApi;
use Illuminate\Support\Collection;
use Illuminate\Support\Facades\Cache;
use Illuminate\Support\Facades\DB;
use Illuminate\Support\Facades\Log;
use Illuminate\Support\Str;

class QuestionLocalService
{
    public function listQuestions(int $page = 1, int $perPage = 50, array $filters = []): array
    {
        $query = $this->applyFilters(Question::query(), $filters);
        $paginator = $query->orderByDesc('id')->paginate($perPage, ['*'], 'page', $page);

        $data = $this->mapQuestions(collect($paginator->items()));

        return [
            'data' => $data,
            'meta' => [
                'page' => $paginator->currentPage(),
                'per_page' => $paginator->perPage(),
                'total' => $paginator->total(),
                'total_pages' => $paginator->lastPage(),
            ],
        ];
    }

    public function getQuestionById(int $id): ?array
    {
        $question = Question::find($id);
        if (!$question) {
            return null;
        }

        return $this->mapQuestion($question);
    }

    public function getQuestionByCode(string $questionCode): ?array
    {
        $question = Question::where('question_code', $questionCode)->first();
        if (!$question) {
            return null;
        }

        return $this->mapQuestion($question);
    }

    public function updateQuestionByCode(string $questionCode, array $payload): bool
    {
        $question = Question::where('question_code', $questionCode)->first();
        if (!$question) {
            return false;
        }

        $question->fill($this->normalizePayload($payload));
        $question->save();

        return true;
    }

    public function deleteQuestionByCode(string $questionCode): bool
    {
        $question = Question::where('question_code', $questionCode)->first();
        if (!$question) {
            return false;
        }

        $question->delete();
        return true;
    }

    public function deleteQuestionById(int $id): bool
    {
        $question = Question::find($id);
        if (!$question) {
            return false;
        }

        $question->delete();
        return true;
    }

    public function searchQuestions(string $query, int $limit = 20): array
    {
        $questions = Question::query()
            ->search($query)
            ->orderByDesc('id')
            ->limit($limit)
            ->get();

        return [
            'data' => $this->mapQuestions($questions),
        ];
    }

    public function getQuestionsByIds(array $ids): array
    {
        if (empty($ids)) {
            return ['data' => []];
        }

        $questions = Question::query()
            ->whereIn('id', $ids)
            ->orderByDesc('id')
            ->get();

        return [
            'data' => $this->mapQuestions($questions),
        ];
    }

    public function getQuestionsByKpCode(string $kpCode, int $limit = 100): array
    {
        $questions = Question::query()
            ->where('kp_code', $kpCode)
            ->orderByDesc('id')
            ->limit($limit)
            ->get();

        return [
            'data' => $this->mapQuestions($questions),
        ];
    }

    public function getStatistics(array $filters = []): array
    {
        $baseQuery = $this->applyFilters(Question::query(), $filters);
        $total = (clone $baseQuery)->count();

        $byDifficulty = (clone $baseQuery)
            ->selectRaw('difficulty, COUNT(*) as total')
            ->groupBy('difficulty')
            ->pluck('total', 'difficulty')
            ->toArray();

        $byTypeRaw = (clone $baseQuery)
            ->selectRaw('question_type, COUNT(*) as total')
            ->groupBy('question_type')
            ->pluck('total', 'question_type')
            ->toArray();

        $byType = [];
        foreach ($byTypeRaw as $type => $count) {
            $label = $this->mapQuestionTypeLabel((string) $type);
            $byType[$label] = ($byType[$label] ?? 0) + $count;
        }

        $byKp = (clone $baseQuery)
            ->selectRaw('kp_code, COUNT(*) as total')
            ->groupBy('kp_code')
            ->pluck('total', 'kp_code')
            ->toArray();

