<?php

namespace App\Services;

use Illuminate\Support\Facades\DB;
use Illuminate\Support\Facades\Schema;

class QuestionDifficultyResolver
{
    private const TABLE = 'question_difficulty_calibrations';
    private const SERVED_DIFF_CONFIDENCE_DENOMINATOR = 20.0;

    private ?bool $tableReady = null;

    /**
     * @param  array<int, int|string>  $questionIds
     * @return array<int, array<string, float|null>> question_bank_id => calibration snapshot
     */
    public function mapCalibratedDifficulty(array $questionIds): array
    {
        if (! $this->isReady()) {
            return [];
        }

        $questionIds = collect($questionIds)
            ->map(fn ($id) => (int) $id)
            ->filter(fn ($id) => $id > 0)
            ->unique()
            ->values()
            ->all();
        if ($questionIds === []) {
            return [];
        }

        return DB::table(self::TABLE)
            ->whereIn('question_bank_id', $questionIds)
            ->get(['question_bank_id', 'original_difficulty', 'calibrated_difficulty', 'weighted_attempts'])
            ->mapWithKeys(function ($row) {
                $qid = (int) ($row->question_bank_id ?? 0);
                if ($qid <= 0) {
                    return [];
                }

                return [
                    $qid => [
                        'original_difficulty' => $row->original_difficulty !== null ? (float) $row->original_difficulty : null,
                        'calibrated_difficulty' => $row->calibrated_difficulty !== null ? (float) $row->calibrated_difficulty : null,
                        'weighted_attempts' => $row->weighted_attempts !== null ? (float) $row->weighted_attempts : null,
                    ],
                ];
            })
            ->all();
    }

    /**
     * 批量给题目数组计算组卷使用难度 served_diff：
     * served_diff = alpha * calibrated + (1 - alpha) * original
     * alpha = min(1, weighted_attempts / 20)
     * 前提：仅当 calibrated_difficulty 存在时才融合；否则保持原始 difficulty 不变。
     *
     * @param  array<int, array<string, mixed>>  $questions
     * @return array<int, array<string, mixed>>
     */
    public function applyCalibratedDifficulty(array $questions): array
    {
        if ($questions === []) {
            return $questions;
        }

        $ids = [];
        foreach ($questions as $q) {
            $id = (int) ($q['id'] ?? $q['question_id'] ?? $q['question_bank_id'] ?? 0);
            if ($id > 0) {
                $ids[] = $id;
            }
        }
        $map = $this->mapCalibratedDifficulty($ids);
        if ($map === []) {
            return $questions;
        }

        foreach ($questions as &$q) {
            $id = (int) ($q['id'] ?? $q['question_id'] ?? $q['question_bank_id'] ?? 0);
            if ($id <= 0 || ! array_key_exists($id, $map)) {
                continue;
            }

            $snapshot = $map[$id] ?? [];
            $calibrated = $snapshot['calibrated_difficulty'] ?? null;
            if ($calibrated === null) {
                continue;
            }

            $original = isset($q['difficulty']) && is_numeric($q['difficulty'])
                ? (float) $q['difficulty']
                : (float) ($snapshot['original_difficulty'] ?? $calibrated);
            $weightedAttempts = max(0.0, (float) ($snapshot['weighted_attempts'] ?? 0.0));
            $alpha = min(1.0, $weightedAttempts / self::SERVED_DIFF_CONFIDENCE_DENOMINATOR);
            $servedDifficulty = ($alpha * (float) $calibrated) + ((1.0 - $alpha) * $original);

            $q['difficulty'] = round($servedDifficulty, 4);
            $q['difficulty_source'] = $alpha >= 0.9999 ? 'calibrated' : 'served_blend';
            $q['difficulty_original'] = round($original, 4);
            $q['difficulty_calibrated'] = round((float) $calibrated, 4);
            $q['difficulty_alpha'] = round($alpha, 4);
            $q['difficulty_weighted_attempts'] = round($weightedAttempts, 4);
        }
        unset($q);

        return $questions;
    }

    private function isReady(): bool
    {
        if ($this->tableReady !== null) {
            return $this->tableReady;
        }

        $this->tableReady = Schema::hasTable(self::TABLE);

        return $this->tableReady;
    }
}