<?php
/**
 * 成绩快照：把某次「拉取到的成绩」落盘成一份带标签的时间点存档，
 * 用于跨时间 / 跨试卷的趋势对比（例如某学生几次考试的分数变化）。
 *
 * 存储位置：data/snapshots/<projectId>/<unix秒>_<md5(标签)>.json
 * 每份快照内容为 { label, at, project:{id,name}, stats, students:[{sid,name,cls,grp,score,best_score,attempts,last_submit_at}] }
 */
declare(strict_types=1);

final class Snapshot
{
    private static function dir(string $projectId): string
    {
        $d = NY_DATA . '/snapshots/' . preg_replace('/[^A-Za-z0-9_-]/', '_', $projectId);
        if (!is_dir($d)) {
            @mkdir($d, 0777, true);
        }
        return $d;
    }

    /** 从聚合结果里抽取轻量学生摘要（只保留趋势对比需要的字段） */
    public static function summarize(array $result, string $label): array
    {
        $students = [];
        foreach ((array)($result['rows'] ?? []) as $r) {
            $students[] = [
                'sid'            => (string)($r['sid'] ?? ''),
                'name'           => (string)($r['name'] ?? ''),
                'cls'            => (string)($r['cls'] ?? ''),
                'grp'            => (string)($r['grp'] ?? ''),
                'score'          => ($r['score'] ?? null) === null ? null : (float)$r['score'],
                'best_score'     => ($r['best_score'] ?? null) === null ? null : (float)$r['best_score'],
                'attempts'       => (int)($r['attempts'] ?? 1),
                'last_submit_at' => (string)($r['last_submit_at'] ?? ($r['submit_at'] ?? '-')),
            ];
        }
        // 按学号排序，保证趋势表行序稳定
        usort($students, static function ($a, $b): int {
            $sa = $a['sid']; $sb = $b['sid'];
            if (is_numeric($sa) && is_numeric($sb)) {
                return $sa <=> $sb;
            }
            return strnatcmp((string)$sa, (string)$sb);
        });

        return [
            'label'    => trim($label) === '' ? '快照 ' . date('m-d H:i') : trim($label),
            'at'       => time(),
            'at_txt'   => date('Y-m-d H:i:s'),
            'project'  => [
                'id'   => (string)($result['project']['id'] ?? ''),
                'name' => (string)($result['project']['name'] ?? ''),
            ],
            'stats'    => $result['stats'] ?? [],
            'students' => $students,
        ];
    }

    /** 保存一份快照，返回文件名 */
    public static function save(string $projectId, array $snap): string
    {
        $dir  = self::dir($projectId);
        $name = time() . '_' . substr(md5($snap['label'] . $snap['at']), 0, 8) . '.json';
        @file_put_contents($dir . '/' . $name, json_encode($snap, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES), LOCK_EX);
        return $name;
    }

    /** 列出某项目的全部快照（按时间倒序） */
    public static function list(string $projectId): array
    {
        $dir = self::dir($projectId);
        $out = [];
        foreach (glob($dir . '/*.json') ?: [] as $f) {
            $raw = @file_get_contents($f);
            if ($raw === false) {
                continue;
            }
            $j = json_decode($raw, true);
            if (!is_array($j)) {
                continue;
            }
            $out[] = [
                'file'    => basename($f),
                'label'   => (string)($j['label'] ?? basename($f)),
                'at'      => (int)($j['at'] ?? 0),
                'at_txt'  => (string)($j['at_txt'] ?? ''),
                'project' => $j['project'] ?? [],
                'count'   => count((array)($j['students'] ?? [])),
            ];
        }
        usort($out, static fn($a, $b) => ($b['at'] <=> $a['at']));
        return $out;
    }

    /** 读取单份快照完整内容 */
    public static function get(string $projectId, string $file): ?array
    {
        $file = basename($file);   // 防路径穿越
        $path = self::dir($projectId) . '/' . $file;
        if (!is_file($path)) {
            return null;
        }
        $j = json_decode((string)@file_get_contents($path), true);
        return is_array($j) ? $j : null;
    }

    /** 删除单份快照 */
    public static function delete(string $projectId, string $file): bool
    {
        $file = basename($file);
        $path = self::dir($projectId) . '/' . $file;
        if (is_file($path)) {
            return @unlink($path);
        }
        return false;
    }

    /**
     * 跨快照趋势：以学号为行、各快照为列，输出每个学生在每份快照里的成绩。
     * 用 best_score（真实最高分）作为趋势值，未出现记 null。
     */
    public static function trend(array $snapshots): array
    {
        // 按时间升序排，最早的列在最前
        $snaps = $snapshots;
        usort($snaps, static fn($a, $b) => ($a['at'] <=> $b['at']));

        $cols = [];
        $bySid = [];
        foreach ($snaps as $sn) {
            $colKey = (string)$sn['at'] . ':' . (string)$sn['label'];
            $cols[] = ['key' => $colKey, 'label' => (string)$sn['label'], 'at_txt' => (string)($sn['at_txt'] ?? '')];
            foreach ((array)($sn['students'] ?? []) as $st) {
                $sid = (string)($st['sid'] ?? '');
                if ($sid === '') {
                    continue;
                }
                if (!isset($bySid[$sid])) {
                    $bySid[$sid] = [
                        'sid'    => $sid,
                        'name'   => (string)($st['name'] ?? ''),
                        'cls'    => (string)($st['cls'] ?? ''),
                        'scores' => [],
                    ];
                }
                $bySid[$sid]['scores'][$colKey] = ($st['best_score'] ?? null) === null
                    ? null
                    : (float)$st['best_score'];
            }
        }

        $rows = array_values($bySid);
        // 按学号排序
        usort($rows, static function ($a, $b): int {
            if (is_numeric($a['sid']) && is_numeric($b['sid'])) {
                return $a['sid'] <=> $b['sid'];
            }
            return strnatcmp((string)$a['sid'], (string)$b['sid']);
        });

        return ['columns' => $cols, 'rows' => $rows];
    }
}