        $bySource = (clone $baseQuery)
            ->selectRaw('source, COUNT(*) as total')
            ->groupBy('source')
            ->pluck('total', 'source')
            ->toArray();

        return [
            'total' => $total,
            'by_difficulty' => $byDifficulty,
            'by_type' => $byType,
            'by_kp' => $byKp,
            'by_source' => $bySource,
        ];
    }

    public function generateQuestions(array $params): array
    {
        $kpCode = $params['kp_code'] ?? null;
        // 允许 kp_code 为空，此时从所有可用题目中选择
        if (!$kpCode) {
            // 从 params 中获取 kp_codes 数组
            $kpCodes = $params['kp_codes'] ?? [];
            if (is_string($kpCodes)) {
                $kpCodes = array_map('trim', explode(',', $kpCodes));
            }
            if (is_array($kpCodes) && !empty($kpCodes)) {
                $kpCode = $kpCodes[0]; // 使用第一个知识点
            } else {
                // 如果没有指定知识点，从数据库中随机选择一个可用的知识点
                $availableKp = Question::query()
                    ->whereNotNull('kp_code')
                    ->where('kp_code', '!=', '')
                    ->distinct()
                    ->pluck('kp_code')
                    ->first();

                if ($availableKp) {
                    $kpCode = $availableKp;
                } else {
                    return [
                        'success' => false,
                        'message' => '系统中没有可用的题目，请先添加题目数据',
                    ];
                }
            }
        }

        $count = max(1, (int) ($params['count'] ?? 1));
        $keyword = (string) ($params['keyword'] ?? '');
        $type = $params['type'] ?? null;
        $difficulty = $params['difficulty'] ?? null;
        $skills = $params['skills'] ?? [];

        $solutionService = app(AiSolutionService::class);

        $created = [];

        DB::transaction(function () use (
            $count,
            $kpCode,
            $keyword,
            $type,
            $difficulty,
            $skills,
            $solutionService,
            &$created,
            $params
        ) {
            for ($i = 1; $i <= $count; $i++) {
                $questionCode = $this->generateQuestionCode();
                $stemSuffix = $keyword ? "（{$keyword}）" : '';
                $stem = "【AI生成】{$kpCode} 题目 {$i}{$stemSuffix}";

                $options = null;
                $answer = null;
                $questionType = $type ?? 'CALCULATION';

                if (in_array($questionType, ['CHOICE', 'MULTIPLE_CHOICE'], true)) {
                    $options = [
                        ['label' => 'A', 'text' => '选项 A'],
                        ['label' => 'B', 'text' => '选项 B'],
                        ['label' => 'C', 'text' => '选项 C'],
                        ['label' => 'D', 'text' => '选项 D'],
                    ];
                    $answer = 'A';
                }

                $solution = $solutionService->generateSolution($stem, [
                    'kp_code' => $kpCode,
                    'difficulty' => $difficulty,
                    'question_type' => $questionType,
                ]);

                $question = Question::create([
                    'question_code' => $questionCode,
                    'kp_code' => $kpCode,
                    'stem' => $stem,
                    'options' => $options,
                    'answer' => $answer,
                    'solution' => $solution['solution'] ?? null,
                    'difficulty' => $difficulty,
                    'source' => 'ai::local',
                    'question_type' => $questionType,
                    'meta' => [
                        'skills' => $skills,
                        'prompt_template' => $params['prompt_template'] ?? null,
                        'strategy' => $params['strategy'] ?? null,
                        'generated_at' => now()->toDateTimeString(),
                        'solution_steps' => $solution['steps'] ?? [],
                    ],
                ]);

                $created[] = $this->mapQuestion($question);
            }
        });

        return [
            'success' => true,
            'message' => '生成完成',
            'count' => count($created),
            'data' => $created,
        ];
    }

    public function importQuestions(array $questions): array
    {
        if (empty($questions)) {
            return [
                'success' => false,
                'message' => '题目为空',
                'count' => 0,
            ];
        }

        $created = 0;

