<?php

namespace App\Services\Merchant;

use App\Models\QrBooking;
use App\Models\QrCode;
use Carbon\Carbon;
use Illuminate\Support\Collection;

class BookingSlotService
{
    /** @var list<string> */
    private const DAY_KEYS = ['sun', 'mon', 'tue', 'wed', 'thu', 'fri', 'sat'];

    /**
     * @return list<array{starts_at: string, ends_at: string, label: string}>
     */
    public function availableSlots(QrCode $qrCode, string $date, int $serviceIndex): array
    {
        $content = $qrCode->content();
        $services = $content['services'] ?? [];
        $service = $services[$serviceIndex] ?? null;
        if (! is_array($service)) {
            return [];
        }

        $duration = max(15, (int) ($service['duration_minutes'] ?? 30));
        $day = Carbon::parse($date)->startOfDay();
        if ($day->isPast() && ! $day->isToday()) {
            return [];
        }

        $windows = $this->windowsForDay($content, $day);
        if ($windows === []) {
            return [];
        }

        $booked = QrBooking::query()
            ->where('qr_code_id', $qrCode->id)
            ->whereIn('status', [QrBooking::STATUS_PENDING, QrBooking::STATUS_CONFIRMED])
            ->whereDate('starts_at', $day->toDateString())
            ->get(['starts_at', 'ends_at']);

        $slots = [];
        foreach ($windows as $window) {
            $cursor = $day->copy()->setTimeFromTimeString($window['start']);
            $windowEnd = $day->copy()->setTimeFromTimeString($window['end']);

            while ($cursor->copy()->addMinutes($duration)->lte($windowEnd)) {
                $slotEnd = $cursor->copy()->addMinutes($duration);
                if ($day->isToday() && $cursor->lte(now())) {
                    $cursor->addMinutes($duration);
                    continue;
                }

                if (! $this->overlapsBooked($cursor, $slotEnd, $booked)) {
                    $slots[] = [
                        'starts_at' => $cursor->toIso8601String(),
                        'ends_at' => $slotEnd->toIso8601String(),
                        'label' => $cursor->format('g:i A'),
                    ];
                }

                $cursor->addMinutes($duration);
            }
        }

        return $slots;
    }

    /** @return list<array{start: string, end: string}> */
    private function windowsForDay(array $content, Carbon $day): array
    {
        $key = self::DAY_KEYS[$day->dayOfWeek];
        $availability = $content['availability'] ?? [];
        $windows = $availability[$key] ?? [];

        if (! is_array($windows) || $windows === []) {
            $opens = (string) ($content['opens_at'] ?? '09:00');
            $closes = (string) ($content['closes_at'] ?? '17:00');
            $activeDays = $content['active_days'] ?? ['mon', 'tue', 'wed', 'thu', 'fri'];

            if (! in_array($key, (array) $activeDays, true)) {
                return [];
            }

            return [['start' => $opens, 'end' => $closes]];
        }

        $normalized = [];
        foreach ($windows as $window) {
            if (! is_array($window)) {
                continue;
            }
            $start = trim((string) ($window['start'] ?? ''));
            $end = trim((string) ($window['end'] ?? ''));
            if ($start !== '' && $end !== '') {
                $normalized[] = ['start' => $start, 'end' => $end];
            }
        }

        return $normalized;
    }

    /** @param  Collection<int, QrBooking>  $booked */
    private function overlapsBooked(Carbon $start, Carbon $end, Collection $booked): bool
    {
        foreach ($booked as $booking) {
            if ($start < $booking->ends_at && $end > $booking->starts_at) {
                return true;
            }
        }

        return false;
    }
}