<?php

declare(strict_types=1);

namespace ProCalendarWP\Events;

use DateTimeImmutable;
use DateTimeZone;
use InvalidArgumentException;

final class EventTime
{
    public function __construct(public readonly DateTimeImmutable $start, public readonly DateTimeImmutable $end, public readonly string $timezone)
    {
        if ($end < $start) {
            throw new InvalidArgumentException('The event end must not precede its start.'); // phpcs:ignore WordPress.Security.EscapeOutput.ExceptionNotEscaped -- Exception messages are data; REST encodes them and admin callers escape output.
        }
    }

    public static function fromLocal(string $start, string $end, string $timezone, bool $firstFold = false): self
    {
        if (! in_array($timezone, timezone_identifiers_list(), true) && ! preg_match('/^[+-](?:0\d|1[0-4]):[0-5]\d$/D', $timezone)) {
            throw new InvalidArgumentException('Unknown timezone.'); // phpcs:ignore WordPress.Security.EscapeOutput.ExceptionNotEscaped -- Exception messages are data; REST encodes them and admin callers escape output.
        }
        $zone = new DateTimeZone($timezone);
        $startDate = self::parse($start, $zone, $firstFold);
        $endDate = self::parse($end, $zone, $firstFold);
        return new self($startDate, $endDate, $timezone);
    }

    public function startUtc(): DateTimeImmutable
    {
        return $this->start->setTimezone(new DateTimeZone('UTC'));
    }

    public function endUtc(): DateTimeImmutable
    {
        return $this->end->setTimezone(new DateTimeZone('UTC'));
    }

    /** Preserve generated UTC instants when a fold has identical local clock readings. */
    public static function fromStored(int $eventId, string $start, string $end, string $timezone, bool $firstFold = false): self
    {
        $stored = get_post_meta($eventId, '_pcwp_recurrence_time', true);
        $normalize = static fn (string $value): string => strlen($value) === 16 ? $value . ':00' : $value;
        if (is_array($stored) && ! ($firstFold && ($stored['rfc'] ?? null) === false) && ($stored['timezone'] ?? '') === $timezone && ($stored['start_local'] ?? '') === $normalize($start) && ($stored['end_local'] ?? '') === $normalize($end)) {
            try {
                $zone = new DateTimeZone($timezone);
                $startUtc = new DateTimeImmutable((string) $stored['start_utc'], new DateTimeZone('UTC'));
                $endUtc = new DateTimeImmutable((string) $stored['end_utc'], new DateTimeZone('UTC'));
                if ($startUtc->setTimezone($zone)->format('Y-m-d\TH:i:s') === $normalize($start) && $endUtc->setTimezone($zone)->format('Y-m-d\TH:i:s') === $normalize($end)) {
                    return new self($startUtc->setTimezone($zone), $endUtc->setTimezone($zone), $timezone);
                }
            } catch (\Exception) {
                // A stale or incomplete generated pair falls back to strict editorial validation.
            }
        }
        return self::fromLocal($start, $end, $timezone, $firstFold || (is_array($stored) && ! empty($stored['rfc'])));
    }

    private static function parse(string $value, DateTimeZone $zone, bool $firstFold): DateTimeImmutable
    {
        $format = strlen($value) === 16 ? '!Y-m-d\TH:i' : '!Y-m-d\TH:i:s';
        $date = DateTimeImmutable::createFromFormat($format, $value, $zone);
        $errors = DateTimeImmutable::getLastErrors();
        if ($date === false || (is_array($errors) && ($errors['warning_count'] > 0 || $errors['error_count'] > 0))) {
            throw new InvalidArgumentException('Invalid local date and time.'); // phpcs:ignore WordPress.Security.EscapeOutput.ExceptionNotEscaped -- Exception messages are data; REST encodes them and admin callers escape output.
        }
        $expected = strlen($value) === 16 ? $date->format('Y-m-d\TH:i') : $date->format('Y-m-d\TH:i:s');
        if ($expected !== $value) {
            throw new InvalidArgumentException('The local date and time does not exist in this timezone.'); // phpcs:ignore WordPress.Security.EscapeOutput.ExceptionNotEscaped -- Exception messages are data; REST encodes them and admin callers escape output.
        }
        if ($firstFold) {
            $wall = (new DateTimeImmutable($date->format('Y-m-d H:i:s'), new DateTimeZone('UTC')))->getTimestamp();
            $previousOffset = null;
            foreach ($zone->getTransitions($date->getTimestamp() - 86400, $date->getTimestamp() + 86400) ?: [] as $transition) {
                if ($previousOffset !== null && $transition['offset'] < $previousOffset && $wall >= $transition['ts'] + $transition['offset'] && $wall < $transition['ts'] + $previousOffset) {
                    return (new DateTimeImmutable('@' . ($wall - $previousOffset)))->setTimezone($zone);
                }
                $previousOffset = $transition['offset'];
            }
        }
        return $date;
    }
}