        DB::transaction(function () use ($questions, &$created) {
            foreach ($questions as $payload) {
                $questionCode = $payload['question_code'] ?? $this->generateQuestionCode();
                $question = Question::firstOrNew(['question_code' => $questionCode]);
                $question->fill($this->normalizePayload($payload));
                $question->save();
                $created++;
            }
        });

        return [
            'success' => true,
            'message' => '导入完成',
            'count' => $created,
        ];
    }

    public function selectQuestionsForExam(int $totalQuestions, array $filters): array
    {
        $query = Question::query();

        // 【新增】只获取审核通过的题目（audit_status = 0 表示合格）
        $query->where('audit_status', 0);

        if (!empty($filters['kp_codes'])) {
            $query->whereIn('kp_code', $filters['kp_codes']);
        }

        if (!empty($filters['skills'])) {
            $skills = array_values(array_filter($filters['skills']));
            if (!empty($skills)) {
                $query->where(function ($q) use ($skills) {
                    foreach ($skills as $skill) {
                        $q->orWhereJsonContains('meta->skills', $skill);
                    }
                });
            }
        }

        $questions = $query->get();

        $selected = $this->applyRatioSelection($questions, $totalQuestions, $filters);

        return $this->mapQuestions(collect($selected));
    }

    public function getKnowledgePointOptions(): array
    {
        return KnowledgePoint::query()
            ->orderBy('kp_code')
            ->pluck('name', 'kp_code')
            ->toArray();
    }

    public function getSkillNameMapping(?string $kpCode = null): array
    {
        return [];
    }

    private function applyFilters($query, array $filters)
    {
        if (!empty($filters['kp_code'])) {
            $query->where('kp_code', $filters['kp_code']);
        }

        if (!empty($filters['difficulty'])) {
            $query->where('difficulty', $filters['difficulty']);
        }

        if (!empty($filters['type'])) {
            $query->where('question_type', $filters['type']);
        }

        if (!empty($filters['search'])) {
            $query->search($filters['search']);
        }

        return $query;
    }

    private function normalizePayload(array $payload): array
    {
        $normalized = [
            'question_code' => $payload['question_code'] ?? null,
            'kp_code' => $payload['kp_code'] ?? null,
            'stem' => $payload['stem'] ?? ($payload['content'] ?? ''),
            'options' => $payload['options'] ?? null,
            'answer' => $payload['answer'] ?? null,
            'solution' => $payload['solution'] ?? null,
            'difficulty' => $payload['difficulty'] ?? null,
            'source' => $payload['source'] ?? null,
            'tags' => $payload['tags'] ?? null,
            'question_type' => $payload['question_type'] ?? ($payload['type'] ?? null),
            'meta' => $payload['meta'] ?? null,
        ];

        if (isset($payload['skills'])) {
            $meta = $normalized['meta'] ?? [];
            $meta['skills'] = is_array($payload['skills'])
                ? $payload['skills']
                : array_filter(array_map('trim', explode(',', (string) $payload['skills'])));
            $normalized['meta'] = $meta;
        }

        return array_filter($normalized, static fn ($value) => $value !== null);
    }

    private function mapQuestions(Collection $questions): array
    {
        $kpCodes = $questions->pluck('kp_code')->filter()->unique()->values();
        $kpMap = $this->resolveKnowledgePointNames($kpCodes->all());

        return $questions->map(function (Question $question) use ($kpMap) {
            $data = $this->mapQuestion($question);
            $data['kp_name'] = $kpMap[$question->kp_code] ?? null;
            return $data;
        })->values()->all();
    }

    private function mapQuestion(Question $question): array
    {
        $meta = $question->meta ?? [];

