<?php

namespace App\Services;

use App\Models\Course;
use App\Models\CourseSign;
use App\Models\User;
use Illuminate\Support\Facades\DB;

class SchoolmateEnrollmentService
{
    /**
     * 仅选择未删除、尚未成为校友且有有效审核通过报名的学员。
     * 多门课程取最早开课日期；指定课程补齐不受自动入库开关限制。
     */
    public function pendingUsers($courses)
    {
        return User::query()
            ->joinSub($this->eligibleSources($courses), 'schoolmate_sources', function ($join) {
                $join->on('users.id', '=', 'schoolmate_sources.user_id');
            })
            ->whereRaw('COALESCE(users.is_schoolmate, 0) != 1')
            ->select('users.*', 'schoolmate_sources.source_start_date');
    }

    private function eligibleSources($courses)
    {
        return CourseSign::query()
            ->join('courses', 'courses.id', '=', 'course_signs.course_id')
            ->whereNull('courses.deleted_at')
            ->whereIn('courses.id', (clone $courses)->select('courses.id'))
            ->where('course_signs.status', 1)
            ->select('course_signs.user_id')
            ->selectRaw('MIN(courses.start_date) as source_start_date')
            ->groupBy('course_signs.user_id');
    }

    public function ineligibleSchoolmates($courses)
    {
        return User::query()
            ->where('users.is_schoolmate', 1)
            ->whereNotIn('users.id', $this->eligibleSources($courses)
                ->select('course_signs.user_id')->whereNotNull('course_signs.user_id'));
    }

    /**
     * 锁定用户后重新核验，避免按批次查询时取得的旧资格更新用户。
     * 返回 1 表示入库，-1 表示取消，0 表示无需变更。
     */
    public function reconcile(int $userId, $courses): int
    {
        return DB::transaction(function () use ($userId, $courses) {
            $user = User::whereKey($userId)->lockForUpdate()->first();
            if (!$user) {
                return 0;
            }

            $source = $this->eligibleSources($courses)
                ->where('course_signs.user_id', $userId)->first();
            if ($source && $user->is_schoolmate != 1) {
                return User::batchUpdateToSchoolmate([$userId], $source->source_start_date);
            }

            if (!$source && $user->is_schoolmate == 1) {
                $user->is_schoolmate = 0;
                $user->schoolmate_time = null;
                return $user->save() ? -1 : 0;
            }

            return 0;
        });
    }

    public function automaticCourses()
    {
        // 保留开课前一天入库的原行为，同时补查历史及开课后审核通过的学员。
        return Course::where('auto_schoolmate', 1)
            ->whereNotNull('start_date')
            ->whereDate('start_date', '<=', now()->addDay()->toDateString());
    }

    public function promote(int $userId, string $startDate): int
    {
        return DB::transaction(function () use ($userId, $startDate) {
            // 手工补齐和自动任务同时运行时，不覆盖已有校友的入库时间。
            $user = User::whereKey($userId)->lockForUpdate()->first();
            if (!$user || $user->is_schoolmate == 1) {
                return 0;
            }

            return User::batchUpdateToSchoolmate([$userId], $startDate);
        });
    }
}