<?php

namespace App\Service;

use App\HomeAssistant\HomeAssistantClient;
use DateTimeImmutable;
use DateTimeInterface;
use DateTimeZone;
use RuntimeException;

final class CalendarExportService
{
    private const string DUSSELDORF_ADDRESS = 'CHECK24 \nHeinricht-Heine-Allee 53\n40213 Düsseldorf\nDeutschland';
    private const string KAMEN_ADDRESS = 'Privat \nHeidkamp 21\n59174 Kamen\nDeutschland';
    private const string COMPANY_NAME = 'CHECK24';
    private const string TIMEZONE = 'Europe/Berlin';
    private const string PERSON_ENTITY = 'person.tim';
    private const string OFFICE_STATE = 'CHECK24';

    public function __construct(
        private readonly HomeAssistantClient $homeAssistantClient
    ) {
    }

    public function generateIcsContent(array $days, array $absences): string
    {
        $icsContent = [
            'BEGIN:VCALENDAR',
            'VERSION:2.0',
            'PRODID:-//CHECK24//Work Calendar//EN',
            'CALSCALE:GREGORIAN',
            'METHOD:PUBLISH',
            $this->generateTimezone(),
        ];

        foreach ($days as $day) {
            if ($this->isWeekend($day) || ($day['isUrlaub'] ?? false)) {
                continue;
            }

            $dayDate = clone $day['date'];
            $startAndEndTimes = $this->getWorkTimesFromHomeAssistant($dayDate);
            
            if ($startAndEndTimes === null) {
                $eventStart = clone $day['date'];
                $eventStart->setTime(9, 0, 0);
                
                $eventEnd = clone $day['date'];
                $eventEnd->setTime(17, 30, 0);
            } else {
                [$eventStart, $eventEnd] = $startAndEndTimes;
            }
            
            $isHomeOffice = $day['isFtk'] ?? false;
            $location = $isHomeOffice ? self::KAMEN_ADDRESS : self::DUSSELDORF_ADDRESS;

            $name = match ($isHomeOffice) {
                true => 'CHECK24 🏠',
                false => 'CHECK24 🏢',
            };
            
            $icsContent[] = 'BEGIN:VEVENT';
            $icsContent[] = 'UID:' . $this->generateUid($eventStart);
            $icsContent[] = 'DTSTAMP:' . $this->formatDateTime(new DateTimeImmutable('now', new DateTimeZone(self::TIMEZONE)));
            $icsContent[] = 'DTSTART;TZID=' . self::TIMEZONE . ':' . $this->formatDateTimeLocal($eventStart);
            $icsContent[] = 'DTEND;TZID=' . self::TIMEZONE . ':' . $this->formatDateTimeLocal($eventEnd);
            $icsContent[] = 'SUMMARY:' . $name;
            $icsContent[] = 'LOCATION:' . $location;
            $icsContent[] = 'END:VEVENT';
        }

        $icsContent[] = 'END:VCALENDAR';

        return implode("\r\n", $icsContent);
    }

    private function getWorkTimesFromHomeAssistant(DateTimeInterface $date): ?array
    {
        $startOfDay = DateTimeImmutable::createFromInterface($date)->setTime(0, 0, 0);
        $typicalEndOfDay = DateTimeImmutable::createFromInterface($date)->setTime(17, 30, 0);
        
        try {
            $stateHistory = $this->homeAssistantClient->getEntityStateHistory(
                self::PERSON_ENTITY,
                $startOfDay, 
                $typicalEndOfDay
            );
            
            if (empty($stateHistory) || empty($stateHistory[0])) {
                return null;
            }
            
            $startTime = null;
            $endTime = null;
            $states = $stateHistory[0];
            
            foreach ($states as $i => $state) {
                if ($state['state'] === self::OFFICE_STATE) {
                    $startTime = new DateTimeImmutable($state['last_changed']);
                    
                    for ($j = $i + 1; $j < count($states); $j++) {
                        if ($states[$j]['state'] !== self::OFFICE_STATE) {
                            $endTime = new DateTimeImmutable($states[$j]['last_changed']);
                            break;
                        }
                    }
                    
                    if ($startTime !== null && $endTime === null) {
                        $endTime = clone $startTime;
                        $endTime = $endTime->modify('+9 hours');
                    }
                    
                    break;
                }
            }
            
            if ($startTime === null || $endTime === null) {
                return null;
            }

            $startTime = $startTime->setTimezone(new DateTimeZone('Europe/Berlin'));
            $endTime = $endTime->setTimezone(new DateTimeZone('Europe/Berlin'));
            
            return [$startTime, $endTime];
        } catch (RuntimeException) {
            return null;
        }
    }

    private function isWeekend(array $day): bool
    {
        return $day['weekday'] >= 6;
    }

    private function formatDateTime(DateTimeImmutable $dateTime): string
    {
        return $dateTime->setTimezone(new DateTimeZone('UTC'))->format('Ymd\THis\Z');
    }

    private function formatDateTimeLocal(DateTimeInterface $dateTime): string
    {
        return $dateTime->format('Ymd\THis');
    }

    private function generateUid(DateTimeInterface $dateTime): string
    {
        return $dateTime->format('Ymd') . '-' . md5($dateTime->format('Ymd') . '-CHECK24') . '@check24.de';
    }
    
    private function generateTimezone(): string
    {
        return implode("\r\n", [
            'BEGIN:VTIMEZONE',
            'TZID:' . self::TIMEZONE,
            'X-LIC-LOCATION:' . self::TIMEZONE,
            'BEGIN:DAYLIGHT',
            'TZOFFSETFROM:+0100',
            'TZOFFSETTO:+0200',
            'TZNAME:CEST',
            'DTSTART:19700329T020000',
            'RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU',
            'END:DAYLIGHT',
            'BEGIN:STANDARD',
            'TZOFFSETFROM:+0200',
            'TZOFFSETTO:+0100',
            'TZNAME:CET',
            'DTSTART:19701025T030000',
            'RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU',
            'END:STANDARD',
            'END:VTIMEZONE',
        ]);
    }
}