        $data = [
            'id' => $question->id,
            'question_code' => $question->question_code,
            'kp_code' => $question->kp_code,
            'stem' => $question->stem,
            'options' => $question->options,
            'answer' => $question->answer,
            'solution' => $question->solution,
            'difficulty' => $question->difficulty,
            'source' => $question->source,
            'tags' => $question->tags,
            'type' => $question->question_type,
            'question_type' => $question->question_type,
            'skills' => $meta['skills'] ?? [],
            'meta' => $meta,
            'created_at' => $question->created_at?->toDateTimeString(),
            'updated_at' => $question->updated_at?->toDateTimeString(),
        ];

        return MathFormulaProcessor::processQuestionData($data);
    }

    private function generateQuestionCode(): string
    {
        return 'Q' . Str::upper(Str::random(10));
    }

    private function mapQuestionTypeLabel(string $type): string
    {
        return match (strtoupper($type)) {
            'CHOICE' => '选择题',
            'MULTIPLE_CHOICE' => '多选题',
            'FILL_IN_THE_BLANK', 'FILL' => '填空题',
            'CALCULATION', 'WORD_PROBLEM', 'ANSWER' => '解答题',
            'PROOF' => '证明题',
            default => '其他',
        };
    }

    private function applyRatioSelection(Collection $questions, int $totalQuestions, array $filters): array
    {
        $questionsByType = $questions->groupBy(fn (Question $q) => $q->question_type ?? 'CALCULATION');
        $questionsByDifficulty = $questions->groupBy(function (Question $q) {
            $difficulty = (float) ($q->difficulty ?? 0);
            if ($difficulty <= 0.4) {
                return 'easy';
            }
            if ($difficulty <= 0.7) {
                return 'medium';
            }
            return 'hard';
        });

        $typeRatio = $filters['question_type_ratio'] ?? [];
        $difficultyRatio = $filters['difficulty_ratio'] ?? [];

        $selected = collect();

        if (!empty($typeRatio)) {
            foreach ($typeRatio as $type => $ratio) {
                $bucket = $questionsByType->get($type, collect());
                $count = (int) round($totalQuestions * (float) $ratio);
                $selected = $selected->merge($bucket->shuffle()->take($count));
            }
        }

        if (!empty($difficultyRatio)) {
            foreach ($difficultyRatio as $key => $ratio) {
                $bucketKey = $this->normalizeDifficultyKey($key);
                $bucket = $questionsByDifficulty->get($bucketKey, collect());
                $count = (int) round($totalQuestions * (float) $ratio);
                $selected = $selected->merge($bucket->shuffle()->take($count));
            }
        }

        if ($selected->isEmpty()) {
            return $questions->shuffle()->take($totalQuestions)->values()->all();
        }

        if ($selected->count() < $totalQuestions) {
            $missing = $totalQuestions - $selected->count();
            $fill = $questions->diff($selected)->shuffle()->take($missing);
            $selected = $selected->merge($fill);
        }

        return $selected->values()->all();
    }

    private function normalizeDifficultyKey(string $key): string
    {
        if (in_array($key, ['easy', 'medium', 'hard'], true)) {
            return $key;
        }

        $value = (float) $key;
        if ($value <= 0.4) {
            return 'easy';
        }
        if ($value <= 0.7) {
            return 'medium';
        }
        return 'hard';
    }

    private function resolveKnowledgePointNames(array $kpCodes): array
    {
        $kpCodes = array_values(array_filter(array_unique($kpCodes)));
        if (empty($kpCodes)) {
            return [];
        }

        $cacheKey = 'kp-name-map-' . md5(implode('|', $kpCodes));
        return Cache::remember($cacheKey, now()->addMinutes(30), function () use ($kpCodes) {
            $kpMap = KnowledgePoint::query()
                ->whereIn('kp_code', $kpCodes)
                ->pluck('name', 'kp_code')
                ->toArray();

