<?php

namespace App\Support;

use Carbon\CarbonImmutable;
use Illuminate\Support\Facades\DB;

final class BackflowPeriod
{
    public const TIMEZONE = 'Asia/Shanghai';
    public const DAILY_FROM_KEY = 'backflow_daily_from';

    public static function dailyFrom(): ?string
    {
        return DB::connection()->getSchemaBuilder()->hasTable('share_system_state')
            ? DB::table('share_system_state')->where('key', self::DAILY_FROM_KEY)->value('value') : null;
    }

    public static function forDate(string $date, ?string $dailyFrom): string
    {
        return $dailyFrom !== null && $date >= $dailyFrom ? $date : substr($date, 0, 7);
    }

    /** Inclusive start and exclusive end, both in Beijing. */
    public static function bounds(string $period, ?string $dailyFrom): array
    {
        if (strlen($period) === 10) {
            return [$period, CarbonImmutable::parse($period, self::TIMEZONE)->addDay()->toDateString()];
        }
        $start = $period . '-01';
        $end = CarbonImmutable::parse($start, self::TIMEZONE)->addMonth()->toDateString();
        return [$start, $dailyFrom === null ? $end : max($start, min($end, $dailyFrom))];
    }

    public static function waitsForSettlement(string $period, ?string $dailyFrom): bool
    {
        return strlen($period) === 10 || ($dailyFrom !== null && $period === substr($dailyFrom, 0, 7));
    }
}