<?php

namespace App\Services\Calendar;

use Carbon\CarbonInterface;
use Illuminate\Support\Carbon;

class ICalendarParser
{
    /**
     * @return array<int, ParsedCalendarEvent>
     */
    public function parse(string $ical, ?CarbonInterface $from = null, ?CarbonInterface $to = null): array
    {
        $ical = (new CalendarOccurrenceExpander)->expand(
            $ical,
            $from ?? Carbon::now()->subDay(),
            $to ?? Carbon::now()->addDays((int) config('relais_sms.caldav.lookahead_days', 90)),
        );
        $lines = $this->unfoldLines($ical);
        $events = [];
        $eventLines = null;
        $alarmLines = null;
        $alarms = [];

        foreach ($lines as $line) {
            $upper = strtoupper($line);

            if ($upper === 'BEGIN:VEVENT') {
                $eventLines = [];
                $alarms = [];

                continue;
            }

            if ($upper === 'END:VEVENT') {
                if ($eventLines !== null) {
                    $event = $this->parseEvent($eventLines, $alarms);
                    if (! $event->cancelled) {
                        $events[] = $event;
                    }
                }

                $eventLines = null;
                $alarmLines = null;
                $alarms = [];

                continue;
            }

            if ($eventLines === null) {
                continue;
            }

            if ($upper === 'BEGIN:VALARM') {
                $alarmLines = [];

                continue;
            }

            if ($upper === 'END:VALARM') {
                if ($alarmLines !== null) {
                    $alarms[] = $this->parseAlarm($alarmLines);
                }

                $alarmLines = null;

                continue;
            }

            if ($alarmLines !== null) {
                $alarmLines[] = $line;

                continue;
            }

            $eventLines[] = $line;
        }

        return array_values(array_filter($events, fn (ParsedCalendarEvent $event): bool => $event->uid !== ''));
    }

    /**
     * @param  array<int, string>  $lines
     * @param  array<int, ParsedCalendarAlarm>  $alarms
     */
    private function parseEvent(array $lines, array $alarms): ParsedCalendarEvent
    {
        $uid = '';
        $summary = null;
        $description = null;
        $location = null;
        $startsAt = null;
        $endsAt = null;
        $attendees = [];
        $recurrenceId = null;
        $cancelled = false;

        foreach ($lines as $line) {
            $property = $this->parseProperty($line);
            $name = strtoupper($property['name']);

            match ($name) {
                'UID' => $uid = $this->decodeText($property['value']),
                'SUMMARY' => $summary = $this->decodeText($property['value']),
                'DESCRIPTION' => $description = $this->decodeText($property['value']),
                'LOCATION' => $location = $this->decodeText($property['value']),
                'DTSTART' => $startsAt = $this->parseDateTime($property['value'], $property['params']),
                'DTEND' => $endsAt = $this->parseDateTime($property['value'], $property['params']),
                'RECURRENCE-ID' => $recurrenceId = $this->parseDateTime($property['value'], $property['params']),
                'STATUS' => $cancelled = strtoupper($property['value']) === 'CANCELLED',
                'ATTENDEE', 'ORGANIZER' => $attendees[] = $this->parseAttendee($property['value'], $property['params']),
                default => null,
            };
        }

        return new ParsedCalendarEvent(
            uid: $uid,
            summary: $summary,
            description: $description,
            location: $location,
            startsAt: $startsAt,
            endsAt: $endsAt,
            attendees: array_values(array_filter(
                $attendees,
                fn (array $attendee): bool => $attendee['email'] !== '',
            )),
            alarms: $alarms,
            recurrenceId: $recurrenceId,
            cancelled: $cancelled,
        );
    }

    /**
     * @param  array<int, string>  $lines
     */
    private function parseAlarm(array $lines): ParsedCalendarAlarm
    {
        $action = '';
        $trigger = '';
        $triggerMinutes = null;
        $absoluteRemindAt = null;

        foreach ($lines as $line) {
            $property = $this->parseProperty($line);
            $name = strtoupper($property['name']);

            if ($name === 'ACTION') {
                $action = strtoupper($property['value']);
            }

            if ($name === 'TRIGGER') {
                $trigger = $property['value'];

                if (strtoupper((string) ($property['params']['VALUE'] ?? '')) === 'DATE-TIME') {
                    $absoluteRemindAt = $this->parseDateTime($property['value'], $property['params']);
                } else {
                    $triggerMinutes = $this->parseDurationMinutes($property['value']);
                }
            }
        }

        return new ParsedCalendarAlarm(
            action: $action,
            trigger: $trigger,
            triggerMinutes: $triggerMinutes,
            absoluteRemindAt: $absoluteRemindAt,
        );
    }