            $missing = array_values(array_filter($kpCodes, fn ($code) => empty($kpMap[$code])));
            if (empty($missing)) {
                return $kpMap;
            }

            try {
                $api = app(KnowledgeServiceApi::class);
                $all = $api->listKnowledgePoints();
                foreach ($all as $kp) {
                    $code = $kp['kp_code'] ?? null;
                    $name = $kp['cn_name'] ?? $kp['name'] ?? null;
                    if ($code && $name && in_array($code, $missing, true)) {
                        $kpMap[$code] = $name;
                    }
                }
            } catch (\Throwable $e) {
                // Fallback: keep existing mapping
            }

            return $kpMap;
        });
    }

    /**
     * 根据难度系数分布选择题目
     *
     * @param array $questions 候选题目数组
     * @param int $totalQuestions 总题目数
     * @param int $difficultyCategory 难度类别 (1-4)
     *   - 1: 0-0.25范围占50%，其他占50%
     *   - 2: 0.25-0.5范围占50%，<0.25占25%，>0.5占25%
     *   - 3: 0.5-0.75范围占50%，<0.5占25%，>0.75占25%
     *   - 4: 0.75-1范围占50%，其他占50%
     * @param array $filters 其他筛选条件
     * @return array 分布后的题目
     */
    public function selectQuestionsByDifficultyDistribution(array $questions, int $totalQuestions, int $difficultyCategory = 1, array $filters = []): array
    {
        Log::info('QuestionLocalService: 根据难度系数分布选择题目', [
            'total_questions' => $totalQuestions,
            'difficulty_category' => $difficultyCategory,
            'input_questions' => count($questions)
        ]);

        if (empty($questions)) {
            Log::warning('QuestionLocalService: 输入题目为空');
            return [];
        }

        // 【恢复】简化逻辑，避免复杂处理
        $distribution = $this->calculateDifficultyDistribution($difficultyCategory, $totalQuestions);

        Log::info('QuestionLocalService: 难度分布计算', [
            'distribution' => $distribution,
            'target_count' => $totalQuestions
        ]);

        // 按难度范围分桶
        $buckets = $this->groupQuestionsByDifficultyRange($questions, $difficultyCategory);

        Log::info('QuestionLocalService: 题目分桶', [
            'buckets' => array_map(fn($bucket) => count($bucket), $buckets),
            'total_input' => count($questions)
        ]);

        // 根据分布选择题目
        $selected = [];
        $usedIds = [];

        foreach ($distribution as $level => $config) {
            $targetCount = $config['count'];
            if ($targetCount <= 0) {
                Log::debug('QuestionLocalService: 跳过难度层级', [
                    'level' => $level,
                    'target_count' => $targetCount
                ]);
                continue;
            }

            $rangeKey = $this->mapDifficultyLevelToRangeKey($level, $difficultyCategory);
            $bucket = $buckets[$rangeKey] ?? [];

            Log::debug('QuestionLocalService: 处理难度层级', [
                'level' => $level,
                'range_key' => $rangeKey,
                'target_count' => $targetCount,
                'bucket_size' => count($bucket)
            ]);

            // 随机打乱
            shuffle($bucket);

            // 选择题目
            $taken = 0;
            foreach ($bucket as $question) {
                if ($taken >= $targetCount) break;

                $questionId = $question['id'] ?? null;
                if ($questionId && !in_array($questionId, $usedIds)) {
                    $selected[] = $question;
                    $usedIds[] = $questionId;
                    $taken++;
                }
            }

            // 【修复】如果某个难度范围题目不足，记录日志但不截断
            if ($taken < $targetCount) {
                Log::warning('QuestionLocalService: 难度范围题目不足，允许后续补充', [
                    'level' => $level,
                    'range_key' => $rangeKey,
                    'target' => $targetCount,
                    'actual' => $taken,
                    'bucket_size' => count($bucket),
                    'note' => '将在后续步骤中从其他范围补充题目'
                ]);
            } else {
                Log::debug('QuestionLocalService: 难度层级选择', [
                    'level' => $level,
                    'target' => $targetCount,
                    'actual' => $taken,
                    'bucket_size' => count($bucket),
                    'range_key' => $rangeKey
                ]);
            }
        }

        Log::info('QuestionLocalService: 分布选择后统计', [
            'selected_count' => count($selected),
            'target_count' => $totalQuestions,
            'need_more' => max(0, $totalQuestions - count($selected))
        ]);

        // 如果数量不足，从剩余题目中补充
        if (count($selected) < $totalQuestions) {
            Log::warning('QuestionLocalService: 开始补充题目（难度分布无法满足要求）', [
                'need_more' => $totalQuestions - count($selected),
                'selected_count' => count($selected),
                'difficulty_category' => $difficultyCategory,
                'note' => '由于难度分布限制，将从所有剩余题目中补充'
            ]);

            $remaining = [];
            foreach ($questions as $q) {
                $id = $q['id'] ?? null;
                if ($id && !in_array($id, $usedIds)) {
                    $remaining[] = $q;
                }
            }

            Log::info('QuestionLocalService: 剩余题目统计', [
                'remaining_count' => count($remaining),
                'need_more' => $totalQuestions - count($selected)
            ]);

            // 【修复】打乱剩余题目顺序，确保随机性
            shuffle($remaining);
            $needMore = $totalQuestions - count($selected);
            $supplementCount = min($needMore, count($remaining));
            $selected = array_merge($selected, array_slice($remaining, 0, $supplementCount));

            Log::warning('QuestionLocalService: 补充完成', [
                'supplement_added' => $supplementCount,
                'final_count_before_truncate' => count($selected),
                'remaining_unused' => count($remaining) - $supplementCount
            ]);
        }

        // 截断至目标数量
        $selected = array_slice($selected, 0, $totalQuestions);

        Log::info('QuestionLocalService: 难度分布选择完成', [
            'final_count' => count($selected),
            'target_count' => $totalQuestions,
            'success' => count($selected) === $totalQuestions,
            'input_count' => count($questions),
            'distribution_applied' => true
        ]);

        return $selected;
    }

    /**
     * 计算难度分布配置
     *
     * @param int $category 难度类别 (1-4)
     * @param int $totalQuestions 总题目数
     * @return array 分布配置
     */
    private function calculateDifficultyDistribution(int $category, int $totalQuestions): array
    {
        // 标准化：25% 低级，50% 基准，25% 拔高
//        $lowPercentage = 25;
//        $mediumPercentage = 50;
//        $highPercentage = 25;

        // 根据难度类别调整分布
        switch ($category) {
            case 1:
                // 基础型：0-0.25占50%，其他占50%
                $mediumPercentage = 90; // 0-0.25作为基准
                $lowPercentage = 0;    // 其他低难度
                $highPercentage = 10;   // 其他高难度
                break;

            case 2:
                // 进阶型：0.25-0.5占50%，<0.25占25%，>0.5占25%
                $mediumPercentage = 50; // 0.25-0.5作为基准
                $lowPercentage = 25;    // <0.25
                $highPercentage = 25;   // >0.5
                break;

            case 3:
                // 中等型：0.5-0.75占50%，<0.5占25%，>0.75占25%
                $mediumPercentage = 50; // 0.5-0.75作为基准
                $lowPercentage = 25;    // <0.5
                $highPercentage = 25;   // >0.75
                break;

            case 4:
                // 拔高型：0.75-1占50%，其他占50%
                $mediumPercentage = 50; // 0.75-1作为基准
                $lowPercentage = 25;    // 其他低难度
                $highPercentage = 25;   // 其他高难度
                break;
            default:
                $lowPercentage = 25;
                $mediumPercentage = 50;
                $highPercentage = 25;
        }

        // 计算题目数量
        $lowCount = (int) round($totalQuestions * $lowPercentage / 100);
        $mediumCount = (int) round($totalQuestions * $mediumPercentage / 100);
        $highCount = $totalQuestions - $lowCount - $mediumCount;

        return [
            'low' => [
                'percentage' => $lowPercentage,
                'count' => $lowCount,
                'label' => '低级难度'
            ],
            'medium' => [
                'percentage' => $mediumPercentage,
                'count' => $mediumCount,
                'label' => '基准难度'
            ],
            'high' => [
                'percentage' => $highPercentage,
                'count' => $highCount,
                'label' => '拔高难度'
            ]
        ];
    }