    /**
     * @return array{name: string, params: array<string, string>, value: string}
     */
    private function parseProperty(string $line): array
    {
        [$left, $value] = $this->splitPropertyValue($line);
        $parts = $this->splitOutsideQuotes($left, ';');
        $name = array_shift($parts) ?: '';
        $params = [];

        foreach ($parts as $part) {
            [$key, $paramValue] = array_pad(explode('=', $part, 2), 2, '');

            if ($key !== '') {
                $params[strtoupper($key)] = trim($paramValue, '"');
            }
        }

        return [
            'name' => $name,
            'params' => $params,
            'value' => $value,
        ];
    }

    /**
     * A CalDAV parameter can contain a URI, for example
     * MEMBER="mailto:circle+id@example.test". The colon in that quoted URI is
     * not the separator between the property metadata and its value.
     *
     * @return array{string, string}
     */
    private function splitPropertyValue(string $line): array
    {
        $quoted = false;

        for ($index = 0, $length = strlen($line); $index < $length; $index++) {
            if ($line[$index] === '"') {
                $quoted = ! $quoted;

                continue;
            }

            if ($line[$index] === ':' && ! $quoted) {
                return [substr($line, 0, $index), substr($line, $index + 1)];
            }
        }

        return [$line, ''];
    }

    /**
     * @return array<int, string>
     */
    private function splitOutsideQuotes(string $value, string $delimiter): array
    {
        $parts = [];
        $part = '';
        $quoted = false;

        for ($index = 0, $length = strlen($value); $index < $length; $index++) {
            $character = $value[$index];

            if ($character === '"') {
                $quoted = ! $quoted;
            }

            if ($character === $delimiter && ! $quoted) {
                $parts[] = $part;
                $part = '';

                continue;
            }

            $part .= $character;
        }

        $parts[] = $part;

        return $parts;
    }

    /**
     * @param  array<string, string>  $params
     * @return array{email: string, name: ?string}
     */
    private function parseAttendee(string $value, array $params): array
    {
        $email = preg_replace('/^mailto:/i', '', trim($value)) ?? '';

        return [
            'email' => strtolower($email),
            'name' => isset($params['CN']) ? $this->decodeText($params['CN']) : null,
        ];
    }

    /**
     * @param  array<string, string>  $params
     */
    private function parseDateTime(string $value, array $params): ?Carbon
    {
        $value = trim($value);

        if ($value === '') {
            return null;
        }

        $timezone = $params['TZID'] ?? config('app.timezone', 'UTC');

        if (str_ends_with($value, 'Z')) {
            return Carbon::createFromFormat('Ymd\THis\Z', $value, 'UTC')?->utc();
        }

        if (str_contains($value, 'T')) {
            return Carbon::createFromFormat('Ymd\THis', $value, $timezone)?->utc();
        }

        return Carbon::createFromFormat('Ymd', $value, $timezone)?->startOfDay()->utc();
    }

    private function parseDurationMinutes(string $value): ?int
    {
        $value = strtoupper(trim($value));

        if (! preg_match('/^([+-])?P(?:(\d+)D)?(?:T(?:(\d+)H)?(?:(\d+)M)?(?:(\d+)S)?)?$/', $value, $matches)) {
            return null;
        }

        $sign = ($matches[1] ?? '') === '-' ? -1 : 1;
        $days = (int) ($matches[2] ?? 0);
        $hours = (int) ($matches[3] ?? 0);
        $minutes = (int) ($matches[4] ?? 0);
        $seconds = (int) ($matches[5] ?? 0);

        return $sign * (($days * 24 * 60) + ($hours * 60) + $minutes + (int) ceil($seconds / 60));
    }

    /**
     * @return array<int, string>
     */
    private function unfoldLines(string $ical): array
    {
        $rawLines = preg_split('/\r\n|\n|\r/', $ical) ?: [];
        $lines = [];

        foreach ($rawLines as $line) {
            if ($line === '') {
                continue;
            }

            if ((str_starts_with($line, ' ') || str_starts_with($line, "\t")) && $lines !== []) {
                $lines[array_key_last($lines)] .= substr($line, 1);

                continue;
            }

            $lines[] = $line;
        }

        return $lines;
    }

    private function decodeText(string $value): string
    {
        return str_replace(
            ['\\n', '\\N', '\\,', '\\;', '\\\\'],
            ["\n", "\n", ',', ';', '\\'],
            $value,
        );
    }
}