    /**
     * 将题目按难度范围分桶
     *
     * @param array $questions 题目数组
     * @param int $category 难度类别
     * @return array 分桶结果
     */
    private function groupQuestionsByDifficultyRange(array $questions, int $category): array
    {
        $buckets = [
            'primary_low' => [],    // 主要低难度范围
            'primary_medium' => [], // 主要中等难度范围
            'primary_high' => [],   // 主要高难度范围
            'secondary' => [],      // 次要范围
            'other' => []           // 其他
        ];

        foreach ($questions as $question) {
            $difficulty = (float) ($question['difficulty'] ?? 0);
            $rangeKey = $this->classifyQuestionByDifficulty($difficulty, $category);
            $buckets[$rangeKey][] = $question;
        }

        return $buckets;
    }

    /**
     * 根据难度值和类别分类题目
     *
     * @param float $difficulty 难度值 (0-1)
     * @param int $category 难度类别 (1-4)
     * @return string 范围键
     */
    private function classifyQuestionByDifficulty(float $difficulty, int $category): string
    {
        switch ($category) {
            case 1:
                // 基础型：0-0.25作为主要中等，0.25-1作为其他
                if ($difficulty >= 0 && $difficulty <= 0.25) {
                    return 'primary_medium';
                }
                return 'other';

            case 2:
                // 进阶型：0.25-0.5作为主要中等，<0.25作为主要低，>0.5作为主要高
                if ($difficulty >= 0.25 && $difficulty <= 0.5) {
                    return 'primary_medium';
                } elseif ($difficulty < 0.25) {
                    return 'primary_low';
                }
                return 'primary_high';

            case 3:
                // 中等型：0.5-0.75作为主要中等，<0.5作为主要低，>0.75作为主要高
                if ($difficulty >= 0.5 && $difficulty <= 0.75) {
                    return 'primary_medium';
                } elseif ($difficulty < 0.5) {
                    return 'primary_low';
                }
                return 'primary_high';

            case 4:
                // 拔高型：0.75-1作为主要中等，0-0.75作为其他
                if ($difficulty >= 0.75 && $difficulty <= 1.0) {
                    return 'primary_medium';
                }
                return 'other';

            default:
                return 'other';
        }
    }

    /**
     * 将难度层级映射到范围键
     *
     * @param string $level 难度层级 (low/medium/high)
     * @param int $category 难度类别
     * @return string 范围键
     */
    private function mapDifficultyLevelToRangeKey(string $level, int $category): string
    {
        // 【修复】难度分布映射逻辑：确保 'other' 桶中的题目能被正确选择
        // 对于 difficulty_category=1，'other' 桶中的题目应该映射到 'secondary' 桶
        switch ($category) {
            case 1:
                return match($level) {
                    'low' => 'secondary',  // 修复：映射到 secondary 桶，而非 other
                    'medium' => 'primary_medium',
                    'high' => 'secondary',  // 修复：映射到 secondary 桶，而非 other
                    default => 'secondary'
                };

            case 2:
                return match($level) {
                    'low' => 'primary_low',
                    'medium' => 'primary_medium',
                    'high' => 'primary_high',
                    default => 'other'
                };

            case 3:
                return match($level) {
                    'low' => 'primary_low',
                    'medium' => 'primary_medium',
                    'high' => 'primary_high',
                    default => 'other'
                };

            case 4:
                return match($level) {
                    'low' => 'secondary',  // 修复：映射到 secondary 桶，而非 other
                    'medium' => 'primary_medium',
                    'high' => 'secondary',  // 修复：映射到 secondary 桶，而非 other
                    default => 'secondary'
                };

            default:
                return 'other';
        }
    }
}